Prevalence and genomic characterization of Listeria monocytogenes and Salmonella spp. in chorizos, ready-to-eat sliced meat products and raw burgers marketed in Portugal
Authors: Cristina Varela Flores, Ana Carolina Coelho, Rosália Furtado, Sílvia Marcos, Maria João Barreira, Anabela Coelho, João Rodrigues, Camila Fernandes,.....
Ger. J. Microbiol.
2026.
vol. 6, Iss. 3
pp:27-45
Doi: https://doi.org/10.51585/gjm.2026.3.0068
Abstract:
The increasing consumption of ready-to-eat (RTE) processed meats and convenience products, such as burgers, presents significant food safety concerns due to minimal or inadequate heat treatment, which may allow pathogen survival. This study assessed the prevalence of Listeria monocytogenes and Salmonella spp. in RTE-sliced meats, non-sliced chorizos/pork sausages, and raw burgers available in Portugal. Whole-genome sequencing (WGS) was employed to characterize virulence factors as well as stress, disinfectant, and antimicrobial resistance determinants. Core-genome multilocus sequence typing (cg-MLST) was used to evaluate the genetic relatedness among isolates and with clinical strains from the EFSA-ECDC One Health WGS database. Among 246 samples analyzed, L. monocytogenes was detected in 79 (32.1%), with prevalence rates of 2.7% in sliced meats, 22.9% in non-sliced chorizos, and 73.3% in raw burgers. Salmonella spp. was identified in seven samples (2.8%), predominantly in raw burgers (8.0%) and infrequently in chorizos (1%). WGS of 76 L. monocytogenes isolates identified 16 sequence types across four serovar groups. Frequent detection of stress survival islets SSI-1 (44.7%) and SSI-2 (13.2%), disinfectant resistance determinants Tn6188_qac transposon (14.5%) and brcABC cassette (2.6%), and widespread distribution of pathogenicity islands LIPI-1, LIPI-3, and LIPI-4 were observed. Among Salmonella spp. isolates, four serotypes were identified (Goettingen, Derby, Agona, and monophasic Typhimurium), with Typhimurium strains classified as multidrug-resistant. cgMLST analysis revealed complex contamination pathways, indicating both localized persistence and broader dissemination of genetically related strains within the food production chain, some of which were genetically linked to strains isolated from human samples. The detection of L. monocytogenes in over half of Salmonella spp. positive samples highlights complex contamination dynamics and underscores the need for integrated mitigation strategies. These findings demonstrate the persistence of virulent, antimicrobial-resistant, and disinfectant-tolerant strains in the food chain and underscore the critical importance of enhanced surveillance to mitigate risks to consumers.
Keywords:
Antiviral drug discovery, Feline infectious peritonitis, FIPV main protease, Network pharmacology, Safety pharmacology
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