Susceptibility patterns and characterization of beta-lactamases in clinical isolates of Bacteroides fragilis.

Strains of Bacteroides fragilis isolated from clinical specimens are known to be frequently resistant to penicillins or cephalosporins. The production of beta-lactamases is the major mechanism in this resistance. Up to now at least five types of beta-lactamase enzymes have been described in the Bacteroides fragilis group. The purpose of this study was to evaluate the susceptibility to different antibiotics and the prevalence of the beta-lactamase types among 100 Bacteroides fragilis strains isolated from clinical specimens in Italy. MICs of 11 antibiotics were determined by the reference agar dilution method and by the new E test (AB Biodisk, Sweden). Results showed an acceptable correlation between the MICs determined for most strains, although those obtained by the E test tended to be lower. In the beta-lactam resistant strains the enzyme activity and isoelectric points were determined on crude enzyme extract.