Synergistic activity of gentamicin with trimethoprim or sulfamethoxazole-trimethoprim against Escherichia coli and Klebsiella pneumoniae.
The effect of combinations of gentamicin with trimethoprim or sulfamethoxazole-trimethoprim against clinical isolates of Escherichia coli (11 strains) and Klebsiella pneumoniae (12 strains) was examined by using a microdilution checkerboard technique. All isolates were susceptible to each antimicrobial agent. Synergism, defined as at least a 2-log(2)-dilution lowering of the minimal inhibitory concentration of either antibiotic in the combination compared with the minimal inhibitory concentration of the antibiotic alone, was observed with 15 of 23 (65%) isolates tested against trimethoprim and gentamicin and 14 of 23 (61%) isolates tested against sulfamethoxazole-trimethoprim and gentamicin. A 3-log(2)-dilution lowering of the minimal inhibitory concentration of either antibiotic was observed in 7 of 23 (30%) trimethoprim and gentamicin trials and 3 of 23 (13%) sulfamethoxazole-trimethoprim and gentamicin trials. Antagonism was observed in 3 of 46 combination trials and only with strains of K. pneumoniae.
D004357:Drug Synergism; D004926:Escherichia coli / Q000187:drug effects*; D005839:Gentamicins / Q000494:pharmacology*; D007711:Klebsiella pneumoniae / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D013420:Sulfamethoxazole / Q000494:pharmacology*; D014295:Trimethoprim / Q000494:pharmacology*
D005839:Gentamicins; D014295:Trimethoprim; D013420:Sulfamethoxazole