Antibiotic resistance conferred by a conjugative plasmid and a class I integron in Vibrio cholerae O1 El Tor strains isolated in Albania and Italy

Multidrug-resistant Vibrio cholerae O1 El Tor strains isolated during the 1 994 outbreak of cholera in Albania and Italy were characterized for the mol ecular basis of antibiotic resistance. All strains were found to be resista nt to tetracycline, streptomycin, spectinomycin, trimethoprim, sulfathiazol e, and the vibriostatic compound O/129 (2,4-diamino-6,7-diisopropylteridine ). Resistance genes were self-transferable by a conjugative plasmid of abou t 60 MDa, with the exception of spectinomycin resistance, which was conferr ed by the aadA1 gene cassette located in the bacterial chromosome within a class 1 integron. The resistance to trimethoprim and O/129 was conferred by the dfrA1 gene, which was present on the plasmid. Although the dfrA1 gene is known to be borne on an integron cassette, class 1, 2, or 3 intI genes w ere not detected as part of the plasmid DNA from the strains studied.