<i>Salmonella enterica</i> multilocus sequence typing and its correlation with serotypes

<i>Salmonella enterica</i> is a foodborne pathogen of significant public health concern worldwide. In Thailand, <i>S. enterica</i> has also been ranked among the top five most significant bacterial agents of foodborne illnesses by the Ministry of Public Health. Conventionally, biochemical tests and antigen-antibody agglutination have been used to identify and subtype <i>S. enterica</i>, respectively. The objective of this study was to identify the serotypes of 180 <i>S. enterica</i> isolates. Multilocus sequence typing (MLST) was used to deduce the <i>S. enterica</i> serotypes based on sequence type (ST) correlation as shown in the MLST database (http://mlst.warwick.ac.uk/mlst/). Initially, MLST was used to confirm serotypes of 53 previously identified isolates of <i>S</i>. Enteritidis, <i>S</i>. Typhimurium, <i>S</i>. Hadar, <i>S</i>. Virchow, and <i>S</i>. Infantis isolated in Thailand. MLST and serotype correlation confirmed 52 (of 53) known isolates. MLST was performed in 127 <i>S. enterica</i> isolates of unknown serotypes from various sources. Serotypes of all 127 <i>S. enterica</i> isolates were successfully deduced based on STs. With MLST and PCR-based identification, we have shown that the majority of isolates are of monophasic <i>S</i>. Typhimurium (ST34; 43 isolates) and serotype Rissen (ST469; 37 isolates), in agreement with the top serotypes commonly found in Thailand based on the WHO National <i>Salmonella</i> and <i>Shigella</i> Center. We have also confirmed that MLST is a powerful <i>Salmonella</i> subtyping method which could be used not only as a tracking tool for an outbreak investigation at nucleotide level but also as a serotype predictor for making correlations with food safety regulations.