Combined Detection and Strain Typing of Yersinia enterocolitica Directly from Pork and Poultry Enrichments

Introduction: Yersinia enterocolitica is responsible for an estimated 98,000 cases of foodborne illness per year in the U.S., causing both intestinal and extraintestinal disease. Its prevalence in retail pork and poultry, believed to the primary sources of these infections, ranges widely from 0 to 69%.  Conventional screening of food samples for this pathogen is problematic, requiring enrichment for 48 h or more in specialized media followed by isolation and speciation. Furthermore, Y. enterocolitica strains vary in their virulence, with serogroups O:3, O:8, O:9, and O:5,27 (of >60 total) most commonly associated with human disease. 

Purpose: There is considerable need for a Y. enterocolitica combined detection/typing system that provides expedient, epidemiologically useful information at moderate cost. 

Methods: We recently developed a novel approach to characterizing Salmonella, STEC, and Listeria strains directly from poultry and beef enrichment cultures.  This enrichment, amplification, and sequence-based typing (EAST) approach was extended to Y. enterocolitica by targeting two polymorphic tandem-repeat containing loci, YeMT1 and YeMT2.

Results: Sequence analyses of 130 NCBI database strains yielded Simpson’s diversity indexes of 0.98 and 0.97, respectively, for these loci.  Cluster analyses of these sequences further showed that YeMT typing was largely congruent with serotype, biotype, and phylogroup.  Application of YeMT-EAST to Y. enterocolitica-inoculated ground pork enrichments prepared as per FSIS guidelines (48 h in ITC medium) demonstrated that 10⁴ CFU/ml or less (after enrichment) were sufficient for detection and typing.  Initial studies with uninoculated ground pork and turkey enrichments revealed contamination with strains that cluster with previously characterized human fecal isolates.  YeMT-EAST was subsequently tested with uninoculated retail chicken parts using conventional enrichment conditions (24 h in BPW medium); surprisingly, 10 of 11 samples (91%) were positive.  However, cluster analysis suggests that these contaminants represent less pathogenic strains. 

Significance: YeMT-EAST represents a potentially important new tool for investigating Y. enterocolitica epidemiology.