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Pathogenic bacteria of the genus Yersinia (Y. enterocolitica, Y. pseudotuberculosis and Y. pestis) are pathogens of the invasive type. Although they provoke diseases as different as plague and enterocolitis, the molecular bases of their virulence appear to be surprisingly similar: a 70 kb plasmid confers a degree of resistance to the primary immune response and the presence or absence of chromosome encoded functions modulates virulence. The knowledge of the virulence functions that now emerges suggests the conversion of Y. enterocolitica as a life carrier.

The metabolic products (non-volatile fatty acids) of 24 strains belonging to four Yersinia enterocolitica groups (typical, sucrose negative, rhamnose positive, melibiose and rhamnose positive) were examined by gas liquid chromatography. All strains produced lactic, pyruvic and succinic acids. This technique did not allow any classification for taxonomic purpose. The evolution of lactic and succinic acid production was monitored for 72 h in shaked and non-shaked cultures. The concentration of both acids increased in the first 24 h, then decreased and increased again after 38 h. Shaked culture produced a lesser amount of lactic acid than did non-shaked culture. Only traces of succinic acid were detected in shaked culture. The quantities of metabolic products of the four strains grown in five media were significantly different. These observations suggest that the composition of the medium, the bacterial growth, inoculum size, incubation technique and the incubation time are important factors in metabolic production by aeroanerobic bacteria. Only constant results in the face of such varying factors could be of taxonomic value.

1) The phage typing of Y. enterocolitica has been made on more than 4,000 strains of various origins by means of 2 sets of phages. The 1st one, composed of 12 phages extracted from lysogenic strains of the same species has permitted to distinguish 10 phages types numbered from I to VIII and from IXa to IXb among the 3,323 lysotypable strains on the 4,366 examinated. 2) The search of the beta-galactosidase has differentiated the phage type IXa in its 2 varieties, the IXa 1, beta-galactosidase negative and the IXa 2, beta-galactosidase positive. 3) The 1,043 untypable strains by the 1st set were forming 2 very different groups. One of them, the X was insensitive to the 12 phages of the 1st set; the other XI, showed such a variety of lytic reactions to the phages of the 1st set that it was impossible to consider the rare samples of each of them as phage types. 4) The group X, submitted to a "complementary phage typing" by means of a second set of phages isolated from sewage water, has been subdivised into about 20 undergroups, from which only, 7 have been studies up to now, numbered from X 1 to X 7...