Frequency and transmissibility of trimethoprim resistance in enterobacteria from urinary infections.

In a survey of 8,986 enterobacterial strains from urinary tract infections collected between September 1980 and June 1981, the overall frequency of resistance to trimethoprim was 3.5%. Strains collected from long-stay patients showed the highest frequency (7.7%); those from general practice the lowest frequency (2.3%), while those from hospital in-patients and out-patients were intermediate with 4.7 and 3.2 respectively. All these differences were statistically significant. In a further study of 117 resistant strains, Escherichia coli accounted for 47% of strains and Proteus sp. for 27%. Transfer of trimethoprim resistance occurred in 44% of E. coli strains and 22% of Klebsiella. A significant increase in the frequency of resistant strains was noted between the first 5 months of the study and the second 5.