The in vitro susceptibility of 43 strains of Clostridium perfringens to nine antibiotics was determined by a standardized test for rapid-growing anaerobes. Good correlation was established between the agar dilution susceptibility and the disc diffusion susceptibility results. The inhibition zone diameters around the antibiotic discs, however, were generally much smaller than those of gram-negative anaerobes previously studied. All of the strains tested were susceptible in vitro to chloramphenicol, clindamycin, doxycycline, minocycline, penicillin, and vancomycin. Erythromycin showed poor in vitro activity against this organism, with only 7% of the strains susceptible, 72% intermediate in susceptibility, and 21%o resistant. In tests of the 43 strains against lincomycin, 58% were susceptible, 32.5°% were intermediate in susceptibility, and 9.5% were resistant. Against tetracycline, 37% of the strains were intermediate in susceptibility and the rest were susceptible.

Twenty-seven strains of Capnocytophaga were tested for their susceptibility to 18 antimicrobial agents by an agar dilution technique. All strains were susceptible to achievable blood levels of penicillin G, cefaclor, cefoxitin, cefoperazone, moxalactam, clindamycin, chloramphenicol, and tetracycline. Most were susceptible to achievable levels of cefamandole, erythromycin, and metronidazole, and more than 10% were resistant to achievable levels of cephalexin and cephradine. With antimicrobial agents used in selective media, all strains were resistant to colistin, kanamycin, and nalidixic acid at commonly recommended concentrations, but some strains were susceptible to commonly recommended concentrations of bacitracin and vancomycin.Bacteria in the genus Capnocytophaga (6) (fornerly CDC group DF-1 and Bacteroides ochraceus [5,10] The antimicrobial agents were incorporated into Brucella Agar (Difco Laboratories, Detroit, Mich.) supplemented with vitamin K (10 jsg/ ml)-laked sheep blood (5%), and the tests were performed as previously described (7). Anaerobic incubation was utilized because Capnocytophaga grows well anaerobically and the strains Bacteroides fragilis ATCC 25285 and B. thetaiotaomicron ATCC 29741 could be used as controls. Laked blood agar plates containing no antimicrobial agent were inoculated and incubated anaerobically and aerobically as growth and contamination controls.Our results are summarized in Table 1. With the agents most frequently used in dental practice, all strains were susceptible to achievable blood levels of penicillin and tetracycline, and at least 90% were susceptible to achievable levels of erythromycin. The oral cephalosporins, cephalexin and cephradine, were not as active against the strains as was cefaclor. Parenteral beta-lactam antimicrobial agents of potential use in serious infections were active against all strains at achievable levels. Chloramphenicol and clindamycin were also active against all strains. These results are in general agreement with previously published reports (2,4,8

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