Plasmid-mediated antibiotic resistance and colicinogeny among Salmonellae in Rio de Janeiro, Brazil

A set of 25 multiple drug-resistant strains selected from Salmonellae isolated from sewage in Rio de Janeiro contained S. typhimurium (60%) and S. agona (20%) as the most frequent serotypes. There was resistance to ampicillin (Ap), 92%; chloramphenicol (Cm), 76%; gentamicin (Gm), 84%; kanamycin (Km), 84%; streptomycin (Sm), 96%; tetracycline (Tc), 76%; trimethoprim-sulfamethoxazole (SuTp), 84% and nalidixic acid (Na), 52%. The most frequent resistance patterns observed were Ap Cm Gm Km Sm Tc SuTp Na and Ap Cm Gm Km Sm Tc SuTp. Two strains, bearing the streptomycin, tetracycline double-resistance pattern were colicinogenic, producing type Ib colicin. The col+ character was cotransferable with the double-resistance; all these markers were associated with the presence of a single 60 Mdal plasmid.