Identification of Salmonella enterica Typhimurium and variants using a novel multiplex PCR assay

• Genes STM4495, oafA, fliC, and fljB as targets.
• One primer set was selected for each gene.
• A novel multiplex PCR method was developed.
• This PCR assay was specific and sensitive for detecting S. Typhimurium and variants.
• All 1,4,[5],12:i:- strains were identified as ST34 with multidrug resistances.

Salmonella Typhimurium is one of the most common Salmonella serovars and possesses many variants. The detection of this pathogen and its variants is imperative to trace the source of infection, to explore the transmission, and to prevent the spread of disease. A PCR assay was used and primers were designed against the gene STM4495 specific for S. Typhimurium, and oafA, fliC, and fljB encoding the O5, H1 and H2 antigens of S. Typhimurium. A novel multiplex PCR method was developed to detect S. Typhimurium and its variants, including Copenhagen, 1,4,12:-:1,2, 1,4,[5],12:i:- and 1,4,5,12:-:-. The detection limit of this method was found to be as low as 1.1pg/PCR for S. Typhimurium DNA template. S. Typhimurium and its variants were detected rapidly and accurately. Of 2350 isolates, 294 strains of S. Typhimurium, 13 strains of 1,4,[5],12:i:- and 1 strain of Copenhagen variant, were identified, consistent with serological testing. Thus, this multiplex PCR assay complements the serological method and enhances detection accuracy. All 1,4,[5],12:i:- strains were identified as ST34 by MLST analysis, which carried multidrug resistances. The expansion of multidrug-resistant S. Typhimurium variant strains must be controlled to limit further transmission from animal food to humans.