Transposable resistance to trimethoprim and 0/129 in Vibrio cholerae

Vibrio cholerae biotype el tor strain BM2508, resistant to trimethoprim, 0/129, streptomycin and spectinomycin was isolated from the faeces of a child with severe diarrhoea. Resistance to trimethoprim and 0/129 was due to a dihydrofolate reductase type I and resistance to streptomycin-spectinomycin to a 3'',9-aminoglycoside-aminocyclitol adenylyltransferase. The resistance genes were not transferable to Escherichia coli and, as inferred from ultracentrifugation in cesium chloride-ethidium bromide and agarose gel electrophoresis of crude bacterial lysates, were located on the chromosome. The resistance genes were transposed to multiple sites of plasmids belonging to incompatibility groups 6-C and P, introduced in BM2508 and were subsequently transferred to E. coli (rec-), Salmonella typhimurium, V. cholerae and V. parahaemolyticus strains where they re-transposed into the chromosome. Analysis of plasmid DNA from the transconjugants by agarose gel electrophoresis following digestion with HindIII and by Southern hybridization using a ColEl::Tn7 probe indicated the presence of a 14-kilobase transposon, Tn1527, closely related to Tn7. The emergence of Tn1527 in V. cholerae may lead to prophylactic and therapeutic failures due to trimethoprim resistance and to bacterial misidentification because of cross resistance to 0/129.