EVALUATION OF DIFFERENT TECHNIQUES FOR THE DIFFERENTIATION OF PATHOGENIC AND NON PATHOGENIC STRAINS OF YERSINIA-ENTEROCOLITICA

Different methods and tests have been used to evaluate the pathogenic potential of distinct Y. enterocolitica serotypes and biotypes. We tes ted a total of 60 Y. enterocolitica strains, being 25 of human origin (serotype O3 biotype 4 and serotype O5 biotype 1); 6 of animal origin (serotype O3 biotype 4); 19 isolated from the environment (serotype O5 .27 biotypes 1 and 2); and 8 isolated from food (serotype O5 biotype 1 and serotype 05.27 biotype 1). The methods used were based on plasmid gene expression (autoagglutination, calcium-dependence at 37 degrees C and Congo Red absorption tests), chromosomal gene expression (assays for pyrazinamidase activity, salicin fermentation and esculin hydroly sis), and invasion of HEp-2 cells. All but one of the Y. enterocolitic a O3 strains, were found to be potentially pathogenic when submitted t o the pyrazinamidase-salicin-esculin tests. In contrast, the results o btained with the assays related to plasmidial gene expression were not so uniform, probably due to plasmid loss. The least homogeneous resul ts were obtained with the HEp-2 cell invasion test. Y. enterocolitica O5 behaved in a uniform manner when tested with the first two groups o f tests (based on chromosomal and plasmidial gene expression), but not when tested with the HEp-2 invasion assay. The strains of serotype O5 .27 biotype 1 presented a uniform behavior hen submitted to the chromo somic-related tests, showing no pathogenicity. However, they did not p rovide conclusive results with the tests related to plasmidial gene ex pression or HEp-2 cell invasion. We conclude that the tests related to chromosomal gene expression (esculin-salicin-pyrazinamidase) are simp le and highly effective for the detection of potentially pathogenic Y. enterocolitica isolated from clinical cases.