Efficacy of Cannabidiol in Reducing Virulence of Listeria monocytogenes

<i>Listeria monocytogenes</i> (LM) is a major foodborne pathogen causing illnesses ranging from gastroenteritis to severe systemic infections. The key virulence factors include bacterial motility, hemolysin and lecithinase production, and invasion of host tissues. This study investigated the anti-virulence effects of cannabidiol (CBD), the main non-psychoactive compound in <i>Cannabis sativa</i>, against LM. The minimum inhibitory concentration (MIC, 2289 μM; 719.8 µg/mL) and sub-inhibitory concentration (SIC, 11.92 μM; 3.75 µg/mL) of CBD were determined for LM strains Scott A and ATCC 19115. Cultures were treated with SIC, 6× SIC, 1/4× MIC, and MIC to assess effects on motility, hemolysin and lecithinase production, and adhesion and invasion of human intestinal (Caco-2) and brain endothelial (HBMEC) cells, alongside virulence gene expression by RT-qPCR. Cannabidiol's efficacy was also determined using a <i>Galleria mellonella</i> larval infection model at SIC and 6× SIC. Cannabidiol at 6× SIC significantly reduced motility, toxin production, and host cell adhesion and invasion (<i>p</i> < 0.05). RT-qPCR revealed downregulation of key virulence genes, including <i>prfA</i>, <i>hly</i>, <i>plcA</i>, <i>plcB</i>, <i>iap</i>, <i>motA</i>, <i>motB</i>, <i>actA</i>, <i>inlA</i>, and <i>inlB</i>. In vivo, CBD enhanced larval survival in a dose-dependent manner and cytotoxicity was observed at concentrations above 33.75 µg/mL. These results indicate that CBD, at non-bactericidal levels, effectively suppresses multiple virulence mechanisms in LM, highlighting its potential as a novel anti-virulence agent for food safety and therapeutic applications.