Activity of Netilmicin Compared with Those of Gentamicin and Tobramycin Against Enterobacteria and Pseudomonas aeruginosa

The inhibitory activity of netilmicin against 500 isolates of gram-negative bacteria was compared with those of gentamicin and tobramycin. Netilmicin was considerably less active than tobramycin and slightly less inhibitory than gentamicin for Pseudomonas aeruginosa but was at least as active against Escherichia coli and Klebsiella pneumoniae as were the other two antibiotics. A few Klebsiella and Serratia isolates resistant to gentamicin and tobramycin were inhibited by netilmicin. All three antibiotics were strongly bactericidal for E. coli, K. pneumoniae and P. aeruginosa but had less lethal activity against the otherwise susceptible Serratia isolates tested. Some necessary precautions in reading minimal inhibitory concentrations on agar media are stressed, and some possible advantages of a 4-h bactericidal test, using a constant antibiotic concentration, are defined.