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Appl Environ Microbiol. 1971 December; 22(6): 1147-1151
Copyright © 1971 American Society for Microbiology. All Rights Reserved.

Tobramycin (Nebramycin Factor 6): In Vitro Activity Against Pseudomonas aeruginosa¹

Infectious Disease Service, Department of Medicine, Memorial Sloan-Kettering Cancer Center, and Cornell University Medical College, New York, New York 10021

ABSTRACT

Tobramycin (factor 6 of the nebramycin complex) is a new aminoglycoside antibiotic isolated from Streptomyces tenebrarius which is active against S. aureus, Enterobacteriaceae, and Pseudomonas aeruginosa. Susceptibility to tobramycin of 96 strains of P. aeruginosa, including 45 recent isolates from blood, was studied by using agar and broth dilution methods. The minimum inhibitory concentration (MIC) for 83 of 96 strains was 3.12 µg/ml or lower in Mueller Hinton agar; MIC values were two to eight times lower in Mueller Hinton broth tests. Agar dilution MIC values were generally lower than those obtained in parallel tests with gentamicin. Killing curves obtained from serial sampling of broth cultures showed a 100- to 10,000-fold decline in viability of log-phase organisms within 30 min of exposure to the drug. Two-dimensional agar dilution tests with carbenicillin and tobramycin with 79 strains showed additive or synergistic effects; no antagonism was documented. Seventy-eight of 79 strains were inhibited by a combination of 50 µg of carbenicillin per ml and 1.56 µg of tobramycin per ml, blood levels which seem attainable in man. Tobramycin appears to be a potent, rapidly bactericidal antibiotic against P. aeruginosa and merits clinical evaluation.

¹ This paper was presented in part at the 71st Annual Meeting of the American Society for Microbiology, Minneapolis, Minn., 4 May 1971.