Evaluation of the E test, a novel method of quantifying antimicrobial activity

Area of Science:

• Microbiology
• Clinical Diagnostics
• Antimicrobial Susceptibility Testing

Background:

• Accurate determination of Minimum Inhibitory Concentrations (MICs) is crucial for effective antimicrobial therapy.
• Conventional MIC methods can be labor-intensive and time-consuming.
• The E test offers a novel approach to MIC determination using a pre-formed antibiotic gradient.

Purpose of the Study:

• To evaluate the performance of the E test for MIC determination.
• To compare E test results with a conventional agar dilution MIC method.
• To assess the accuracy and usability of the E test in a diverse range of bacterial organisms and antimicrobial agents.

Main Methods:

• The E test utilizes a plastic strip with a pre-defined gradient of an antimicrobial agent.
• MICs were determined using the E test and compared against results from a standard agar dilution MIC method.
• Testing involved ten different antimicrobial agents and a variety of bacterial species, totaling 1304 individual tests.

Main Results:

• A high degree of correlation was observed between the E test and the agar dilution MIC method.
• 98.85% of the results obtained by both methods agreed within 2 log2 dilution steps.
• The E test demonstrated technical simplicity, similar to the disc diffusion method.

Conclusions:

• The E test is a technically straightforward and user-friendly method for determining antimicrobial MICs.
• Its ease of use and versatility make it an attractive alternative to conventional dilution susceptibility tests.
• The E test provides accurate and reliable MIC values, supporting its clinical utility.