Aqueous extracts of spices inhibit biofilm in Listeria monocytogenes by downregulating release of eDNA

Abstract

Listeria monocytogenes is a Gram-positive mesophilic foodborne pathogen whose pathogenicity is regulated by various environmental stress factors. The ability to form robust biofilm makes it difficult to eradicate this bacteria from food processing environments. Also, there is an increase in the antibiotic resistant food isolates of L. monocytogenes. Therefore, there is a constant need for the development of novel food preservation techniques and therapeutics. In this study, we sought to determine the effectiveness of clove and cinnamon water extracts on the listerial biofilm initiation, dispersion, and expression of the virulence genes. It was observed that the spice water extracts not only inhibited the biofilm formation of L. monocytogenes but also accelerated the dispersion. The spice extracts at higher concentrations were found to be bactericidal to L. monocytogenes. The extracts downregulated the expression of virulence genes and the release of extracellular DNA (eDNA) in the biofilm. The decreased ability to form biofilm could be attributed to the inhibition of eDNA secretion. Thus the water extracts of cinnamon and clove can be used as food preservatives against the biofilm formation of L. monocytogenes.