Submitted to: Journal of Rapid Methods and Automation in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/1995
Publication Date: N/A
Interpretive Summary: Yersinia enterocolitica, a bacterium which can cause severe intestinal distress when consumed in contaminated food, is of particular concern because it can grow at refrigerator temperatures and only some strains cause illness. Disease is only caused by those strains of bacteria which contain an extra piece of genetic material. This extra genetic material may easily be lost during most methods used for the isolation and identification of disease causing organisms in food or clinical samples. Accordingly, isolation methods for Y. enterocolitica were evaluated, and the results indicated that these procedures did not cause any loss of disease causing extra genetic material. Thus, these techniques will allow action agencies and clinical laboratories to easily isolate and identify strains which cause illness.
Technical Abstract: The enrichment procedures used to isolate Yersinia enterocolitica may induce the loss of the virulent plasmid from the organism. Plasmid loss would result in the loss of virulence and the concomitant disappearance of the associated phenotypic characteristics. This report presents information on the effect of five current enrichment procedures including trypticase soy broth, phosphate buffered saline, peptone enriched phosphate buffered saline, phosphate buffered saline with sorbitol, and bile salts and MacConkey broth on plasmid stability. Virulence assays using crystal violet binding, low-calcium response, Congo red uptake, hydrophobicity by latex particle agglutination, and autoagglutination as well as plasmid DNA analysis showed that Y. enterocolitica did not lose the virulence plasmid during isolation at 28 C and the cells were still virulent. Moreover, post-enrichment treatment with alkali to reduce competing microflora, when used in conjunction with these five enrichment techniques, did not cause the loss of the virulence plasmid.