Susceptibility of nonfermentative gram-negative bacilli to tobramycin

There has been increasing interest in the pathogenic role of nonfermentative gram-negative bacilli in human infections. Except for Pseudomonas aeruginosa, the susceptibility pattern of these organisms to tobramycin has not been evaluated thoroughly. The activity of tobramycin, as compared with that of gentamicin, was tested by the serial broth dilution technique against 178 isolates of nonfermentative gram-negative bacilli obtained from various sources. P. aeruginosa, Pseudomonas stutzeri, Acinetobacter calcoaceticus var. anitratum (Herellea vaginicola), A. calcoaceticus var. Iwoffi (Mima olymorpha), Pseudomonas alcaligenes, and Pseudomonas acidovorans accounted for 82% of all cultures tested. The vast majority of these organisms were susceptible to both tobramycin and gentamicin. Resistance was most common with Alcaligenes odorans; six of 12 isolates were resistant to gentamicin and tobramycin. There was only one isolate of Pseudomonas diminuta; it was highly resistant to both antibiotics.