Salmonella enterica biofilm is capable of VBNC state formation and virulence gene expression during low temperature food storage.

As a frequently identified foodborne pathogen, Salmonella enterica can enter into the viable but nonculturable (VBNC) state and form biofilm, thereby posing high risk to food safety. In this study, 4 types of rice and flour foods, 4 microbial growth status including different biofilm formation stages in comparison with planktonic state, and 2 storage temperatures (4 °C and -20 °C), were applied to explore the VBNC state formation within S. enterica biofilms during low temperature food storage. The ability of S. enterica cells to express virulence gene invA during low temperature storage was also determined. Partial or all S. enterica cells could enter into the VBNC state depending on food type and storage temperature, leading to false negative detection results by culture-based methods. Mature biofilms acquiring high resistance were easier to enter into the VBNC state. Comparing food composition and storage conditions in different food samples, temperature and nutrient were assumed as major factors for the induction of VBNC state. In addition, decreased but continuous invA gene expression was recorded during storage, and the entry into the VBNC state did not influence invA gene expression. The combination of both biofilm and VBNC state which are hard to remove and detect and have high persistence could increase the risks posed by the contamination of S. enterica in food products. Persistence of virulence-associated gene expression in VBNC cells causes further safety issues. These findings provided risk warning for contamination of S. enterica VBNC cells within biofilms during low temperature food storage.