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Front Microbiol. 2015 Apr 10;6:259. doi: 10.3389/fmicb.2015.00259. eCollection 2015.

Tyrosine decarboxylase activity of enterococci grown in media with different nutritional potential: tyramine and 2-phenylethylamine accumulation and tyrDC gene expression.

Author information

1
Department of Agricultural and Food Sciences, University of Bologna Cesena, Italy.
2
Interdepartmental Center for Industrial Agri-Food Research, University of Bologna Cesena, Italy.
3
Department of Biotechnology, University of Verona Verona, Italy.
4
Department of Agricultural and Food Sciences, University of Bologna Cesena, Italy ; Interdepartmental Center for Industrial Agri-Food Research, University of Bologna Cesena, Italy.

Abstract

The ability to accumulate tyramine and 2-phenylethylamine by two strains of Enterococcus faecalis and two strains Enterococcus faecium was evaluated in two cultural media added or not with tyrosine. All the enterococcal strains possessed a tyrosine decarboxylase (tyrDC) which determined tyramine accumulation in all the conditions tested, independently on the addition of high concentration of free tyrosine. Enterococci differed in rate and level of biogenic amines accumulation. E. faecalis EF37 and E. faecium FC12 produced tyramine in high amount since the exponential growth phase, while 2-phenylethylamine was accumulated when tyrosine was depleted. E. faecium FC12 and E. faecalis ATCC 29212 showed a slower tyraminogenic activity which took place mainly in the stationary phase up to 72 h of incubation. Moreover, E. faecalis ATCC 29212 produced 2-phenylethylamine only in the media without tyrosine added. In BHI added or not with tyrosine the tyrDC gene expression level differed considerably depending on the strains and the growth phase. In particular, the tyrDC gene expression was high during the exponential phase in rich medium for all the strains and subsequently decreased except for E. faecium FC12. Even if tyrDC presence is common among enterococci, this study underlines the extremely variable decarboxylating potential of strains belonging to the same species, suggesting strain-dependent implications in food safety.

KEYWORDS:

2-phenylethylamine; enterococci; intraspecific variability; tyrDC gene expression; tyramine

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