Antimicrobial susceptibilities and molecular epidemiology of Salmonella enterica serotype enteritidis strains isolated in Hong Kong from 1986 to 1996

The incidence of salmonellosis has been increasing in Hong Kong since 1989. The most common Salmonella enterica serotype isolated in 1994 was S. enteritidis. The antimicrobial susceptibilities and molecular epidemiology of 275 S. enteritidis strains isolated in this locality between 1986 and 1996 were studied. Over 99% of the isolates were susceptible to 17 of the 19 antimicrobial agents tested. One isolate harbored an autotransferring plasmid that confers resistance to tetracycline and trimethoprim-sulfamethoxazole. Another isolate harbored a mobilizable plasmid that confers resistance to ampicillin and cephalothin. This isolate was found to produce a P-lactamase with a pi of 5.2. A total of 264 isolates (96%) were found to harbor one to five plasmids, and the majority (254) harbored a 60-kb plasmid. Of these isolates, 94% contained identical 60-kb plasmids. Based on plasmid profiles, plasmid and chromosomal fingerprints, ribotypes, and randomly amplified polymorphic DNA (RAPD) patterns, 170 (62%) isolates were allocated to group 1b. About 90% of isolates had identical or similar DNA fingerprints, ribotypes, and RAPD patterns, suggesting that a predominant clone of S. enteritidis was circulating in Hong Kong during the period being studied.