Abstract
Listeria (L.) monocytogenes is a foodborne pathogen that can cause disease, mainly in elderly, pregnant or immunocompromised persons through consumption of contaminated food, including pork products. It is widespread in the environment and can also be found in asymptomatic carrier animals, for example, in different tissues of pigs. To learn more about their nature, 16 Listeria spp. isolates found in tonsils and intestinal content of pigs and 13 isolates from the slaughterhouse environment were characterized using next-generation sequencing (NGS). A wide distribution of clonal complexes was observed in pigs, as well as in the pork production chain, suggesting multiple sources of entry. Hypervirulent clones were found in pig tonsils, showing the potential risk of pigs as source of isolates causing human disease. The presence of closely related isolates along the production chain suggests a cross-contamination in the slaughterhouse or recontamination from the same source, strengthening the importance of efficient cleaning and disinfection procedures. The phenotypical antimicrobial resistance status of L. monocytogenes isolates was examined via broth microdilution and revealed a low resistance level. Nevertheless, genotypical resistance data suggested multiple resistances in some non-pathogenic L. innocua isolates from pig samples, which might pose a risk of spreading resistances to pathogenic species.
Highlights
Sixteen isolates of Listeria spp. used in this study were found in porcine samples; their distribution and prevalence in pigs were reported by Oswaldi et al [18]
Two L. monocytogenes and five L. innocua isolates originated from slaughterhouse A, taken on sampling dates 1 to 4, whereas the remaining five
L. monocytogenes and four L. innocua isolates came from slaughterhouse B on sampling dates 5 and 6
Summary
Listeria (L.) monocytogenes, a Gram-positive bacterium, is the cause of human listeriosis, a rare foodborne illness with a high hospitalization and case-fatality rate [1]. Listeria species are known [2], among which L. monocytogenes and L. ivanovii are considered mammalian pathogens. While infections caused by L. ivanovii are seldom and mainly affect ruminants, L. monocytogenes is associated with most human and animal listeriosis disease cases [3]. Other Listeria species are generally considered non-pathogenic, there are some rare cases of disease reported caused by L. innocua [4,5] and L. seeligeri [6]
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