Susceptibility of Clostridium ramosum to antimicrobial agents.

The susceptibility of 49 strains of Clostridium ramosum to 10 antibiotics was determined by agar dilution and disk diffusion tests. Results showed that, among the anaerobes, C. ramosum is second only to Bacteroides fragilis in its resistance to antimicrobial agents. All strains were susceptible to penicillin, carbenicillin, chloramphenicol, vancomycin, and metronidazole at readily achievable blood levels. Most strains (83%) were susceptible to erythromycin. There was a high level of resistance to clindamycin in 16% of the strains. All isolates were resistant to rifampin and gentamicin, and most were resistant to lincomycin. Assessment of susceptibility by measurement of inhibition zone diameters with disk diffusion tests was not satisfactory.