[Evaluation of intestinal pathogenicity of Yersinia spp. strains isolated from human feces]

Yersinia enterocolitica is a human pathogen which an acts on the intestine by basically enteroinvasive mechanism. Its virulence has been related with the presence of a plasmid of 40-50 MD which codes a series of properties. There are strains of Y. enterocolitica and of other species assimilated to the Y. enterocolitica group which lack the virulence plasmid. In these cases there is a problem in evaluating the pathogenic ability on the intestine of these bacterias when isolated in faeces.

A study of 30 Yersinia spp. strains including growth in a magnesium oxalate medium, Reg-Congo and agar (CR-MOX), sculine hydrolisis (Sc), pyrazinamidase activity (Pyz) and salicine fermentation (Sal) was performed. In addition, the presence of virulence plasmid (VP) was determined.

Twenty-two strains identified as Y. enterocolitica presented the virulence pattern (CR-MOX+, Pyz-, Sal/Sc-) and 21 were VP+. Seven strains isolated were CR-MOX-, Pyz+, Sal/Sc+ and VP- being typed as Y. fredericksenii (6) and Y. kristensenii (1). The remaining strain was CR-MOX- and VP- but Pyz, Sal/Sc were also negative, being identified as Y. enterocolitica.

By the tests referred the authors were able to identify and evaluate the pathogenicity of Yersinia spp. isolated in faeces. These techniques may be used in the microbiology laboratory as a method which aids to evaluate the diagnosis of intestinal infections caused by Yersinia spp.