Modeling the Aminogenic Potential of Enterococcus faecalis EF37 in Dry Fermented Sausages through Chemical and Molecular Approaches

Abstract

Amino acid decarboxylase activity of the Enterococcus faecalis strain EF37 was monitored during fermentation and ripening of a traditional dry fermented sausage from Northern Italy (Salame Veronese) by means of microbiological, chemical, and molecular approaches in relation to three technological factors: fermentation temperature, sodium chloride concentration, and amount of glucose added to the meat mixture. Besides the analytical determination of tyramine and phenylethylamine accumulation and the counts of enterococci, the presence and quantification of the tyrosine decarboxylase gene (tdc) and its mRNA transcript were also investigated by using real-time PCR. According to the mathematical models obtained, all of the three factors studied were statistically significant and microbiologically relevant for the early development of enterococci, although the fermentation temperature had a more relevant influence on the enterococcal viable cells of the ripened product. Sodium chloride concentration was the most determinant factor of the final tyramine and 2-phenylethylamine accumulation and also of the levels of tdc present in the final product. In contrast, an effect of glucose concentration on tdc expression was observed in the last period of ripening. Moreover, increasing amounts of sodium chloride and decreasing fermentation temperature resulted in a reduced tdc expression. This is the first time that bacterial tyrosine decarboxylase potential is directly examined through a molecular approach in a fermented meat. The quantification of tdc and its transcript can help to elucidate the critical steps and factors during food manufacturing at which bacterial aminogenesis is possible, thus allowing researchers to propose technological measures to control decarboxylase activities.

Scientific Opinion on risk based control of biogenic amine formation in fermented foods

“…For example, a multiplex PCR method for the simultaneous detection of LAB with the potential to produce histamine-, tyramine and putrescine-has been described (Marcobal et al, 2005). Furthermore, a quantitative real-time PCR for histamine-producing LAB (Fernández et al, 2006;Lucas et al, 2008) and for tyramine-producing bacteria has also been successfully applied to different stages of cheese manufacture including the final product (Ladero et al, 2008;Ladero et al, 2010b;Gardini et al, 2008). Molecular methods have also been designed to study histidine-and tyrosine-decarboxylase gene expression under conditions relevant for food fermentation (Rossi et al, 2011), including cheese making and sausage fermentation , respectively.…”

Effects of NaCl, lactose and availability of oxygen on tyramine production by the Enterococcus durans CCDM 53

“…ions play an essential role in the tyrosine decarboxylation pathway. On the contrary, Gardini et al [18,27] noticed higher production of BA by the E. faecalis strain (especially of tyramine a phenylethylamine) under in vitro conditions and also in skim milk or in dry fermented sausages at lower concentrations of NaCl (up to 20 g/L).…”

“…Buňková et al [13] presented very similar conclusions for the L. lactis strains. Gardini et al [27] noticed the maximum production of tyramine of E. faecalis after 5 days of ripening of dry fermented sausages doped with glucose; the effect of additions of glucose on production of tyramine (and also on growth of enterococci) became negligible at the end of ripening. Bover-Cid et al [15] did not mention any significant effect of additions of glucose on production of tyramine by L. curvatus.…”

An agmatine-inducible system for the expression of recombinant proteins in Enterococcus faecalis

“…Some strains of E. faecalis have commercial uses, e.g., as probiotics that promote a beneficial gut environment [42] and in food fermentation processes [1,[43][44][45]. Other strains, however, can pose food safety problems and yet others are a leading cause of opportunistic, hospitalacquired infections (including urinary tract infections, septicaemia, bacteraemia and endocarditis) [2].…”