Susceptibility of Gram-Negative Anaerobic Bacilli to Gentamicin and Other Aminoglycosides

Previous studies have shown that kanamycin, neomycin, and paromomycin are relatively inactive against gram-negative anaerobic bacilli. However, there were differences noted between the drugs that had implications in terms of: (1) oral therapy with aminoglycosides; (2) likelihood of anaerobic or other superinfection following various modes of therapy with aminoglycosides; (3) the use of these compounds in selective media for anaerobes; and (4) susceptibility tests for the characterization of strains. The present study compared the activity of gentamicin with the above three aminoglycosides, and with framycetin, against various anaerobic gram-negative bacilli, using a plate-dilution test. Gentamicin was more active than the other compounds against Bacteroides fragilis, Bacteroides melaninogenicus, and Sphaerophorus and was intermediate in activity against the others.