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Minimum Bactericidal Concentration (MBC)
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Summary
Minimum bactericidal concentration is a test that determines the lowest concentration of an antimicrobial agent required to kill โฅ99.9% of the initial bacterial population. This test is conducted after the minimum inhibitory concentration(MIC) test. MBC is essential for conforming bactericidal activity and is widely used in antibiotic development, disinfectant efficacy testing and research and development purposes.
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Qualitative assay to evaluate the susceptibility or resistance of pathogenic bacteria to antibacterial agents.
Determining lowest concentration of an antimicrobial agent that inhibits visible growth of a microorganism
Quick understanding of the test
Minimum Bactericidal Concentration
Application
- Serial dilutions of antimicrobial test compounds are made and are inoculated with test microorganisms.
- These dilutions are further transferred into 96-well Microtiter Plates. In parallel, a growth control and sterile control are also used in the test procedure.
- Microtiter plate is further incubated at a specific temperature and duration.
- After incubation bacterial growth is observed.
- The lowest concentration of dilution with no turbidity or visible growth is referred as MIC (Minimum Inhibitory Concentration).
- Dilutions showing MIC are plated on a suitable growth medium and incubated to determine the viable cells.
- Multiple antimicrobial agents can be evaluated against a wide range of microorganisms.
- The test provides actionable insights for reformulation or product efficacy enhancement.
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What is Minimum bactericidal concentration (MBC) ?
The Minimum Bactericidal Concentration (MBC) test determines the lowest concentration of an antibacterial agent required to kill 99.9% of the original test microorganisms within a specified time frame. It is typically performed after establishing the Minimum Inhibitory Concentration (MIC). While the MIC identifies the lowest concentration that visibly inhibits microbial growth, the MBC demonstrates the lowest level of antimicrobial agent resulting in microbial death. This test is crucial in pharmaceutical development, clinical microbiology, and industrial applications, helping ensure that antimicrobial agents achieve effective bactericidal activity.
Minimum Bactericidal Concentration (MBC) Test Method
Inoculum preparation
- Culture of test microorganisms that is grown overnight is diluted in growth-supporting broth (Mueller Hinton Broth) between 1 x 10^5 and 1 x 10^6 CFU/ml.
Serial dilution method
- Serial dilutions of antimicrobial test compounds are made.
- All the dilutions of test compounds are inoculated with an equal volume of test microorganisms.
Microtitre plate incubation
- These dilutions are further transferred into 96-well Microtiter Plates. In parallel, a growth control (bacterial suspension without any antimicrobial agent) and sterile control (media without bacteria where no bacterial growth is observed after incubation) are also used in the test procedure.
- Microtiter plate is further incubated at a specific temperature and duration.
Subculturing and viable plate count
- After incubation bacterial growth is observed, turbidity indicates the growth of the microorganism, and lowest concentration of dilution with no turbidity or visible growth is referred as MIC (Minimum Inhibitory Concentration).
- 2-3 dilutions showing MIC are plated on a suitable growth medium and incubated to determine the viable cells.
- The lowest concentration that shows 99.9% reduction of the tested bacteria is MBC.
How to interpret MBC results
Minimum bactericidal concentration is the lowest concentration of an antimicrobial agent that kills โฅ99.9% of the initial bacterial population. Once no-turbid samples are identified under MIC, they are subcultured onto antimicrobial-free agar and the bacterial growth is assessed. The results are interpreted by identifying the lowest concentration with no colony growth and it is reported as MBC.
MBC vs MIC
Parameter | Minimum Inhibitory Concentration (MIC) | Minimum Bactericidal Concentration (MBC) |
Definition | The lowest concentration of an antimicrobial agent inhibiting visible growth of a microorganism after overnight incubation. | The lowest concentration of an antimicrobial agent required to kill โฅ99.9% of the initial bacterial population |
Primary outcome measured | Inhibition of bacterial growth | Bactericidal property (Bacterial killing) |
Underlying principle | Absence of visible turbidity indicates inhibition of growth | Absence of colony formation following subculture confirms bacterial killing |
Method of determination | Broth dilution or agar dilution techniques | Subculturing aliquots from MIC test wells or tubes onto antimicrobial-free agar |
Result | Clear broth or agar with no visible microbial growth | No growth of colonies after incubation of subcultures from MIC |
Relationship between parameters | MIC value is always less than or equal to the MBC value | MBC value is equal to or greater than the MIC value |
Typical application | Antibiotic selection, antimicrobial susceptibility testing, resistance surveillance | Differentiation between bacteriostatic and bactericidal agents, evaluation of disinfectants and antimicrobial products |
Applications of Minimum Bactericidal Concentration
- Therapeutic Guidance: It guides clinicians to use the appropriate dosages of antibiotics so that they could treat patients effectively without resistance.
- Research and Development: MBC is an integral part of drug development and will be used to evaluate the new antibiotics with well-established ones in terms of their potency.
- Infection Control: It will assist in formulating guidelines of disinfection and sterilization procedures in healthcare environments.
Strengths of Minimum Bactericidal Concentration (MBC)
- The MBC test helps in determining the minimum concentration of an agent required to achieve a bactericidal effect.
- The MBC test is an effective and relatively cost-efficient method for screening multiple antimicrobial agents for potency.
- The MBC test parameters are simple to control in a laboratory setting, enabling easy comparisons of various antimicrobial agents simultaneously.
- This method involves an extended contact time to make sure the anti-microbial agent really measures how much is needed to kill them.
- Knowing the MBC helps clinicians or product developers determine the concentration needed for full kill, not just inhibition.
- For sterilization, disinfectants, or bactericidal drugs, MBC gives stronger evidence of effectiveness than MIC alone.
Limitations of Minimum Bactericidal Concentration Test (MBC)
- An MBC must be determined separately for each microorganism, as different microbes often have varying MBC values for the same antimicrobial agent.
- MBC test results do not indicate the concentration required to disinfect or sanitize surfaces within short contact times, such as 10 minutes.
- Using highly nutritive growth media like Tryptic Soy Broth can interfere with accurate MBC results; therefore, Mueller-Hinton Broth is recommended for this method.
Advantages of Minimum Bactericidal Concentration Test (MBC)
- Differentiates Bacteriostatic from Bactericidal Agents:
It helps distinguish whether an agent inhibits bacterial growth or eradicates bacteria, providing critical insights for product development and clinical applications. - Standardized and Quantifiable Results:Offers consistent, reproducible results through standardized methodologies, ensuring reliability in research and clinical practice.
- Complements MIC Tests: MBC tests provide a more comprehensive understanding of the effects of antimicrobials, complementing MIC tests and offering a fuller picture of their pharmacodynamic properties.
Why choose our lab for MBC Testing
At Microbe Investigations Switzerland (MIS), we offer comprehensive testing services including Minimum Bactericidal Concentration (MBC), Minimum Inhibitory Concentration (MIC), and Zone of Inhibition (ZOI) testing to accurately measure how effectively your products inhibit and kill harmful microorganisms.
Our detailed results help you validate product claims, meet regulatory requirements, and build trust with customers and stakeholders. Whether youโre developing new disinfectants, sanitizers, or antimicrobial coatings, MIS delivers precise, reliable data you can count on.
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Frequently Asked Questions
DR. Martinoz Scholtz
The Minimum Bactericidal Concentration (MBC) test determines the minimum concentration of antibacterial agents required to kill 99.9% of test microorganisms in the original inoculum within a specified time frame
This test is applicable for drugs, antiseptics, disinfectants, and other liquid formulations.
The turnaround time for this test is 1-2 weeks .
At Microbe Investigations Switzerland, we test for MBC using the following bacteria: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species.
Minimum bactericidal concentration is the lowest concentration of an antibiotic at which bacteria are killed whereas minimum inhibitory concentration is the lowest concentration at which bacterial growth is inhibited.
Testing for Minimum Bactericidal Concentration (MBC) is crucial in clinical diagnostics so that proper dosing is prescribed, making the outcome of treatment effective in killing the pathogen and preventing resistance.
MBC stands for Minimum bactericidal concentration.
No, MBC is a laboratory test performed in vitro on bacterial cultures, not a clinical blood test.
99.9% reduction means the antibacterial agent can kill โฅ99.9% of the initially introduced bacterial population. It is equal to 3 log reduction in viable cells.
After determining the MIC, samples are taken from from wells or tubes with no visible growth and subcultured onto drug-free agar. The lowest concentration showing no colony growth after incubation is reported as the MBC.
MBC evaluates if an antibiotic kills the bacteria rather than just inhibiting growth. This supports right dose selection and killing claims.
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