Epidemiological analysis of Salmonella enteritidis isolates in Singapore

Salmonella enteritidis is the most common non-typhoidal Salmonella species isolated in Singapore causing gastroenteritis and occasional bacteremia with secondary complications. The number of S. enteritidis isolates rose in 1993 and since then, it was the commonest Salmonella sp. isolated. In 1997, a total of 139 S. enteritidis was isolated and this comprised 19.2% of all non-typhoidal Salmonella sp. isolated.

We studied the antimicrobial susceptibilities, phage types and molecular epidemiology of 89 of these S. enteritidis strains. Fifty per cent were stool isolates whilst 33.3% were isolated from blood samples.

All the isolates were susceptible to cephalothin, ceftriaxone, ciprofloxacin, aztreonam, gentamicin, amikacin, kanamycin, neomycin, streptomycin and nalidixic acid; whilst 75.3% were resistant to sulphonamide, 15.7% to tetracycline, 7.9% to co-trimoxazole, 6.7% to trimethoprim, 2.2% to ampicillin and 2.2% to chloramphenicol. The most frequent phage types were phage type 4 (64%), followed by phage type 1 (12.4%) and phage type 8 (2.2%). Seventy four of the 89 (83.1%) S. enteritidis isolates analysed by pulsed-field gel electrophoresis showed an indistinguishable pattern A when digested by restriction enzyme Xba I suggesting the presence of a predominant clone of S. enteritidis circulating in Singapore in 1997.