Listeria monocytogenes remains a major foodborne pathogen associated with ready-to-eat (RTE) products, including smoked fish. This study investigated the occurrence, molecular characteristics, virulence gene profiles, and antimicrobial susceptibility of L. monocytogenes isolated from retail smoked fish in Poland. A total of 46 samples (cold- and hot-smoked products) collected from 15 producers and five retail chains were analyzed using ISO 11290-1:2017 for qualitative detection and ISO 11290-2:2017 for enumeration. Listeria spp. were detected in 5/46 samples (10.9%), including 4 isolates confirmed as L. monocytogenes (8.7%). All positive samples originated from cold-smoked salmon, with a prevalence of 4/13 (30.8%) in this product category. The quantitative analysis indicated that contamination levels in all positive samples were below 100 CFU/g. Molecular serogrouping and multiplex PCR demonstrated the presence of key virulence-associated genes, including hlyA, prfA, plcB, and actA, consistent with potentially pathogenic profiles. Pulsed-field gel electrophoresis (PFGE) revealed clustering of isolates, indicating genetic relatedness among strains obtained from different retail sources. Antimicrobial susceptibility testing using the MICRONAUT system showed that all L. monocytogenes isolates were susceptible to first-line therapeutic agents, including ampicillin and penicillin, according to EUCAST/CLSI criteria. Although contamination levels were low and isolates remained susceptible to clinically relevant antimicrobials, the detection of virulence-associated strains in RTE smoked fish highlights the need for continuous monitoring and strict hygienic control in the production and retail chain. These findings contribute to regional surveillance data on L. monocytogenes in smoked fish products in Poland.
Strzałkowska et al. (Fri,) studied this question.
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