Occurrence of heterogeneous R-plasmids during two concurrent epidemics due to multidrug-resistantSalmonella oranienburg

During two different epidemics that started in August–September, 1980, 140 and 6 multidrug-resistant strains ofSalmonella oranienburg were isolated from a Children's Hospital in New Delhi (epidemic 1) and H.N. Das Hospital in Bombay (epidemic 2) respectively. Out of 140, 123 strains showed high levels of resistance to ampicillin, kanamycin, streptomycin, sulfamethoxazole, tetracycline, and trimethoprim. All six strains of epidemic 2 and two strains of epidemic 1 were also found resistant to chloramphenicol in addition to the above antibiotics. The genetic characterization of conjugative R-plasmids harbored by these strains revealed that, while strains of epidemic 1 carry a fi^–, 96 megadalton, an unclassified plasmid, the strains isolated during epidemic 2 contain a fi^–, 62 megadalton plasmid of incompatibility group I₁. All the six strains of epidemic 2 were found to produce bacteriocin of Col Ib group. Plasmid transfer studies revealed that the genes for antibiotic resistance and bacteriocin production were coded on a single plasmid of 62 megadalton. The data show the significance of detailed genetic analysis while dealing with the clonal outbreaks due to same resistant serotypes.