A survey of trimethoprim resistance in the enteric bacterial flora of farm animals.

For 29 months the Veterinary Investigation Centres, covering the whole of Great Britain, forwarded trimethoprim-resistant gram negative enteric bacteria to the Wellcome Research Laboratories. These were examined for degree of resistance, presence and type of R factors. Trimethoprim resistance was found in 0.6% of the total number of strains examined by the Veterinary Investigation Centres. Trimethoprim R factors were demonstrated in one quarter of the resistant strains, and R factors were found in two strains of Salmonella typhimurium. It was concluded that while the incidence of trimethoprim resistance revealed by the survey gave no cause for alarm, the detection of resistant strains, and particularly R factors, indicated that the drug should continue to be used only for specific therapeutic purposes.