Viable but Nonculturable Listeria monocytogenes May Resuscitate After Transfer From Stainless Steel Biofilms to Vacuum-Packed Smoked Herring

Listeria monocytogenes is a persistent foodborne pathogen capable of surviving sanitation and low-temperature conditions commonly encountered in food processing environments. Under environmental stress, this bacterium can enter a viable but non-culturable (VBNC) state, characterized by retained viability but loss of culturability, making it undetectable by conventional microbiological methods. This study aimed to determine whether VBNC L. monocytogenes populations originating from biofilms can be transferred to a ready-to-eat (RTE) seafood product and subsequently resuscitate during refrigerated storage. Biofilms were formed for 24 h on stainless steel coupons at 8 °C and exposed to a quaternary ammonium–based disinfectant. Total, viable, and cultivable populations were quantified using qPCR, PMA-qPCR, and plate counts. QA treatment significantly reduced cultivable populations (3.0-log reduction) while maintaining high viable populations (≈5.2 log GE/cm 2 ), suggesting VBNC induction. Treated and untreated biofilms were then brought into contact with sterile smoked-salted herring pieces to simulate cross-contamination. L. monocytogenes populations were transferred in all cases, with viable populations reaching approximately 4–6 log GE/g for untreated biofilms and around 3 log GE/g for QA-treated biofilms, where most populations were in a VBNC state. During vacuum-packed refrigerated storage (7 days at 4 °C followed by 14 days at 8 °C), populations on herring surfaces progressively regained culturability, with cultivable populations increasing from low initial levels to 5–7 log CFU/g by the end of the product shelf life (21 days) These findings show that VBNC L. monocytogenes populations present on food-contact surfaces can be transferred to RTE seafood and regain culturability during storage. This highlights a potential contamination pathway and supports the need to consider VBNC populations in hygiene monitoring and risk assessment strategies for vacuum-packed foods.