A multiplex polymerase chain reaction method for rapid identification of Citrobacter freundii and Salmonella species, including Salmonella Typhi

Background and Purpose: Salmonella enterica is one of the most common enteric pathogens worldwide. Conventional methods of isolation of Salmonella strains take 4-7 days to complete, are laborious and require substantial manpower. We devised a polymerase chain reaction (PCR) method that simultaneously uses three pairs of specific primers to detect inv, spv, and via genes of Salmonella. Methods: Three primer pairs were designed, including: SPVC-1 and SPVC-2, based on the nucleotide sequences of the spvC gene; INVA-1 and INVA-2, based on the invA gene; and VIAB-1 and VIAB-2, based on the viaB gene. PCR was performed using these three primers to identify 14 clinically important bacterial organisms, including Citrobacter freundii, S. enterica serovars Typhi and Paratyphi C, Dublin, and other non-typhoidal Salmonella that harbor a virulence plasmid. Results: The following strains were readily identified using the PCR: (1) C. freundii; (2) S. Typhi; and S. Paratyphi C; (3) S. Dublin (virulence antigen-positive); and (4) Salmonella serovars that harbor an spy-type virulence plasmid. S. enterica could also be identified, but required further testing to determine serovar. Conclusions: This PCR method allows S. Typhi to be identified immediately so that appropriate antibiotic treatment can be initiated without delay.