Helicobacter pylori is an infectious agent commonly associated with gastrointestinal diseases. The use of probiotics to treat this infection has been documented, however, their potential antimicrobial metabolites have not yet been investigated. In the present study, the effect of reuterin produced by Lactobacillus reuteri on H. pylori growth and virulence gene expression was evaluated. It was observed that reuterin caused significant (P < 0.05) H. pylori growth inhibition at concentrations from 0.08 to 20.48 mM, with minimal inhibitory concentrations (MICs) of 20.48 mM for H. pylori ATCC700824 and 10.24 mM for H. pylori ATCC43504. In a reuterin bacterial killing assay, it was observed that half of the MIC value for H. pylori (ATCC700824) significantly (P < 0.01) reduced colony numbers from 5.65 ± 0.35 to 3.78 ± 0.35 Log CFU/mL after 12 h of treatment and then increased them to 5.25 ± 0.23 Log CFU/mL at 24 h; at its MIC value (20.48 mM), reuterin abrogated (P < 0.01) H. pylori (ATCC700824) growth after 20 h of culture. In addition, reuterin significantly (P < 0.01) reduced H. pylori (ATCC 43504) colony numbers from 5.65 ± 0.35 to 4.1 ± 0.12 Log10 CFU/mL from 12 to 24 h of treatment and abrogated its growth at its MIC value (10.24 mM), after 20 h of treatment. Reuterin did not alter normal human gastric Hs738.St/Int cell viability at the concentrations tested for H. pylori strains. Furthermore, 10 μM reuterin was shown to significantly (P < 0.01) reduce mRNA relative expression levels of H. pylori virulence genes vacA and flaA at 3 h post-treatment, whose effect was higher at 6 h post-treatment, as measured by RT-qPCR. The observed direct antimicrobial effect and the downregulation of expression of virulence genes on H. pylori by reuterin may contribute to the understanding of the mechanisms of action of probiotics against H. pylori.
Lactic acid bacteria (LAB) are well known for their beneficial effects on human health in the intestine and immune system; however, there are few studies on the impact they can generate in oral health. The aim of this study was to test and compare in vitro antimicrobial activity of L. reuteri on pathogenic bacteria involved in the formation of dental caries: S. mutans, S. gordonii, and periodontal disease: A. naeslundii and T. forsythia. Also, we determined the growth kinetics of each bacterium involved in this study. Before determining the antimicrobial action of L. reuteri on cariogenic bacteria and periodontal disease, the behavior and cell development time of each pathogenic bacterium were studied. Once the conditions for good cell growth of each of selected pathogens were established according to their metabolic requirements, maximum exponential growth was determined, this being the reference point for analyzing the development or inhibition by LAB using the Kirby Bauer method. Chlorhexidine 0.12 % was positive control. L. reuteri was shown to have an inhibitory effect against S. mutans, followed by T. forsythia and S. gordonii, and a less significant effect against A. naeslundii. Regarding the effect shown by L. reuteri on the two major pathogens, we consider its potential use as a possible functional food in the prevention or treatment of oral diseases.
a b s t r a c t 3-Hydroxy-␥-decalactone is the precursor of dec-2 and dec-3-en-4-olides which are valuable aroma compounds not yet produced. To promote the accumulation of this lactone, the yeast Yarrowia lipolytica was placed in different environmental conditions aiming at altering -oxidation fluxes. The concentration of substrate, pH, aeration and dissolved oxygen level were modified. We observed an important accumulation at low aeration (0.40 molar yields) and, to a lesser extent, at lower pH (0.15). As oxygen played a key-role, we evaluated its effect at fixed dissolved oxygen and at the pH which was the most favourable to the biotransformation (pH 4.5). At 5% and 30% dissolved oxygen, yields reached 0.50. -Oxidation fluxes are very dependent on the presence of oxygen and conditions of accumulation of 3-hydroxy-␥-decalactone with very high yields were identified. These results are an important step in the production of the two decenolides. Moreover, they show the high dependence of -oxidation fluxes on environmental conditions and relate these conditions to the accumulation of intermediates, results that are of interest to all the processes using yeast on lipids or alkanes.
Aims: To detect rate‐limiting steps in the production of lactones by studying the combined effect of pH and aeration on their accumulation. Methods and Results: A Doehlert experimental design was chosen to evaluate the accumulation of four lactones in the pH (3·5–7·3) and KLa (4·1 h‐1 to 26 h‐1) experimental domain. The accumulation of γ‐decalactone was higher at pH around 5 and increased at low aeration reaching 496 mg l–1 at pH 6·35 and KLa 4·5 h–1. The specific accumulation increased at low aeration. The 3‐hydroxy‐γ‐decalactone accumulation was higher at low pH and high aeration conditions: 660 mg l–1 at pH 4·4 and 26 h–1. For dec‐2‐en‐4‐olide and dec‐3‐en‐4‐olide, lower amounts were reached (104 mg l–1 and 66 mg l–1, respectively). Conclusions: Although the accumulation of the four lactones should be related to catalytic steps requiring oxygen, the accumulation of γ‐decalactone was higher in low aeration conditions whereas the one of 3‐hydroxy‐γ‐decalactone was promoted for high aeration. Decenolides accumulate independently of pH or aeration. Significance and Impact of the Study: This study gives new insights into the catabolism of lipids, such as the role of co‐factor regulation and the fact that the 3‐hydroxylactone dehydration step is insensitive to pH or aeration.
beta-Oxidation is a cyclic pathway involved in the degradation of lipids. In yeast, it occurs in peroxisomes and the first step is catalyzed by an acyl-CoA oxidase (Aoxp). The yeast Yarrowia lipolytica possesses several genes (POX) coding for Aoxps. This study is based on the factorial analysis of results obtained with the many POX derivative strains that have been constructed previously. The effect of interactions between Aoxps on the acyl-CoA oxidase (Aox) activity was important even at the second order. We then investigated the effect of Aox activity on growth and lactone production. Aox activity was correlated with acidification of the medium by cells and with cellular growth but not with lactone production, although Aox activity on short chains was inversely correlated with lactone accumulation. Due to the poor correlation between Aox activity and lactone production, the modeling of this parameter gave no satisfactory results but growth depending on Aox activity was modeled.
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