EFFECT OF PH ON IN-VITRO ANTIMICROBIAL SUSCEPTIBILITY OF THE BACTEROIDES-FRAGILIS GROUP

We studied the effect of pH (7.1, 6.3, and 5.8) on the in vitro suscep tibilities of 59 isolates of Bacteroides fragilis and 60 isolates of o ther B. fragilis group species to trovafloxacin, ciprofloxacin, clinda mycin, ampicillin-sulbactam, piperacillin-tazobactam, imipenem, and me ropenem. For each agent tested the geometric mean MIC was highest at p H 5.8, intermediate at pH 6.3, and lowest at pH 7.1. The magnitude of the pH effect varied greatly among different antibiotics. These data s how that an acidic pH decreases the in vitro susceptibilities of the B . fragilis group to several antibiotics.