Antibacterial activity of selenium-enriched lactic acid bacteria against common food-borne pathogens in vitro

Abstract

Selenium (Se) is an essential trace element for human health and animal nutrition. The aim of this study was to evaluate the inhibitory activities of Se-enriched lactic acid bacteria (LAB), Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus, against pathogenic Salmonella typhimurium, Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes in vitro. The results indicated that the accumulation amount of Se by Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus reached 12.05 ± 0.43 µg/mL and 11.56 ± 0.25 µg/mL, respectively, accompanied by the relative maximum living cells when sodium selenite was 80 µg/mL. Oxford cup double plate assay showed that bacterial culture solution and cell-free culture supernatant (CFCS) from Se-enriched LAB exerted stronger antibacterial activity than those from the non-Se strains. The growth of pathogenic bacterial culture with CFCS at any growth stages was worse than that without CFCS; moreover, the inhibiting effect of CFCS of Se-enriched LAB was more significant than that of non-Se strains. Results from a scanning electron microscope equipped with energy dispersion X-ray spectrometry showed that elemental Se nanoparticles, which characteristically energy peak around 1.42 keV, were deposited on the cell surfaces of Lactobacillus delbrueckii ssp. bulgaricus. In addition, CFCS of Se-enriched LAB induced more serious cell structure damage of pathogenic bacteria than did non-Se LAB.

Serine-enriched minimal medium enhances conversion of selenium into selenocysteine by Streptococcus thermophilus

“…Accumulation amount of Se by Strep. thermophilus has been studied previously (Yang et al, 2018), and it is close (11.56 ± 0.25 mg/L) to the value found in this research for FC fermentation (10.75 ± 0.51 mg/L).…”

“…The selenite concentration calculated as the inhibition point was 140 mg/L. Similar data were reported by Yang et al (2018) for Strep. thermophilus, who found 80 mg/L to be the optimal selenite concentration to reach a maximum cell growth; besides, a decrease in cell amount was observed at 140 to 160 mg/L of sodium selenite.…”

Antibacterial Activity of Bifidobacterium breve Against Clostridioides difficile

“…The cell pellets and cell-free culture supernatant (CFCS) of YH68 were collected by centrifugation at 12,000 r/min for 10 min, and the cell pellets were then resuspended in sterile saline. The antibacterial activities of the cell pellets and CFCS of YH68 against CD were tested by the Oxford cup method as reported previously (Yang et al, 2018). Briefly, 10 mL of molten solid BHI medium was poured into plates and allowed to solidify as the bottom layer, and sterilized Oxford cups were then placed on the surface of the medium.…”

Characterization of antimicrobial activity of three Lactobacillus plantarum strains isolated from Chinese traditional dairy food

“…The antimicrobial activity was evaluated by well diffusion method (Bonev, Hooper, & Parisot, 2008;Yang et al, 2017). The cultures of L. plantarum strains were grown in MRS broth (pH 6.5) for 24 hr to measure the antimicrobial properties of extracellular metabolites of L. plantarum strains.…”