Martin, William J.

The minimal inhibitory concentrations of 601 clinical isolates of anaerobic bacteria to 10 different antimicrobial agents were determined by an agar-dilution technique. Nearly all strains were resistant to kanamycin and gentamicin, although moderate activity to both drugs was noted with Fusobacterium sp., anaerobic cocci, some strains of Bacteroides melaninogenicus , and nonsporeforming gram-positive bacilli. Chloramphenicol at 12.5 μg/ml inhibited all but three of the strains tested. Tetracycline at 6.25 μg/ml had high activity against all groups tested, with the exception that only 39% of strains of Bacteroides fragilis were inhibited at this concentration. Excluding certain species of Bacteroides , the majority of anaerobes were inhibited by penicillin at 3.1 μg/ml or less and by cephalothin at 12.5 μg/ml or less. Lincomycin at 6.2 μg/ml or less was active against nearly all strains. Erythromycin at a concentration of 3.1 μg/ml was active against B. fragilis ; however, erythromycin was less active against the other groups. Most of the minimal inhibitory concentrations of lincomycin exceeded those of clindamycin by fourfold. Rifampin inhibited virtually all strains at 3.1 μg/ml.