title: Synergy of penicillin and decreasing concentration of aminoglycosides against enterococci from patients with infective endocarditis.
abstract: To determine whether low concentrations of aminoglycosides in combination with penicillin could effectively kill enterococci in vitro, we tested penicillin (20 micrograms/ml) in combination with decreasing concentrations of either streptomycin (20, 10, 5, and 1 micrograms/ml) or gentamicin (5, 3, 1, and 0.5 micrograms/ml) against 13 strains of streptomycin-susceptible and 7 strains of streptomycin-resistant enterococci isolated from patients with infective endocarditis. At 24 h, penicillin plus each increment in streptomycin concentration resulted in a statistically significant increase in killing of streptomycin-susceptible enterococci, compared with the next lower streptomycin concentration (P less than 0.01). At 24 h, against streptomycin-susceptible and streptomycin-resistant enterococci, there were no statistically significant differences in killing between combinations containing 5 micrograms of gentamicin per ml and those containing 3 micrograms/ml. Against streptomycin-susceptible enterococci, there were statistically significant differences in killing between combinations containing 3 micrograms of gentamicin per ml and those containing 1 micrograms/ml. Against streptomycin-resistant enterococci, statistically significant differences in killing were detected with combinations containing 5 micrograms of gentamicin per ml and those containing 1 microgram/ml.
mesh_terms: D004357:Drug Synergism; D004697:Endocarditis, Bacterial / Q000382:microbiology*; D004755:Enterobacteriaceae / Q000187:drug effects*; D005839:Gentamicins / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D010406:Penicillins / Q000494:pharmacology*; D013307:Streptomycin / Q000494:pharmacology*
chemical_list: D005839:Gentamicins; D010406:Penicillins; D013307:Streptomycin