Abstract: This study determined the effects of ferulic acid on the growth, gene expression and tyramine accumulation of Enterococcus faecalis XL-M66 and E. faecium XL-M76. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to analyze the expression of tyramine synthesis-related genes in the tyrosine decarboxylation pathway in E. faecalis XL-M66 and E. faecium XL-M76. Additionally, the accumulation of tyramine during 48 h culture was monitored by high performance liquid chromatography (HPLC). Results showed that ferulic acid had little effect on the transcription of the tyrosine decarboxylase (tyrDC) and tyrosine/tyramine permease (tyrP) genes (P > 0.05) in the absence of the substrate tyrosine, but promoted the transcription of the tyrosyl-tRNA synthetase (tyrS) gene (P < 0.05). On the contrary, in the presence of tyrosine, ferulic acid had little effect on the expression of the tyrS gene (P > 0.05), but it could significantly (P < 0.05) inhibit the expression of the tyrDC and tyrP genes. Moreover, ferulic acid significantly (P < 0.05) inhibited the growth of E. faecalis XL-M66 and E. faecium XL-M76 and reduced tyramine production by 27.0% and 19.9%, respectively.

Key words: ferulic acids, Enterococcus faecalis, Enterococcus faecium, tyramine, tyrosine decarboxylase, reverse transcription quantitative polymerase chain reaction