Validation of Predicted Virulence Factors in Listeria monocytogenes Identified Using Comparative Genomics

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. F2365 Delta inlC2, F2365 Delta eiic, and F2365 Delta tkt exhibited a significant (p < 0.05) reduction in adhesion to Caco-2 cells compared to parent F2365 strain. The invasion of F2365 Delta aguB, F2365 Delta inlC2, and F2365 Delta bglG 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 F2365 Delta aguB, F2365 Delta inlC2, F2365 Delta eiic, F2365 Delta tkt, and F2365 Delta bglG strains. This study demonstrates that aguB, inlC2, eiic, tkt, and bglG play a role in L. monocytogenes pathogenicity.