Jorge Sánchez

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

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.

Bacteriocin production by lactic acid bacteria isolated from fish, seafood and fish products

Analysis of 1245 lactic acid bacteria (LAB) isolates obtained from fish, seafood and fish products showed that 197 exerted direct antimicrobial activity against 20 spoilage and food-borne pathogenic microorganisms. Further evaluation of 64 LAB isolates selected on the basis of their direct antimicrobial activity revealed 25 secreted bacteriocins. Biochemical characterization, PCR analysis and/or DNA sequencing of the superoxide dismutase gene (sodA) and/or 16S rRNA gene (16S rDNA), and/or SDS-PAGE analyses of the 64 selected isolates allowed the identification of 24 of them as Enterococcus faecium, 22 as Enterococcus faecalis, seven as Pediococcus pentosaceus, five as Weissella cibaria, three as Lactobacillus sakei subsp. carnosus, one as L. sakei subsp. sakei, one as Lactobacillus curvatus subsp. curvatus and one as Leuconostoc mesenteroides subsp. cremoris. PCR analyses for the detection of genes encoding previously described bacteriocins performed on the 25 bacteriocinogenic strains showed that 19 strains (18 enterococci and 1 lactobacilli) amplified, at least, one of the tested genes, and up to four and two target genes were simultaneously detected in a single enterococcal and lactobacilli strain, respectively. Moreover, in vitro safety evaluation of E. faecium strains was carried out by detection of potential virulence factors, analysis of hemolysin, gelatinase and protease production, and susceptibility testing to antibiotics of relevance for human and veterinary industry. The results reported herein demonstrate the suitability of fish, seafood and fish products for the isolation of LAB (mainly enterococci), including (multi)bacteriocinogenic strains, encoding bacteriocins active against Listeria monocytogenes and other food-borne pathogens of interest for the food industry.

Draft genome sequence of the bacteriocinogenic strain Enterococcus faecalis DBH18, isolated from mallard ducks (Anas platyrhynchos)

ABSTRACT Here, we report the draft genome sequence of Enterococcus faecalis DBH18, a bacteriocinogenic lactic acid bacterium (LAB) isolated from mallard ducks (Anas platyrhynchos). The assembly contains 2,836,724 bp, with a G+C content of 37.6%. The genome is predicted to contain 2,654 coding DNA sequences (CDSs) and 50 RNAs.