Abstract
Listeria monocytogenes is an intracellular facultative pathogen that causes listeriosis, a foodborne zoonotic infection. There are differences in the pathogenic potential of L. monocytogenes subtypes and strains. Comparison of the genome sequences among L. monocytogenes pathogenic strains EGD-e and F2365 with nonpathogenic L. innocua CLIP1182 and L. monocytogenes 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. F2365ΔinlC2, F2365Δeiic, and F2365Δtkt exhibited a significant (p < 0.05) reduction in adhesion to Caco-2 cells compared to parent F2365 strain. The invasion of F2365ΔaguB, F2365ΔinlC2, and F2365ΔbglG decreased significantly (p < 0.05) compared with the parent strain. Bacterial loads in mouse liver and spleen infected by F2365 was significantly (p < 0.05) higher than it was for F2365ΔaguB, F2365ΔinlC2, F2365Δeiic, F2365Δtkt, and F2365ΔbglG strains. This study demonstrates that aguB, inlC2, eiic, tkt, and bglG play a role in L. monocytogenes pathogenicity.
Highlights
Listeria monocytogenes is a Gram-negative intracellular foodborne pathogen that can cause invasive infection with high mortality rates
The mutant strains exhibited a similar growth rate to the wild type F2365 strain when grown in brain heart infusion (BHI) as enriched medium or minimal medium (MM) (Figure 1)
A ∆inlC2 mutant was defective in adhesion and invasion to epithelial cells and showed significant attenuation in the mouse model. These results suggest that inlC2 contributes to L. monocytogenes virulence
Summary
Listeria monocytogenes is a Gram-negative intracellular foodborne pathogen that can cause invasive infection with high mortality rates. To search for novel virulence factors of Listeria, our group previously performed orthology analysis to identify proteins present in pathogenic strains (EGD-e and F2365) but absent in nonpathogenic strains of the same or closely related species (L. monocytogenes strain HCC23 and L. innocua strain CLIP1182) [12]. 1 internalin (WP_003728063); PTS fructose transporter subunit EIIC (WP_003722829); putative transketolase (WP_003725545); and transcription antiterminator BglG family (AAT05528). These five proteins were selected out of 58 proteins to represent different functional groups and classes. We assessed the contribution to virulence of five L. monocytogenes genes identified solely by comparative genomics. Our findings validate the use of comparative genomics, orthology analysis, as a predictive method to identify putative virulence genes
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