MODELING THE GROWTH OF YERSINIA-ENTEROCOLITICA IN DONATED BLOOD

Background: Sepsis and death subsequent to the transfusion of blood containing Yersinia enterocolitica is an increasing problem. The organisms probably originate from bacteremia in the donor and can subsequently multiply at low temperature. Study Design and Methods: Reported here are experiments with a strain of Y. enterocolitica associated with a ase of transfusion-associated bacteremia. Results: It was found that the rapid early killing of Y. enterocolitica injected into donated blood does not require viable phagocytes and can be explained by complement-mediated killing. Complement resistance in Y. enterocolitica is known to be plasmid-coded. It is expressed at 37 degrees C, but not at 20 degrees C, and is favored by calcium-deficient culture media. Y. enterocolitica organisms induced to express complement resistance were still killed in donated blood, though the initial rate was slower. Such organisms multiplied in plasma at 37 degrees C, but were killed after 6 hours of incubation at 20 degrees C, presumably because complement resistance genes are switched off at this temperature. Conclusion: This experiment is thought to reflect the natural history of Y. enterocolitica contamination of blood, in which complement-resistant organisms in the donor blood encounter lower temperatures after donation. These observations suggest that the practice of plasma depletion may have contributed to the increased incidence of mortality due to Y. enterocolitica contamination of donated blood.