Sensitivity to vinyl phenol derivatives produced by phenolic acid decarboxylase activity in Escherichia coli and several food-borne Gram-negative species.

Ferulic, p-coumaric, and caffeic acids are phenolic acids present in soil, food, and gut, which have antimicrobial effects. Some Gram (+) bacteria metabolize these phenolic acids into vinyl derivatives due to phenolic acid decarboxylase activity (PAD) involved in the phenolic acid stress response (PASR). In this study, the antimicrobial activity of phenolic acids and their vinyl derivatives was tested on a panel of desirable and undesirable food-borne bacteria, especially Gram (-) species of Salmonella, Enterobacter, Klebsiella, and Pseudomonas, most of them without PAD activity. Native and engineered Escherichia coli strains either expressing or not PAD activity were included. Gram (-) bacteria of the panel were not significantly inhibited by phenolic acids at 3 mM, but were dramatically inhibited by the corresponding vinyl derivatives. On the contrary, Gram (+) bacteria displaying the PASR face the toxicity of phenolic acids by PAD activity and are not inhibited by vinyl phenols. In E. coli, the genes aaeB and marA, encoding efflux pumps for antimicrobial compounds, are upregulated by the addition of p-coumaric acid, but not by its derivative 4-vinyl phenol (p-hydroxystyrene). These results suggest that phenolic acids and their vinyl phenol derivatives produced by PAD (+) species could have a significant impact on undesirable or pathogenic food-borne Gram (-) bacteria in complex microbial ecosystems.