PrfA, the master virulence regulator of Listeria monocytogenes: structural-functional insights, regulatory architecture, and antivirulence strategies.

Listeria monocytogenes causes listeriosis, a foodborne illness with case fatality rates of 20-30%. This bacterium tolerates a broad range of environments and can invade and replicate within human cells, properties that depend critically on PrfA (Positive Regulatory Factor A), a CRP/FNR-family transcriptional regulator. PrfA has two functional domains: an N-terminal β-barrel that binds ligands and a C-terminal helix-turn-helix motif that contacts PrfA-box sequences in target promoters. Activation is triggered by host-derived glutathione, which induces conformational changes permitting transcription of virulence genes encoding internalins, listeriolysin O, and ActA; this response is graded rather than binary. Beyond this core mechanism, PrfA integrates σB-dependent stress signals, temperature-sensitive RNA structures in the prfA transcript, CodY-mediated metabolic cues, and oligopeptide-based inhibitory inputs, allowing virulence output to be tuned across shifting environmental conditions. PrfA also governs biofilm formation and intracellular persistence, contributing to both acute pathogenesis and long-term survival in food-processing environments. This review addresses the structure and regulatory circuitry of PrfA, then surveys antivirulence strategies targeting this protein using natural compounds, synthetic inhibitors, and nanomaterial-based approaches.