Recognition of pathogenic Yersinia enterocolitica by crystal violet binding and polymerase chain reaction.

Cefsulodin-Irgasan-Novobiocin (CIN) agar is used for the selective isolation and enumeration of Yersinia enterocolitica from clinical specimens and food. The medium contains crystal violet and about 1 mmol l-1 calcium and can be used for the phenotypic characterization of strains that carry a virulence plasmid. At 32 degrees C, irrespective of pathogenicity, colonies are translucent with a pale pink centre surrounded by a transparent border ('bullseye'), while at 37 degrees C pathogenic strains grow as calcium-dependent microcolonies which, because of crystal violet binding, are intensely coloured. These results were confirmed by the polymerase chain reaction with primers directed at the virF gene, which is present only in pathogenic strains of Y. enterocolitica. Pathogenic strains of Y. enterocolitica can be recognized by growth at 37 degrees C on Yersinia selective agar.