Combined Action of Sulphamethoxazole and Trimethoprim Against Clinically-Isolated Sulphonamide–Resistant Bacteria

Abstract
42 strains of gram-negative bacteria, isolated from clinical material, resistant to trimethoprim (TM), sulphamethoxazole (SMZ) or both, have been tested for synergistic sensitivity to TM + SMZ. The combination showed no synergy against strains ‘highly resistant’ to SMZ (MIC > 1 mg/ml). Indifference was invariably observed. However, synergy was seen with strains ‘moderately resistant’ to SMZ (MIC 100–1,000 ug/ml). Our results indicate that present techniques for the testing of urinary tract isolates for sensitivity to co-trimoxazole need revision.