Antimicrobial activity of Enterococcus faecium L50, a strain producing enterocins L50 (L50A and L50B), P and Q, against beer-spoilage lactic acid bacteria in broth, wort (hopped and unhopped), and alcoholic and non-alcoholic lager beers.

摘要

Enterococcus faecium L50 produces enterocin L50 (L50A and L50B) (EntL50, EntL50A and EntL50B), enterocin P (EntP) and enterocin Q (EntQ) and displays a broad antimicrobial spectrum against the most relevant beer-spoilage lactic acid bacteria (LAB) (i.e., Lactobacillus brevis and Pediococcus damnosus), which is mainly due to the production of EntL50 (EntL50A and EntL50B). Bacteriocin assays using in vitro-synthesized EntL50 (EntL50A and EntL50B) showed that both individual peptides possess antimicrobial activity on their own, EntL50A being the most active, but when the two peptides were combined a synergistic effect was observed. The only virulence genes detected in E. faecium L50 were efaAfm (cell wall adhesin) and ccf (sex pheromone), and this strain was susceptible to most clinically relevant antibiotics. E. faecium L50 survived but did not grow nor showed antimicrobial activity in hopped and unhopped wort, and alcoholic (1 and 5% ethanol, v/v) and non-alcoholic (0% ethanol, v/v) commercial lager beers. However, when unhopped wort was supplemented with 50% (v/v) MRS broth, E. faecium L50 grew and exerted antimicrobial activity similarly as in MRS broth. The enterocins produced by this strain were bactericidal (5 log decrease) against P. damnosus and Lb. brevis in a dose- and substrate-dependent manner when challenged in MRS broth, wort (hopped and unhopped), and alcoholic (1 and 5% ethanol, v/v) and non-alcoholic (0% ethanol, v/v) lager beers at 32 degrees C, and no bacterial resistances were detected even after incubation for 6-15 days. The enterocins in wort and lager beer (5% ethanol, v/v) withstood the heat treatments commonly employed in the brewing industry during mashing, wort boiling, fermentation, and pasteurization, and retained most of their antimicrobial activity in lager beer (5% ethanol, v/v) after long-term storage at 8 and 25 degrees C.