Trimethoprim is a synthetic compound which arrests the step in bacterial purine synthesis immediately succeeding that interfered with by sulphonamides. Acting alone it inhibits the growth of a wide range of bacteria in generally much lower concentrations than sulphonamides. Its action with a sulphonamide is strongly synergic and bactericidal.Studies are described of suitable cultural conditions...

The faecal flora was studied in eight children admitted to hospital for treatment of a first urinary infection with sulphonamides. The original, sulphonamide-sensitive Escherichia coli organisms were found to disappear, to be replaced by other E. coli serotypes that were almost invariably resistant to sulphonamides. Some of these serotypes carried R-factors for multiple antibiotic resistance.Po...