Susceptibility to erythromycin of anaerobes of the genera Bacteroides, Fusobacterium, Sphaerophorus, Veillonella, Clostridium, Corynebacterium, Peptococcus, Peptostreptococcus.

The minimal inhibitory concentrations (MIC) of erythromycin were determined by broth dilution tests for 313 anaerobic strains, most of which were clinical isolates. All the gram-positive anaerobes tested (84 Peptococcaceae, including 21 Peptostreptococcus anaerobius and 15 Peptococcus variabilis; 65 Corynebacterium acnes and 29 Clostridium strains, including 13 C. perfringens) were sensitive (MIC values 0.012 through 3.12 microgram erythromycin/ml); so were 111 cultures of gram-negative anaerobes (52 Bacteroides fragilis, 12 B. thetaiotaomicron, 7 B. vulgatus, 13 B. oralis, 4 B. melaninogenicus, 10 Sphaerophorus necrophorus, 2 Veillonella sp., 11 members of other species). Erythromycin at concentrations of 6.25 through 200.0 microgram/ml was active against 24 strains (1 B. fragilis, 4 Fusobacterium fusiforme, 9 Sph. freundi, 10 Sph. varius). The present results are compared to the limited number of reports existing with regard to the susceptibility of anaerobes to erythromycin.