Trimethoprim resistant dihydrofolate reductases in normal faecal flora isolated in India

Abstract

SUMMARYA high incidence of resistance to trimethoprim has been shown in the normal faecal flora in a population in south India. The dihydrofolate reductase (dhfr) genes mediating transferable resistance to trimethoprim have been identified. Unusually, in this study, thedhfrV was shown to be the predominant resistance gene (dhfrV 50% of tranaconjugants,dhfrIa 30%), thedhfrIb was also detected being distinguished from thedhfrV by an oligo-probe. However, when non-transferable resistance was considered, thedhfrIa was the most prevalent of thedhfrs identified. All those plasmids harbouring thedhfrIa were shown to possess Tn7. All the plasmids that probed positive for thedhfrV and thedhfrIb were shown to be associated with the integrase of the Tn21-like transposons, but 8 of thedhfrV genes were not associated with the Tn21resolvase. ThedhfrIV was shown to be present in all seven plasmids that produced low level trimethoprim-resistance. ThedhfrV. first characterized in Sri Lanka, would seem to have a local distribution in this region of Asia but is distinguishable from thedhfrIb only by the use of an oligo-probe.