Detection of Yersinia enterocolitica in Pigs and Pork Products

Introduction Yersinia enterocolitica is a zoonotic organism affecting both humans and livestock. In humans, Y. enterocolitica infection can result in severe abdominal pain, which mimics appendicitis. Swine have been implicated as the principal animal reservoir for human pathogenic Y. enterocolitica. Infections in pigs may localize in the tonsils (3). Several outbreaks of yersiniosis have involved consumption of pork (6, 9). Because swine are a source of pathogenic Yersinia (3, 5), rapid methods are needed to determine its prevalence in surveys of pork or of market weight hogs. Three enrichments have been described in the literature. Irgasan, ticarcillin, and potassium chlorate (ITC) (11), modified trypticase soy broth (MTSB) (1), and Phosphate buffered saline (PBS) (12). However, the sensitivity of these methods has not been compared. The sequence of the ail gene, which is present only in virulent strains of Y. enterocolitica, has been previously reported (7). The PCR primers amplifying the ail gene sequence have been described (4), and PCR detection of the ail gene has been used to confirm typical bulls-eye colonies grown on cefsulodin-irgasan-novobiocin (CIN) agar after enrichment (1). A PCR ELISA has been described for the field diagnosis of filarial infections (8). The PCR ELISA is based on immobilization of PCR products to streptavidin-coated wells of a microtiter plate. The PCR product is visualized using a biotin-labeled internal oligonucleotide probe specific to the amplicon, an enzyme-conjugated antibody, and a substratebased colorimetric detection system (8). We have adapted this format to the detection of Y. enterocolitica (10). The present study made use of digoxigenin labeled PCR products providing good sensitivity and a streamlined detection procedure. The purpose of this study was to optimize the PCR ELISA assay that targets the amplification of the ail gene. Secondly, we wished to compare ITC, MTSB, and PBS enrichments for the detection of Y. enterocolitica in pigs and pork products (Figure 1).