Characterization of Salmonella enterica serovar Enteritidis isolates recovered from blood and stool specimens in Thailand.

Background: Bacteremia due to Salmonella spp. is a life-threatening condition and is commonly associated with immune compromise. A 2009 observational study estimated risk factors for the ten most common non-typhoidal Salmonella (NTS) serovars isolated from Thai patients between 2002-2007. In this study, 60.8% of Salmonella enterica serovar Enteritidis isolates (n = 1517) were recovered from blood specimens and infection with Salmonella serovar Enteritidis was a statistically significant risk factor for bacteremia when compared to other NTS serovars. Based on this information, we characterized a subset of isolates collected in 2008 to determine if specific clones were recovered from blood or stool specimens at a higher rate. Twenty blood isolates and 20 stool isolates were selected for antimicrobial resistance testing (MIC), phage typing, PFGE, and MLVA.

Result: Eight antibiogrammes, seven MLVA types, 14 XbaI/BlnI PFGE pattern combinations, and 11 phage types were observed indicating considerable diversity among the 40 isolates characterized. Composite analysis based on PFGE and MLVA data revealed 22 genotypes. Seven of the genotypes containing two or more isolates were from both stool and blood specimens originating from various months and zones. Additionally, those genotypes were all further discriminated by phage type and/or antibiogramme. Ninety percent of the isolates were ciprofloxacin resistant.

Conclusions: The increased percentage of bloodstream infections as described in the 2009 observational study could not be attributed to a single clone. Future efforts should focus on assessing the immune status of bacteriaemic patients and identifying prevention and control measures, including attribution studies characterizing non-clinical (animal, food, and environmental) isolates.