Bactericidal efficacy of Sch 20569 and amikacin against gentamicin-sensitive and -resistant organisms.

Sch 20569 is a semisynthetic derivative of gentamicin with activity against many gentamicin-resistant gram-negative bacilli. We compared its bactericidal action with that of gentamicin and amikacin against 171 clinical isolates of Enterobacteriaceae, Staphylococcus aureus, and Pseudomonas aeruginosa. Sch 20569 and amikacin showed markedly greater activity than gentamicin against Escherichia coli, Klebsiella, Enterobacter, Citrobacter, and indole-positive Proteus, primarily by virtue of their lethal effect on gentamicin-resistant strains (minimal bactericidal concentration >/= 12.5 mug/ml). Indole-negative Proteus isolates were uniformly sensitive to Sch 20569, whereas several were resistant to both gentamicin and amikacin. Amikacin was most active against Providencia, as was gentamicin against Serratia. All three agents exhibited similar activity against Pseudomonas. Staphylococcus aureus was more sensitive to gentamicin and Sch 20569 than to amikacin.