Probiotic Effects and Metabolic Products of Enterococcus faecalis LD33 with Respiration Capacity.

Yuehua Jiao,Fei Liu,Shuang Zhang,Lanwei Zhang,Nditange Shigwedha,Han Yang

doi:10.3390/foods11040606

Abstract

Respiration metabolism could improve the long-term survival of lactic acid bacteria (LAB); however, its effect on potential probiotic traits of LAB was not reported. The difference made by Enterococcus faecalis LD33 that was cultured under respiration-permissive and fermentation conditions, such as the biomass, metabolites, antimicrobial activity, tolerance to acid and bile salt, adhesion capabilities, and the ability to inhibit the proliferation of cancer cells were studied. Under a respiration-permissive condition, the final biomass of the culture was about twice as compared to that of fermentation condition. When the metabolites were measured, glucose was exhausted within 8 h. Two-folds of acetic acid, triple of both acetoin and diacetyl, and less than half of lactic acid, were accumulated under the respiratory-permissive condition. No discrimination of growth inhibition on Salmonella enterica serovar Typhimurium ATCC 14028 and Shigella sonnei ATCC 25931 was observed when Enterococcus faecalis LD33 was cultured under both conditions; however, under respiration-permissive condition, the strain presented significant antimicrobial activities to Listeria monocytogenes ATCC19111 and Staphylococcus aureus ATCC6538P. Enterococcus faecalis LD33 displayed relatively strong bile salt tolerance and adherence capability but weaker acid tolerance when undergoing respiration metabolism. There was no significant difference in the anti-cancer effect of the viable bacterial cells on both growth modes; however, the supernatant showed a higher inhibition effect on HT-29 cells than the live bacteria, and there was no significant difference between the supernatant and the 5-Fluorouracil (7 μg/mL). Consequently, the Enterococcus faecalis LD33 undergoing respiration metabolism could bring higher biomass, more flavor metabolites, and better antimicrobial and anti-cancer activities. This study extends our knowledge of respiratory metabolism in LAB and its impact on probiotic traits. E. faecalis LD33 qualifies as a suitable strain against foodborne pathogens, cancer therapy, and eventual application in the food and pharmaceutical industries.

Highlights

Lactic acid bacteria (LAB) are a phylogenetically diverse group named for their principal attribute in food fermentations, that is, the production of lactic acid [1]
The growth kinetics of E. faecalis LD33 cultured under both conditions were primarily similar during the first 3 h of growth
The results suggested that inhibition effects of E. faecalis LD33 cultured under different conditions were different

Summary

Introduction

Lactic acid bacteria (LAB) are a phylogenetically diverse group named for their principal attribute in food fermentations, that is, the production of lactic acid [1]. LAB of several species, including Lactococcus lactis, Enterococcus faecalis, Streptococcus and Lactobacillus [10,11,12,13], are genetically equipped for aerobic respiration, providing them with a double metabolic life. They can switch from fermentation to aerobic respiration metabolism if equipped with exogenous heme (and menaquinones for some species, especially Lactobacillus) [14,15,16]. Aerobic respiration positively impacts on the robustness and stress resistance of the strains, which can be beneficial for usage in food fermentation as probiotics and starter cultures [21,22,23]

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