Listeria monocytogenes: from a saprophytic to a cytosolic virulent pathogen

Listeria monocytogenes is a facultative intracellular bacterium that commonly resides in soil as a saprophyte but is capable of transitioning into a pathogen when ingested by invertebrate hosts, including humans and various animals. Listeria monocytogenes is a well-recognized foodborne pathogen responsible for diverse clinical manifestations, from mild self-limiting gastroenteritis to severe invasive diseases, such as septicemia, meningitis, encephalitis, and pregnancy-associated complications, such as spontaneous abortion. Pathogenesis is governed by sophisticated regulatory networks that orchestrate gene expression and coordinate virulence. This review provides an in-depth analysis of the microbiological traits of L. monocytogenes as a foodborne pathogen, emphasizing the virulence mechanisms of this bacterium in both vertebrate and invertebrate hosts. Key virulence factors include internalin-mediated host cell adhesion and invasion, flagella-driven motility, the positive regulatory factor A (PrfA)-regulated transcriptional control of major virulence genes, the listeriolysin O-induced disruption of phagosomal membranes, the phospholipase-mediated evasion of host defense mechanisms, actin polymerization-dependent intracellular and intercellular spread, sigma factor-driven stress responses, biofilm formation and the development of resistance to antimicrobial agents. Strategies for microbiological control of virulence are also discussed.