beta-lactamase production by oral anaerobic gram-negative species in infants in relation to previous antimicrobial therapy

The frequency of beta-lactamase production in gram-negative bacteria has in creased considerably during recent Sears. In this study, beta-lactamase pro duction by oral anaerobic gram-negative rods isolated from saliva was longi tudinally examined for 44 Caucasian infants at the ages of 2, 6, and 12 mon ths in relation to their documented exposure to antibiotics. Isolates showi ng decreased susceptibility to penicillin G (1 mu g/ml) were examined for b eta-lactamase production by using a chromogenic cephalosporin disk test. be ta-Lactamase-positive, gram-negative anaerobic species were found in 11, 55 , and 89% of each age group, respectively. beta-Lactamase production was mo st frequent among organisms of the Prevotella melaninogenica group. At 12 m onths, 73% of the infants harbored beta-lactamase-producing members of the P, melaninogenica group, 55% had nonpigmented Prevotella species, 25% had P orphyromonas catoniae, 23% had Fusobacterium nucleatum, and 5% had Capnocyt ophaga species. Several beta-lactamase-producing species could be simultane ously found in the infants' mouths. The presence of beta-lactamase-producin g species was significantly associated with the infants' exposure to antibi otics through antimicrobial treatments given to the infants and/or their mo thers.