Salmonella krefeld in Thailand: I. Epidemiology, infection and drug resistance.

Information from the National Salmonella Shigella Center (NSSC), Thailand indicated that the most frequently isolated Salmonella serotype from humans during 1974-1975 was Salmonella typhi (33.1%), during 1976-1982 was S. krefeld (26.6%) and during 1983-1987 was S. derby (12.6%). Antimicrobial susceptibility study of various Salmonella serotypes indicated that S. krefeld was the serotype with multiple drug resistance persisting for the longest period of time. Human salmonellosis due to S. krefeld is very rare. During 1976-1978, a large outbreak of S. krefeld gastroenteritis occurred in Thailand, mainly in children. The outbreak spread countrywide and is currently endemic. Gastrointestinal symptoms are severe in young infants. Systemic invasion with bacteremia, meningitis and pneumonitis were reported. The antimicrobial susceptibility pattern of isolates varied from sensitive to multiply drug resistant. The common antibiotic resistances were to ampicillin (75-92%), chloramphenicol (33-75%), kanamycin (67-90%) and sulfamethoxazole-trimethoprim (15-52%). Resistance to gentamicin and sulfamethoxazole-trimethoprim declined after the period of the epidemic. Antimicrobial resistance patterns of 150 S. krefeld strains isolated in Thailand during 1978-1987 showed multiple drug resistance with up to seven drugs. The most common patterns were ApCmKmSuTp and ApCmKmSmSuTc.

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

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.