B-235. Yersinia pestis Type-Three Secretion System-Dependent Inhibition of Human Polymorphonuclear Leukocyte Function

J. L. Spinner, S. D. Kobayashi;
Univ. of Idaho, Moscow, ID.

Background: Human polymorphonuclear leukocytes (PMNs or neutrophils) are the primary innate host defense against invading bacterial pathogens. Neutrophils are rapidly recruited to sites of infection and ingest microorganisms through a process known as phagocytosis. Following phagocytosis by human PMNs, microorganisms are killed by reactive oxygen species (ROS) and microbicidal products contained within granules. Yersinia pestis, the causative agent of plague, is capable of rapid replication and dissemination from sites of infection in the host. Previous studies have demonstrated that expression of the type III secretion system (TTSS) and Yersinia outer proteins (Yops) in the related enteropathogenic Yersinia spp. inhibits PMN and macrophage functions. Additionally, Y. pestis is shown to survive in macrophages. However, Y. pestis fate following interaction with human PMNs is less clear. Our specific hypothesis is that Y. pestis expressing the TTSS and Yops inhibits phagocytosis, ROS production, and subsequent killing by human PMNs. Methods: Phagocytosis was determined by differential fluorescence microscopy. ROS production was measured using the fluorescent indicator 2’, 7’-dichlorodihydrofluorescein diacetate and a 96 well plate reader. Human PMN bactericidal activity towards Y. pestis was determined by incubation of bacteria with isolated PMNs followed by viable plate counts. Intracellular bacterial fate was similarly assessed following removal of extracellular Y. pestis with gentamicin. Results: Y. pestis was found to inhibit phagocytosis, ROS production, and killing by human PMNs through a TTSS and Yop dependent manner. However, exclusion of uningested TTSS-expressing Y. pestis with gentamicin revealed that intracellular bacteria are eliminated by human PMNs similar to bacteria lacking the TTSS. Conclusion: Y. pestis TTSS and Yops contribute to extracellular survival following interactions with human PMNs and that intracellular fate is independent of TTSS and Yop inhibition of neutrophil ROS production.

161/B. Microbial Communities

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