Vwa+ phenotype of Yersinia enterocolitica.

Expression of the Vwa+ phenotype of Yersinia pestis in vitro is known to reflect maximum induction of virulence (or V and W antigens) at 37 degrees C with concomitant restriction of cell division. Both phenomena are potentiated by 20 mM Mg2+ and prevented by cultivation at 26 or 37 degrees C with 2.5 mM Ca2+. We have now compared this classic plasmid-mediated phenotype with those of Vwa+ Yersinia pseudotuberculosis and Yersinia enterocolitica which, unlike Y. pestis, produce ancillary outer membrane peptides unrelated to the V and W antigens. All of 10 wild-type strains of Y. enterocolitica (serotypes O:3, O:4,32, O:8, O:9, O:15, and O:21) exhibited a nutritional requirement for Ca2+ at 37 degrees C and produced significant V antigen. Like Y. pseudotuberculosis, autoagglutination of Vwa+ Y. enterocolitica was dependent upon prior growth at 37 degrees C but was not influenced by Ca2+. Autoagglutination of Y. pestis was never observed. Resistance of Y. enterocolitica to 10% human serum was typically dependent upon prior growth at 37 degrees C, either with or without added Ca2+, and carriage of a Vwa plasmid. In contrast, serum resistance of Y. pseudotuberculosis was temperature but not plasmid dependent and that of Y. pestis was constitutive.