P-017. Comparative Genomic Evaluation of Listeria monocytogenes Strains Involved in Invasive and Gastroenteritis Listeriosis Outbreaks

L. S. Burall, A. R. Datta;
US FDA, Laurel, MD.

Listeria monocytogenes is the causative agent of human listeriosis, a foodborne illness affecting the elderly, immunocompromised and pregnant women. Although most of the major listeriosis outbreaks were characterized by septicemia, meningitis, abortion and death (invasive listeriosis), several human listeriosis outbreaks were reported to have gastroenteritis as the only symptom. In an effort to understand the differences between the organisms associated with these diverse disease outcomes, the genomes of two invasive strains, F2365 and H7858, were compared to the genome of a gastroenteritis strain, HPB2262. BLAST analyses of the proteins encoded in F2365 and HPB2262 were performed to determine whether the proteins were conserved or unique. Homologs were identified as proteins whose BLAST results met two of the following criteria: an e-value≤0.05, a score >200, or an identity ≥30% over at least half of the protein. The unique proteins were then compared with H7858 proteins to verify these results. This analysis identified 153 proteins as unique to the invasive strains. A significant portion of these are hypothetical or conserved hypothetical proteins (n=54). Two gene clusters with at least seven genes were largely missing from the gastroenteritis strain but present in both the invasive strains. These proteins are mostly unknown, though a few may have functions, including one with a putative regulatory role. Also, 97 proteins were identified as unique to the gastroenteritis strain. The majority of these proteins were hypothetical proteins (n=57) or phage-associated (n=38). Two genes had a non-phage functional role, a DNA methyltransferase and an inorganic pyrophosphatase. These observations suggest that differences between the invasive and gastroenteritis strains may be linked to higher genetic volatility in the gastroenteritis strain from the phage and a subset of uncharacterized proteins that likely give unique evolutionary roles to the different strains. Further study is needed to characterize these differences to explain the higher virulence of the invasive strains and the pathogenesis of the gastroenteritis strains.