Genetic basis of trimethoprim and O/129 resistance in Vibrio cholerae.

Because of its important consequences on prophylaxis and therapy of cholera and on bacterial identification, we have studied the genetic basis of cross-resistance to trimethoprim and O/129 of strains of Vibrio cholerae O1 independently isolated in Africa. Two classes of bacteria were found. In the first class, the strains were also resistant to ampicillin and kanamycin and to high levels of streptomycin by synthesis of a 3"- or 6-aminoglycoside phosphotransferase. The strains hybridized weakly with a Tn7 probe and all the resistance characters were transferable en bloc to Escherichia coli. The second class included strains which, in addition to trimethoprim and O/129, were resistant to moderate levels of streptomycin and spectinomycin by production of a 3",9-aminoglycoside-aminocyclitol adenylyltransferase. The resistance characters were not self-transferable to E. coli and the host strain hybridized strongly with Tn7. It therefore appears, that both plasmids and transposons are responsible for the dissemination of resistance to trimethoprim and O/129 in Vibrio.