Plasmid trimethoprim resistance in Vibrio cholerae: migration of the type I dihydrofolate reductase gene out of the Enterobacteriaceae.

Two strains of Vibrio cholerae biotype el tor were isolated in Tanzania. Each possessed a single resistance plasmid of 113 kbases belonging to the C incompatibility group. Both plasmids conferred resistance to sulphamethoxazole, ampicillin, streptomycin, chloramphenicol, tetracycline and trimethoprim. They are the first plasmids derived from V. cholerae strains, isolated in Southern Africa, to confer trimethoprim resistance. The trimethoprim resistance resulted from the plasmid-mediated production of a trimethoprim resistant dihydrofolate reductase which was very similar to the type I plasmid enzyme. This is the first example of movement of the gene encoding the type I dihydrofolate reductase into genera of other families besides the Enterobacteriaceae.