Characterization and chromosomal mapping of antimicrobial resistance genesin Salmonella enterica serotype Typhimurium

Two hundred and twenty-six Salmonella enterica serotype Typhimurium isolate s were examined for the presence of integron-associated gene cassettes. All but two of the non-DT104? isolates, together with DTL04 isolates, containe d gene cassettes, Amplicons of 1.5 kbp each were found in tyro non-DT104 is olates, encoding a dhfrI gene (trimethoprim resistance) linked to an aad4 g ene (streptomycin and spectinomycin resistance), by site-specific recombina tion, DT104 isolates of resistance (R) type ACSSuT possessed the recently d escribed 1.0-and 1.2-kbp gene cassettes. Macrorestriction analysis with Xba I and DNA probing mapped ant(3")-1a,bla(PSE-1) and dhfrI genes to large mul tiresistant gene clusters in a DT170a isolate and a DT193 isolate. In contr ast, all DT104 isolates (R-type ACSSuT) possessed a conserved 10-kbp Xba1 D NA fragment, Our study highlights the occurrence of integrons (and antimicr obial resistance determinants) among serotype Typhimurium isolates other th an DT104. Larger and previously unrecognized multiresistance gene clusters were identified in these isolates by DNA probing.