Genomic and transcriptomic analysis of biofilm formation in foodborne Listeria monocytogenes isolates under combined environmental stress.

Listeria monocytogenes is a foodborne pathogen capable of forming biofilms that contribute to persistent contamination. Here, 70 foodborne isolates from China were characterized by whole-genome sequencing and biofilm formation assays under combined environmental stresses including temperature, pH, and NaCl. Multilocus sequence typing (MLST) revealed 85.7% belonged to lineage II predominantly CC8, and 14.3% to lineage I predominantly CC87. Stress adaptation genes including Stress Survival Islet 1, Stress Survival Islet 2, bapL, and inlL showed differential distribution among clone complexes. Biofilm formation was generally enhanced at pH 6 but reduced at pH 5 or under 5% NaCl. Notably, CC8 and CC87 exhibited significant differences in biofilm formation under combined low temperature at 4 °C and low pH at 6 conditions. Two representative strains from CC8 and CC87 respectively were selected for transcriptomic sequencing to explore the molecular mechanisms underlying the differences in biofilm formation. Under combined stress, CC8 and CC87 displayed distinct transcriptional profiles. Upregulated genes in CC8 were significantly enriched in glycolysis/gluconeogenesis and pyrimidine metabolism pathways, while CC87 showed downregulation of two-component system pathways. Collectively, these findings reveal clone complex-dependent variations in biofilm formation, differential distribution of stress adaptation genes, and specific metabolic patterns in L. monocytogenes. These differences provide new insights into the adaptive strategies of L. monocytogenes under environmental stress and highlight the importance of considering clone diversity in food safety risk assessment.