| Summary: | <i>Listeria monocytogenes</i> is an intracellular facultative pathogen that causes listeriosis, a foodborne zoonotic infection. There are differences in the pathogenic potential of <i>L. monocytogenes</i> subtypes and strains. Comparison of the genome sequences among <i>L. monocytogenes</i> pathogenic strains EGD-e and F2365 with nonpathogenic <i>L. innocua</i> CLIP1182 and <i>L. monocytogenes</i> strain HCC23 revealed a set of proteins that were present in pathogenic strains and had no orthologs among the nonpathogenic strains. Among the candidate virulence factors are five proteins: putrescine carbamoyltransferase; InlH/InlC2 family class 1 internalin; phosphotransferase system (PTS) fructose transporter subunit EIIC; putative transketolase; and transcription antiterminator BglG family. To determine if these proteins have a role in adherence and invasion of intestinal epithelial Caco-2 cells and/or contribute to virulence, five mutant strains were constructed. F2365Δ<i>inlC2</i>, F2365Δ<i>eiic</i>, and F2365Δ<i>tkt</i> exhibited a significant (<i>p</i> < 0.05) reduction in adhesion to Caco-2 cells compared to parent F2365 strain. The invasion of F2365Δ<i>aguB</i>, F2365Δ<i>inlC2</i>, and F2365Δ<i>bglG</i> decreased significantly (<i>p</i> < 0.05) compared with the parent strain. Bacterial loads in mouse liver and spleen infected by F2365 was significantly (<i>p</i> < 0.05) higher than it was for F2365Δ<i>aguB</i>, F2365Δ<i>inlC2</i>, F2365Δ<i>eiic</i>, F2365Δ<i>tkt</i>, and F2365Δ<i>bglG</i> strains. This study demonstrates that <i>aguB</i>, <i>inlC2</i>, <i>eiic</i>, <i>tkt</i>, and <i>bglG</i> play a role in <i>L. monocytogenes</i> pathogenicity.
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