Bactericidal Efficacy of Sch 20569 and Amikacin Against Gentamicin-Sensitive and -Resistant Organisms

Abstract

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 μg/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.