Genetic analysis of virulence plasmid from a serogroup 9 Yersinia enterocolitica strain: role of outer membrane protein P1 in resistance to human serum and autoagglutination.

Enteropathogenic strains of Yersinia enterocolitica harbor a virulence plasmid (70 kilobases) which specifies, at 37 degrees C, a calcium requirement for growth, autoagglutinability, resistance to the bactericidal activity of human serum, and the expression of some outer membrane proteins (OMPs). To map the genes encoding these properties, the virulence plasmid of a serogroup 9 strain (W22708) was subjected to transposon mutagenesis. A set of 68 independent mutations was obtained in Escherichia coli by transposon Tn813 (a tnpR mutant of Tn21)-mediated cointegration with the self-transmissible R388 plasmid. The resulting cointegrates were introduced and studied in Y. enterocolitica W22708. One mutant lost the calcium dependence property. Two other mutants presented a peculiar phenotype: they grew poorly at 37 degrees C, especially in the presence of calcium. Lastly, two mutants were affected in the properties of autoagglutination and resistance to human serum. Analysis of the OMP pattern of these two mutants revealed the absence of the largest OMP, called P1 (I. Bölin, and H. Wolf-Watz, Infect. Immun. 43:72-78, 1984). Complementation of one of these mutations with the cloned structural gene of OMP P1 restored the wild-type phenotype. However, OMP P1 was not sufficient by itself to specify the serum resistance property and a rapid autoagglutination of the host.