Design and Optimization of a yst-PCR to Detect Yersinia enterocolitica in Meat Food

In this study, a polymerase chain reaction (PCR) directed to the yst chromosomal gene (yst-PCR) was used as a rapid, sensitive, and specific method to detect Yersinia enterocolitica strains belonging to different biotypes in foods; a competitive Internal Amplification Control (cIAC) is also developed. The cIAC had a molecular weight of 417 bp and was detected until a concentration of 0.85 ng/mu L. No other strains of other Yersinia species, nor Enterobacteriales order were detected by this PCR. In pure culture, the detection limit (DL) of the yst-PCR was lower for ystA(+) strain (10 colony-forming unit [CFU]/mL) than for ystB(+) strain (1 x 10(2) CFU/mL); which was the concentration detected in Y. enterocolitica inoculated minced meat. The proposed protocol included an enrichment step in peptone sorbitol bile (PSB) broth at 25(degrees)C for 24 h followed by isolation on Mac Conkey agar and chromogenic medium. An aliquot of the PSB broth homogenate and a loopful from the confluent zone of solid media were collected to perform DNA extraction for yst-PCR, and typical colonies were characterized by biochemical assays. Among 30 non-contaminated food samples, 4 samples were yst-positive and no Y. enterocolitica isolates were obtained. It is suggested that this yst-PCR could be used in the investigation of Y. enterocolitica in foods.