Regression-line analysis of trimethoprim-sulfamethoxazole activity against Neisseria gonorrhoeae.
A standardized disk diffusion test was developed and used to test the susceptibility of 102 strains of Neisseria gonorrhoeae to combinations of trimethoprim and sulfamethoxazole (TMP/SMX) by relating zone diameters of inhibition to minimal inhibitory concentrations (MIC's). MIC's for TMP/SMX in ratios of 1:20 ranged from 0.08/1.52 to 2.5/47.5 mug/ml and zones of inhibition ranged from 34 to 10 mm. The coefficient of correlation (r) was -0.75. For comparison, a regression line was similarly calculated for ampicillin. MIC's ranged from 0.02 to 0.32 mug/ml and zones of inhibition ranged from 50 to 31 mm; r was -0.71. With establishment of MIC breakpoints to define the categories, susceptible, intermediate, and resistant, the disk duffusion test would be as reliable for estimating susceptibility of gonococci to TMP/SMX as for estimating susceptiblity to ampicillin.
D004338:Drug Combinations; D006801:Humans; D008826:Microbial Sensitivity Tests; D009344:Neisseria gonorrhoeae / Q000187:drug effects*; D013420:Sulfamethoxazole / Q000008:administration & dosage / Q000494:pharmacology*; D014295:Trimethoprim / Q000008:administration & dosage / Q000494:pharmacology*
D004338:Drug Combinations; D014295:Trimethoprim; D013420:Sulfamethoxazole