Survival of Yersinia enterocolitica in the environment.

When Yersinia enterocolitica was introduced into soils (or physiological saline), very little decrease in the population was observed throughout the test period. If the soil was allowed to air dry slowly, only 0.1% (2.8 x 10(3) colony forming units/g of soil) of the original population added still remained viable by day 10. On the other hand, the introduced organisms disappeared rapidly in river water but their longevities could be extended significantly if a eucaryote inhibitor was added to the river water or the river water was passed through a 0.8-micron membrane filter to remove eucaryotic predators. Furthermore, the rapid decrease of the Yersinia population coincided with an increase in numbers of protozoans. However, when Yersinia was added to filter-sterilized river water or when small numbers of the organism, below the threshold level believed necessary for active predation to occur, were added to the river water, no response in predators was observed; nevertheless, the population of Yersinia still showed a continued decline. When the organism was introduced into sephadex-treated river water or groundwater, its survival improved significantly compared with its survival in nontreated water samples. Low ambient temperature dramatically increased its ability to survive in the aquatic environment. It is concluded that, in addition to the temperature factor, the longevity of Y. enterocolitica in river water is chiefly regulated by predators and toxin producers.