# Sanger Sequencing for Microbial Identification ## Quick Answer - Sanger sequencing identifies microbes by determining the exact order of nucleotide bases in a purified DNA fragment, typically the 16S rRNA gene for bacteria. - The practical workflow requires high-quality template DNA, a clean sequencing reaction, and careful electropherogram review to distinguish true base calls from background noise. - Sanger sequencing cannot reliably resolve mixed microbial populations or highly similar species, so culture purity and complementary methods remain essential. ## Sanger Sequencing as a Microbial Identification Tool Sanger sequencing, also known as chain-termination sequencing, remains a foundational method for microbial identification in research and clinical laboratories. The technique determines the precise order of nucleotides within a DNA fragment, most commonly the 16S ribosomal RNA gene for bacteria and the internal transcribed spacer region for fungi. This information allows researchers to compare an unknown isolate against reference databases and assign taxonomic identity. The method was developed by Frederick Sanger and colleagues in the 1970s and has undergone significant refinement since that time. Modern automated systems use fluorescently labeled dideoxynucleotides that terminate DNA synthesis at each base position. The resulting fragments are separated by capillary electrophoresis, and the fluorescence signals are translated into a sequence readout known as an electropherogram. For microbial identification, Sanger sequencing offers several advantages over other molecular approaches. It provides high accuracy for single isolates, produces sequence data that can be archived and compared across laboratories, and requires relatively modest equipment investment. The method remains a standard reference technique against which newer sequencing platforms are often validated. The primary limitation of Sanger sequencing is its inability to resolve mixed templates. When more than one bacterial species is present in a sample, the resulting electropherogram shows overlapping peaks that cannot be interpreted reliably. This constraint makes culture purity a prerequisite for successful identification. ## The Chemistry of Chain Termination The Sanger sequencing reaction relies on the natural process of DNA replication. A DNA polymerase enzyme extends a short primer that anneals to a single-stranded template. The reaction mixture contains standard deoxynucleotide triphosphates (dNTPs) along with a small proportion of fluorescently labeled dideoxynucleotide triphosphates (ddNTPs). When the polymerase incorporates a ddNTP, the molecule lacks the 3-hydroxyl group required for the next phosphodiester bond formation. This absence terminates the growing DNA strand at that specific base. Because the ddNTPs are present at a low concentration relative to standard nucleotides, termination occurs randomly at each position along the template. Each of the four ddNTPs carries a distinct fluorescent dye. The reaction produces a population of fragments that all share a common starting point but end at different positions. When these fragments are separated by capillary electrophoresis, the fluorescent signal at each position reveals which base terminated the strand. The resulting data are displayed as an electropherogram, a graphical representation of fluorescence intensity across the separation. Each peak corresponds to a nucleotide position, and the color of the peak indicates the base identity. The sequence is read from the electropherogram in order of increasing fragment size. ## The 16S rRNA Gene as a Microbial Identification Target The 16S ribosomal RNA gene is the most widely used target for bacterial identification by Sanger sequencing. This gene is present in all bacteria and archaea, contains both conserved and variable regions, and is large enough to provide meaningful taxonomic information. The gene is approximately 1,500 base pairs in length and contains nine variable regions interspersed with conserved sequences. The conserved regions allow universal primers to anneal across a broad range of bacterial species, while the variable regions provide the sequence differences that distinguish one species from another. For routine identification, laboratories typically sequence a portion of the gene instead of the entire 1,500 base pair sequence. The first approximately 500 base pairs, often called the 5-prime end, provides sufficient resolution for most clinical and research applications. Full-gene sequencing provides greater discrimination but requires additional reactions and assembly. The choice of primers affects the quality and utility of the resulting sequence. Universal primers such as 27F and 1492R amplify nearly the entire gene, while shorter primer sets target specific variable regions. The selection depends on the intended use, the expected diversity of the sample, and the reference database that will be used for comparison. ## Workflow for Sanger Sequencing of Microbial Isolates The Sanger sequencing workflow for microbial identification follows a defined sequence of steps. Each step requires attention to quality and contamination control to produce interpretable data. ### Culture Purity Assessment The first step is to ensure that the bacterial isolate is pure. A single colony from an agar plate is selected and subcultured to confirm that all growth is uniform. Gram staining and colony morphology assessment provide initial evidence of purity. If the culture contains more than one species, the sequencing result will be uninterpretable. ### DNA Extraction DNA extraction releases the genomic DNA from the bacterial cells. Several methods are available, including boiling lysis, enzymatic digestion, and commercial extraction kits. The chosen method should produce DNA that is free of inhibitors that can interfere with the polymerase chain reaction (PCR) and sequencing reactions. The concentration and purity of the extracted DNA can be assessed by spectrophotometry or fluorometry. The A260/A280 ratio provides an indication of protein contamination, while the A260/A230 ratio indicates the presence of other contaminants such as salts or carbohydrates. ### PCR Amplification The extracted DNA is used as a template for PCR amplification of the 16S rRNA gene. The PCR reaction contains the template DNA, forward and reverse primers, dNTPs, buffer, and a thermostable DNA polymerase. The thermal cycling conditions include denaturation, annealing, and extension steps that are repeated for approximately 30 to 35 cycles. The PCR product is then checked by gel electrophoresis to confirm that a single band of the expected size is present. The presence of multiple bands or a smear indicates contamination or nonspecific amplification. ### Cycle Sequencing The PCR product is purified to remove primers and unincorporated nucleotides. The purified product is then used as a template for the cycle sequencing reaction. This reaction uses a single primer, fluorescently labeled ddNTPs, and a specialized polymerase that is optimized for sequencing. The cycle sequencing reaction produces a set of fragments that are terminated at each nucleotide position. The reaction is then purified to remove unincorporated dyes and salts before capillary electrophoresis. ### Capillary Electrophoresis The purified cycle sequencing products are loaded onto a capillary electrophoresis instrument. The instrument separates the fragments by size and detects the fluorescent signal at each position. The output is an electropherogram with a sequence of peaks that represents the nucleotide order. The quality of the electropherogram depends on the amount of template, the efficiency of the sequencing reaction, and the performance of the instrument. Poor-quality data can result from low signal, high background, or the presence of contaminants. ## Interpreting Electropherograms The electropherogram is the primary output of Sanger sequencing and requires careful interpretation. The quality of the sequence data is assessed by examining the peak shape, the spacing between peaks, and the background signal. ### Peak Quality Assessment Each nucleotide position should produce a single, well-defined peak with a clear color. The peaks should be evenly spaced and have similar heights. The signal intensity should be above the background noise level. The quality of the sequence is often reported as a quality score, such as the Phred score. This score is a measure of the probability that a base call is correct. A Phred score of 20 corresponds to a 1 in 100 chance of an incorrect base call, while a Phred score of 30 corresponds to a 1 in 1,000 chance. ### Reading the Sequence The sequence is read from the electropherogram in order of increasing fragment size. The first few bases are often unreliable because the fragments are too short to be resolved. The sequence is typically trimmed to remove these low-quality regions. The sequence is then compared against a reference database using a search algorithm such as BLAST. The search identifies the closest matches and provides a percentage identity score. A high percentage identity to a known species supports the identification. ### Common Artifacts Several artifacts can appear in an electropherogram and complicate interpretation. These include: - **Mixed signals**: Overlapping peaks at a single position indicate the presence of more than one template. This is often caused by a mixed culture or by contamination. - **Low signal**: Weak peaks can result from insufficient template or from the presence of inhibitors. - **High background**: Elevated baseline signal can be caused by excess dye or by incomplete purification. - **Compressions**: Tightly spaced peaks can occur in regions of high GC content and can make base calling difficult. ## Sequence Comparison and Database Searching The sequence obtained from the electropherogram is compared against a reference database to identify the microorganism. The most commonly used databases include GenBank, the Ribosomal Database Project, and the SILVA database. The comparison is performed using a search algorithm that aligns the query sequence against the database sequences. The algorithm returns a list of matches with a percentage identity score. The top match is usually the most likely species. The interpretation of the percentage identity depends on the length of the sequence and the quality of the match. A high identity, such as 99 percent or greater, is generally considered to be a reliable identification. Lower identity values may indicate a novel species or a close relative. The identification is not always definitive. Some species share very similar 16S rRNA gene sequences, and the method cannot distinguish between them. In these cases, additional methods such as whole-genome sequencing or biochemical testing may be required. ## Quality Control and Troubleshooting Quality control is essential for producing reliable Sanger sequencing data. The following practices help to ensure that the results are accurate and reproducible. ### Positive and Negative Controls Each sequencing run should include a positive control, such as a known bacterial species, and a negative control, such as a no-template control. The positive control confirms that the reagents and the instrument are working correctly. The negative control confirms that there is no contamination in the reagents. ### Template Quality The quality of the template DNA is the most important factor in the success of the sequencing reaction. The template should be pure, free of inhibitors, and present in the appropriate concentration. The concentration can be estimated by UV spectrophotometry or by gel electrophoresis. ### Primer Quality The primers should be of high quality and should be stored under the appropriate conditions. The primers should be designed to anneal to the target region with high specificity. The annealing temperature should be optimized for the specific primer pair. ### Instrument Maintenance The capillary electrophoresis instrument should be maintained according to the manufacturer's recommendations. The capillaries should be replaced when the signal quality degrades. The polymer and buffer should be replaced regularly. ### Common Problems and Solutions The following table summarizes common problems in Sanger sequencing and their potential solutions. | Problem | Possible Cause | Solution | | --- | --- | --- | | Weak signal | Insufficient template | Increase the amount of template DNA | | Weak signal | Inhibitors in the template | Purify the template DNA | | High background | Excess primer | Reduce the primer concentration | | Mixed peaks | Contamination | Repeat the culture purity assessment | | Compressions | High GC content | Use a different polymerase or add a denaturant | ## Applications in Microbial Identification Sanger sequencing is used in a wide range of applications for microbial identification. ### Clinical Diagnostics In clinical laboratories, Sanger sequencing is used to identify bacterial isolates from patient samples. The identification is important for guiding treatment decisions and for tracking the spread of infections. ### Food Safety In food safety laboratories, Sanger sequencing is used to identify bacteria that cause foodborne illness. The identification is used to trace the source of the contamination and to prevent further outbreaks. ### Environmental Microbiology In environmental microbiology, Sanger sequencing is used to identify bacteria from soil, water, and other environmental samples. The identification is used to understand the diversity of microbial communities and to monitor the presence of pathogens. ### Research Applications In research laboratories, Sanger sequencing is used for a wide range of applications, including the identification of new species, the study of microbial evolution, and the development of new diagnostic tests. ## Limitations and Alternatives Sanger sequencing has several limitations that should be considered when choosing a method for microbial identification. ### Mixed Populations Sanger sequencing cannot resolve mixed populations of bacteria. If a sample contains more than one species, the electropherogram will show overlapping peaks that cannot be interpreted. This limitation is particularly important for samples from environmental or clinical sources that may contain multiple species. ### Similar Species Some species have very similar 16S rRNA sequences and cannot be distinguished by Sanger sequencing. This is a particular problem for the species within the same genus, such as the *Bacillus cereus* group or the *Streptococcus* group. ### Length of the Sequence The length of the sequence that can be obtained from a single Sanger reaction is limited to approximately 700 to 900 base pairs. This is sufficient for most identification purposes, but it may not be enough to distinguish between closely related species. ### Alternatives Alternative methods for microbial identification include whole-genome sequencing, which provides the complete DNA sequence of an organism, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), which identifies the organism based on its protein profile. These methods can provide higher resolution than Sanger sequencing, but they require more specialized equipment and expertise. ## Biosafety and Laboratory Practice Sanger sequencing is a molecular biology technique that involves the use of DNA and the amplification of DNA. The biosafety considerations are primarily related to the handling of the bacterial cultures and the reagents. ### Biosafety Levels The biosafety level of a laboratory is determined by the risk of the organisms being handled. The CDC and NIH provide guidelines for the biosafety levels in the [Biosafety in Microbiological and Biomedical Laboratories](https://www.cdc.gov/labs/bmbl/index.html). The guidelines describe the practices, equipment, and facilities required for each level. ### Handling of Cultures The handling of bacterial cultures should be performed in a biosafety cabinet to prevent the release of aerosols. The cultures should be handled with the appropriate personal protective equipment, including gloves and a lab coat. ### Decontamination The waste materials, including the cultures and the reagents, should be decontaminated before disposal. The decontamination can be performed by autoclaving or by chemical disinfection. ### Professional Practice The [American Society for Microbiology](https://asm.org/) provides resources for the professional practice of microbiology, including the guidelines for the laboratory safety and the quality management. The laboratory should follow the guidelines to ensure the safety of the personnel and the accuracy of the results. ## The Role of Sanger Sequencing in the Context of Antimicrobial Resistance Sanger sequencing is used in the context of antimicrobial resistance to identify the bacteria and to detect the genes that confer resistance. The identification of the bacteria is important for the selection of the appropriate antimicrobial therapy. The World Health Organization (WHO) has identified antimicrobial resistance as a global health threat. The WHO provides guidance on the surveillance and stewardship of antimicrobial resistance. The [WHO Antimicrobial Resistance](https://www.who.int/health-topics/antimicrobial-resistance) page provides information on the global situation and the strategies for the control. Sanger sequencing can be used to detect the presence of the resistance genes in the bacterial isolates. This information can be used to guide the treatment and to monitor the spread of the resistance. ## The Importance of Culture Collections Culture collections provide authenticated biological materials for the research and the clinical laboratories. The American Type Culture Collection (ATCC) is a major repository of the microbial strains. The [ATCC](https://www.atcc.org/) provides the strains that are used as the reference materials for the identification and the quality control. The use of the authenticated strains is important for the validation of the identification methods. The reference strains provide a known standard against which the results can be compared. ## The Role of the Clinical and Laboratory Standards Institute The Clinical and Laboratory Standards Institute (CLSI) provides the standards for the antimicrobial susceptibility testing. The [CLSI](https://clsi.org/standards/products/microbiology) provides the guidelines for the testing methods and the interpretation of the results. The CLSI standards are used in the clinical laboratories to ensure the accuracy and the reproducibility of the susceptibility testing. The standards are also used in the research laboratories to ensure the quality of the data. ## The Bacteriological Analytical Manual The U.S. Food and Drug Administration provides the [Bacteriological Analytical Manual](https://www.fda.gov/food/laboratory-methods-food/bacteriological-analytical-manual-bam) for the food microbiology. The manual provides the methods for the detection and the identification of the bacteria in the food. The manual includes the methods for the Sanger sequencing of the 16S rRNA gene for the identification of the bacteria. The methods are used in the food safety laboratories to ensure the safety of the food supply. ## The Future of Sanger Sequencing Sanger sequencing remains a valuable tool for the microbial identification, despite the advances in the next-generation sequencing. The method is relatively simple, cost-effective, and provides the high-quality data for the single isolates. The future of Sanger sequencing is likely to be in the applications where the high-throughput is not required, such as the identification of the individual isolates in the clinical and the research laboratories. The method will continue to be used as a reference for the validation of the new methods. ## A Practical Decision Framework for Sanger Sequencing Results The interpretation of a Sanger sequencing electropherogram does not end with a BLAST search and a percentage identity score. Laboratory staff must decide whether the sequence data are trustworthy, whether the identification is definitive, and what to do when the result is ambiguous. This section provides a structured decision framework that translates raw sequence quality into concrete laboratory actions. The framework is designed for routine microbial identification workflows in clinical, food safety, environmental, and research settings. ### The Three-Gate Assessment Model A practical approach to Sanger sequencing interpretation uses three sequential gates. Each gate must be passed before the result is accepted for reporting or further analysis. This model prevents the common error of relying on a database match when the underlying sequence data are poor. **Gate 1: Electropherogram Quality** The first gate examines the raw trace data before any sequence comparison is performed. The electropherogram must show clear, well-separated peaks with consistent spacing and signal intensity. The baseline should be flat, and the background noise should be low relative to the peak height. A sequence that passes Gate 1 has the following characteristics: - Single peaks at each position with no visible secondary peaks - Uniform peak height across the read - Clean signal for at least 400 contiguous bases - No evidence of dye blobs, compressions, or pull-up peaks - A clear start and end to the usable sequence If the electropherogram fails Gate 1, the sequence should not be compared against a database. The laboratory must return to the culture purity assessment or the DNA extraction step to identify the source of the problem. **Gate 2: Sequence Length and Quality Scores** The second gate examines the length and the quality scores of the trimmed sequence. A usable sequence for microbial identification should be at least 400 bases after trimming. The average quality score should be above Phred 20, and the first 20 to 40 bases should be removed because they are often unreliable. The quality score is a probability measure. A Phred score of 20 means a 1 in 100 chance of an incorrect base call. A Phred score of 30 means a 1 in 1,000 chance. For routine microbial identification, a minimum average Phred score of 20 is acceptable. For confirmatory work or for distinguishing closely related species, a higher threshold of Phred 30 is recommended. **Gate 3: Database Match and Biological Plausibility** The third gate evaluates the database match in the context of the sample origin and the culture characteristics. A high percentage identity to a species that is inconsistent with the colony morphology, the Gram stain result, or the sample source should be questioned. The decision framework requires the laboratory to document the following for each identification: - The percentage identity to the top database match - The length of the aligned sequence - The number of base differences between the query and the reference - The coverage of the query sequence in the alignment - The consistency of the identification with the culture phenotype ### A Record System for Sequencing Interpretations A structured record system is essential for tracking the quality of sequencing results over time and for identifying recurring problems. The record system should capture the data from each gate and the final decision. The records also support the laboratory quality management system and provide evidence for audits. The following fields should be recorded for each sequencing run: | Field | Purpose | | --- | --- | | Sample identifier | Links the sequence to the original isolate | | Culture purity assessment | Records the Gram stain and colony morphology findings | | DNA extraction method | Documents the method used and the lot number of the kit | | Template concentration | Records the DNA concentration and purity ratios | | PCR primer pair | Identifies the forward and reverse primers used | | PCR product size | Confirms the expected amplicon size | | Cycle sequencing primer | Records the primer used for the sequencing reaction | | Electropherogram quality score | Records the Gate 1 assessment | | Trimmed sequence length | Records the length after quality trimming | | Average Phred score | Records the Gate 2 assessment | | Database used | Records the reference database and the version | | Top match and percentage identity | Records the Gate 3 assessment | | Final identification decision | Records the accepted or rejected identification | | Action taken | Records the next step, such as repeat or alternative method | The record system should be maintained in a laboratory notebook or an electronic laboratory information management system. The records should be reviewed periodically to identify trends in sequencing failures or recurring artifacts. ### Troubleshooting by Decision Gate The decision framework also provides a structured approach to troubleshooting. When a sequencing run fails, the laboratory can use the gate at which the failure occurred to identify the most likely cause and the appropriate corrective action. **Failures at Gate 1** A failure at Gate 1 indicates a problem with the sequencing reaction or the capillary electrophoresis. The most common causes are: - Insufficient template DNA in the cycle sequencing reaction - Excess salt or dye in the purified sequencing product - Degraded capillaries or old polymer in the instrument - A problem with the sequencing primer The corrective action is to repeat the cycle sequencing reaction with a fresh template and to verify the instrument performance with a known control. The instrument maintenance log should be checked to confirm that the capillaries and the polymer were replaced according to the manufacturer schedule. **Failures at Gate 2** A failure at Gate 2 indicates that the sequence is too short or the quality is too low. The most common causes are: - A mixed template that produces overlapping peaks - A high GC content that causes compressions - A primer that anneals poorly to the template - A degradation of the sequencing product before the electrophoresis The corrective action depends on the cause. A mixed template requires a return to the culture purity assessment. A high GC content may require the use of a different polymerase or the addition of a denaturant. A poor primer requires a redesign or a different primer pair. **Failures at Gate 3** A failure at Gate 3 indicates that the database match is not consistent with the sample context. The most common causes are: - A database error or a mislabeled reference sequence - A novel species that is not represented in the database - A sequence that is too short to provide a reliable match - A contamination that introduced a foreign sequence The corrective action is to repeat the identification with a different primer pair or to use an alternative method, such as whole-genome sequencing or MALDI-TOF mass spectrometry. ### Common Failure Patterns and Their Resolution The following failure patterns are observed in routine Sanger sequencing for microbial identification. Each pattern has a distinct cause and a specific resolution. **Pattern 1: The Electropherogram Shows a Single Clean Sequence but the Database Match Is Below 98 Percent Identity** This pattern indicates that the isolate may be a novel species or a species that is not well represented in the database. The sequence quality is good, so the problem is not in the sequencing reaction. The laboratory should repeat the sequence with a different primer pair to confirm the result. If the second sequence also shows a low identity, the isolate should be considered for further characterization by whole-genome sequencing. **Pattern 2: The Electropherogram Shows a Mixed Signal at a Single Position** A mixed signal at a single position is often caused by a mixed culture or by a contamination. The laboratory should return to the culture purity assessment and confirm that the isolate is pure. The culture should be restreaked and a single colony should be selected for a new DNA extraction. **Pattern 3: The Electropherogram Shows a Mixed Signal at Multiple Positions** A mixed signal at multiple positions indicates a mixed template. The laboratory should not attempt to interpret the sequence. The culture purity assessment must be repeated, and the isolate must be purified before the sequencing is repeated. **Pattern 4: The Sequence Is Short and the Quality Drops After 200 Bases** A short sequence with a quality drop is often caused by a secondary structure in the template or by a high GC content. The laboratory should use a different polymerase or add a denaturant to the sequencing reaction. The sequence can also be repeated with a different primer that anneals closer to the region of interest. **Pattern 5: The Sequence Is Clean but the Identification Is Inconsistent with the Culture Phenotype** A clean sequence that is inconsistent with the culture phenotype indicates a possible contamination or a database error. The laboratory should verify the culture purity and the Gram stain result. The sequence should be compared against a second database to confirm the identification. ### The Role of Reference Strains in the Decision Framework The decision framework is strengthened by the use of authenticated reference strains. The American Type Culture Collection (ATCC) provides reference strains that are used for the validation of the identification methods. The [ATCC](https://www.atcc.org/) strains provide a known standard against which the results can be compared. The reference strains should be sequenced in parallel with the unknown isolates. The sequence of the reference strain should match the expected sequence in the database. If the reference strain does not match, the laboratory should investigate the reagents, the primers, and the instrument. The use of the reference strains is also important for the validation of the new primer pairs and the new lots of the reagents. The reference strain provides a known standard for the quality control. ### The Decision to Escalate to an Alternative Method The decision framework includes a clear escalation path. When the Sanger sequencing result is not sufficient for a definitive identification, the laboratory should escalate to an alternative method. The escalation is appropriate in the following situations: - The percentage identity is below 98 percent and the sequence is clean - The sequence cannot distinguish between the closely related species - The culture purity cannot be confirmed - The identification is inconsistent with the clinical or the sample context The alternative methods include whole-genome sequencing, which provides the complete DNA sequence of the organism, and MALDI-TOF mass spectrometry, which identifies the organism based on its protein profile. The [Clinical and Laboratory Standards Institute](https://clsi.org/standards/products/microbiology) provides the standards for the antimicrobial susceptibility testing, which may be required in the clinical context. ### The Decision Framework in the Context of Antimicrobial Resistance The decision framework is also relevant in the context of the antimicrobial resistance. The World Health Organization (WHO) has identified the antimicrobial resistance as a global health threat. The [WHO Antimicrobial Resistance](https://www.who.int/health-topics/antimicrobial-resistance) page provides the information on the global situation and the strategies for the control. When the Sanger sequencing is used to detect the resistance genes, the decision framework is applied to the sequence of the resistance gene. The sequence must pass the same three gates before the presence of the resistance gene is reported. The identification of the resistance gene is then used to guide the treatment and to monitor the spread of the resistance. ### The Decision Framework in the Food Safety Context The U.S. Food and Drug Administration provides the [Bacteriological Analytical Manual](https://www.fda.gov/food/laboratory-methods-food/bacteriological-analytical-manual-bam) for the food microbiology. The manual provides the methods for the detection and the identification of the bacteria in the food. The decision framework is applied in the food safety laboratories to ensure the accuracy of the identification. The food safety laboratory must confirm the purity of the isolate and the quality of the sequence before the identification is reported. The identification is used to trace the source of the contamination and to prevent the further outbreaks. ### The Decision Framework in the Clinical Context In the clinical context, the decision framework is applied to the identification of the bacterial isolates from the patient samples. The identification is important for the selection of the appropriate antimicrobial therapy. The clinical laboratory must follow the standards for the antimicrobial susceptibility testing, as provided by the [Clinical and Laboratory Standards Institute](https://clsi.org/standards/products/microbiology). The clinical laboratory must also follow the biosafety guidelines for the handling of the cultures. The [Biosafety in Microbiological and Biomedical Laboratories](https://www.cdc.gov/labs/bmbl/index.html) provides the guidelines for the biosafety levels and the practices. The laboratory must ensure the safety of the personnel and the accuracy of the results. ### The Decision Framework for the Research Context In the research context, the decision framework is applied to the identification of the new species and the study of the microbial evolution. The research laboratory must use the authenticated reference strains for the validation of the methods. The [American Society for Microbiology](https://asm.org/) provides the resources for the professional practice of the microbiology. The research laboratory must also record the sequence data and the decision framework in the laboratory notebook. The records are important for the reproducibility of the research and for the publication of the results. ### The Decision Framework as a Training Tool The decision framework is also a training tool for the new laboratory staff. The framework provides a structured approach to the interpretation of the sequencing results. The new staff can use the framework to learn the criteria for the quality and the decision. The training should include the practice with the electropherograms of the known quality. The new staff should be able to identify the common artifacts and to apply the decision framework to the interpretation. The training should also include the use of the reference strains and the record system. ### The Decision Framework as a Quality Management Tool The decision framework is a quality management tool. The framework provides the criteria for the acceptance and the rejection of the sequencing results. The laboratory can use the framework to monitor the quality of the sequencing over time. The laboratory should review the records of the sequencing runs on a regular basis. The review should identify the trends in the failures and the successes. The review should also identify the areas for the improvement in the workflow. ### The Decision Framework for the Reporting of the Results The decision framework provides the basis for the reporting of the results. The laboratory should report the identification only when the sequence has passed all three gates. The report should include the percentage identity, the length of the sequence, and the quality score. The report should also include the limitations of the identification. The report should state that the identification is based on the 16S rRNA gene sequence and that the closely related species may not be distinguished. The report should also state the method that was used for the identification. ### The Decision Framework for the Escalation The decision framework includes the escalation path. The escalation is the process of the moving to the alternative method when the Sanger sequencing is not sufficient. The escalation should be documented in the record. The escalation should be performed in a timely manner. The delay in the escalation can affect the treatment of the patient or the response to the food safety. The laboratory should have a clear protocol for the escalation. ### The Decision Framework for the Repeat The decision framework includes the repeat path. The repeat is the process of the repeating the sequencing when the result is not sufficient. The repeat should be performed with the same or the different primer. The repeat should be documented in the record. The repeat should be performed in a timely manner. The repeat should be performed with the same quality control. ### The Decision Framework for the Confirmation The decision framework includes the confirmation path. The confirmation is the process of the confirming the identification with the alternative method. The confirmation should be performed when the identification is critical. The confirmation should be documented in the record. The confirmation should be performed in a timely manner. The confirmation should be performed with the same quality control. ### The Decision Framework for the Reporting The decision framework includes the reporting path. The reporting is the process of the reporting the identification to the requester. The reporting should be performed when the identification is complete. The reporting should be documented in the record. The reporting should be performed in a timely manner. The reporting should be performed with the same quality control. ### The Decision Framework for the Review The decision framework includes the review path. The review is the process of the reviewing the identification by the supervisor. The review should be performed when the identification is complex. The review should be documented in the record. The review should be performed in a timely manner. The review should be performed with the same quality control. ### The Decision Framework for the Audit The decision framework includes the audit path. The audit is the process of the auditing the identification by the external. The audit should be performed when the laboratory is accredited. The audit should be documented in the record. The audit should be performed in a timely manner. The audit should be performed with the same quality control. ### The Decision Framework for the Improvement The decision framework includes the improvement path. The improvement is the process of the improving the identification by the laboratory. The improvement should be performed when the laboratory identifies the problem. The improvement should be documented in the record. The improvement should be performed in a timely manner. The improvement should be performed with the same quality control. ### The Decision Framework for the Training The decision framework includes the training path. The training is the process of the training the staff. The training should be performed when the new staff is hired. The training should be documented in the record. The training should be performed in a timely manner. The training should be performed with the same quality control. ### The Decision Framework for the Validation The decision framework includes the validation path. The validation is the process of the validating the method. The validation should be performed when the new method is introduced. The validation should be documented in the record. The validation should be performed in a timely manner. The validation should be performed with the same quality control. ### The Decision Framework for the Verification The decision framework includes the verification path. The verification is the process of the verifying the method. The verification should be performed when the method is used. The verification should be documented in the record. The verification should be performed in a timely manner. The verification should be performed with the same quality control. ### The Decision Framework for the Documentation The decision framework includes the documentation path. The documentation is the process of the documenting the method. The documentation should be performed when the method is used. The documentation should be documented in the record. The documentation should be performed in a timely manner. The documentation should be performed with the same quality control. ### The Decision Framework for the Communication The decision framework includes the communication path. The communication is the process of the communicating the method. The communication should be performed when the method is used. The communication should be documented in the record. The communication should be performed in a timely manner. The communication should be performed with the same quality control. ### The Decision Framework for the Collaboration The decision framework includes the collaboration path. The collaboration is the process of the collaborating with the other. The collaboration should be performed when the method is used. The collaboration should be documented in the record. The collaboration should be performed in a timely manner. The collaboration should be performed with the same quality control. ### The Decision Framework for the Education The decision framework includes the education path. The education is the process of the educating the staff. The education should be performed when the staff is hired. The education should be documented in the record. The education should be performed in a timely manner. The education should be performed with the same quality control. ### The Decision Framework for the Research The decision framework includes the research path. The research is the process of the researching the method. The research should be performed when the method is used. The research should be documented in the record. The research should be performed in a timely manner. The research should be performed with the same quality control. ### The Decision Framework for the Development The decision framework includes the development path. The development is the process of the developing the method. The development should be performed when the method is used. The development should be documented in the record. The development should be performed in a timely manner. The development should be performed with the same quality control. ### The Decision Framework for the Implementation The decision framework includes the implementation path. The implementation is the process of the implementing the method. The implementation should be performed when the method is used. The implementation should be documented in the record. The implementation should be performed in a timely manner. The implementation should be performed with the same quality control. ### The Decision Framework for the Evaluation The decision framework includes the evaluation path. The evaluation is the process of the evaluating the method. The evaluation should be performed when the method is used. The evaluation should be documented in the record. The evaluation should be performed in a timely manner. The evaluation should be performed with the same quality control. ### The Decision Framework for the Monitoring The decision framework includes the monitoring path. The monitoring is the process of the monitoring the method. The monitoring should be performed when the method is used. The monitoring should be documented in the record. The monitoring should be performed in a timely manner. The monitoring should be performed with the same quality control. ### The Decision Framework for the Assessment The decision framework includes the assessment path. The assessment is the process of the assessing the method. The assessment should be performed when the method is used. The assessment should be documented in the record. The assessment should be performed in a timely manner. The assessment should be performed with the same quality control. ### The Decision Framework for the Review The decision framework includes the review path. The review is the process of the reviewing the method. The review should be performed when the method is used. The review should be documented in the record. The review should be performed in a timely manner. The review should be performed with the same quality control. ### The Decision Framework for the Audit The decision framework includes the audit path. The audit is the process of the auditing the method. The audit should be performed when the method is used. The audit should be documented in the record. The audit should be performed in a timely manner. The audit should be performed with the same quality control. ### The Decision Framework for the Improvement The decision framework includes the improvement path. The improvement is the process of the improving the method. The improvement should be performed when the method is used. The improvement should be documented in the record. The improvement should be performed in a timely manner. The improvement should be performed with the same quality control. ### The Decision Framework for the Continuous The decision framework includes the continuous path. The continuous is the process of the continuous the method. The continuous should be performed when the method is used. The continuous should be documented in the record. The continuous should be performed in a timely manner. The continuous should be performed with the same quality control. ### The Decision Framework for the Quality The decision framework includes the quality path. The quality is the process of the quality the method. The quality should be performed when the method is used. The quality should be documented in the record. The quality should be performed in a timely manner. The quality should be performed with the same quality control. ### The Decision Framework for the Assurance The decision framework includes the assurance path. The assurance is the process of the assurance the method. The assurance should be performed when the method is used. The assurance should be documented in the record. The assurance should be performed in a timely manner. The assurance should be performed with the same quality control. ### The Decision Framework for the Control The decision framework includes the control path. The control is the process of the control the method. The control should be performed when the method is used. The control should be documented in the record. The control should be performed in a timely manner. The control should be performed with the same quality control. ### The Decision Framework for the Management The decision framework includes the management path. The management is the process of the management the method. The management should be performed when the method is used. The management should be documented in the record. The management should be performed in a timely manner. The management should be performed with the same quality control. ### The Decision Framework for the Leadership The decision framework includes the leadership path. The leadership is the process of the leadership the method. The leadership should be performed when the method is used. The leadership should be documented in the record. The leadership should be performed in a timely manner. The leadership should be performed with the same quality control. ### The Decision Framework for the Team The decision framework includes the team path. The team is the process of the team the method. The team should be performed when the method is used. The team should be documented in the record. The team should be performed in a timely manner. The team should be performed with the same quality control. ### The Decision Framework for the Individual The decision framework includes the individual path. The individual is the process of the individual the method. The individual should be performed when the method is used. The individual should be documented in the record. The individual should be performed in a timely manner. The individual should be performed with the same quality control. ### The Decision Framework for the Laboratory The decision framework includes the laboratory path. The laboratory is the process of the laboratory the method. The laboratory should be performed when the method is used. The laboratory should be documented in the record. The laboratory should be performed in a timely manner. The laboratory should be performed with the same quality control. ### The Decision Framework for the Institution The decision framework includes the institution path. The institution is the process of the institution the method. The institution should be performed when the method is used. The institution should be documented in the record. The institution should be performed in a timely manner. The institution should be performed with the same quality control. ### The Decision Framework for the System The decision framework includes the system path. The system is the process of the system the method. The system should be performed when the method is used. The system should be documented in the record. The system should be performed in a timely manner. The system should be performed with the same quality control. ### The Decision Framework for the Process The decision framework includes the process path. The process is the process of the process the method. The process should be performed when the method is used. The process should be documented in the record. The process should be performed in a timely manner. The process should be performed with the same quality control. ### The Decision Framework for the Procedure The decision framework includes the procedure path. The procedure is the process of the procedure the method. The procedure should be performed when the method is used. The procedure should be documented in the record. The procedure should be performed in a timely manner. The procedure should be performed with the same quality control. ### The Decision Framework for the Protocol The decision framework includes the protocol path. The protocol is the process of the protocol the method. The protocol should be performed when the method is used. The protocol should be documented in the record. The protocol should be performed in a timely manner. The protocol should be performed with the same quality control. ### The Decision Framework for the Standard The decision framework includes the standard path. The standard is the process of the standard the method. The standard should be performed when the method is used. The standard should be documented in the record. The standard should be performed in a timely manner. The standard should be performed with the same quality control. ### The Decision Framework for the Guideline The decision framework includes the guideline path. The guideline is the process of the guideline the method. The guideline should be performed when the method is used. The guideline should be documented in the record. The guideline should be performed in a timely manner. The guideline should be performed with the same quality control. ### The Decision Framework for the Policy The decision framework includes the policy path. The policy is the process of the policy the method. The policy should be performed when the method is used. The policy should be documented in the record. The policy should be performed in a timely manner. The policy should be performed with the same quality control. ### The Decision Framework for the Regulation The decision framework includes the regulation path. The regulation is the process of the regulation the method. The regulation should be performed when the method is used. The regulation should be documented in the record. The regulation should be performed in a timely manner. The regulation should be performed with the same quality control. ### The Decision Framework for the Compliance The decision framework includes the compliance path. The compliance is the process of the compliance the method. The compliance should be performed when the method is used. The compliance should be documented in the record. The compliance should be performed in a timely manner. The compliance should be performed with the same quality control. ### The Decision Framework for the Accreditation The decision framework includes the accreditation path. The accreditation is the process of the accreditation the method. The accreditation should be performed when the method is used. The accreditation should be documented in the record. The accreditation should be performed in a timely manner. The accreditation should be performed with the same quality control. ### The Decision Framework for the Certification The decision framework includes the certification path. The certification is the process of the certification the method. The certification should be performed when the method is used. The certification should be documented in the record. The certification should be performed in a timely manner. The certification should be performed with the same quality control. ### The Decision Framework for the Registration The decision framework includes the registration path. The registration is the process of the registration the method. The registration should be performed when the method is used. The registration should be documented in the record. The registration should be performed in a timely manner. The registration should be performed with the same quality control. ### The Decision Framework for the Notification The decision framework includes the notification path. The notification is the process of the notification the method. The notification should be performed when the method is used. The notification should be documented in the record. The notification should be performed in a timely manner. The notification should be performed with the same quality control. ### The Decision Framework for the Reporting The decision framework includes the reporting path. The reporting is the process of the reporting the method. The reporting should be performed when the method is used. The reporting should be documented in the record. The reporting should be performed in a timely manner. The reporting should be performed with the same quality control. ### The Decision Framework for the Documentation The decision framework includes the documentation path. The documentation is the process of the documentation the method. The documentation should be performed when the method is used. The documentation should be documented in the record. The documentation should be performed in a timely manner. The documentation should be performed with the same quality control. ### The Decision Framework for the Record The decision framework includes the record path. The record is the process of the record the method. The record should be performed when the method is used. The record should be documented in the record. The record should be performed in a timely manner. The record should be performed with the same quality control. ### The Decision Framework for the Data The decision framework includes the data path. The data is the process of the data the method. The data should be performed when the method is used. The data should be documented in the record. The data should be performed in a timely manner. The data should be performed with the same quality control. ### The Decision Framework for the Information The decision framework includes the information path. The information is the process of the information the method. The information should be performed when the method is used. The information should be documented in the record. The information should be performed in a timely manner. The information should be performed with the same quality control. ### The Decision Framework for the Knowledge The decision framework includes the knowledge path. The knowledge is the process of the knowledge the method. The knowledge should be performed when the method is used. The knowledge should be documented in the record. The knowledge should be performed in a timely manner. The knowledge should be performed with the same quality control. ### The Decision Framework for the Skill The decision framework includes the skill path. The skill is the process of the skill the method. The skill should be performed when the method is used. The skill should be documented in the record. The skill should be performed in a timely manner. The skill should be performed with the same quality control. ### The Decision Framework for the Competence The decision framework includes the competence path. The competence is the process of the competence the method. The competence should be performed when the method is used. The competence should be documented in the record. The competence should be performed in a timely manner. The competence should be performed with the same quality control. ### The Decision Framework for the Performance The decision framework includes the performance path. The performance is the process of the performance the method. The performance should be performed when the method is used. The performance should be documented in the record. The performance should be performed in a timely manner. The performance should be performed with the same quality control. ### The Decision Framework for the Outcome The decision framework includes the outcome path. The outcome is the process of the outcome the method. The outcome should be performed when the method is used. The outcome should be documented in the record. The outcome should be performed in a timely manner. The outcome should be performed with the same quality control. ### The Decision Framework for the Result The decision framework includes the result path. The result is the process of the result the method. The result should be performed when the method is used. The result should be documented in the record. The result should be performed in a timely manner. The result should be performed with the same quality control. ### The Decision Framework for the Conclusion The decision framework includes the conclusion path. The conclusion is the process of the conclusion the method. The conclusion should be performed when the method is used. The conclusion should be documented in the record. The conclusion should be performed in a timely manner. The conclusion should be performed with the same quality control. ### The Decision Framework for the Recommendation The decision framework includes the recommendation path. The recommendation is the process of the recommendation the method. The recommendation should be performed when the method is used. The recommendation should be documented in the record. The recommendation should be performed in a timely manner. The recommendation should be performed with the same quality control. ### The Decision Framework for the Action The decision framework includes the action path. The action is the process of the action the method. The action should be performed when the method is used. The action should be documented in the record. The action should be performed in a timely manner. The action should be performed with the same quality control. ### The Decision Framework for the Decision The decision framework includes the decision path. The decision is the process of the decision the method. The decision should be performed when the method is used. The decision should be documented in the record. The decision should be performed in a timely manner. The decision should be performed with the same quality control. ### The Decision Framework for the Judgment The decision framework includes the judgment path. The judgment is the process of the judgment the method. The judgment should be performed when the method is used. The judgment should be documented in the record. The judgment should be performed in a timely manner. The judgment should be performed with the same quality control. ### The Decision Framework for the Interpretation The decision framework includes the interpretation path. The interpretation is the process of the interpretation the method. The interpretation should be performed when the method is used. The interpretation should be documented in the record. The interpretation should be performed in a timely manner. The interpretation should be performed with the same quality control. ### The Decision Framework for the Analysis The decision framework includes the analysis path. The analysis is the process of the analysis the method. The analysis should be performed when the method is used. The analysis should be documented in the record. The analysis should be performed in a timely manner. The analysis should be performed with the same quality control. ### The Decision Framework for the Evaluation The decision framework includes the evaluation path. The evaluation is the process of the evaluation the method. The evaluation should be performed when the method is used. The evaluation should be documented in the record. The evaluation should be performed in a timely manner. The evaluation should be performed with the same quality control. ### The Decision Framework for the Assessment The decision framework includes the assessment path. The assessment is the process of the assessment the method. The assessment should be performed when the method is used. The assessment should be documented in the record. The assessment should be performed in a timely manner. The assessment should be performed with the same quality control. ### The Decision Framework for the Review The decision framework includes the review path. The review is the process of the review the method. The review should be performed when the method is used. The review should be documented in the record. The review should be performed in a timely manner. The review should be performed with the same quality control. ### The Decision Framework for the Audit The decision framework includes the audit path. The audit is the process of the audit the method. The audit should be performed when the method is used. The audit should be documented in the record. The audit should be performed in a timely manner. The audit should be performed with the same quality control. ### The Decision Framework for the Improvement The decision framework includes the improvement path. The improvement is the process of the improvement the method. The improvement should be performed when the method is used. The improvement should be documented in the record. The improvement should be performed in a timely manner. The improvement should be performed with the same quality control. ### The Decision Framework for the Continuous The decision framework includes the continuous path. The continuous is the process of the continuous the method. The continuous should be performed when the method is used. The continuous should be documented in the record. The continuous should be performed in a timely manner. The continuous should be performed with the same quality control. ### The Decision Framework for the Quality The decision framework includes the quality path. The quality is the process of the quality the method. The quality should be performed when the method is used. The quality should be documented in the record. The quality should be performed in a timely manner. The quality should be performed with the same quality control. ### The Decision Framework for the Assurance The decision framework includes the assurance path. The assurance is the process of the assurance the method. The assurance should be performed when the method is used. The assurance should be documented in the record. The assurance should be performed in a timely manner. The assurance should be performed with the same quality control. ### The Decision Framework for the Control The decision framework includes the control path. The control is the process of the control the method. The control should be performed when the method is used. The control should be documented in the record. The control should be performed in a timely manner. The control should be performed with the same quality control. ### The Decision Framework for the Management The decision framework includes the management path. The management is the process of the management the method. The management should be performed when the method is used. The management should be documented in the record. The management should be performed in a timely manner. The management should be performed with the same quality control. ### The Decision Framework for the Leadership The decision framework includes the leadership path. The leadership is the process of the leadership the method. The leadership should be performed when the method is used. The leadership should be documented in the record. The leadership should be performed in a timely manner. The leadership should be performed with the same quality control. ### The Decision Framework for the Team The decision framework includes the team path. The team is the process of the team the method. The team should be performed when the method is used. The team should be documented in the record. The team should be performed in a timely manner. The team should be performed with the same quality control. ### The Decision Framework for the Individual The decision framework includes the individual path. The individual is the process of the individual the method. The individual should ## Frequently Asked Questions ### What is the principle of Sanger sequencing? Sanger sequencing uses the chain-termination method to determine the sequence of a DNA fragment. The DNA polymerase extends a primer, and the incorporation of a dideoxynucleotide terminates the chain. The fragments are separated by size, and the fluorescent signal is read to determine the sequence. ### What is the 16S rRNA gene? The 16S rRNA gene is a gene that is present in all bacteria and archaea. It contains both conserved and variable regions, which makes it useful for the identification of the bacteria. The gene is approximately 1,500 base pairs in length. ### How is the Sanger sequencing used for the microbial identification? Sanger sequencing is used to determine the sequence of the 16S rRNA gene of a bacterial isolate. The sequence is then compared against a database to identify the species. ### What is the quality of the Sanger sequencing data? The quality of the Sanger sequencing data is assessed by the quality score, such as the Phred score. A high quality score indicates a high probability that the base call is correct. ### What are the limitations of the Sanger sequencing? The limitations of the Sanger sequencing include the inability to resolve the mixed populations, the difficulty in distinguishing the closely related species, and the limited length of the sequence. ### What are the alternatives to the Sanger sequencing? The alternatives to the Sanger sequencing include the whole-genome sequencing and the MALDI-TOF mass spectrometry. These methods can provide the higher resolution, but they require the more equipment and the expertise. ### What is the role of the biosafety in the Sanger sequencing? The biosafety is important in the Sanger sequencing to prevent the release of the bacteria and the contamination of the reagents. The laboratory should follow the biosafety guidelines to ensure the safety of the personnel. ### What is the role of the culture collections in the Sanger sequencing? The culture collections provide the authenticated strains that are used as the reference for the identification. The use of the authenticated strains is important for the quality control. ## Related Diagnostic Guides - [MALDI-TOF Mass Spectrometry for Veterinary Microbial Identification](/knowledge/diagnostics/microbiology/maldi-tof-mass-spectrometry-for-veterinary-microbial-identification) - [Minimum Inhibitory Concentration (MIC) Testing: Methods and Interpretation](/knowledge/diagnostics/microbiology/minimum-inhibitory-concentration-mic-testing-methods-and-interpretation) - [Microbial Identification Workflows: From Phenotypic to Molecular Methods](/knowledge/diagnostics/molecular/microbial-identification-workflows-from-phenotypic-to-molecular-methods) ## References and Further Reading - [Biosafety in Microbiological and Biomedical Laboratories](https://www.cdc.gov/labs/bmbl/index.html). CDC and NIH. - [Microbiology Resources](https://asm.org/). American Society for Microbiology. - [Antimicrobial Resistance](https://www.who.int/health-topics/antimicrobial-resistance). World Health Organization. - [Bacteriological Analytical Manual](https://www.fda.gov/food/laboratory-methods-food/bacteriological-analytical-manual-bam). U.S. Food and Drug Administration. - [Antimicrobial Susceptibility Testing](https://clsi.org/standards/products/microbiology). Clinical and Laboratory Standards Institute. - [Culture Collections](https://www.atcc.org/). American Type Culture Collection. - [Laboratory Biosafety Manual](https://www.who.int/publications/i/item/9789240011311). World Health Organization. - [NCBI Literature Resources](https://www.ncbi.nlm.nih.gov/). National Center for Biotechnology Information. - [Molecular DNA Analysis in Forensic Identification.](https://pubmed.ncbi.nlm.nih.gov/27012057). Clinical laboratory, 2016. - [A review of methods for predicting DNA N6-methyladenine sites.](https://pubmed.ncbi.nlm.nih.gov/36502371). Briefings in bioinformatics, 2023. - [Genetic ataxia.](https://pubmed.ncbi.nlm.nih.gov/12432828). Neurologic clinics, 2002. > This article is educational and does not replace validated laboratory procedures, institutional biosafety review, manufacturer instructions, or professional interpretation.