# Troubleshooting Failed Quality Control in Microbial Identification ## Quick Answer - Failed quality control in microbial identification requires a systematic root-cause investigation covering reference strains, reagents, equipment, and operator technique before repeating the test. - Begin corrective action by verifying the purity and viability of the reference culture, then confirm reagent integrity and instrument calibration using documented records. - A single failed QC result does not invalidate patient or sample results until the root cause is confirmed and corrective action is documented. ## Understanding Quality Control in Microbial Identification Quality control in microbial identification laboratories serves as the verification system that confirms identification systems perform as expected. Clinical and public health laboratories rely on reference strains with known characteristics to validate that biochemical panels, mass spectrometry systems, and molecular methods produce accurate results. The [American Society for Microbiology](https://asm.org/) provides professional education and laboratory practice resources that emphasize the central role of quality control in maintaining workforce competence and diagnostic reliability. Quality control failures occur when a reference strain produces an unexpected result, when control organisms fail to grow, or when identification scores fall below acceptable thresholds. These failures demand immediate attention because they signal that patient or sample results generated during the affected period may be unreliable. The [U.S. Food and Drug Administration Bacteriological Analytical Manual](https://www.fda.gov/food/laboratory-methods-food/bacteriological-analytical-manual-bam) describes official methods for food microbiology testing where quality control procedures are integral to method validation and ongoing performance verification. The troubleshooting process requires a structured approach that separates the identification system itself from the materials and people involved in the test. A failed control can originate from a degraded reference strain, expired reagents, malfunctioning equipment, or procedural errors. Each potential cause requires specific investigation steps and documentation before the system can be returned to service. ## At a Glance The table below summarizes the primary categories of quality control failure in microbial identification, the typical evidence that points to each category, and the first corrective action to consider. | Failure Category | Typical Observation | First Corrective Action | | --- | --- | --- | | Reference strain problem | Expected organism fails to grow or produces atypical reactions | Subculture from a fresh authenticated stock and repeat the test | | Reagent or media failure | Controls show no growth, poor growth, or unexpected biochemical reactions | Verify lot numbers, expiration dates, and storage conditions | | Equipment malfunction | Instrument errors, inconsistent readings, or calibration flags | Run instrument diagnostics and verify calibration records | | Operator technique error | Results vary between operators or repeated runs show inconsistent patterns | Review standard operating procedures and observe technique | ## Reference Strain Verification Reference strains are the foundation of microbial identification quality control. These organisms have documented biochemical profiles, genetic characteristics, and expected identification results that serve as the benchmark for system validation. The [American Type Culture Collection](https://www.atcc.org/) maintains authenticated biological materials that laboratories use as quality control references, and the provenance and handling of these materials directly affect QC outcomes. ### Authenticated Stock Sources Reference strains must come from a recognized culture collection or an equivalent accredited source. Strains obtained from clinical specimens, environmental samples, or other laboratories without documented authentication do not provide a reliable baseline for quality control. The strain identity must be confirmed at the time of acquisition and periodically verified according to laboratory policy. When a QC failure occurs, the first question is whether the strain being tested is actually the organism it is supposed to be. Cross-contamination during storage, mislabeling of vials, or the use of a strain that has been passaged too many times can all produce a strain that no longer matches the expected identification profile. ### Storage and Subculture Practices Reference strains require specific storage conditions to maintain viability and genetic stability. Most reference cultures are stored frozen at ultra-low temperatures or lyophilized for long-term preservation. Working cultures that are maintained on agar slants or plates have a limited lifespan and must be replaced from the authenticated stock on a defined schedule. Repeated subculture of a reference strain can lead to phenotypic drift, where the organism changes its biochemical expression over time. This drift can produce QC results that fail because the strain no longer expresses the expected characteristics. Laboratories should maintain a two-tier system with a master stock that is rarely opened and a working stock that is used for routine QC. ### Viability and Purity Checks Before a reference strain is used for QC, its viability and purity must be confirmed. A viability check ensures that the organism is alive and capable of growth under the test conditions. A purity check confirms that the culture contains only the intended organism and has not been contaminated with another species. A failed QC result that is accompanied by poor growth, mixed colony morphology, or unexpected colony characteristics suggests that the strain itself is the problem. The laboratory should repeat the test with a fresh subculture from the master stock before investigating the identification system. ## Reagent and Media Assessment Reagents and media are the chemical and nutritional environment that supports microbial growth and drives the biochemical reactions used for identification. These materials have defined compositions, storage requirements, and expiration dates that must be followed to produce reliable results. ### Expiration and Storage Conditions Each reagent and medium has an expiration date that is established by the manufacturer based on stability studies. Using expired materials can produce failed QC results because the chemical components may have degraded, the pH may have shifted, or the selective and differential properties may have been lost. Storage conditions are equally important. Some reagents require refrigeration, some require protection from light, and some must be used within a specific time after opening. A laboratory that stores reagents incorrectly can cause QC failures even when the materials are within their expiration dates. ### Lot-to-Lot Variability Manufacturers may produce different lots of the same reagent or medium with minor variations in composition. These variations are usually within acceptable limits, but they can occasionally affect the performance of an identification system. When a new lot of reagent is introduced, the laboratory should verify that the lot performs as expected before it is used for patient testing. A QC failure that occurs immediately after a new lot of reagent or medium is introduced points to a lot-specific problem. The laboratory should contact the manufacturer and report the failure while retaining the affected lot for investigation. ### Preparation and Sterility Media that is prepared in the laboratory must follow the manufacturer instructions for preparation, sterilization, and cooling. Overheating can destroy nutrients or alter the pH of the medium. Under-sterilization can leave contaminating organisms that interfere with the identification reactions. The sterility of prepared media should be verified by incubating a sample of each batch and checking for growth. A QC failure that is accompanied by growth in the sterility control indicates that the media preparation process is the source of the problem. ## Equipment and Instrumentation Automated identification systems rely on instruments that measure growth, biochemical reactions, or mass spectra. These instruments require regular calibration, maintenance, and verification to produce accurate results. ### Calibration and Maintenance Each instrument has a documented calibration schedule that is established by the manufacturer and the laboratory quality management system. Calibration verifies that the instrument is measuring within acceptable tolerances. Maintenance includes cleaning, replacement of worn parts, and software updates. A QC failure that occurs after a maintenance event, a power outage, or a software update should trigger a review of the instrument status. The laboratory should verify that the instrument has completed its calibration cycle and that no error messages or flags are present. ### Software and Database Updates Automated identification systems rely on software and databases that contain the reference spectra or biochemical profiles used to identify organisms. These databases are updated periodically to include new species or to correct errors in existing entries. An outdated database can cause a QC failure because the reference strain may be identified correctly by the system but the database may not contain the correct profile. The laboratory should verify that the software and database versions are current and that the update was completed successfully. A QC failure that occurs after a database update may indicate that the update was incomplete or that the update introduced an error. ### Environmental Conditions Instruments have operating ranges for temperature, humidity, and power supply. An instrument that is operated outside these ranges can produce inconsistent readings. The laboratory should verify that the instrument is in the correct environment and that the environmental monitoring records are within the acceptable range. ## Operator Technique and Procedure The operator is the final component of the identification system. The technique used to prepare the inoculum, load the instrument, and interpret the results can introduce errors that produce a failed QC. ### Inoculum Preparation The inoculum must be prepared to the correct density and from the correct growth phase. An inoculum that is too heavy or too light can produce incorrect biochemical reactions or mass spectrometry results. The operator must follow the manufacturer instructions for the preparation of the inoculum, including the choice of medium, the incubation time, and the suspension fluid. ### Sample Loading and Handling The operator must load the sample into the instrument correctly. This includes the correct placement of the sample, the correct volume, and the correct timing. An error in any of these steps can produce a failed QC result. ### Interpretation of Results The operator must interpret the results according to the manufacturer instructions. This includes the reading of color changes, the interpretation of growth patterns, and the use of the software to generate the identification. An operator who misinterprets a result can report a QC failure when the system is actually working correctly. ## Common Failure Patterns The following patterns are commonly observed when QC fails in microbial identification. Recognizing the pattern can help the laboratory narrow the root cause. ### Total Failure of Growth When the reference strain does not grow at all, the problem is likely in the media, the inoculum, or the viability of the strain. The laboratory should check the media for sterility and expiration, verify the inoculum density, and confirm that the strain is viable. ### Atypical Biochemical Profile When the reference strain grows but produces biochemical reactions that do not match the expected profile, the problem may be in the reagents, the strain, or the database. The laboratory should check the reagent lot and expiration, verify the strain identity, and confirm the database version. ### Inconsistent Results Between Runs When the same reference strain produces different results in different runs, the problem is likely in the operator technique or the instrument. The laboratory should review the operator technique and verify the instrument calibration. ### Instrument Error Messages When the instrument reports an error or a flag, the problem is likely in the instrument or the sample. The laboratory should review the error message, check the instrument status, and repeat the test with a fresh sample. ## Decision Tree for Corrective Action The following decision tree provides a structured approach to identifying the root cause of a QC failure. The laboratory should follow the steps in order and document the results of each step. ```mermaid flowchart TD A[QC Failure Observed] --> B{Verify Reference Strain} B -->|Strain is viable and pure| C{Check Reagents and Media} B -->|Strain is not viable or pure| D[Replace from Master Stock] C -->|Reagents and media are valid| E{Check Equipment} C -->|Reagents are expired or contaminated| F[Replace Reagents or Media] E -->|Equipment is calibrated| G{Review Operator Technique} E -->|Equipment is not calibrated| H[Calibrate Equipment] G -->|Technique is correct| I[Contact Manufacturer] G -->|Technique is incorrect| J[Retrain Operator] D --> C F --> C H --> C J --> C I --> K[Document and Escalate] ``` ## Records and Documentation Documentation is the backbone of a quality control program. Every QC test, every failure, and every corrective action must be recorded in a way that is traceable and auditable. ### QC Records The QC record should include the date of the test, the reference strain used, the lot number of the reagents and media, the instrument used, the operator, and the result. This information allows the laboratory to trace a failure to a specific strain, lot, or operator. ### Corrective Action Records When a QC failure occurs, the corrective action must be documented. The record should include the date of the failure, the root cause, the action taken, and the date the action was completed. The record should also include the results of the repeat QC test that confirms the system is working correctly. ### Escalation Criteria The laboratory should have a defined process for escalating a QC failure that cannot be resolved by the routine corrective actions. The escalation should include the manufacturer of the identification system, the laboratory supervisor, and the quality assurance team. The escalation should be documented and the outcome should be recorded. ## Biosafety and Containment The handling of reference strains and the performance of QC tests must follow the biosafety principles described in the [Biosafety in Microbiological and Biomedical Laboratories](https://www.cdc.gov/labs/bmbl/index.html). The risk assessment for the reference strain determines the biosafety level required for the work. ### Risk Assessment The laboratory must perform a risk assessment for each reference strain. The risk assessment considers the pathogenicity of the organism, the route of transmission, and the concentration of the organism. The risk assessment determines the biosafety level, the containment equipment, and the personal protective equipment required. ### Containment and Decontamination The laboratory must use the appropriate containment equipment, such as a biological safety cabinet, when working with reference strains. The work area must be decontaminated after the work is complete. The decontamination method must be effective against the organism being used. ### Waste Disposal The waste generated during QC testing must be disposed of according to the laboratory biosafety and waste management procedures. The waste must be decontaminated before it is removed from the laboratory. ## Antimicrobial Resistance Context The [World Health Organization](https://www.who.int/health-topics/antimicrobial-resistance) describes antimicrobial resistance as a global public health concern. The accuracy of microbial identification is a prerequisite for the accurate detection of antimicrobial resistance. A failed QC in the identification system can lead to the misidentification of an organism, which can lead to the incorrect reporting of antimicrobial resistance. ### The Role of Identification in Resistance Surveillance The identification of the organism is the first step in the detection of antimicrobial resistance. The organism must be correctly identified before the antimicrobial susceptibility test is performed. A failed QC in the identification system can lead to the wrong organism being tested, which can produce a false resistance result. ### The Impact of Failed QC on Stewardship The [Clinical and Laboratory Standards Institute](https://clsi.org/standards/products/microbiology) provides standards for antimicrobial susceptibility testing. The accuracy of the identification is a prerequisite for the accuracy of the susceptibility test. A failed QC in the identification system can lead to the wrong antimicrobial therapy being prescribed, which can contribute to the development of antimicrobial resistance. ## Professional Escalation Criteria The laboratory should escalate a QC failure when the internal corrective actions do not resolve the problem. The following criteria indicate that the failure should be escalated. ### Repeated Failures A QC failure that occurs more than once for the same reference strain, reagent, or instrument should be escalated. The repeated failure indicates that the problem is not a random event and that a systematic issue exists. ### Failure After Corrective Action A QC failure that occurs after the corrective action has been taken indicates that the corrective action was not effective. The failure should be escalated to the manufacturer or the quality assurance team. ### Failure with a New Lot A QC failure that occurs with a new lot of reagents or media should be escalated to the manufacturer. The manufacturer should be informed of the failure and the lot number. ### Failure with a New Instrument A QC failure that occurs with a new instrument should be escalated to the manufacturer. The manufacturer should be informed of the failure and the instrument serial number. ## A Practical Failure Investigation Framework for Microbial Identification QC A structured investigation framework converts a failed quality control event from a reactive problem into a manageable process with defined steps, clear ownership, and measurable outcomes. The framework described below is designed for laboratories that use automated identification systems, biochemical panels, or mass spectrometry platforms. It is intended to be adapted to the specific instruments and methods in use at each facility. ### The Five Phase Investigation Model The investigation model divides the response to a failed QC into five distinct phases. Each phase has a defined objective, a set of actions, and a decision point that determines whether the investigation proceeds to the next phase or returns to an earlier one. This structure prevents the common error of repeating the same test without understanding why it failed. **Phase One: Containment and Documentation** The objective of the first phase is to stop the use of the affected system and to capture all information about the failure while it is fresh. The operator who observed the failure should record the date and time, the reference strain used, the lot numbers of all reagents and media, the instrument identification, the software version, and the exact result that was obtained. This information is the foundation of the entire investigation. The laboratory should also identify the scope of the affected work. If the failed QC was performed at the start of a run, the results from that run are suspect. If the failed QC was performed after a run, the results from the previous run may also be affected. The laboratory should document the time period during which the system was in use and the patient or sample results that were generated during that period. The containment action is to remove the affected system from service. This means that no new patient or sample testing should be performed on the system until the investigation is complete and the system is verified to be working correctly. The laboratory should also notify the relevant personnel, including the laboratory supervisor and the quality assurance team, that a QC failure has occurred. **Phase 2: Evidence Collection** The objective of the second phase is to gather all physical and documentary evidence that could explain the failure. This evidence is collected before any corrective action is taken, because the corrective action may destroy the evidence. The evidence to collect includes the following: - The failed QC panel or plate, if it has been retained. The panel should be photographed or scanned to document the exact pattern of reactions. - The reference strain culture that was used for the test. The culture should be examined for purity and viability, and a subculture should be made for further testing. - The reagents and media that were used, including the lot numbers, expiration dates, and storage conditions. The laboratory should verify that the storage temperature was within the acceptable range and that the materials were not exposed to conditions that could degrade them. - The instrument records, including the calibration status, the maintenance history, and any error messages or flags that were generated during the run. - The operator records, including the identity of the operator, the training records, and the standard operating procedure that was followed. The evidence should be organized in a way that allows the investigation team to review it systematically. A simple table that lists each piece of evidence, its source, and its relevance to the failure can be useful. **Phase 3: Root Cause Analysis** The objective of the third phase is to identify the root cause of the failure. The root cause is the underlying condition that led to the failure, not the immediate symptom. For example, the immediate symptom may be that the reference strain did not grow. The root cause may be that the media was expired, that the inoculum was prepared incorrectly, or that the strain was not viable. The root cause analysis should use the evidence collected in the previous phase. The laboratory should compare the observed results with the expected results for the reference strain. The laboratory should also compare the conditions of the failed test with the conditions that are specified in the standard operating procedure. The analysis should consider each of the potential causes in turn. The reference strain should be checked for viability, purity, and identity. The reagents and media should be checked for expiration, storage, and lot-to-lot variability. The equipment should be checked for calibration, maintenance, and environmental conditions. The operator technique should be reviewed for compliance with the standard operating procedure. The root cause analysis should be documented. The documentation should include the evidence that was reviewed, the potential causes that were considered, and the evidence that supported or ruled out each potential cause. The documentation should also include the final conclusion about the root cause. **Phase 4: Corrective Action** The objective of the fourth phase is to implement the corrective action that addresses the root cause. The corrective action should be specific to the root cause that was identified. If the root cause was an expired reagent, the corrective action is to replace the reagent with a fresh lot. If the root cause was an operator error, the corrective action is to retrain the operator. If the root cause was an instrument malfunction, the corrective action is to repair or recalibrate the instrument. The corrective action should be documented before it is implemented. The documentation should include the action to be taken, the person responsible for taking the action, and the date by which the action will be completed. The documentation should also include the expected outcome of the action. The corrective action should be implemented in a way that is verifiable. For example, if the corrective action is to replace a reagent, the new reagent should be checked for the correct lot number and expiration date before it is used. If the corrective action is to retrain an operator, the operator should be observed performing the procedure and the observation should be documented. **Phase 5: Verification and Release** The objective of the fifth phase is to verify that the corrective action has resolved the problem and to release the system back into service. The verification should be performed by repeating the QC test that failed. The repeat test should be performed using the same reference strain, the same method, and the same conditions that were used for the failed test. The repeat test should be performed by the same operator or by a different operator, depending on the root cause. If the root cause was an operator error, the repeat test should be performed by the same operator after retraining. If the root cause was a reagent or equipment problem, the repeat test should be performed by a different operator to confirm that the problem is resolved. The repeat test must pass before the system is released back into service. The laboratory should document the repeat test result and the date and time of the release. The laboratory should also document the review of the patient or sample results that were generated during the affected period. The review of the affected results should be performed by the laboratory supervisor or the quality assurance team. The review should determine whether the failed QC affects the accuracy of the results. The review should be documented, and the decision to accept or reject the results should be recorded. ### The Investigation Record The investigation record is the written documentation of the entire process. The record should be complete enough that a person who was not involved in the investigation can understand what happened, what was done, and why. The record should also be complete enough to support an audit or an inspection. The investigation record should include the following sections: - The initial failure report, including the date, time, operator, reference strain, and result. - The containment actions that were taken, including the removal of the system from service and the notification of personnel. - The evidence that was collected, including the reference strain, the reagents, the instrument records, and the operator records. - The root cause analysis, including the evidence reviewed, the potential causes considered, and the conclusion. - The corrective action that was implemented, including the action, the responsible person, and the completion date. - The verification results, including the repeat QC test result and the date of the release. - The review of the affected patient or sample results, including the decision and the rationale for the decision. The investigation record should be reviewed and approved by the laboratory supervisor or the quality assurance team. The record should be retained according to the laboratory document control policy. ### The Role of the Investigation in the Quality Management System The investigation of a failed QC is not an isolated event. It is part of the laboratory quality management system. The investigation provides information that can be used to improve the quality of the laboratory operations. The investigation can identify trends in QC failures. For example, if the laboratory has multiple QC failures that are caused by expired reagents, the laboratory may need to improve its inventory management. If the laboratory has multiple failures that are caused by operator error, the laboratory may need to improve its training program. The investigation can also identify problems with the identification system itself. If the laboratory has repeated failures with a specific reagent lot, the laboratory should report the problem to the manufacturer. The manufacturer may need to investigate the lot and may need to issue a recall or a corrective action. The investigation should be reviewed as part of the laboratory quality management review. The review should consider the number of QC failures, the root causes of the failures, and the effectiveness of the corrective actions. The review should also consider whether the investigation process itself is effective and whether it needs to be improved. ### Common Mistakes in the Investigation Process The investigation process can be undermined by common mistakes. The laboratory should be aware of these mistakes and should take steps to avoid them. **Mistake 1: Repeating the Test Without Investigation** The most common mistake is to repeat the failed QC test without investigating the cause of the failure. This approach is tempting because it is fast and simple. However, it is not effective. If the root cause of the failure is not identified and corrected, the repeat test will also fail. The repeat test will also not provide any information about the cause of the failure. The laboratory should not repeat the failed test until the investigation has been completed. The investigation should be the first step, and the repeat test should be the last step. **Mistake 2: Focusing on a Single Cause** The second mistake is to focus on a single cause and to ignore the other potential causes. For example, the laboratory may assume that the failure is caused by the reference strain and may not investigate the reagents or the equipment. This approach can miss the actual root cause of the failure. The laboratory should consider all of the potential causes of the failure. The investigation should be systematic and should consider the reference strain, the reagents, the equipment, and the operator. **Mistake 3: Not Documenting the Investigation** The third mistake is to not document the investigation. The laboratory may perform the investigation and identify the root cause, but may not document the process or the outcome. This approach is a problem because the documentation is required for the quality management system. The documentation is also required for the audit and the inspection. The laboratory should document the investigation from the beginning to the end. The documentation should be complete and should be retained. **Mistake 4: Not Reviewing the Affected Results** The fourth mistake is to not review the patient or sample results that were generated during the affected period. The laboratory may correct the problem and release the system back into service, but may not review the results that were generated while the system was not working correctly. This approach is a problem because the results may be inaccurate and may need to be corrected. The laboratory should review the affected results and determine whether the results are accurate. The review should be documented and the decision should be recorded. ### The Investigation and the Laboratory Culture The investigation of a failed QC is a technical process, but it is also a cultural process. The laboratory culture determines how the investigation is conducted and how the results are used. A laboratory with a positive culture will view the failed QC as an opportunity to improve. The laboratory will investigate the failure openly and honestly. The laboratory will use the results of the investigation to improve the quality of the system. A laboratory with a negative culture will view the failed QC as a problem to be hidden. The laboratory may not investigate the failure, or may not document the investigation. The laboratory may blame the operator or the manufacturer for the failure. This approach is not effective and can lead to repeated failures. The laboratory should promote a positive culture around the QC investigation. The laboratory should encourage the staff to report the failures and to participate in the investigation. The laboratory should recognize the staff who identify the root cause and implement the corrective action. ### The Investigation and the Manufacturer The investigation of a failed QC may involve the manufacturer of the identification system. The laboratory should contact the manufacturer when the root cause of the failure is not identified, when the failure is repeated, or when the failure is related to a specific lot of a reagent or a specific instrument. The manufacturer should be provided with the information about the failure, including the reference strain, the reagent lot, the instrument serial number, and the results of the investigation. The manufacturer may be able to provide the laboratory with additional information about the system or the reagent. The manufacturer may also be able to investigate the issue and provide a corrective action. The laboratory should document the communication with the manufacturer. The documentation should include the date of the communication, the person who was contacted, and the information that was provided. The documentation should also include the outcome of the communication. ### The Investigation and the Training The investigation of a failed QC may identify a need for training. The training may be needed for the operator who performed the test, or for the entire laboratory staff. The training may be needed to correct a specific error, or to improve the general understanding of the identification system. The training should be documented. The documentation should include the date of the training, the topic of the training, the trainer, and the attendees. The documentation should also include the assessment of the training, if an assessment was performed. The training should be effective. The training should be designed to address the specific root cause of the failure. The training should also be designed to prevent the failure from occurring again. ### The Investigation and the Quality Assurance The investigation of a failed QC is a quality assurance activity. The quality assurance team should be involved in the investigation. The quality assurance team should review the investigation and the corrective action. The quality assurance team should also monitor the effectiveness of the corrective action. The quality assurance team should also use the investigation to improve the quality management system. The quality assurance team should identify the trends in the QC failures and should recommend the improvements to the system. The quality assurance team should also review the investigation process and should recommend the improvements to the process. The quality assurance team should also ensure that the investigation is documented and that the documentation is retained. The quality assurance team should also ensure that the investigation is conducted in a timely manner and that the corrective action is implemented in a timely manner. ### The Investigation and the Accreditation The investigation of a failed QC is also an accreditation requirement. The laboratory accreditation standards require the laboratory to have a process for the investigation of the QC failures. The laboratory must be able to demonstrate that the process is implemented and that the process is effective. The laboratory should be able to provide the documentation of the investigation to the accreditation body. The documentation should include the investigation record, the corrective action record, and the verification record. The documentation should also include the review of the affected results. The laboratory should be prepared for the accreditation inspection. The laboratory should be able to explain the investigation process and to provide the examples of the investigations that have been performed. The laboratory should also be able to demonstrate that the investigations have been effective in preventing the recurrence of the failures. ### The Investigation and the Continuous Improvement The investigation of a failed QC is an opportunity for continuous improvement. The laboratory should use the investigation to improve the quality of the identification system and the quality of the laboratory operations. The laboratory should review the investigation and identify the opportunities for improvement. The opportunities for improvement may include the improvement of the reagent management, the improvement of the training program, the improvement of the instrument maintenance, or the improvement of the standard operating procedures. The laboratory should implement the improvements and should monitor the effectiveness of the improvements. The laboratory should also document the improvements and should review the improvements as part of the quality management review. The continuous improvement is a cycle. The laboratory should identify the opportunities for improvement, implement the improvements, monitor the effectiveness of the improvements, and identify the new opportunities for improvement. The investigation of the QC failure is a key part of this cycle. ## Frequently Asked Questions ### What is the first step when a QC result fails? The first step is to verify the reference strain. Check the viability and purity of the strain and confirm that it is the correct organism. If the strain is not viable or is contaminated, replace it from the master stock and repeat the test. ### How long should a reference strain be stored? The storage time depends on the storage method and the manufacturer instructions. Frozen stocks at -80 degrees Celsius can be stored for years, while working cultures on agar are typically stored for weeks. The laboratory should follow the documented storage schedule. ### Can a failed QC be caused by a single operator error? Yes, an operator error in the preparation of the inoculum, the loading of the sample, or the interpretation of the results can cause a failed QC. The operator should review the procedure and repeat the test. ### What should be done if a QC failure occurs after a new lot of reagents is used? The laboratory should retain the new lot and contact the manufacturer. The manufacturer should be informed of the failure and the lot number. The laboratory should also check the storage and expiration of the new lot. ### How often should the instrument be calibrated? The calibration schedule is defined by the manufacturer and the laboratory quality control. The instrument should be calibrated according to the schedule and after any maintenance or software update. ### What is the role of the database in a QC failure? The database contains the profiles used to identify the organism. An outdated or incomplete database can cause a QC failure. The laboratory should verify that the database is current and that the update was successful. ### When should a QC failure be escalated to the manufacturer? A QC failure should be escalated when it is repeated, when it occurs after a corrective action, when it occurs with a new lot of reagents, or when it occurs with a new instrument. The manufacturer should be informed of the failure and the relevant details. ### What is the impact of a QC failure on patient results? A QC failure does not automatically invalidate patient results. The laboratory should review the results generated during the affected period and determine whether the failure affects the accuracy of the results. The laboratory should document the review and the decision. ## Using the Evidence | Source | Best use in this topic | Important limitation | |---|---|---| | [Biosafety in Microbiological and Biomedical Laboratories](https://www.cdc.gov/labs/bmbl/index.html) | official guidance | Check the linked page for current local requirements | | [Microbiology Resources](https://asm.org/) | official guidance | Check the linked page for current local requirements | | [Antimicrobial Resistance](https://www.who.int/health-topics/antimicrobial-resistance) | official guidance | Check the linked page for current local requirements | ## Related Diagnostic Guides - [Microbiology Quality Control: Essential Practices for Reliable Culture Results](/knowledge/diagnostics/microbiology/microbiology-quality-control-essential-practices-for-reliable-culture-results) - [MALDI-TOF Mass Spectrometry for Veterinary Microbial Identification](/knowledge/diagnostics/microbiology/maldi-tof-mass-spectrometry-for-veterinary-microbial-identification) - [Quality Control in Clinical Chemistry: Best Practices and Troubleshooting](/knowledge/diagnostics/clinical-pathology/quality-control-in-clinical-chemistry-best-practices-and-troubleshooting) - [Hematology Quality Control: Ensuring Accuracy in Automated Analyzers](/knowledge/diagnostics/clinical-pathology/hematology-quality-control-ensuring-accuracy-in-automated-analyzers) ## 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. - [Application of problem-based learning in EBERs-ISH theoretical and practical teaching.](https://doi.org/10.1186/s12909-026-08864-x). 2026. - [Steam sterilization: Review of autoclaves, validation, instrument packing, and sterility failures.](https://doi.org/10.4103/ijo.ijo_2023_25). 2026. - [Protocol to generate microglia-containing cerebral organoids to model HIV neuroinflammation.](https://doi.org/10.1016/j.xpro.2026.104604). 2026. > This article is educational and does not replace validated laboratory procedures, institutional biosafety review, manufacturer instructions, or professional interpretation.