MLVA and phage typing as complementary tools in the epidemiological investigation of Salmonella enterica serovar Typhimurium clusters

In South Australia serotyping and phage typing are employed for routine Salmonella surveillance. Molecular techniques such as Multiple-locus variable number tandem repeat analysis (MLVA) are increasingly utilized to aid outbreak investigations. During 2007 three Salmonella enterica serovar Typhimurium outbreaks involving phage types DT9, DT29, and DT44 were investigated. Human, food and environmental isolates were also typed by MLVA. In the DT9 outbreak cluster MLVA demonstrated distinct groupings that corresponded to epidemiological differences in time, place, and descriptive information on potential transmission mechanisms. In contrast, the human and food isolates of both the DT29 and DT44 clusters had identical MLVA profiles for all but one case. These data correlated with the epidemiology suggesting that these isolates were closely related and probably a single agent. These findings illustrate that phage typing and MLVA can provide different but complementary information for epidemiological investigations of Salmonella outbreaks.