Listeria monocytogenes – An examination of food chain factors potentially contributing to antimicrobial resistance

• AMR is emerging and underestimated in food chain-linked Listeria monocytogenes.
• Niches in food and food production environments may promote AMR gene exchange.
• Common food chain interventions alter AMR through stress response mechanisms.
• Increased AMR may lead to decreased control of L. monocytogenes during food production.
• AMR acquired in the food chain may lead to failed therapeutic listeriosis treatment.

When compared to common bacterial agents associated with foodborne disease, Listeria monocytogenes is an infrequent but pernicious pathogen linked to disproportionally high levels of morbidity and mortality in susceptible individuals. To improve clinical outcomes, invasive infections require prudent administration of antimicrobial agents. While L. monocytogenes has historically been susceptible to antimicrobials effective against Gram positive bacteria, there have been reports of antimicrobial resistance (AMR) in this organism, including in isolates originating from food-producing animals, food processing environments (FPE), and food (i.e. the food chain). Considering human listeriosis is acquired predominantly through foodborne transmission, this is concerning. In particular, food chain factors may influence L. monocytogenes AMR through i. horizontal exchange of AMR genes, ii. induction of AMR-related stress responses through sub-lethal exposure to factors controlling microbial growth in food, and iii. recurring exposure to disinfectants in the FPE. In light of the significant technical challenges of fully understanding the influence of the food chain on AMR, this review examines how environments and conditions spanning the food continuum may influence current AMR trends through genetic, physiological, and selection pressure-based perspectives. When combined with effective surveillance, such knowledge will be useful in prolonging the efficacy of the currently available repertoire of therapeutic treatment options.