Schumacher, U.K. *,Wittorf, S., and Werner, H.
Dept. Med. Microbiol., Eberhard-Karls-University, D-72076 Tübingen, Germany

The purpose of this study was to evaluate the ability of the E test method to determine susceptibilities of 142 strains belonging to Prevotella bivia and nine other Prevotella species to beta-lactams, meropenem, several known anti-anaerobic drugs and two fluoroquinolones, ciprofloxacin and sparfloxacin. MICs were determined by the reference agar dilution method using supplemented brucella agar and were compared to the E test results obtained with the same agar. Overall, 78.3% of the E test results were within one dilution of the agar dilution MICs and 90.9% fell within two dilutions. Testing beta-lactams except piperacillin in combination with tazobactam, there was a tendency of the E test MICs to be slightly lower than the agar dilution MICs. In 50% of the strains the E test MICs of the piperacillin/tazobactam combination were higher than two dilution steps compared to the agar dilution MICs, although this differences did not result in categorical discrepancies. 71 of 78 strains were inhibited by the beta-lactamase inhibitor tazobactam as a single agent in concentrations of 2µg/ml or less determined by the agar dilution method. Major differences resulting in categorical discrepancies were found in 11.2% of the strains by testing metronidazole and 2.8% by testing sparfloxacin.

Except testing metronidazole the E test may be considered to be a suitable alternative for testing individual isolates of Prevotella species using interpretative categories.