MLVA polymorphism of Salmonella enterica subspecies isolated from humans, animals, and food in Cambodia.

Background: Salmonella (S.) enterica is the main cause of salmonellosis in humans and animals. The epidemiology of this infection involves large geographical distances, and strains related to an episode of salmonellosis therefore need to be reliably discriminated. Due to the limitations of serotyping, molecular genotyping methods have been developed, including multiple loci variable number of tandem repeats (VNTR) analysis (MLVA). In our study, 11 variable number tandem-repeats markers were selected from the S. enterica Typhimurium LT2 genome to evaluate the genetic diversity of 206 S. enterica strains collected in Cambodia between 2001 and 2007.

Findings: Thirty one serovars were identified from three sources: humans, animals and food. The markers were able to discriminate all strains from 2 to 17 alleles. Using the genotype phylogeny repartition, MLVA distinguished 107 genotypes clustered into two main groups: S. enterica Typhi and other serovars. Four serovars (Derby, Schwarzengrund, Stanley, and Weltevreden) were dispersed in 2 to 5 phylogenic branches. Allelic variations within S. enterica serovars was represented using the minimum spanning tree. For several genotypes, we identified clonal complexes within the serovars. This finding supports the notion of endemo-epidemic diffusion within animals, food, or humans. Furthermore, a clonal transmission from one source to another was reported. Four markers (STTR3, STTR5, STTR8, and Sal20) presented a high diversity index (DI > 0.80).

Conclusions: In summary, MLVA can be used in the typing and genetic profiling of a large diversity of S. enterica serovars, as well as determining the epidemiological relationships of the strains with the geography of the area.