Resistance to trimethoprim among urinary tract isolates in the United Kingdom.

Sequential surveys of resistance to trimethoprim (TMP) were made from 1978 to 1980 among urinary tract isolates of enterobacteria from the Nottingham area of the United Kingdom. These surveys revealed an increasing trend toward levels of resistance to TMP, both in hospitals and in the general environment. Because of this trend, the chances of initial infection with an organism resistant to TMP are increased. Much of this increased resistance can be accounted for by the accelerated spread of TMP resistance plasmids and transposons. The appearance of chromosomally located resistance to TMP mediated by a transposon in the absence of a plasmid is unfortunate because of the potential stability of this form of resistance. The clinical isolation of organisms resistant to TMP but sensitive to sulfonamides, coupled with the increasing use of TMP by itself in the United Kingdom, emphasizes the need for continued monitoring of the relationship between resistance to TMP and to sulfonamides in urinary tract pathogens.