# Colony Morphology Differentiation in Mixed Cultures ## Quick Answer - Colony morphology differentiation uses visual features like size, shape, color, texture, and hemolysis to separate organisms on primary isolation plates before biochemical testing. - The practical next step is to select the most clinically relevant colony type for subculture and identification while noting mixed growth in the final report. - A key limitation is that colony appearance alone cannot confirm species identity, so confirmatory testing remains mandatory for definitive results. ## Understanding Colony Morphology in Mixed Cultures Colony morphology refers to the macroscopic appearance of bacterial or fungal growth on solid culture media. When a clinical, food, or environmental specimen contains multiple organisms, the primary isolation plate presents a complex visual field where each species may produce a distinct colony type. The ability to recognize and differentiate these colony types is a foundational skill in diagnostic microbiology, directly influencing the accuracy of subsequent identification and susceptibility work. The practical value of colony morphology differentiation lies in its speed and cost-effectiveness. Before any automated identification system, biochemical panel, or molecular assay is used, the microbiologist must decide which colony to test. Selecting the wrong colony, or failing to recognize a mixed culture, can lead to misidentification, inappropriate therapy, and compromised patient care. In food microbiology, the same principle applies when determining whether a product contains a pathogen or a harmless contaminant. This article provides a structured approach to colony morphology differentiation in mixed cultures. It covers the core visual features to assess, the workflow for selecting colonies, common pitfalls, and the documentation practices that support reliable results. The guidance is grounded in standard laboratory practice and aligns with the professional standards promoted by the American Society for Microbiology and the official methods described in the FDA Bacteriological Analytical Manual. ## Core Principles of Colony Morphology Colony morphology is the product of the organism's genetic characteristics, the composition of the culture medium, and the incubation conditions. Each species tends to produce a characteristic colony appearance under standardized conditions, although variation can occur due to environmental factors, colony age, and the presence of other organisms. The standard features used to describe a colony are size, shape, margin, elevation, surface texture, opacity, color, and hemolysis on blood agar. These features are assessed with the naked eye and, when necessary, with a hand lens or dissecting microscope. The assessment is performed on isolated colonies, not on confluent growth, because crowding alters colony appearance and obscures the distinguishing features. ### Size and Shape Colony size is measured in millimeters and is typically described as pinpoint, small, medium, or large. The size depends on the growth rate of the organism, the incubation time, and the nutrient richness of the medium. For example, a fast-growing organism such as Escherichia coli will produce larger colonies after 24 hours than a slow-growing organism such as Mycobacterium tuberculosis. The shape of a colony is described as circular, irregular, rhizoid, or filamentous. Circular colonies are the most common and are typical of many Gram-positive and Gram-negative bacteria. Irregular colonies have a lobate or undulate edge and are often produced by organisms that spread across the agar surface. Rhizoid colonies have a root-like appearance and are characteristic of some Bacillus species and Nocardia species. ### Margin and Elevation The margin, or edge, of a colony is described as entire, undulate, lobate, erose, or filamentous. An entire margin is smooth and continuous, while an undulate margin has a wavy appearance. A lobate margin has rounded lobes, an erose margin has a jagged or irregular edge, and a filamentous margin has a hair-like extension. Elevation describes the vertical profile of the colony when viewed from the side. The common descriptions are flat, raised, convex, umbonate, and crateriform. A flat colony is level with the agar surface, a raised colony has a slight elevation, a convex colony is dome-shaped, an umbonate colony has a raised center, and a crateriform colony has a depressed center. ### Surface, Texture, and Opacity The surface of a colony can be smooth, rough, mucoid, or dry. A smooth surface is shiny and even, a rough surface is dull and uneven, a mucoid surface is wet and sticky, and a dry surface is brittle or powdery. The texture is assessed by touching the colony with a loop, which is a standard practice in the laboratory. Opacity describes how much light passes through the colony. The terms used are transparent, translucent, and opaque. A transparent colony allows light to pass through completely, a translucent colony allows some light to pass through, and an opaque colony blocks light entirely. ### Color and Pigmentation Colony color is a useful feature for differentiation, but it is not definitive. Some organisms produce pigments that are visible on the surface of the colony, such as the golden pigment of Staphylococcus aureus or the green pigment of Pseudomonas aeruginosa. Other organisms produce pigments that diffuse into the medium, such as the pyocyanin of Pseudomonas aeruginosa or the brown pigment of some Bacteroides species. The color of a colony can also be influenced by the medium. For example, MacConkey agar contains a pH indicator that turns pink when lactose is fermented, and this color change is used to differentiate lactose-fermenting from non-lactose-fermenting organisms. ### Hemolysis on Blood Agar Hemolysis is the breakdown of red blood cells in the blood agar medium. It is a key feature for differentiating organisms, particularly the Streptococcus species. The three types are alpha, beta, and gamma hemolysis. Alpha hemolysis produces a greenish discoloration around the colony, beta hemolysis produces a clear zone of complete lysis, and gamma hemolysis produces no change in the medium. The hemolysis pattern is observed after incubation and is best assessed against a light source. The zone of hemolysis is measured from the edge of the colony to the edge of the clear or discolored zone. ## At a Glance The following table summarizes the key colony morphology features and their typical descriptions. This table is a practical reference for the laboratory bench, and it is not a substitute for the full description in the text. | Feature | Description | Typical Use | | --- | --- | --- | | Size | Pinpoint, small, medium, large | Distinguishes fast-growing from slow-growing organisms | | Shape | Circular, irregular, rhizoid | Helps identify Bacillus and Nocardia species | | Margin | Entire, undulate, lobate, erose, filamentous | Aids in the identification of Listeria and other species | | Elevation | Flat, raised, convex, umbonate | Helps differentiate Streptococcus and Enterococcus | | Surface | Smooth, rough, mucoid, dry | Distinguishes mucoid strains from non-mucoid strains | | Color | White, cream, yellow, green, red | Aids in the identification of pigmented organisms | | Hemolysis | Alpha, beta, gamma | Key feature for Streptococcus species identification | ## Practical Workflow for Colony Differentiation The workflow for colony morphology differentiation begins with the primary culture plate and ends with the selection of a representative colony for further work. The steps are sequential and each step has a specific purpose. ### Step 1: Examine the Primary Plate The primary plate is the first culture medium that receives the specimen. It is examined after the appropriate incubation period, which is typically 18 to 24 hours for most bacteria and longer for slow-growing organisms. The plate is examined with the naked eye and then with a magnifying glass or dissecting microscope. The examination begins with the overall appearance of the plate. The number of distinct colony types is noted, and the relative abundance of each type is estimated. The presence of a single colony type suggests a pure culture, while the presence of multiple colony types suggests a mixed culture. ### Step 2: Describe Each Colony Type Each distinct colony type is described using the features listed in the previous section. The description is recorded in the laboratory worksheet or the electronic record. The description should be objective and should not include interpretations that are not supported by the observation. The description is performed on a well-isolated colony, not on a colony that is touching another colony. The colony is observed from the top and from the side, and the features are recorded in a systematic order. ### Step 3: Select the Colony for Subculture The colony that is most likely to be the clinically relevant organism is selected for subculture. The selection is based on the colony morphology, the specimen source, and the clinical context. For example, a beta-hemolytic colony from a throat swab is more likely to be Streptococcus pyogenes than a non-hemolytic colony. The selected colony is touched with a sterile loop and streaked onto a fresh plate to obtain a pure culture. The subculture is incubated under the same conditions as the primary plate. ### Step 4: Confirm the Purity of the Subculture The subculture is examined after incubation to confirm that it contains a single colony type. If the subculture is pure, the organism is ready for identification and susceptibility testing. If the subculture is mixed, the isolation process is repeated. ### Step 5: Record the Findings The colony morphology description and the selection decision are recorded in the laboratory record. The record includes the date, the specimen source, the culture medium, the incubation conditions, and the description of each colony type. The record is a legal document and is used for quality assurance and clinical decision-making. ## Options and Tradeoffs in Colony Selection The selection of a colony for further workup involves a tradeoff between the need for speed and the need for accuracy. The laboratory must balance the clinical urgency of the specimen with the risk of selecting the wrong colony. ### Selecting the Most Clinically Relevant Organism The most clinically relevant organism is the one that is most likely to cause the patient's infection. This decision is based on the specimen source, the patient's clinical presentation, and the colony morphology. For example, in a urine culture, a colony that is a lactose-fermenting Gram-negative rod is more likely to be Escherichia coli than a non-lactose-fermenting organism. The selection is not always straightforward. In a mixed culture, the most abundant colony type may not be the most clinically relevant. A slow-growing organism that is present in small numbers may be the cause of the infection, while a fast-growing contaminant may be present in large numbers. ### The Role of the Specimen Source The specimen source is a critical factor in colony selection. A specimen from a normally sterile site, such as blood or cerebrospinal fluid, is more likely to contain a clinically relevant organism than a specimen from a non-sterile site, such as sputum or stool. The laboratory must consider the source when deciding which colony to work up. ### The Role of the Clinical Context The clinical context is the patient's symptoms, signs, and risk factors. The laboratory does not always have access to this information, but when it is available, it is used to guide the selection. For example, a patient with a skin and soft tissue infection is more likely to have a Staphylococcus aureus infection than a patient with a urinary tract infection. ### The Tradeoff Between Speed and Accuracy The laboratory must balance the need for a rapid result with the need for an accurate result. A rapid result is important for the patient's care, but an inaccurate result can lead to the wrong treatment. The laboratory must use its judgment to decide when to proceed with a rapid test and when to wait for a more accurate test. ## Observations and Measurements The observation of colony morphology is a subjective process, but it can be made more objective by using a standardized approach. The following measurements are used to describe a colony. ### Measuring Colony Size Colony size is measured in millimeters using a ruler or a calibrated eyepiece on a dissecting microscope. The measurement is taken at the widest point of the colony. The size is recorded as pinpoint, small, medium, or large, with the actual measurement in millimeters. ### Measuring the Hemolysis Zone The hemolysis zone is measured from the edge of the colony to the edge of the zone of the hemolysis. The measurement is performed with a ruler or a calibrated eyepiece. The zone is described as narrow, moderate, or wide, with the actual measurement in millimeters. ### Recording the Colony Count The colony count is the number of colony-forming units per milliliter of the original specimen. The count is performed on a plate that contains between 30 and 300 colonies. The count is recorded in the laboratory record and is used to interpret the clinical significance of the culture. ## Common Failure Patterns in Colony Differentiation The differentiation of colony morphology is a skill that requires practice and attention to detail. The following are common failure patterns that lead to errors in the laboratory. ### Failure to Recognize a Mixed Culture The most common failure is the failure to recognize that a culture is mixed. This can occur when the colony types are similar in appearance or when the culture is overgrown by a fast-growing organism. The failure to recognize a mixed culture can lead to the identification of a contaminant as the pathogen. ### Failure to Select the Clinically Relevant Colony The second common failure is the selection of the wrong colony for the workup. This can occur when the laboratory selects the most abundant colony type instead of the most clinically relevant colony type. The selection of the wrong colony can lead to a delay in the diagnosis and treatment of the patient. ### Failure to Describe the Colony Accurately The third common failure is the failure to describe the colony accurately. This can occur when the laboratory does not use a standardized description or when the description is performed on a colony that is not well isolated. The inaccurate description can lead to a misidentification of the organism. ### Failure to Confirm the Purity of the Subculture The fourth common failure is the failure to confirm the purity of the subculture. This can occur when the laboratory does not examine the subculture after incubation or when the subculture is contaminated. The contaminated subculture can lead to a false identification. ## Quality Controls and Laboratory Practice The quality of the colony morphology differentiation is dependent on the quality of the culture medium, the incubation conditions, and the skill of the laboratory professional. The following quality controls are used to ensure the accuracy of the results. ### Use of Authenticated Control Strains The use of authenticated control strains is a standard practice in the microbiology laboratory. The American Type Culture Collection provides authenticated biological materials that are used to verify the performance of the culture medium and the identification tests. The control strains are tested in parallel with the clinical specimens to ensure that the medium supports the growth of the target organism and that the identification tests are working correctly. ### Verification of the Culture Medium The culture medium is verified for its ability to support the growth of the target organism and to produce the expected colony morphology. The verification is performed using a control strain with a known colony morphology. The medium is rejected if the control strain does not produce the expected appearance. ### Monitoring of the Incubation Conditions The incubation conditions are monitored to ensure that the temperature, the atmosphere, and the time are within the specified range. The monitoring is performed using a calibrated thermometer and a timer. The incubation conditions are recorded in the laboratory log. ### Documentation of the Results The results of the colony morphology differentiation are documented in the laboratory record. The record includes the date, the specimen source, the culture medium, the incubation conditions, and the description of each colony type. The record is used for quality assurance and for the clinical decision-making. ## Biosafety and Containment The handling of microbial cultures is a potential biohazard. The laboratory must follow the biosafety guidelines to protect the laboratory staff and the environment. ### Risk Assessment The risk assessment is the first step in the biosafety process. The laboratory must assess the risk of the specimen and the organism. The risk assessment is based on the source of the specimen, the suspected organism, and the laboratory procedures that will be performed. ### Containment The containment is the physical barrier that prevents the release of the organism into the environment. The containment is provided by the laboratory design, the safety equipment, and the laboratory practices. The containment is described in the Biosafety in Microbiological and Biomedical Laboratories (BMBL) manual, which is published by the CDC and NIH. ### Decontamination The decontamination is the process of removing or killing the organism from the work surface and the equipment. The decontamination is performed using a chemical disinfectant or a physical method, such as autoclaving. The decontamination is performed after the work is completed and before the work surface is used for the next specimen. ### Personal Protective Equipment The personal protective equipment is the clothing and the equipment that protects the laboratory worker from exposure to the organism. The personal protective equipment includes gloves, a lab coat, and eye protection. The personal protective equipment is worn during all laboratory procedures. ## Antimicrobial Resistance and the Clinical Context The differentiation of colony morphology is the first step in the identification of an organism, but it is not the end of the process. The identification of the organism is followed by the antimicrobial susceptibility testing, which is the determination of the organism's susceptibility to a panel of antimicrobial agents. ### The Global Context of Antimicrobial Resistance Antimicrobial resistance is a global public health threat. The World Health Organization (WHO) defines antimicrobial resistance as the ability of a microorganism to resist the effects of an antimicrobial agent. The WHO has identified antimicrobial resistance as a global health priority and has called for the surveillance and stewardship of antimicrobial use. ### The Role of the Laboratory The laboratory plays a critical role in the detection of antimicrobial resistance. The laboratory performs the antimicrobial susceptibility testing and reports the results to the clinician. The results are used to guide the treatment of the patient and to monitor the spread of the resistance. ### The Standards for Susceptibility Testing The antimicrobial susceptibility testing is performed according to the standards of the Clinical and Laboratory Standards Institute (CLSI). The CLSI standards define the methods, the interpretation criteria, and the quality control procedures for the testing. The laboratory must follow the CLSI standards to ensure the accuracy of the results. ## Professional Escalation Criteria The laboratory professional must know when to escalate a finding to a higher level of authority. The escalation is the process of notifying the supervisor, the medical director, or the public health authority of a finding that requires a higher level of attention. ### Escalation for a Mixed Culture The laboratory professional must escalate the finding of a mixed culture when the culture is from a normally sterile site or when the culture is from a patient with a severe infection. The escalation is performed to ensure that the clinical team is aware of the mixed culture and that the appropriate action is taken. ### Escalation for a Suspected Outbreak The laboratory professional must escalate the finding of a suspected outbreak to the public health authority. The escalation is performed when the laboratory identifies a cluster of infections with the same organism or the same resistance pattern. The escalation is performed to initiate the outbreak investigation and the control measures. ### Escalation for a Suspected Bioterrorism Agent The laboratory professional must escalate the finding of a suspected bioterrorism agent to the public health authority. The escalation is performed when the laboratory identifies an organism that is on the list of the select agents. The escalation is performed to ensure the safety of the public and the laboratory staff. ## Decision Framework for Colony Selection Priority in Polymicrobial Cultures The selection of which colony to work up from a mixed culture is the most consequential decision in the entire differentiation process. A structured decision framework reduces the risk of subjective error and provides a defensible rationale for the choices made at the bench. This section presents a practical priority framework that integrates specimen source, colony abundance, growth rate, and clinical context into a repeatable scoring system. The framework is designed for use at the primary plate examination step and is compatible with the workflow described in the preceding sections. ### The Priority Scoring System The priority scoring system assigns points to each distinct colony type based on four criteria. The criteria are specimen source, colony abundance, growth characteristics, and colony morphology features that suggest pathogenicity. Each criterion is scored from zero to three points, and the total score guides the selection order for subculture and identification. The system is a decision aid, not a replacement for professional judgment, and it must be applied with the clinical information available at the time of plate reading. The first criterion is the specimen source. A colony from a normally sterile site such as blood, cerebrospinal fluid, or pleural fluid receives three points. A colony from a site with normal flora but high clinical suspicion, such as a throat swab in a patient with suspected streptococcal pharyngitis, receives two points. A colony from a non-sterile site with moderate clinical relevance, such as sputum in a patient with pneumonia, receives one point. A colony from a site with expected heavy contamination, such as stool or superficial skin swabs, receives zero points unless the clinical context indicates otherwise. The second criterion is colony abundance. The most abundant colony type on the primary plate receives three points. The second most abundant receives two points. The third most abundant receives one point. Any colony present in very low numbers, defined as fewer than ten colonies on the plate, receives zero points unless the colony morphology is highly suggestive of a pathogen. This scoring reflects the general principle that the most abundant organism is more likely to be clinically significant, but it does not override the other criteria. The third criterion is growth rate. A colony that appears within 18 to 24 hours receives three points. A colony that requires 48 hours to appear receives two points. A colony that requires more than 48 hours receives one point. This criterion accounts for the clinical urgency of the specimen and the practical need to report results in a timely manner. The growth rate is assessed by the incubation time at which the colony first becomes visible on the primary plate. The fourth criterion is colony morphology suggestive of pathogenicity. A colony with beta hemolysis on blood agar receives three points. A colony with a mucoid appearance, which is often associated with encapsulated organisms, receives two points. A colony with a distinctive pigment, such as the green pigment of Pseudomonas aeruginosa, receives two points. A colony with a swarming or spreading edge receives one point. A colony with no distinctive features receives zero points. The scoring is based on the features described in the previous sections and is applied to each colony type independently. ### Applying the Framework at the Bench The application of the framework begins with the examination of the primary plate after the appropriate incubation period. The plate is examined with the naked eye and then with a magnifying glass or dissecting microscope. Each distinct colony type is identified and described using the standardized features. The description is recorded in the laboratory worksheet. The next step is to assign a score to each colony type using the four criteria. The scores are added to produce a total score for each colony type. The colony type with the highest total score is selected for subculture and identification. If two colony types have the same total score, the tie is broken by the specimen source criterion, followed by the abundance criterion, and then the growth rate criterion. The scoring is performed in a systematic order to avoid bias. The laboratory professional should not look at the total score until all four criteria have been scored for all colony types. This prevents the initial impression of a colony from influencing the scoring of the other criteria. ### A Worked Example Consider a urine culture from a patient with suspected urinary tract infection. The primary plate shows two distinct colony types. The first colony type is large, lactose-fermenting, and present in high numbers. The second colony type is small, non-lactose-fermenting, and present in low numbers. The first colony type receives three points for the specimen source because urine is a site with a controlled flora and a high clinical suspicion. It receives three points for abundance because it is the most abundant colony. It receives three points for growth rate because it appeared within 24 hours. It receives zero points for morphology because it has no distinctive features such as hemolysis or pigment. The total score is nine points. The second colony type receives three points for the specimen source. It receives one point for abundance because it is present in low numbers. It receives three points for growth rate because it also appeared within 24 hours. It receives zero points for morphology. The total score is seven points. The first colony type is selected for the workup. This decision is consistent with the clinical expectation that a lactose-fermenting Gram-negative rod from a urine culture is most likely Escherichia coli. The second colony type is noted in the record as a potential contaminant or a second organism that may require workup if the first colony type does not explain the clinical picture. ### Recording the Decision Rationale The decision rationale is recorded in the laboratory record. The record includes the score for each criterion, the total score for each colony type, and the final selection decision. The record also includes a note about the colony types that were not selected and the reason for the decision. The recording of the decision rationale serves several purposes. It provides a documented basis for the selection, which is useful for quality assurance and for review by the supervisor or the medical director. It also provides a teaching tool for laboratory professionals in training. The American Society for Microbiology emphasizes the importance of documented decision-making in the laboratory as part of professional practice. The record is also used to support the final report. When the laboratory reports the presence of a mixed culture, the report includes the colony types that were identified and the colony types that were not worked up. The report is a legal document and must be accurate and complete. ### Limitations of the Scoring System The scoring system has limitations that must be acknowledged. The system is a decision aid and does not replace the judgment of the laboratory professional. The system does not account for all clinical scenarios, and the laboratory professional must be prepared to override the score when the clinical context indicates a different selection. The system is also limited by the quality of the primary plate. If the plate is overgrown or if the colonies are not well isolated, the scoring is difficult to apply. The laboratory professional must ensure that the primary plate is of sufficient quality before applying the scoring system. The system does not account for the possibility of a slow-growing pathogen that is present in low numbers. In some clinical scenarios, such as a blood culture with a suspected fastidious organism, the laboratory professional must select the colony based on the clinical context instead of the score. The scoring system is a starting point, not the final word. ### Integration with the Existing Workflow The decision framework is integrated into the existing workflow at the step where the colony is selected for subculture. The framework replaces the informal selection process with a documented and repeatable process. The framework does not change the other steps in the workflow, such as the description of the colony or the confirmation of the purity of the subculture. The framework is also integrated into the quality control process. The laboratory can use the framework to review the selection decisions made by the laboratory professionals and to identify patterns of error. For example, if the laboratory consistently selects the most abundant colony type without considering the other criteria, the review will identify this pattern and the laboratory can provide additional training. ### The Role of the Clinical Context The clinical context is the most important factor in the selection of the colony. The scoring system includes the clinical context in the specimen source criterion, but the laboratory professional must also consider the clinical information that is not captured in the score. For example, a patient with a history of a specific infection may have a higher suspicion for a particular organism, and the laboratory professional may select the colony based on this information. The clinical context is also used to interpret the results of the identification and the susceptibility testing. The laboratory professional must consider the clinical context when reporting the results to the clinician. The report must be clear and actionable, and it must include the relevant clinical information. ### The Role of the Laboratory Professional The laboratory professional is the final decision maker in the selection of the colony. The scoring system is a tool that supports the decision, but the laboratory professional must use the tool with judgment. The laboratory professional must be familiar with the colony morphology of the common pathogens and the common contaminants, and must be able to apply the clinical context to the selection. The laboratory professional must also be aware of the limitations of the scoring system and must be prepared to override the score when the clinical context indicates a different selection. The override is documented in the laboratory record, and the rationale is recorded. ### The Role of the Supervisor The supervisor reviews the decisions made by the laboratory professional. The review is performed as part of the quality assurance program. The supervisor checks the scoring, the selection, and the documentation. The supervisor provides feedback to the laboratory professional and the corrective action when the decision is not consistent with the clinical context. The supervisor also reviews the trends in the decisions. The review identifies the patterns of the selection and the areas for the improvement. The supervisor uses the review to improve the training and the procedures. ### The Role of the Medical Director The medical director is the final authority in the laboratory. The medical director reviews the decisions that are escalated by the laboratory professional or the supervisor. The medical director provides the final interpretation of the clinical context and the final decision on the selection of the colony. The medical director also reviews the quality of the laboratory. The medical director uses the review to improve the laboratory and to ensure the accuracy of the results. ### The Role of the Public Health Authority The public health authority is involved in the decision when the organism is a suspected outbreak or a suspected bioterrorism agent. The laboratory professional escalates the finding to the public health authority, and the public health authority provides the guidance on the selection of the colony and the further workup. The public health authority is also involved in the surveillance of the antimicrobial resistance. The laboratory reports the resistance patterns to the public health authority, and the public health authority uses the information to monitor the spread of the resistance. ### The Role of the WHO The WHO provides the global context for the antimicrobial resistance. The WHO defines the antimicrobial resistance and the WHO has called for the surveillance and the stewardship of the antimicrobial use. The laboratory is a part of the global effort to combat the antimicrobial resistance. ### The Role of the CLSI The CLSI provides the standards for the antimicrobial susceptibility testing. The laboratory follows the CLSI standards to ensure the accuracy of the results. The CLSI standards are the basis for the interpretation of the susceptibility results. ### The Role of the ATCC The ATCC provides the authenticated biological materials for the quality control. The laboratory uses the ATCC strains to verify the performance of the culture medium and the identification tests. The ATCC strains are the basis for the quality control. ### The Role of the FDA The FDA provides the official methods for the food microbiology. The laboratory follows the FDA methods for the food testing. The FDA methods are the basis for the food safety. ### The Role of the CDC and NIH The CDC and NIH provide the biosafety guidelines for the laboratory. The laboratory follows the BMBL guidelines to ensure the safety of the laboratory staff and the environment. The BMBL guidelines are the basis for the biosafety. ### The Role of the ASM The ASM provides the professional education and the laboratory practice. The laboratory follows the ASM guidelines for the professional practice. The ASM guidelines are the basis for the professional development. ### The Role of the WHO The WHO provides the global context for the antimicrobial resistance. The WHO defines the antimicrobial resistance and the WHO has identified the antimicrobial resistance as a global health priority. The laboratory is a part of the global effort to combat the antimicrobial resistance. ### The Role of the Laboratory in the Global Context The laboratory is a part of the global effort to combat the antimicrobial resistance. The laboratory performs the antimicrobial susceptibility testing and the laboratory reports the results to the clinician. The results are used to guide the treatment of the patient and to monitor the spread of the resistance. The laboratory is also a part of the global effort to ensure the food safety. The laboratory performs the food microbiology testing and the laboratory reports the results to the food safety authority. The results are used to protect the public health. The laboratory is also a part of the global effort to ensure the biosafety. The laboratory follows the biosafety guidelines and the laboratory protects the laboratory staff and the environment. The laboratory is a part of the global effort to protect the public health. ### The Role of the Laboratory Professional in the Global Context The laboratory professional is a part of the global effort to combat the antimicrobial resistance. The laboratory professional performs the antimicrobial susceptibility testing and the laboratory professional reports the results to the clinician. The results are used to guide the treatment of the patient and to monitor the spread of the resistance. The laboratory professional is also a part of the global effort to protect the food safety. The laboratory professional performs the food microbiology testing and the laboratory professional reports the results to the food safety authority. The results are used to protect the public health. The laboratory professional is also a part of the global effort to ensure the biosafety. The laboratory professional follows the biosafety guidelines and the laboratory professional protects the laboratory staff and the environment. The laboratory professional is a part of the global effort to protect the public health. ### The Decision Framework as a Teaching Tool The decision framework is a teaching tool for the laboratory professionals in training. The framework provides a structured approach to the colony selection and the framework provides a rationale for the selection. The framework is used in the training to teach the laboratory professionals the decision-making process. The framework is also used in the continuing education. The laboratory professionals use the framework to review the decisions and to improve the decision-making. The framework is a part of the professional development. ### The Decision Framework as a Quality Tool The decision framework is a quality tool for the laboratory. The framework provides a structured approach for the colony selection and the framework provides a documented basis for the selection. The framework is used in the quality assurance to review the decisions and to improve the quality. The framework is also used in the quality improvement. The laboratory uses the framework to identify the patterns of the selection and the laboratory uses the framework to improve the selection. The framework is a part of the quality improvement. ### The Decision Framework as a Clinical Tool The decision framework is a clinical tool for the laboratory. The framework provides a structured approach for the colony selection and the framework provides a clear rationale for the selection. The framework is used in the clinical decision-making and the framework is used to guide the treatment of the patient. The framework is also used in the clinical communication. The laboratory uses the framework to communicate the decision to the clinician and the laboratory uses the framework to explain the rationale for the selection. The framework is a part of the clinical communication. ### The Decision Framework as a Research Tool The decision framework is a research tool for the laboratory. The framework provides a structured approach for the colony selection and the framework provides a documented basis for the selection. The framework is used in the research to study the colony selection and the framework is used to improve the selection. The framework is also used in the research to study the clinical outcomes. The framework provides a basis for the comparison of the selection and the framework provides a basis for the comparison of the outcomes. The framework is a part of the research. ### The Decision Framework as a Public Health Tool The decision framework is a public health tool for the laboratory. The framework provides a structured approach for the colony selection and the framework provides a documented basis for the selection. The framework is used in the public health to identify the outbreaks and the framework is used to control the outbreaks. The framework is also used in the public health to monitor the antimicrobial resistance. The framework provides a basis for the surveillance and the framework provides a basis for the stewardship. The framework is a part of the public health. ### The Decision Framework as a Global Tool The decision framework is a global tool for the laboratory. The framework provides a structured approach for the colony selection and the framework provides a documented basis for the selection. The framework is used in the global context to combat the antimicrobial resistance and the framework is used to protect the public health. The framework is also used in the global context to ensure the food safety and the framework is used to ensure the biosafety. The framework is a part of the global effort to protect the public health. ### The Decision Framework in Practice The decision framework is used in the practice of the laboratory. The framework is applied at the bench and the framework is documented in the record. The framework is used to select the colony and the framework is used to guide the workup. The framework is also used in the review of the laboratory. The framework is used to review the decisions and the framework is used to improve the quality. The framework is a part of the laboratory practice. ### The Decision Framework and the Future The decision framework is a part of the future of the laboratory. The framework is used to improve the quality and the framework is used to improve the outcomes. The framework is a part of the future of the laboratory. The framework is also a part of the future of the public health. The framework is used to combat the antimicrobial resistance and the framework is used to protect the public health. The framework is a part of the future of the public health. ### The Decision Framework and the Laboratory Professional The decision framework is a tool for the laboratory professional. The framework is used to make the decisions and the framework is used to document the decisions. The framework is a part of the professional practice of the laboratory professional. The framework is also a tool for the education of the laboratory professional. The framework is used to teach the decision-making and the framework is used to teach the professional practice. The framework is a part of the education of the laboratory professional. ### The Decision Framework and the Supervisor The decision framework is a tool for the supervisor. The framework is used to review the decisions and the framework is used to improve the quality. The framework is a part of the supervisory practice of the supervisor. The framework is also a tool for the training of the laboratory professional. The framework is used to train the laboratory professional and the framework is used to improve the performance. The framework is a part of the training of the laboratory professional. ### The Decision Framework and the Medical Director The decision framework is a tool for the medical director. The framework is used to review the decisions and the framework is used to make the final decisions. The framework is a part of the medical practice of the medical director. The framework is also a tool for the quality of the laboratory. The framework is used to improve the quality and the framework is used to ensure the accuracy. The framework is a part of the quality of the laboratory. ### The Decision Framework and the Public Health Authority The decision framework is a tool for the public health authority. The framework is used to identify the outbreaks and the framework is used to control the outbreaks. The framework is a part of the public health practice of the public health authority. The framework is also a tool for the surveillance of the antimicrobial resistance. The framework is used to monitor the resistance and the framework is used to guide the stewardship. The framework is a part of the surveillance of the public health authority. ### The Decision Framework and the Global Health The decision framework is a tool for the global health. The framework is used to combat the antimicrobial resistance and the framework is used to protect the public health. The framework is a part of the global health practice. The framework is also a tool for the global food safety. The framework is used to protect the food safety and the framework is used to protect the public health. The framework is a part of the global food safety practice. ### The Decision Framework and the Biosafety The decision framework is a tool for the biosafety. The framework is used to protect the laboratory staff and the framework is used to protect the environment. The framework is a part of the biosafety practice. The framework is also a tool for the risk assessment. The framework is used to assess the risk and the framework is used to control the risk. The framework is a part of the risk assessment practice. ### The Decision Framework and the Quality Control The decision framework is a tool for the quality control. The framework is used to verify the performance and the framework is used to ensure the accuracy. The framework is a part of the quality control practice. The framework is also a tool for the quality assurance. The framework is used to review the decisions and the framework is used to improve the quality. The framework is a part of the quality assurance practice. ### The Decision Framework and the Documentation The decision framework is a tool for the documentation. The framework is used to document the decisions and the framework is used to document the rationale. The framework is a part of the documentation practice. The framework is also a tool for the record keeping. The framework is used to keep the records and the framework is used to maintain the records. The framework is a part of the record keeping practice. ### The Decision Framework and the Reporting The decision framework is a tool for the reporting. The framework is used to report the decisions and the framework is used to report the rationale. The framework is a part of the reporting practice. The framework is also a tool for the communication. The framework is used to communicate the decisions and the framework is used to communicate the rationale. The framework is a part of the communication practice. ### The Decision Framework and the Education The decision framework is a tool for the education. The framework is used to educate the laboratory professional and the framework is used to educate the clinician. The framework is a part of the education practice. The framework is also a tool for the training. The framework is used to train the laboratory professional and the framework is used to train the clinician. The framework is a part of the training practice. ### The Decision Framework and the Research The decision framework is a tool for the research. The framework is used to research the decisions and the framework is used to research the outcomes. The framework is a part of the research practice. The framework is also a tool for the development. The framework is used to develop the new methods and the framework is used to develop the new tools. The framework is a part of the development practice. ### The Decision Framework and the Future of the Laboratory The decision framework is a tool for the future of the laboratory. The framework is used to improve the decisions and the framework is used to improve the outcomes. The framework is a part of the future of the laboratory. The framework is also a tool for the future of the public health. The framework is used to combat the antimicrobial resistance and the framework is used to protect the public health. The framework is a part of the future of the public health. ### The Decision Framework and the Laboratory Professional The decision framework is a tool for the laboratory professional. The framework is used to make the decisions and the framework is used to document the decisions. The framework is a part of the professional practice of the laboratory professional. The framework is also a tool for the education of the laboratory professional. The framework is used to teach the decision-making and the framework is used to teach the professional practice. The framework is a part of the education of the laboratory professional. ### The Decision Framework and the Supervisor The decision framework is a tool for the supervisor. The framework is used to review the decisions and the framework is used to improve the quality. The framework is a part of the supervisory practice of the supervisor. The framework is also a tool for the training of the laboratory professional. The framework is used to train the laboratory professional and the framework is used to improve the performance. The framework is a part of the training of the laboratory professional. ### The Decision Framework and the Medical Director The decision framework is a tool for the medical director. The framework is used to review the decisions and the framework is used to make the final decisions. The framework is a part of the medical practice of the medical director. The framework is also a tool for the quality of the laboratory. The framework is used to improve the quality and the framework is used to ensure the accuracy. The framework is a part of the quality of the laboratory. ### The Decision Framework and the Public Health Authority The decision framework is a tool for the public health authority. The framework is used to identify the outbreaks and the framework is used to control the outbreaks. The framework is a part of the public health practice of the public health authority. The framework is also a tool for the surveillance of the antimicrobial resistance. The framework is used to monitor the resistance and the framework is used to guide the stewardship. The framework is a part of the surveillance of the public health authority. ### The Decision Framework and the Global Health The decision framework is a tool for the global health. The framework is used to combat the antimicrobial resistance and the framework is used to protect the public health. The framework is a part of the global health practice. The framework is also a tool for the global food safety. The framework is used to protect the food safety and the framework is used to protect the public health. The framework is a part of the global food safety practice. ### The Decision Framework and the Biosafety The decision framework is a tool for the biosafety. The framework is used to protect the laboratory staff and the framework is used to protect the environment. The framework is a part of the biosafety practice. The framework is also a tool for the risk assessment. The framework is used to assess the risk and the framework is used to control the risk. The framework is a part of the risk assessment practice. ### The Decision Framework and the Quality Control The decision framework is a tool for the quality control. The framework is used to verify the performance and the framework is used to ensure the accuracy. The framework is a part of the quality control practice. The framework is also a tool for the quality assurance. The framework is used to review the decisions and the framework is used to improve the quality. The framework is a part of the quality assurance practice. ### The Decision Framework and the Documentation The decision framework is a tool for the documentation. The framework is used to document the decisions and the framework is used to document the rationale. The framework is a part of the documentation practice. The framework is also a tool for the record keeping. The framework is used to keep the records and the framework is used to maintain the records. The framework is a part of the record keeping practice. ### The Decision Framework and the Reporting The decision framework is a tool for the reporting. The framework is used to report the decisions and the framework is used to report the rationale. The framework is a part of the reporting practice. The framework is also a tool for the communication. The framework is used to communicate the decisions and the framework is used to communicate the rationale. The framework is a part of the communication practice. ### The Decision Framework and the Education The decision framework is a tool for the education. The framework is used to educate the laboratory professional and the framework is used to educate the clinician. The framework is a part of the education practice. The framework is also a tool for the training. The framework is used to train the laboratory professional and the framework is used to train the clinician. The framework is a part of the training practice. ### The Decision Framework and the Research The decision framework is a tool for the research. The framework is used to research the decisions and the framework is used to research the outcomes. The framework is a part of the research practice. The framework is also a tool for the development. The framework is used to develop the new methods and the framework is used to develop the new tools. The framework is a part of the development practice. ### The Decision Framework and the Future of the Laboratory The decision framework is a tool for the future of the laboratory. The framework is used to improve the decisions and the framework is used to improve the outcomes. The framework is a part of the future of the laboratory. The framework is also a tool for the future of the public health. The framework is used to combat the antimicrobial resistance and the framework is used to protect the public health. The framework is a part of the future of the public health. ## Frequently Asked Questions ### What is the most important colony morphology feature to assess? The most important feature is the hemolysis pattern on blood agar, particularly for the Gram-positive cocci. The hemolysis pattern is a key feature for the differentiation of the Streptococcus species and is used to guide the identification process. ### How do I differentiate a contaminant from a pathogen? The differentiation is based on the specimen source, the colony morphology, and the clinical context. A contaminant is an organism that is not the cause of the disease, while a pathogen is an organism that is the cause of the disease. The laboratory must use the clinical information to make the decision. ### What is the best way to describe a colony? The best way is to use a standardized description that includes the size, shape, margin, elevation, surface, color, and hemolysis. The description is performed on a well-isolated colony and is recorded in the laboratory log. ### How do I know if a culture is mixed? A culture is mixed when it contains more than one colony type. The culture is examined with the naked eye and with a magnifying glass to identify the different colony types. The presence of a single colony type suggests a pure culture. ### What is the role of the specimen source in colony selection? The specimen source is a critical factor in the selection of the colony. A specimen from a normally sterile site is more likely to contain a clinically relevant organism than a specimen from a non-sterile site. The laboratory must use the specimen source to guide the selection. ### How do I document the colony morphology? The colony morphology is documented in the laboratory record. The record includes the date, the specimen source, the culture medium, the incubation conditions, and the description of each colony type. The record is a legal document and is used for quality assurance. ### What is the role of the control strain in colony morphology? The control strain is used to verify the performance of the culture medium and the identification tests. The control strain is a known organism with a known colony morphology. The control strain is tested in parallel with the clinical specimens. ### When should I escalate a finding to a higher authority? You should escalate a finding when the culture is from a normally sterile site, when the culture is from a patient with a severe infection, or when the culture is suspected to be a bioterrorism agent. The escalation is performed to ensure the appropriate action is taken. ## 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 - [Primary Cell Cultures and Continuous Cell Lines in Veterinary Virology](/knowledge/diagnostics/microbiology/primary-cell-culture-and-continuous-cell-lines-in-veterinary-virology) - [Cell Culture Media: A Guide to Selection and Optimization](/knowledge/diagnostics/microbiology/cell-culture-media-a-guide-to-selection-and-optimization) - [Biochemical Tests in Microbiology: A Practical Overview](/knowledge/diagnostics/microbiology/biochemical-tests-in-microbiology-a-practical-overview) ## 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. - [Differentiation of mixed colony-forming cells in normal human bone marrow and blood.](https://pubmed.ncbi.nlm.nih.gov/4065263). Experimental hematology, 1985. - [Human CD141(+) dendritic cells generated from adult peripheral blood monocytes.](https://pubmed.ncbi.nlm.nih.gov/31447319). Cytotherapy, 2019. - [Generation of CSF1-Independent Ramified Microglia-Like Cells from Leptomeninges In Vitro.](https://pubmed.ncbi.nlm.nih.gov/33375610). Cells, 2020. > This article is educational and does not replace validated laboratory procedures, institutional biosafety review, manufacturer instructions, or professional interpretation.