Characterization of <i>Listeria monocytogenes</i> Isolates from Pork Production in Southern Sonora, Mexico: Serotyping, Antimicrobial Resistance, Chitosan Susceptibility, and Pathogenicity in a Chicken Embryo Model

Listeria monocytogenes is often found in pork intestines and can contaminate pork production, posing a risk to consumers. This study aimed to characterize 16 L. monocytogenes isolates from fresh and packaged pork loin, identify their serotypes, and assess antibiotic resistance. To evaluate chitosan susceptibility as a potential strategy to control L. monocytogenes in the pork industry and to determine its effectiveness in a eukaryotic model to demonstrate pathogenicity. Sixteen isolates were evaluated, and two were determined as serotype 1/2a, twelve were 1/2b, and none were serotype 4b. Variations were observed in their pathogenicity factors. All isolates could infect chicken embryos except isolate 1.2, which displayed attenuated pathogenicity. The isolates also demonstrated strong biofilm-forming abilities. It was shown that chitosan inhibits the growth of L. monocytogenes, resulting in a viable alternative against this pathogen, but in this work, one isolate exhibited resistance to chitosan. L. monocytogenes strains present in pork meat represent a public health risk. This study characterized L. monocytogenes isolates from pork, revealing diverse serotypes (1/2a, 1/2b) and strong biofilm-forming abilities. While chitosan exhibited antimicrobial activity against most isolates, resistance was observed in one strain. These findings highlight the potential public health risk L. monocytogenes poses in pork and the need for continued research to develop effective control strategies.