Gene profiling and serotyping of multidrug-resistant Listeria monocytogenes isolated from humans, animals, and dairy products

Background Listeria monocytogenes is a foodborne pathogen of a major public health concern due to its ability to cause severe illness and its increasing antimicrobial resistance. This study aimed to determine the prevalence, antimicrobial susceptibility, serotype distribution, and virulence genes profiles of L. monocytogenes isolated from food products, farm animals, and humans in Egypt. Methodology A total of 750 samples were collected, including dairy products, raw meat, animal fecal samples, aborted fetuses, and human stool samples. Isolation and identification were performed according to ISO, (2022) followed by serotyping and molecular characterization of virulence genes ( iap , hlyA , and actA ). Antimicrobial susceptibility testing was conducted using the disk diffusion method according to CLSI guidelines. Results Listeria spp. were detected in 18.5% of food products, 4.75% of animal fecal samples, 18.0% of aborted fetuses, and 17.0% of human samples. The highest contamination rates were observed in Kareish cheese (28.0%) and raw milk (22.0%). Serotype 4b was the most prevalent among isolates. All isolates harbored the iap gene, while the hlyA and actA genes were detected in 80% and 67% of isolates, respectively. Alarmingly, all isolates were resistant to clindamycin and nalidixic acid, and high resistance rates were observed against penicillin (93.3%) and ampicillin (86.7%), although imipenem and amikacin remained effective. Conclusion These findings highlight the circulation of multidrug-resistant and virulent L. monocytogenes strains in Egypt’s food chain and among occupational groups. Enhanced hygiene measures, continuous surveillance, and prudent antibiotic use are urgently needed to mitigate the associated public health risks.