Standardized antimicrobial disc susceptibility testing of anaerobic bacteria: in vitro susceptibility of Clostridium perfringens to nine antibiotics.

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% 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.