Occurrence of Antibiotic Resistance Gene Cassettes aac ( 6 ′) -Ib , dfrA5 , dfrA12 , and ereA2 in Class I Integrons in Non-O1, Non-O139 Vibrio cholerae Strains in India

Abstract

Molecular mechanisms of multidrug resistance in Vibrio cholerae belonging to non-O1, non-O139 serogroups isolated during 1997 to 1998 in Calcutta, India, were investigated. Out of the 94 strains examined, 22 strains were found to have class I integrons. The gene cassettes identified were dfrA1 , dfrA15 , dfrA5 , and dfrA12 for trimethoprim; aac ( 6 ′) -Ib for amikacin and tobramycin; aadA1 and aadA2 for streptomycin and spectinomycin; and ereA2 for erythromycin resistance. To our knowledge, this is the first report of the presence of dfrA5 , dfrA12 , aac ( 6 ′) -Ib, and ereA2 cassettes in class I integrons of V. cholerae . Forty-three of 94 strains also had plasmids, and out of these, 14 contained both class I integrons and plasmids. Pulsed-field gel electrophoresis followed by Southern hybridization revealed that in the 14 plasmid-bearing strains, class I integrons resided either on chromosomes, on plasmids, or on both. Our results indicated that besides class I integrons and plasmids, a conjugative transposon element, SXT, possibly contributed to the multiple antibiotic resistance.