Prevalence, molecular characterization, antibiotic resistance, and investigation of transmission pathways of Listeria monocytogenes strains isolated along the beef production chain

Listeria monocytogenes, the leading cause of fatalities among foodborne pathogens, exhibits remarkable resilience in food industry environments. This study aims to isolate and characterize L. monocytogenes strains along the beef production chain of a vertically integrated industry. Sampling included carcass, hide, and environmental samples collected from a cattle unit and partner slaughterhouse. The samples were examined for the presence of Listeria monocytogenes. The isolates were characterized via molecular serotyping and MALDI-TOF proteomic analysis. Further analyses included antimicrobial susceptibility testing, biofilm formation assessment, and virulence gene investigation. A total of 24 L. monocytogenes strains were isolated. The prevalence in carcasses, hide and slaughterhouse environment was 21.7%, 6.7% and 8.8% respectively. Molecular serogroup IIc predominated, followed by serogroups IIa, IIb, and IVb. Almost all strains showed a moderate or strong ability to produce biofilms and resistance to at least one antimicrobial, with clindamycin, vancomycin, and tetracycline demonstrating the highest rates of resistance. Three strains were also characterized as multidrug-resistant, while all strains possessed at least six virulence genes. The proteomic analysis organized the isolated strains in three clusters, whereas the transmission pathways primarily implicated carcass washing water and hides. Understanding L. monocytogenes dissemination along the beef production chain is vital for preventing transmission to humans and emergence of a listeriosis outbreak.