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

The 'E test' is a method for measuring MICs of antimicrobial agents against bacteria and is based on diffusion of a pre-formed antibiotic gradient from a plastic strip. The performance of the E test was evaluated by comparison with a conventional agar dilution MIC method in tests with ten agents and a variety of organisms. Correlation between MICs by the agar dilution and E test methods was good, 98.85% results were within 2 log2 dilution steps in a total of 1304 tests. The E test is technically straightforward as tests are set up in the same way as the disc diffusion method. The versatility and ease of use of the E test make the method an attractive alternative to conventional dilution tests.