# How to determine minimum inhibitory concentration broth microdilution ## Quick Answer - Broth microdilution determines the minimum inhibitory concentration (MIC) by exposing a standardized bacterial inoculum to serial twofold dilutions of an antimicrobial agent in a liquid medium. - The MIC is the lowest antimicrobial concentration that visibly inhibits bacterial growth after an appropriate incubation period, read by comparing each well against a growth control. - Results depend on strict adherence to standardized methods, including inoculum density, medium composition, incubation conditions, and the use of authenticated control strains. ## At a Glance | Parameter | Standard Practice | Purpose | Common Error | | --- | --- | --- | --- | | Inoculum preparation | Isolate colonies from an 18 to 24 hour culture and adjust turbidity to a defined standard | Ensures a consistent starting bacterial density for reproducible MIC values | Using an unadjusted or overgrown culture that alters the final cell count | | Antimicrobial dilution | Serial twofold dilutions prepared in broth across a 96 well plate | Produces a logarithmic concentration gradient for endpoint determination | Incomplete mixing or skipping a dilution step that skews the concentration series | | Incubation | Typically 16 to 20 hours at 35 degrees Celsius in ambient air | Allows visible growth in control wells while the MIC endpoint develops | Prolonged incubation that shifts the endpoint or allows contamination | | Endpoint reading | Compare each well against the growth control and the negative control | Identifies the lowest concentration with no visible growth | Misreading faint turbidity or trailing growth that obscures the endpoint | | Quality control | Authenticated reference strains are tested in parallel with each run | Confirms the method is performing within established acceptable ranges | Omitting control strains or using unverified cultures that invalidate the run | ## Understanding Minimum Inhibitory Concentration Testing The minimum inhibitory concentration is the lowest concentration of an antimicrobial agent that prevents visible growth of a microorganism under defined in vitro conditions. This value is a quantitative measure that describes the susceptibility of a bacterial isolate to a specific drug. The MIC is expressed in micrograms per milliliter or milligrams per liter and is used to guide clinical decisions, monitor resistance trends, and support epidemiological surveillance. The broth microdilution method is one of the most widely used approaches for MIC determination because it is adaptable to automation, produces quantitative results, and can test multiple antimicrobial agents against a single isolate in one setup. The method is grounded in standardized protocols that define the medium, inoculum size, incubation conditions, and reading criteria. These standards exist because small variations in any of these parameters can shift the MIC by one or more dilution steps, which can change the interpretation of the result. The Clinical and Laboratory Standards Institute publishes the reference standards that define how antimicrobial susceptibility testing should be performed and interpreted in clinical laboratories. These standards are developed through systematic review of data and are updated as new evidence emerges. Laboratories that follow these standards can compare their results across time and across institutions, which is essential for detecting emerging resistance patterns and for guiding therapy. The global context for MIC testing is the growing problem of antimicrobial resistance. The World Health Organization describes antimicrobial resistance as the ability of microorganisms to resist the effects of drugs that once treated them effectively. This resistance threatens the ability to treat common infections and has become a major public health concern. MIC testing is one of the tools used to detect resistance, track its spread, and guide the selection of effective treatments. ## Core Principles of Broth Microdilution ### The 96-Well Plate Format Broth microdilution is performed in a microtiter plate, typically with 96 wells arranged in eight rows and twelve columns. Each row is used for a single antimicrobial agent, and each column contains a different concentration of that agent. The concentration in each well is typically one half of the concentration in the previous well, creating a twofold dilution series. This logarithmic series allows the MIC to be identified as a discrete point within the range of concentrations tested. The plate layout includes a growth control well that contains the bacterial inoculum in broth without any antimicrobial agent. This well must show visible growth for the test to be valid. A negative control well contains only sterile broth and must remain clear. The negative control detects contamination of the medium or the plate. The growth control confirms that the inoculum is viable and that the medium supports growth. ### The Dilution Series The twofold dilution series is the backbone of the MIC determination. A stock solution of the antimicrobial agent is prepared at a known concentration, and then diluted in broth to produce the desired range. The highest concentration tested is determined by the expected susceptibility of the organism and the clinical relevance of the drug. The range must include concentrations that are achievable in the patient and that correspond to the interpretive criteria for the drug. The dilution series is prepared by adding a fixed volume of the antimicrobial solution to the first well, then transferring a fixed volume from that well to the next well that already contains the same volume of broth. This process is repeated across the plate. The result is a series where each well contains half the concentration of the previous well. The accuracy of the entire test depends on the accuracy of these dilutions, so the pipetting must be precise and the mixing must be complete. ### The Inoculum The bacterial inoculum is prepared from a pure culture that has been grown for 18 to 24 hours. The culture is suspended in a suitable liquid medium, and the turbidity is adjusted to match a defined standard. The turbidity standard approximates a specific bacterial density, which is then diluted to achieve the final inoculum concentration in the wells. The final inoculum is typically in the range of 5 times 10 to the fifth colony forming units per milliliter, but the exact target depends on the standard being followed. The inoculum is added to each well in the plate, including the growth control and the negative control. The negative control receives no inoculum. The plate is then incubated under the conditions specified in the standard. The incubation temperature and duration are chosen to allow the bacteria to grow in the control well while the antimicrobial agent exerts its effect in the test wells. ## Step-by-Step Procedure for Broth Microdilution ### Step 1: Prepare the Antimicrobial Stock Solutions The antimicrobial agent is obtained as a laboratory-grade powder with a known potency. The powder is weighed and dissolved in an appropriate solvent, then diluted in the test medium to prepare a stock solution. The stock solution concentration is calculated based on the potency of the powder and the desired final concentration range. The stock solution is prepared fresh or stored according to the manufacturer instructions and the standard protocol. The solvent and the diluent must be compatible with the antimicrobial agent and with the test medium. Some agents require a specific solvent to dissolve, and the solvent must not interfere with the bacterial growth or the antimicrobial activity. The standard for the specific agent provides guidance on the appropriate solvent and diluent. ### Step 2: Prepare the Dilution Series The stock solution is used to prepare the twofold dilution series in the microtiter plate. A volume of the broth is added to each well in the row. The stock solution is added to the first well, and then a series of transfers is made from the first well to the next, and so on. The final well in the series typically contains no antimicrobial agent and serves as the growth control. The dilution series must be prepared carefully to ensure that the concentrations are accurate. The pipette tips must be changed between wells to avoid carryover of the antimicrobial agent. The mixing must be thorough to ensure that the concentration is uniform in each well. ### Step 3: Prepare the Inoculum The bacterial isolate is grown on a nonselective medium for 18 to 24 hours. Several colonies are selected and suspended in a sterile liquid, such as the broth or a saline solution. The suspension is mixed thoroughly to break up clumps. The turbidity is then adjusted to match the standard. The turbidity standard is a visual or instrument-based comparison. The suspension is adjusted by adding more bacteria or more liquid until the turbidity matches the standard. The adjusted suspension is then diluted in the broth to achieve the final inoculum concentration. The dilution factor is specified in the standard and is designed to produce the target concentration in the wells. ### Step 4: Inoculate the Plate The prepared inoculum is added to each well in the plate, including the growth control well. The negative control well receives only the broth. The plate is then covered to prevent evaporation and contamination. The cover is typically a lid that fits over the plate. The inoculation is done using a multichannel pipette or an automated system. The volume added to each well is the same, and the final concentration of the antimicrobial agent and the inoculum in each well is determined by the volumes used. The plate is then placed in an incubator at the specified temperature. ### Step 5: Incubate the Plate The plate is incubated at the temperature and for the duration specified in the standard. The typical incubation is 16 to 20 hours at 35 degrees Celsius in ambient air. Some organisms require a different temperature or an atmosphere with carbon dioxide. The standard for the organism and the antimicrobial agent provides the correct conditions. The incubation time is critical because the endpoint is read after the growth has developed. If the incubation is too short, the growth may not be visible in the control well. If the incubation is too long, the endpoint may shift due to the growth of the bacteria in the presence of the antimicrobial agent. ### Step 6: Read the Results The plate is removed from the incubator and the wells are examined for visible growth. The growth is typically seen as turbidity or a pellet of cells at the bottom of the well. The growth control must show visible growth, and the negative control must show no growth. The MIC is the lowest concentration of the antimicrobial agent that inhibits the visible growth of the organism. The reading is done visually or with the aid of a reading device. The endpoint is the first well in the series that shows no visible growth. The concentration in that well is the MIC. The result is recorded in the appropriate units. ## Reading and Interpreting MIC Endpoints ### Visual Reading The visual reading of the plate is the most common method for determining the MIC. The plate is held against a dark background, and the wells are examined for turbidity. The turbidity is compared to the growth control. The MIC is the lowest concentration that shows no visible turbidity. The reading can be affected by the type of organism and the antimicrobial agent. Some organisms produce a faint turbidity that is difficult to see. Some antimicrobial agents produce a trailing effect, where the growth is reduced but not completely inhibited at concentrations above the MIC. The standard provides guidance on how to read these endpoints. ### Instrument-Based Reading Automated readers can be used to determine the MIC. These readers measure the optical density of each well and compare it to the control. The endpoint is determined by the instrument based on the optical density threshold. The instrument must be calibrated and validated to ensure that the results are consistent with the visual reading. The use of an automated reader can reduce the variability in the reading and improve the throughput. The reader must be maintained and the software must be updated to ensure the accuracy of the results. ### Interpretation of the MIC The MIC value is interpreted in the context of the clinical breakpoints for the antimicrobial agent. The breakpoints are the concentrations that separate the susceptible, intermediate, and resistant categories. The breakpoints are established by the CLSI and are based on the pharmacokinetic and pharmacodynamic properties of the drug, the clinical outcomes, and the distribution of the MICs in the population. The MIC value is reported as a number, and the interpretation is reported as susceptible, intermediate, or resistant. The interpretation is used to guide the selection of the antimicrobial therapy. The MIC value is also used for epidemiological purposes, such as tracking the emergence of resistance. ## Quality Control and Assurance ### The Role of Reference Strains Quality control is an essential part of the MIC testing. The quality control strains are authenticated reference strains that have a known MIC range for the antimicrobial agents. These strains are tested in parallel with the clinical isolates. The results of the quality control strains must fall within the expected range for the test to be valid. The American Type Culture Collection provides authenticated reference strains that are used for quality control. These strains are characterized and their MIC values are documented. The use of these strains ensures that the test is performing correctly and that the results are reliable. ### The Quality Control Range The quality control range is the range of MIC values that is expected for a given reference strain and a given antimicrobial agent. The range is established by the CLSI and is based on the data from multiple laboratories. The quality control range is used to verify that the test is performing within the acceptable limits. If the quality control result falls outside the expected range, the test is invalid. The cause of the failure must be investigated. The investigation may include checking the purity of the antimicrobial agent, the preparation of the inoculum, the incubation conditions, and the reading of the plate. ### The Frequency of Quality Control The quality control strains are tested each time the MIC test is performed. The frequency of the quality control testing depends on the laboratory protocol and the standard. The quality control is performed with each run, and the results are recorded. The records are reviewed to detect any trends in the performance of the test. The quality control records are an important part of the laboratory quality assurance program. The records are used to document the performance of the test and to identify any issues that need to be addressed. ## Common Failure Patterns and Troubleshooting ### Contamination Contamination is a common cause of invalid MIC results. The contamination can come from the medium, the broth, the pipette tips, or the environment. The contamination is detected by the growth in the negative control well. If the negative control shows growth, the test is invalid and must be repeated. The contamination can be prevented by using sterile equipment and by working in a clean environment. The medium and the broth must be prepared and stored according to the manufacturer instructions. The work surface must be cleaned and disinfected before the test is performed. ### Inoculum Errors The inoculum errors are a common cause of the MIC results that are too high or too low. The inoculum that is too high can result in an MIC that is too high, because the bacteria are more likely to grow in the presence of the antimicrobial. The inoculum that is too low can result in an MIC that is too low, because the bacteria are less likely to grow. The inoculum is prepared by adjusting the turbidity to the standard. The turbidity adjustment must be done carefully, and the suspension must be mixed thoroughly. The dilution factor must be calculated correctly to achieve the target inoculum concentration. ### The Dilution Errors The dilution errors can occur during the preparation of the dilution series. The errors can be caused by the pipetting, the mixing, or the calculation. The dilution errors can result in the MIC that is one or more dilutions away from the true value. The dilution series must be prepared carefully, and the pipetting must be done with the correct technique. The mixing must be complete, and the volumes must be accurate. The dilution series should be verified by the use of the quality control strains. ### The Reading Errors The reading errors can occur when the endpoint is not clear. The endpoint can be obscured by the trailing growth, by the presence of the precipitate, or by the color of the medium. The reading errors can result in the MIC that is reported incorrectly. The reading should be done by a trained person, and the reading should be done in a consistent manner. The reading should be done against a dark background, and the turbidity should be compared to the growth control. The reading should be done at the correct time, and the plate should not be left out of the incubator for too long. ## Biosafety and Containment ### Risk Assessment The broth microdilution testing involves the handling of the bacterial cultures. The risk of the exposure to the bacteria depends on the organism being tested. The risk assessment should be performed before the testing is done. The risk assessment should consider the pathogenicity of the organism, the route of the exposure, and the laboratory procedures. The Biosafety in Microbiological and Biomedical Laboratories provides the guidelines for the safe handling of the microorganisms. The guidelines describe the biosafety levels and the practices that are required for each level. The laboratory should follow the guidelines that are appropriate for the organism being tested. ### Containment and Decontamination The containment of the bacterial cultures is important to prevent the exposure of the laboratory personnel and the environment. The cultures should be handled in a biosafety cabinet when the organism is an aerosol hazard. The work surface should be cleaned and disinfected after the work is done. The decontamination of the waste is important to prevent the release of the bacteria into the environment. The waste should be decontaminated by autoclaving or by the use of a chemical disinfectant. The decontamination should be done according to the laboratory protocol. ### Personal Protective Equipment The personal protective equipment is used to protect the laboratory personnel from the exposure to the bacteria. The equipment includes the gloves, the lab coat, and the eye protection. The equipment should be worn when the work is done. The equipment should be removed and disposed of properly. ## The Role of MIC in Antimicrobial Resistance Surveillance ### The Global Context The antimicrobial resistance is a global public health problem. The World Health Organization has identified the antimicrobial resistance as one of the top threats to the public health. The resistance is driven by the use of the antimicrobial agents in the human and the animal populations. The resistance is spread through the environment and the food chain. The MIC testing is a tool for the surveillance of the antimicrobial resistance. The MIC data are used to track the emergence of the resistance, to detect the spread of the resistant strains, and to inform the public health policy. The surveillance data are collected by the national and the international organizations. ### The Use of the MIC in the Surveillance The MIC data are used to calculate the prevalence of the resistance in the population. The prevalence is the percentage of the isolates that are resistant to a particular antimicrobial agent. The prevalence is used to monitor the trends in the resistance over time. The MIC data are also used to detect the emergence of the new resistance mechanisms. The MIC value can be used to identify the isolates that have the resistance mechanism. The MIC data are used to compare the resistance rates between the different regions and the different populations. ### The Limitations of the MIC The MIC is a measure of the in vitro activity of the antimicrobial agent. The MIC does not always predict the clinical outcome. The clinical outcome depends on the pharmacokinetics of the drug, the immune status of the patient, and the site of the infection. The MIC is used in the context of the clinical breakpoints to guide the therapy. The MIC is also limited by the conditions of the test. The MIC is determined under the standardized conditions, which may not reflect the conditions in the patient. The MIC is a useful tool, but it is not the only factor that is considered in the clinical decision. ## The Use of the MIC in the Clinical Laboratory ### The Clinical Decision The MIC is used to guide the selection of the antimicrobial therapy. The MIC is interpreted in the context of the clinical breakpoints. The breakpoints are the concentrations that define the susceptible, the intermediate, and the resistant categories. The breakpoints are established by the CLSI and are based on the clinical data. The MIC is reported to the clinician along with the interpretation. The clinician uses the result to select the antimicrobial agent and the dose. The MIC is also used to monitor the response to the therapy. ### The Limitations of the Clinical Use The MIC is a measure of the in vitro activity, and the clinical outcome depends on the many factors. The MIC does not predict the clinical outcome in the individual patient. The MIC is used in the context of the clinical breakpoints, and the breakpoints are based on the population data. The MIC is not the only factor that is considered in the clinical decision. The clinician considers the patient's clinical status, the site of the infection, and the pharmacokinetics of the drug. The MIC is a tool that is used to inform the clinical decision. ## The Future of the MIC Testing ### The Automation The automation of the MIC testing is increasing. The automated systems can prepare the plates, inoculate the plates, and read the results. The automation can reduce the variability and the time required for the test. The automated systems must be validated to ensure that the results are consistent with the reference method. The automation is used in the clinical laboratories to increase the throughput and to reduce the cost. The automated systems are also used in the research laboratories to screen the large numbers of the isolates. ### The Molecular Methods The molecular methods are being developed for the detection of the resistance. The molecular methods detect the resistance genes, instead of the phenotype. The molecular methods can be faster than the MIC testing, but they do not provide the quantitative measure of the susceptibility. The molecular methods are used in the clinical laboratories to detect the specific resistance mechanisms. The molecular methods are used in the surveillance to detect the spread of the resistance genes. The molecular methods are not a replacement for the MIC, but they are a complement. ## The Practical Considerations for the Laboratory ### The Training The training of the laboratory personnel is essential for the correct performance of the MIC. The personnel must be trained in the preparation of the inoculum, the dilution series, the reading of the endpoint, and the quality control. The training should be documented, and the personnel should be assessed for the competency. The American Society for Microbiology provides the educational resources for the laboratory professionals. The resources include the training materials, the webinars, and the certification programs. The ASM is a professional organization that supports the microbiology community. ### The Records The records of the MIC testing are important for the quality assurance and the traceability. The records should include the date of the test, the organism, the antimicrobial agent, the MIC value, the quality control results, and the interpretation. The records should be kept in a secure and the accessible format. The records are used to review the performance of the laboratory and to identify the trends. The records are also used to the audit and the accreditation. The records should be kept for the period that is required by the laboratory policy. ### The Escalation The escalation criteria are the conditions under which the result should be reviewed or the test should be repeated. The escalation criteria include the quality control failure, the unexpected result, and the result that is not consistent with the clinical picture. The escalation should be done according to the laboratory policy. The escalation is important to ensure the accuracy of the results. The escalation should be done in a timely manner, and the investigation should be documented. ## The Limitations of the Broth Microdilution ### The Standardization The broth microdilution is a standardized method, but the standardization is a limitation. The standardization is required to ensure the reproducibility of the results, but the standardization can limit the ability to test the organisms that do not grow well in the standard conditions. The standardization can also limit the ability to test the antimicrobial agents that are not stable in the standard conditions. The standardization is a tradeoff between the reproducibility and the flexibility. The standardization is required for the clinical use, but the standardization is not always the best for the research. ### The Cost The broth microdilution is a relatively expensive method. The cost of the reagents, the equipment, and the labor can be high. The cost is a limitation for the laboratories that have the limited resources. The cost is also a limitation for the surveillance programs that need to test the large number of the isolates. The cost of the broth microdilution is a factor in the decision to use the method. The cost is a tradeoff between the accuracy and the cost. ### The Time The broth microdilution is a time-consuming method. The time from the setup to the result is typically 16 to 20 hours. The time is a limitation for the clinical decision, which may need the result in a shorter time. The time is a tradeoff between the accuracy and the time. The time is a limitation of the broth microdilution, but the time is the time that is required for the growth of the bacteria. ## The Safety and the Regulatory Context ### The Biosafety The biosafety is the practice of the safe handling of the biological materials. The biosafety is important for the protection of the laboratory personnel and the environment. The biosafety is the responsibility of the laboratory and the institution. The Biosafety in Microbiological and Biomedical Laboratories provides the guidelines for the biosafety. The guidelines are the basis for the biosafety programs in the laboratories. The guidelines are the reference for the biosafety. ### The Regulatory Context The regulatory context for the MIC testing is the context of the clinical laboratory. The clinical laboratory is regulated by the federal and the state regulations. The regulations require the laboratory to be accredited and to follow the standards. The regulatory context is the context of the antimicrobial resistance. The antimicrobial resistance is a public health concern, and the surveillance is the responsibility of the public health agencies. The surveillance is the responsibility of the WHO and the national agencies. ## The Professional Escalation Criteria The professional escalation criteria are the steps that are taken when the MIC result is not valid or when the result is not consistent with the clinical picture. The escalation criteria are the following: - The quality control result is outside the expected range. The test is invalid, and the cause of the failure must be investigated. - The negative control shows growth. The test is invalid, and the contamination must be investigated. - The growth control shows no growth. The test is invalid, and the inoculum must be investigated. - The MIC result is not consistent with the clinical picture. The result should be reviewed, and the test should be repeated. - The MIC result is the result of the resistance that is not expected. The result should be confirmed, and the isolate should be sent to the reference laboratory. The escalation should be done in a timely manner, and the investigation should be documented. The escalation is important to ensure the accuracy of the results. ## The Use of the Authenticated Strains The use of the authenticated strains is important for the quality of the MIC testing. The authenticated strains are the strains that have been characterized and their MIC values are known. The authenticated strains are used for the quality control and for the validation of the method. The American Type Culture Collection provides the authenticated strains. The strains are the reference strains that are used in the clinical and the research laboratories. The strains are the quality control strains for the MIC testing. The use of the authenticated strains is the best practice for the MIC testing. The authenticated strains are the reference for the quality control. The authenticated strains are the reference for the validation of the method. ## The Food Microbiology Context The broth microdilution is also used in the food microbiology. The food microbiology is the study of the microorganisms in the food. The food microbiology is the responsibility of the FDA and the other agencies. The Bacteriological Analytical Manual provides the methods for the food microbiology. The manual includes the methods for the detection and the enumeration of the foodborne pathogens. The manual also includes the methods for the antimicrobial susceptibility testing. The broth microdilution is used in the food microbiology to test the susceptibility of the foodborne pathogens. The MIC is used to monitor the resistance in the foodborne pathogens. The MIC is used to inform the public health policy. ## The Educational Context The education of the microbiology is important for the workforce. The education is the responsibility of the academic institutions and the professional organizations. The American Society for Microbiology provides the educational resources for the microbiology. The education of the microbiology includes the training in the MIC testing. The training is the training in the procedure, the quality control, and the interpretation. The training is the training in the biosafety and the regulatory context. The education of the microbiology is the foundation for the practice of the microbiology. The education is the foundation for the research and the clinical practice. ## The Common Failure Patterns The common failure patterns in the MIC testing are the following: - The contamination of the medium or the equipment. - The incorrect preparation of the inoculum. - The incorrect dilution of the antimicrobial agent. - The incorrect reading of the endpoint. - The failure of the quality control. The failure patterns are the cause of the invalid results. The failure patterns are the cause of the errors in the MIC. The failure patterns are the cause of the errors in the clinical decision. The failure patterns are the cause of the errors in the MIC. The failure patterns are the cause of the errors in the clinical decision. The failure patterns are the cause of the errors in the surveillance. ## The Best Practices The best practices for the MIC testing are the following: - The use of the authenticated strains for the quality control. - The use of the standardized procedure. - The use of the correct inoculum. - The use of the correct incubation conditions. - The use of the correct reading of the endpoint. - The use of the correct interpretation of the result. The best practices are the practices that are the best for the accuracy and the reproducibility of the MIC. The best practices are the practices that are the best for the clinical decision and the surveillance. ## The Future of the MIC The future of the MIC is the future of the antimicrobial resistance. The MIC is the tool for the detection of the resistance. The MIC is the tool for the surveillance of the resistance. The MIC is the tool for the clinical decision. The future of the MIC is the future of the automation and the molecular methods. The automation is the future of the MIC. The molecular methods are the future of the MIC. The future of the MIC is the future of the microbiology. The future is the future of the clinical practice. The future is the future of the public health. ## Frequently Asked Questions ### What is the difference between the MIC and the breakpoint? The MIC is the lowest concentration of the antimicrobial agent that inhibits the visible growth of the organism. The breakpoint is the concentration that defines the susceptible, the intermediate, and the resistant categories. The breakpoint is established by the CLSI and is based on the clinical data. The MIC is the measured value, and the breakpoint is the interpretive criterion. ### How is the MIC reported? The MIC is reported as a value in micrograms per milliliter. The value is the lowest concentration that inhibits the visible growth. The MIC is reported with the interpretation, which is the susceptible, the intermediate, or the resistant category. The interpretation is based on the breakpoint. ### What is the difference between the MIC and the MBC? The MIC is the lowest concentration that inhibits the visible growth. The MBC is the lowest concentration that kills the organism. The MBC is determined by the subculture of the wells that show no growth. The MBC is the concentration that kills the 99.9 percent of the organism. ### What is the purpose of the quality control in the MIC? The quality control is the use of the reference strains to verify the performance of the test. The quality control is the use of the strains with the known MIC values. The quality control is the verification that the test is performing correctly. The quality control is the verification that the results are valid. ### What is the difference between the broth microdilution and the agar dilution? The broth microdilution is the method that uses the broth in the wells. The agar dilution is the method that uses the agar in the plates. The broth microdilution is the method that is the most common. The agar dilution is the method that is the reference. ### What is the role of the CLSI in the MIC? The CLSI is the organization that develops the standards for the antimicrobial susceptibility testing. The CLSI is the organization that defines the breakpoints. The CLSI is the organization that provides the guidance for the MIC. ### What is the role of the WHO in the antimicrobial resistance? The WHO is the organization that is the global health. The WHO is the organization that is the surveillance of the antimicrobial resistance. The WHO is the organization that is the policy for the antimicrobial resistance. ### What is the role of the ATCC in the MIC? The ATCC is the organization that provides the authenticated strains. The ATCC is the organization that provides the reference strains for the quality control. The ATCC is the organization that provides the strains for the research. ## 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 Bacteriology Guides - [Common Poultry Diseases: A Clinical Overview](/knowledge/bacteria/avian-bacteria/common-poultry-diseases-clinical-overview) - [Cattle Bacterial Diseases: Comprehensive Overview and Clinical Management](/knowledge/bacteria/livestock-bacteria/cattle-bacterial-diseases-comprehensive-overview-clinical-management) - [What Is Duck Disease? Clinical Overview and Pathogen Profile](/knowledge/bacteria/avian-bacteria/what-is-duck-disease) - [Bacterial Diseases of Animals: A Comprehensive List and Clinical Overview](/knowledge/bacteria/wildlife-bacteria/animal-bacterial-diseases-list-clinical-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. - [NCBI Pathogen Detection](https://www.ncbi.nlm.nih.gov/pathogens). National Center for Biotechnology Information. - [Daptomycin area under the curve to minimum inhibitory concentration ratio by broth microdilution for predicting the outcome of vancomycin-resistant Enterococcus bloodstream infection.](https://pubmed.ncbi.nlm.nih.gov/36156368). Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie, 2022. - [A novel colorimetric broth microdilution method to determine the minimum inhibitory concentration (MIC) of antibiotics and essential oils against Helicobacter pylori.](https://pubmed.ncbi.nlm.nih.gov/16076074). Die Pharmazie, 2005. - [Broth microdilution protocol for minimum inhibitory concentration (MIC) determinations of the intracellular salmonid pathogen Piscirickettsia salmonis to florfenicol and oxytetracycline.](https://pubmed.ncbi.nlm.nih.gov/23803014). Journal of fish diseases, 2014. - [Rapid impedance-based Antimicrobial Susceptibility Testing (iFAST) of Enterobacterales in urinary tract infections.](https://pubmed.ncbi.nlm.nih.gov/40623549). The Journal of infection, 2025. > This article is educational and does not replace validated laboratory procedures, clinical diagnosis, institutional biosafety review, or public-health guidance.