Resistance to beta-lactam antibiotics and beta-lactamase production of Bacteroides, Porphyromonas and Prevotella strains.

Resistance to beta-lactam antibiotics of 183 clinical isolates belonging to Bacteroides, Porphyromonas and Prevotella was tested by a micro-broth dilution MIC method. Beta-lactamase production was screened by using nitrocefin sticks. Prevalence of resistance to different beta-lactam antibiotics was higher among the Bacteroides strains other than B. fragilis parallel with a beta-lactamase production (88% and 96%, respectively). Resistance was observed less frequently among Porphyromonas and Prevotella strains. Cefoxitin resistance was 11.5% and amoxicillin/clavulanic acid 3.5% among Bacteroides isolates, whereas no resistance was found to these antibiotics among the Porphyromonas and Prevotella strains. All strains tested were susceptible for imipenem. Beta-lactamase production of selected isolates was tested quantitatively. Beta-lactamase of B. fragilis 1 and B. levii differed in their isoelectric points, substrate profiles and inhibition by clavulanic acid, sulbactam and tazobactam.