BETA-LACTAMASE PRODUCTION AND INVITRO ANTIMICROBIAL SUSCEPTIBILITY OFPORPHYROMONAS-GINGIVALIS

Beta-lactamase production by 98 Porphyromonas strains was investigated by the nitrocefin (chromogenic cephalosporin) test. Human isolates of P. gingivalis (91), P. endodontalis (2), and P. asaccharolytica (1) w ere tested, with four closely related Porphyromonas spp. of animal ori gin and four reference strains. The in vitro susceptibility of 64 P. g ingivalis strains was investigated on Brucella blood agar by the E tes t. None of the human Porphyromonas isolates tested produced beta-lacta mase, but one Porphyromonas strain of animal origin, most closely rese mbling P. endodontalis, produced beta-lactamase. P. gingivalis was sus ceptible to almost all of the drugs tested: benzylpenicillin, ampicill in, cefaclor, cefuroxime, erythromycin, clindamycin, tetracycline, dox ycycline, metronidazole and ciprofloxacin; all strains were inhibited at 0.016 mug/ml, 0.023 mug/ml, 0.315 mug/ml, 0.064 mug/ml, 0.19 mug/ml , 0.016 mug/ml, 0.094 mug/ml, 0.047 mug/ml, 0.023 mug/ml, and 0.75 mug /ml of these drugs, respectively. Cotrimoxazole exhibited variable eff icacy against P. gingivalis; the range of MICs was 0.1095-32.0 mug/ml. The results indicate that beta-lactamase production is currently not a problem amongst clinical isolates of P. gingivalis and strains are s usceptible to most antimicrobial agents.