Impaired adaptation to smoke-derived phenolic compounds in Listeria monocytogenes CC204 from smoked salmon and trout.

Abstract

Listeria monocytogenes is a major foodborne pathogen in ready-to-eat smoked fish products. This study evaluated whether clonal complex affiliation contributes to variability in growth responses to stresses representative of smoked salmon and trout processing. Ten strains were studied, including strains from CC121, CC26 and CC204, the three major clonal complexes reported in the French smoked salmon and trout sectors, together with the EGDe reference strain. Strains were exposed to salt, cold, smoke-derived phenolic compounds and combined stress conditions. Growth responses were compared with whole-genome-based phylogeny, and the impaired phenotype observed under phenolic exposure was further investigated using viable counts, live/dead microscopy and comparative genomics. Growth profiles were partly structured by clonal complex, with strains from the same clonal complex showing similar behaviour across stress conditions. Salt and cold reduced growth globally, while smoke-derived phenolic compounds were the most discriminating conditions. CC204 strains showed markedly lower growth rates under phenolic exposure than CC121, CC26 and EGDe. This phenotype was not associated with loss of cultivability or significant loss of membrane integrity. Comparative genomics did not identify a clear gene-content determinant explaining the CC204 phenotype. These results suggest that CC204 has an impaired adaptive response to smoke-derived compounds, likely involving regulatory or physiological mechanisms.