Virulence Plasmid (pYV)-Associated Expression of Phenotypic Virulent Determinants in PathogenicYersiniaSpecies: A Convenient Method for Monitoring the Presence of pYV under Culture Conditions and Its Application for Isolation/Detection ofYersinia pestisin Food

In Yersinia pestis , Y. pseudotuberculosis , and Y. enterocolitica , phenotypic expression of virulence plasmid (pYV: 70-kb)-associated genetic determinants may include low-calcium response (Lcr, pinpoint colony, size = 0.36 mm), colony morphology (size = 1.13 mm), crystal violet (CV) binding (dark-violet colony), Congo Red (CR) uptake (red pinpoint colony, size = 0.36 mm), autoagglutination (AA = cells agglutinate), and hydrophobicity (HP = clumping of cells). Y. pseudotuberculosis is chromosomally closely related to Y. pestis; whereas, Y. enterocolitica is chromosomally more distantly related to Y. pestis and Y. pseudotuberculosis . All three species demonstrate Lcr, CV binding, and CR uptake. The colony morphology/size, AA, and HP characteristics are expressed in both Y. pseudotuberculosis and Y. enterocolitica but not in Y. pestis . Congo red uptake in Y. pestis was demonstrated only on calcium-deficient CR magnesium oxalate tryptic soy agar (CR-MOX), whereas this phenotype was expressed on both CR-MOX and low-calcium agarose media in Y. pseudotuberculosis and Y. enterocolitica . These phenotypes were detectable at 37°C within 24 h in Y. enterocolitica and Y. pseudotuberculosis but did not appear until 48 h in Y. pestis due to its slower growth rate at 37°C. The pYV is unstable (i.e., easily lost under a variety of culture conditions) in all three species but is more unstable in Y. pestis . The specific CR uptake by Y. pestis in CR-MOX and the delayed time interval to express Lcr and CR uptake provide a means to differentiate Y. pestis from Y. enterocolitica and Y. pseudotuberculosis . These differences in pYV expression in Y. pestis can be used for its isolation and detection in food.