Incidence of beta-lactamase production and antimicrobial susceptibility ofanaerobic gram-negative rods isolated from pus specimens of orofacial odontogenic infections

The incidence of beta -lactamase production in anaerobic gram-negative rods isolated from 93 pus specimens of orofacial odontogenic infections and the antimicrobial susceptibility of these isolates against 11 antibiotics were determined. A total of 191 anaerobic gram-negative rods were isolated from the specimens. beta -Lactamase was detected in 35.6% of the black-pigmente d Prevotella and 31.9% of the nonpigmented Prevotella. However, no strains among the other species isolated produced beta -lactamase. Ampicillin, cefa zolin and cefotaxime showed decreased activity as regards beta -lactamase-p ositive Prevotella strains, whereas the activity of ampicillin/sulbactam, c efmetazole, and imipenem continued to be effective against such strains. Al l tested beta -lactam antibiotics were effective against Porphyromonas and Fusobacterium. Erythromycin showed decreased activity against nonpigmented Prevotella and Fusobacterium. Clindamycin, minocycline and metronidazole we re powerful antibiotics against which anaerobic gram-negative rods could be tested. The present study showed that beta -lactamase-positive strains wer e found more frequently in the Prevotella strains than in any of the other species of anaerobic gram-negative rods. The effectiveness of adding sulbac tam to ampicillin was demonstrated, as well as the difference in cephalospo rin activity against beta -lactamase-positive strains.