Epidemiological analysis of Salmonella enterica serotype typhimurium from Hong Kong by ribotyping and pulsed-field gel electrophoresis

We investigated the antimicrobial susceptibilities and molecular epidemiolo gy of 200 strains of Salmonella enterica serotype typhimurium isolated from 1989 to 1996 in Hong Kong. Only 22% of strains were susceptible to all 19 antibiotics tested but all were susceptible to second- and third-generation cephalosporins. Up to 9% of strains vc ere resistant to 0.12 mg/l concentr ations of ciprofloxacin or of loxacin but none were resistant to 1 or 2 mg/ l concentrations of these 2 drugs, respectively. The isolates were grouped into 15 types by ribotyping with restriction endonuclease EcoRI and into 53 types by pulsed-field gel electrophoresis of Xbal-restricted DNA fragments . When DNA fragments of the ribotypes and pulsotypes were pooled and analyz ed 87 types resulted, 76 (87%) of which were of > 90% similarity and were g rouped into 15 clusters. About 60% of the isolates belonged to 3 clusters, which probably represented 3 clones endemic in the community. The rest of t he isolates were of a large variety of types or clusters. For epidemiologic al purposes analysis of pooled results from different molecular techniques would be more discriminative than results from individual techniques alone.