The Action of Trimethoprim–sulphamethoxazole Against Urinary Pathogens

Trimethoprim-sulphamethoxazole sensitivity tests were carried out on 21 strains of coliform bacilli, and eight of these strains were studied in greater detail. All strains were sensitive to trimethoprim alone. A synergistic action was evident in strains sensitive to both compounds, but not in those resistant to sulphonamide. Bactericidal activity attributable to the combination was not demonstrated. The emergence of trimethoprim-resistant mutants from most strains was rapid in the presence of trimethoprim alone, and also from sulphonamide-resistant strains in media containing mixtures of trimethoprim and sulphamethoxazole. Sensitivity testing and the therapeutic implications of in-vitro studies of the antibacterial action of this compound are discussed briefly.