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Antimicrobial Efficacy Testing

How do clinical applications affect the efficacy of antimicrobial products, and how can we test this in the lab?

iFyber offers a suite of antimicrobial efficacy testing solutions for medical devices and drugs including, but not limited to, antimicrobial dressings, bio-engineered tissues, biomaterials, bioactive dressings, and novel anti-infectives.

Our scientists are experienced in developing assays and conducting tests to assess antimicrobial performance in a range of products. These antimicrobial efficacy tests can support R&D teams looking to:

Evaluate the efficacy of antimicrobial agents over time.
Determine the in vitroactivity of new antimicrobials.
Evaluate an antimicrobial product's potency.
Evaluate the effectiveness of antimicrobial finishes on textile materials.

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Antimicrobial Efficacy Testing Services

MIC/MBC Testing

Minimum Inhibitory Concentration (MIC) is defined as the lowest concentration of an antimicrobial agent that prevents visible growth of a microorganism after overnight incubation. This measure is important in determining the in vitro activity of new antimicrobials. The MIC is generally determined using a broth dilution assay, which involves creating serial dilutions of the antimicrobial in a liquid growth medium inoculated with a standardized number of microorganisms. After incubation, the lowest concentration that prevents the medium from becoming turbid is identified as the MIC.

The MIC test is essential for various reasons. Primarily, it helps in identifying a baseline: the appropriate concentration of an antimicrobial required to inhibit growth, ensuring that the final product has the necessary potency to combat infections. The Clinical and Laboratory Standards Institute (CLSI) has established guidelines, such as the CLSI M07-A9, which are considered the gold standard for conducting MIC tests. Additionally, iFyber has the experience to fully customize experimental designs beyond standard procedures.

Once the MIC has been determined, the next step often involves finding the Minimum Bactericidal Concentration (MBC), which is the lowest concentration of an antimicrobial that kills the microorganism. The MBC is determined by taking samples from the MIC test wells that showed no growth and culturing them on antimicrobial-free agar plates. These plates are then incubated for 24 hours at 37°C ± 2°C. The MBC is identified as the lowest concentration at which no bacterial colonies grow on the agar, indicating that the antimicrobial concentration is sufficient to kill the bacteria rather than merely inhibiting their growth.

Determining the MBC is important for understanding the bactericidal capabilities of an antimicrobial agent. While the MIC indicates the potential of an antimicrobial to inhibit growth, the MBC provides a more comprehensive picture of its killing power.

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Time-Kill Assessment

A time-kill assessment is a dynamic method used to evaluate the efficacy of antimicrobial agents over time. This method involves exposing a microbial population to an antimicrobial agent and then measuring the reduction in viable microorganisms at various time intervals. Typically, the test is performed by inoculating a microbial culture in a growth medium containing the antimicrobial agent, followed by sampling at specific time points. These samples are then plated on agar to determine the number of surviving colonies and calculate microbial reduction.

The importance of a time-kill assessment lies in its ability to provide detailed information on the kinetics of antimicrobial activity. Unlike static methods such as Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC), which offer single-point measurements, time-kill studies capture the dynamic interaction between the antimicrobial agent and the microorganisms over time. This is particularly crucial for understanding how quickly an antimicrobial can reduce microbial load, which is vital for treating acute infections where rapid bacterial eradication is necessary. Furthermore, time-kill assays can help identify potential synergistic effects when using combination therapies, guiding the development of more effective treatment regimens.

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Zone of Inhibition (ZOI)

The Zone of Inhibition is a fundamental qualitative test widely used in the medical device and pharmaceutical industries. Researchers developing antimicrobial textiles, surfaces, and liquids use this test for its simplicity and speed in measuring and comparing levels of inhibitory activity. In this method, approximately one million cells from a single strain are spread over an agar plate and incubated with the antimicrobial product. If the bacterial or fungal strain is susceptible to the antimicrobial agent, a clear zone appears on the agar plate; if resistant, no zone is observed. This test is most effective when the antimicrobial can leach out of the material, commonly including leachable antimicrobials embedded in plastics, textiles, solids, surfaces, liquids, gels, and antibiotic solutions.

The significance of the Zone of Inhibition test lies in its simplicity, cost-effectiveness, and ability to deliver quick preliminary results about an antimicrobial's potency. Additionally, it is a valuable tool for monitoring antibiotic resistance, as changes in the size of the Zone of Inhibition over time can indicate shifts in bacterial susceptibility. By providing a straightforward and visual assessment of antimicrobial activity, the Zone of Inhibition test is crucial for the development and implementation of effective antimicrobial therapies.

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AATCC Test Method 100

Test Method 100 evaluates the effectiveness of antimicrobial finishes on textile materials. Test articles are directly inoculated with the test organism and incubated at variable times depending on the application (typically at least 24 hours). The test articles are then placed in neutralizing solution and the microbes are recovered and enumerated.

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