Virulence, cytotoxicity potential and biofilm production ability of Listeria spp. isolated from raw fish in Poland.

Abstract

BACKGROUND: The presence ofspp. in raw fish poses a significant food safety risk, primarily due to the pathogenic potential of. However, comprehensive data on the virulence characteristics ofpopulations, including non-species, isolated from raw fish in Poland are limited. This study aimed to characterize a collection ofspp. isolates by assessing their virulence gene profiles, biofilm-forming capabilities, and cytotoxic potential to better understand the public health risk associated with their presence in the aquatic food chain. RESULTS: A total of 104spp. isolates ( = 24, = 36, = 30, = 14) were analyzed. A clear demarcation in pathogenic potential was observed:isolates universally harbored key virulence determinants, with 95.8% carrying a completePathogenicity Island 1 (LIPI-1), and all belonging to the clinically relevant serogroup 1/2a-3c. This genetic potential was confirmed phenotypically, as cytotoxic activity against four eukaryotic cell lines was exclusively observed in this species. In contrast, otherspecies were non-cytotoxic, although they carried isolated virulence genes (,), suggesting a role as an environmental reservoir. Biofilm formation was a common trait across all species, with 69.2% of isolates demonstrating this ability in a quantitative assay. However, this phenotype was not significantly associated with the presence of thegene ( > 0.05). CONCLUSIONS: Raw fish sold in Poland are a probable vehicle for highly virulentstrains equipped with a full genetic potential for causing human disease. The widespread ability of allspecies to form biofilms highlights a critical mechanism for persistence in food processing environments, where non-pathogenic species may shelter the primary pathogen. These findings underscore the necessity for extensive surveillance and control strategies targeting the entiregenus to mitigate the public health risk associated with raw fish consumption. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12917-026-05323-z.