Salmonella krefeld in Thailand: II. Molecular biology of drug resistance.

ABSTRACT

Human salmonellosis due to Salmonella krefeld is very rare. During 1976-1978, a large outbreak of S. krefeld gastroenteritis occurred in Thailand, mainly in children. The majority of strains were multiply drug resistant with high minimum inhibitory concentration (MIC). The MIC for these drugs were ampicillin (Ap) 256-4096 mg/l, chloramphenicol (Cm) 256-512 mg/l, kanamycin (Km) 512- greater than 4096 mg/l, streptomycin (Sm) greater than 1024 mg/l, sulfamethoxazole (Su) 4096- greater than 8192 mg/l, tetracycline (Tc) 64-128 mg/l and trimethoprim (Tp) 64-256 mg/l. Resistance to Su and Tp declined after the period of the epidemic. The resistance genes were found to be highly transferable at a rate of 10(-2) to 10(-4). All strains with more than five resistance markers had large molecular weight plasmids of 120-140 megadaltons. The restriction profile analysis of plasmids from isolates collected from various regions of the country showed similarity of DNA fragment pattern. These isolates were resistant to Ap, Cm, Km, Sm, Su and Tc.