STUDYING NEW EFFECTOR PROTEINS IN LISTERIA MONOCYTOGENES

Listeria monocytogenes is a Gram positive, facultative intracellular food-borne pathogen that can cause serious illness in mammals. L. monocytogenes is able to invade, replicate and survive within several different cell types of mammalian tissues. Upon invasion, L. monocytogenes initially resides in a membrane-bound compartment from which it escapes into the host cell cytosol, where it replicates.

Pathogenic bacteria are known to modify their intracellular replication niche using so-called effector proteins that are secreted by that bacteria into the host, usually via type III or type IV secretion system. Some bacteria inject only a few effectors into their host’s cells (e.g. Yersinia pestis) while others may inject dozens (e.g. Salmonella enterica) or hundreds (e.g. Legionella pneumophila) effectors. These proteins help the pathogen to survive within the host tissue and suppress immune responses by modifying cellular processes. In L. monocytogenes several virulence factors were characterized that affect the host, yet we hypothesized that many more exist that modulate host processes. The aim of this study was to reveal novel proteins secreted by L. monocytogenes to the host`s cytosol to promote bacterial infection. Using a bioinformatic analysis we identified 24 new putative effector candidates in L. monocytogenes, and examined them using biochemical and genetic approaches. So far, 9 proteins were validated as secreted to the host cytosol by a CYAA translocation assay. Further studies are currently done to confirm their function in virulence.