In vitro studies of tobramycin, an aminoglycoside antibiotic

Tobramycin is an aminoglycoside antibiotic which has excellent antibacterial activity against Pseudomonas, Staphylococcus aureus, and many members of the Enterobacteriaceae. Most strains of Serratia, Providence, Streptococcus, and Diplococcus pneumoniae were resistant to concentrations of tobramycin which could be achieved in man. Tobramycin was effective against certain Pseudomonas strains resistant to gentamicin. The growth medium used to determine the inhibitory level of tobramycin had a significant effect upon the minimal inhibitory concentration. Calcium and magnesium ions inhibited the bactericidal effect of tobramycin. Tobramycin and carbenicillin acted in a synergistic manner. Ethylenediaminetetraacetic acid did not act in a synergistic manner with tobramycin. Broth-dilution susceptibility tests and disc-diffusion tests in agar (10-mug discs) showed excellent correlation except with Proteus strains.