Susceptibility patterns and serotypes of non-typhoidal salmonella in Trinidad

OBJECTIVE: To study the serotype distribution of non-typhoidal salmonella isolated from clinical specimens and to evaluate their susceptibility patterns to the most commonly prescribed antimicrobial agents used in this region.

METHODS: A retrospective study during the period 1993–1999 was carried out at the Eric Williams Medical Sciences Complex Microbiology Laboratory, a teaching hospital in the northwestern part of Trinidad. Strains of non-typhoidal salmonella were serogrouped with polyvalent Salmonella O antiserum and sent to the local Public Health Laboratory for confirmation and further serotyping.

RESULTS: A total of 412 strains of non-typhoidal salmonella were serotyped. Of the 13 serotypes, Salmonella enteritidis was the most prevalent 57%, followed by Salmonella typhimurium, 25%, Salmonella virchow 5% and Salmonella heidelberg, 4%. Three hundred and sixty-two (87.5%) non-typhoidal salmonella were isolated from stool, 38 (9%) from blood, 8 (2%) from urine and 4 about 1% from infected wounds. Of the 13 serotypes only Salmonella enteritidis, Salmonella typhimurium, Salmonella virchow and Salmonella heidelberg were simultaneously isolated from blood and stool. One serotype, Salmonella aberdeen, was encountered for the first time in 1993. All isolates were fully sensitive to chloramphenicol, gentamicin, cefuroxime and ceftrioxone. Resistance to ampicillin, augmentin and co-trimoxazole was less than 4%. One third of all non-typhoidal salmonella isolates were resistant to tetracyclines.

CONCLUSION: The most prevalent serotypes were Salmonella enteritidis and Salmonella typhimurium which accounted for 82% of all isolates. The prevalence of resistance of non-typhoidal salmonella to antibiotics was very low (5%). Therefore, due to this low prevalence of resistance, we did not provide details of resistance in relation to serotype. However, it was observed that of the 137 non-typhoidal salmonella resistant to tetracycline, more than 80% were Salmonella enteritidis and Salmonella typhimurium strains. Of the 9 antibiotics, tetracycline was the only drug to which one-third of the non-typhoidal salmonella were resistant. Due to the risk of resistance continued surveillance of susceptibility patterns of non-typhoidal salmonella to antibiotics must be maintained and encouraged.