Background: Salmonella has been one of the most common agents responsible for outbreaks of foodborne diseases in Australia and worldwide. Historically, these bacteria have been classified into serotypes according to their somatic and flagella antigens. However, recently there have been calls to replace serotyping with multilocus sequence typing (MLST) based classification which recognizes evolutionary groupings. This study aimed to examine the capacity of MLST to differentiate S. enterica serotypes using isolates identified and characterized in the NSW Enteric Reference Laboratory (ERL).
Methods: 127 randomly selected Salmonella enterica isolates representing nine most common serovars observed in NSW between 2010 and 2012 were used in the study. The MLST method was employed targeting housekeeping aroC, dnaN, hemD, hisD, purE, sucA, and thrA gene fragments. Sequence types (ST) were assigned using the MLST server (University College, Cork).
Results: Isolates of Salmonella enterica serovar Typhimurium (STM), the most common serovar among those observed in NSW (91/127 or 72%), were all classified as ST-19. However, STM monophasic isolates were assigned to ST-85 and 34. S. Enteritidis isolates were mainly grouped into ST-11; ST-183 and 180 also were also found. S. Saint Paul was classified as ST-50; S. Bovimorbificans belonged to ST-1499 and 377. S. Virchow was defined as ST-16, S. Infantis as ST-32, S. Birkenhead as ST-424, and S. Stanley as ST-29, respectively. S. Montevideo was associated with ST-138 and 316. No isolates of different serotypes classified in the same ST were identified.
Conclusions: Clearly identifiable ST can accurately differentiate the most common serotypes of S. enterica observed in NSW. MLST can be an alternative to serotyping in the classification of S. enterica for diagnostic and surveillance purposes and could be considered as a method to monitor the evolution and diversity among serovars. However, the discriminatory power of MLST-7 for detecting community outbreaks remains limited.