Comparison of the E Test to agar dilution, broth microdilution, and agar diffusion susceptibility testing techniques by using a special challenge set of bacteria.
The E Test (AB Biodisk, Solna, Sweden) is a new method for performing antimicrobial susceptibility tests. It consists of an impervious carrier (5- by 50-mm strip) with a predefined antimicrobic gradient which is placed on an inoculated agar plate and processed like a disk diffusion test. Results are generated directly as MICs from a continuous concentration gradient covering 15 twofold dilutions, and MICs are read where the edge of the inhibition zone intersects the strip. We compared the E Test with disk diffusion, broth microdilution, and agar dilution tests by using a challenge set of 195 gram-positive and gram-negative bacteria for 14 antimicrobial agents. Also, disk diffusion, broth microdilution, and agar dilution tests were compared with each other. All test method comparisons gave greater than 94% agreement for the category of susceptibility. The E Test category agreement with disk diffusion and broth microdilution was 95.1%, and with agar dilution it was 95.2%. The E Test results were as reliable as the results obtained by the standard antimicrobial susceptibility testing methods.
Baker
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Antimicrobic Investigations Branch, Centers for Disease Control, Atlanta, Georgia 30333.
Stocker
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Culver
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Thornsberry
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D000362:Agar; D001419:Bacteria / Q000187:drug effects*; D003470:Culture Media; D004058:Diffusion; D004352:Drug Resistance, Microbial; D005069:Evaluation Studies as Topic; D008826:Microbial Sensitivity Tests / Q000379:methods*
D003470:Culture Media; D000362:Agar