Genetic diversity of Oenoccoccus oeni isolated from wines treated with phenolic extracts as antimicrobial agents.

Molecular techniques have been applied to study the evolution of wine-associated lactic acid bacteria from red wines produced in the absence and presence of antimicrobial phenolic extracts, eucalyptus leaves and almond skins, and to genetically characterize representative Oenococcus oeni strains. Monitoring microbial populations by PCR-DGGE targeting the rpoB gene revealed that O. oeni was, as expected, the species responsible for malolactic fermentation (MLF). Representative strains from both extract-treated and not-treated wines were isolated and all were identified as O. oeni species, by 16S rRNA sequencing. Typing of isolated O. oeni strains based on the mutation of the rpoB gene suggested a more favorable adaptation of L strains (n = 63) than H strains (n = 3) to MLF. Moreover, PFGE analysis of the isolated O. oeni strains revealed 27 different genetic profiles, which indicates a rich biodiversity of indigenous O. oeni species in the winery. Finally, a higher number of genetic markers were shown in the genome of strains from control wines than strains from wines elaborated with phenolic extracts. These results provide a basis for further investigation of the molecular and evolutionary mechanisms leading to the prevalence of O. oeni in wines treated with polyphenols as inhibitor compounds.

Capability of Lactobacillus plantarum IFPL935 to catabolize flavan-3-ol compounds and complex phenolic extracts.

Lactobacillus plantarum IFPL935 was incubated with individual monomeric flavan-3-ols and dimeric A- and B-type procyanidins to identify new metabolites and to determine the effect of compound structural features on bacterial growth and catabolism. Complex extracts rich in A-type proanthocyanidins and phenolic acids from cranberry were also tested. The results showed that L. plantarum IFPL935 exhibited higher resistance to nongalloylated monomeric flavan-3-ols, A-type dimeric procyanidins, and cranberry extract than to (-)-epicatechin-3-O-gallate and B-type dimeric procyanidins. Despite these findings, the strain was capable of rapidly degrading (-)-epicatechin-3-O-gallate, but not A- or B-type dimeric procyanidins. However, it was able to produce large changes in the phenolic profile of the cranberry extract mainly due to the catabolism of hydroxycinnamic and hydroxybenzoic acids. Of most relevance was the fact that L. plantarum IFPL935 cleaved the heterocyclic ring of monomeric flavan-3-ols, giving rise to 1-(3',4'-dihydroxyphenyl)-3-(2″,4″,6″-trihydroxyphenyl)propan-2-ol, activity exhibited by only a few human intestinal bacteria.

Effect of grape polyphenols on lactic acid bacteria and bifidobacteria growth: resistance and metabolism.

Food polyphenols are able to selectively modify the growth of susceptible micro-organisms. This study describes the effect of a flavan-3-ol enriched grape seed extract (GSE) on the growth of several lactic acid bacteria (LAB) and bifidobacteria and the ability of the resistant strains to metabolize these compounds. Streptococcus thermophilus, Lactobacillus fermentum, Lactobacillus acidophilus and Lactobacillus vaginalis strains showed a remarkable sensitivity to the phenolic extracts assayed, including a GSE fraction consisting mainly in (+)-catechin and (-)-epicatechin (GSE-M). On the other hand, Lactobacillus plantarum, Lactobacillus casei, and Lactobacillus bulgaricus strains reached maximal growth with the GSE fractions, including a rich-oligomeric (GSE-O) fraction. Within bifidobacteria, Bifidobacterium lactis BB12 showed the highest sensitivity to the phenolic extracts assayed, whereas Bifidobacterium breve 26M2 and Bifidobacterium bifidum HDD541 reached maximum growth in presence of GSE-O and GSE-M fractions. Metabolism of flavan-3-ols by LAB and bifidobacteria resistant strains was investigated in vitro. The results revealed that only L. plantarum IFPL935 was able to metabolize the polyphenols studied by means of galloyl-esterase, decarboxylase and benzyl alcohol dehydrogenase activities that led to the formation of gallic acid, pyrogallol and catechol, respectively. An unknown metabolite that does not exhibit a phenolic-acid-type structure was also detected, which suggests a new enzyme activity in L. plantarum IFPL935 able to degrade flavan-3-ol monomers.

Inhibition of uropathogens by lactic acid bacteria isolated from dairy foods and cow's intestine in western Nigeria.

A total of 96 lactic acid bacteria (LAB) were isolated from African indigenous fermented products and cow's intestines to study their inhibitory capability against multi-drug-resistant uropathogens. Escherichia coli accounted for approximately 45% of isolated uropathogens, followed by Staphylococcus spp. (20%). The Gram negative uropathogens were highly resistant to quinolones, co-trimoxazole, teicoplanin and some beta-lactams, while the Staphylococcus spp. showed high resistance to aminoglycosides, beta-lactams and macrolides. Twenty-four LAB isolates were selected based on their antimicrobial activity against two uropathogenic Staphylococcus aureus strains and bacteriocin production. LAB strains showing antimicrobial activity were grouped into smaller groups through amplified ribosomal DNA restriction analysis (ARDRA). Representative strains were identified as Weissella spp., Enterococcus faecium, Lactococcus lactis and Lactobacillus brevis through sequencing of 16S rDNA. The Weissella spp. and L. brevis strains demonstrated remarkable inhibitory activity against seven strains of Gram negative uropathogens. Two strains of L. lactis produced a bacteriocin-like inhibitory substance active against Lactobacillus sakei. In this study, an unusual high rate of co-trimoxazole, quinolones and macrolides resistance among uropathogens from south west Nigeria was discovered. Based on their sensitivity to Weissella spp., there is a potential for using these LAB as a natural approach for the protection against the uropathogens assayed.

Lactobacillus acidophilus La-5 increases lactacin B production when it senses live target bacteria.

Lactobacillus acidophilus La-5 is a probiotic strain used in dairy products. Production of bacteriocin by L. acidophilus La-5 was achieved when it was grown in co-cultures with the yogurt starter species Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. However, bacteriocin induction was not observed when heat-killed cells were used as inducers. This study demonstrates that L. acidophilus La-5 produces lactacin B and that the bacteriocin expression is controlled by an auto-induction mechanism involving the secreted peptide IP_1800. The transcript level of the lactacin B gene cluster expression was investigated in co-cultures between L. acidophilus La-5 and S. thermophilus STY-31 and a remarkable increase of the bacteriocin structural gene (lbaB) transcription was observed. However, lbaB was transcribed constitutively in uninduced L. acidophilus La-5 cells, but the levels of the secreted bacteriocin were not enough to be detected by the agar diffusion assay. A new method for bacteriocin detection was formulated based on the monitoring on real time of Lactobacillus sakei subsp. sakei growth in presence of the supernatant and the cell wall extracts of pure and induced L. acidophilus La-5. These results showed that part of lactacin B secreted remains adhered to cell envelope.