Probiotics and Antimicrobial Proteins

This study investigated the effects of Lacticaseibacillus paracasei K56 (L. paracasei K56) on body weight, body composition, and glycolipid metabolism in mice with high-fat diet-induced obesity and explored the underlying mechanisms. Male C57BL/6J mice were fed a high-fat diet for 8 weeks to induce obesity; then, the obese mice were gavaged with or without L. paracasei K56 for 10 weeks. The body weight, body composition, fat mass, blood lipid, blood glucose, and hormones of the mice were evaluated. Moreover, the fatty acid synthesis (FAS) and peroxisome proliferator-activated receptor γ (PPAR-γ) expressions in the liver were detected via Western blotting. 16S rRNA gene sequencing was adopted to determine the gut microbiota alterations. The high-fat diet successfully induced obesity, as indicated by the abnormal increase in body weight, visceral fat, fat mass, blood lipids, fasting blood glucose, and insulin-resistance. Moreover, the FAS expression in the liver was significantly increased, whereas the PPAR-γ expression was significantly decreased. The relative abundance of Proteobacteria, Actinobacteria and Patescibacteria was also significantly increased, and that of Verrucomicrobia was significantly decreased. However, these indicators of mice supplemented with L. paracasei K56 were significantly opposite to those of obese mice. The Ruminococcuaceae_UCG-013, Akkermansia, Prevotellaceae_UCG-001, Muribaculum, and Lachnospiraceae_NK4A136 groups were significantly negatively correlated with body weight, blood lipids, and blood glucose-related indicators, whereas Coriobacteriaceae_UCG-002, Enterorhabdus, Raoultibacter, Acinetobacter, Romboutsia, Leuconostoc, and Erysipelatoclostridium were significantly positively correlated with these indicators. L. paracasei K56 might be a promising probiotic strain that could effectively slow down the body weight gain, reduce fat accumulation, alleviate insulin-resistance, and restore pancreatic β-cell function in obese mice by regulating the gut microbiota.

The over-prescription of antibiotics for treatment of infections is primarily to blame for the increase in bacterial resistance. Added to the problem is the slow rate at which novel antibiotics are discovered and the many processes that need to be followed to classify antimicrobials safe for medical use. Xenorhabdus spp. of the family Enterobacteriaceae, mutualistically associated with entomopathogenic nematodes of the genus Steinernema, produce a variety of antibacterial peptides, including bacteriocins, depsipeptides, xenocoumacins and PAX (peptide antimicrobial-Xenorhabdus) peptides, plus additional secondary metabolites with antibacterial and antifungal activity. The secondary metabolites of some strains are active against protozoa and a few have anti-carcinogenic properties. It is thus not surprising that nematodes invaded by a single strain of a Xenorhabdus species are not infected by other microorganisms. In this review, the antimicrobial compounds produced by Xenorhabdus spp. are listed and the gene clusters involved in synthesis of these secondary metabolites are discussed. We also review growth conditions required for increased production of antimicrobial compounds.

In the present study, we aimed to investigate the modulatory effects of a potential probiotic bacterium Lactobacillus gasseri ATCC 33323 on Helicobacter pylori-induced inflammatory response and gene expression in human gastric adenocarcinoma (AGS) cell line. The gastric epithelial cells were coinfected with a collection of H. pylori clinical strains alone or in combination with L. gasseri at a multiplicity of infection (MOI) of 1:100 for each bacterium, and incubated for different time points of 3, 6, and 12 h. IL-8 secretion from coinfected AGS cells after incubation at each time point was measured by an enzyme-linked immunosorbent assay (ELISA). The mRNA expression of IL-8, Bcl-2, β-catenin, integrin α5, and integrin β1 genes was determined by quantitative RT-PCR amplification of total RNA extracted from coinfected epithelial cells. L. gasseri significantly (P < 0.05 and P < 0.01) decreased the production of IL-8 in AGS cells coinfected with H. pylori strains at 6 h post-infection. We also detected that L. gasseri significantly (P < 0.05) down-regulated the gene expression level of IL-8 in H. pylori-stimulated AGS cells after 6 and 12 h of coinfection. Similarly, L. gasseri caused a significant decrease (P < 0.05) in mRNA expression of Bcl-2, β-catenin, integrin α5, and integrin β1 genes in AGS cells at 3 and 6 h after infection with H. pylori strains as compared with non-infected control cells. In conclusion, our results demonstrated that L. gasseri ameliorates H. pylori-induced inflammation and could be developed as a supplementation to the current treatment regimens administrated against H. pylori infection.

Recent years have witnessed an explosion in genome sequencing of probiotic strains for accurate identification and characterization. Regulatory bodies are emphasizing on the need for performing phase I safety studies for probiotics. The main hypothesis of this study was to explore the feasibility of using genome databases for safety screening of strains. In this study, we attempted to develop a framework for the safety assessment of a potential probiotic strain, Lactobacillus helveticus MTCC 5463 based on genome mining for genes associated with antibiotic resistance, production of harmful metabolites, and virulence. The sequencing of MTCC 5463 was performed using GS-FLX Titanium reagents. Genes coding for antibiotic resistance and virulence were identified using Antibiotic Resistance Genes Database and Virulence Factors Database. Results indicated that MTCC 5463 carried antibiotic resistance genes associated with beta-lactam and fluoroquinolone. There is no threat of transfer of these genes to host gut commensals because the genes are not plasmid encoded. The presence of genes for adhesion, biofilm, surface proteins, and stress-related proteins provides robustness to the strain. The presence of hemolysin gene in the genome revealed a theoretical risk of virulence. The results of in silico analysis complemented the in vitro studies and human clinical trials, confirming the safety of the probiotic strain. We propose that the safety assessment of probiotic strains administered live at high doses using a genome-wide screening could be an effective and time-saving tool for identifying prognostic biomarkers of biosafety.

This study aimed to evaluate lactic acid bacteria isolates from Saanen goats’ milk for probiotic attributes, thereby determining their potential as direct-fed microbials for goats. Isolates were identified using API 50CH system, 16S rDNA sequencing and matrix-assisted laser desorption ionization-time of flight mass spectrometry. All 17 isolates obtained were identified as Lactobacillus plantarum except one identified as Pediococcus acidilactici. Four isolates identified as L. plantarum (Accession numbers KJ026587.1, KM207826.1, KC83663.1 and KJ958428.1) by at least two of the techniques used and isolate 17 differently identified by all the methods used were selected as representatives and then screened for probiotic properties. These isolates displayed phenotypic probiotic attributes including tolerance to acid and bile salts, ability to adhere to intestines and possession of antagonistic activities against Proteus vulgaris, Staphylococcus aureus, Salmonella typhimurium, Pseudomonas aeruginosa and Escherichia coli. The lactic acid bacteria isolated from Saanen goats’ milk showed potential to be used as sustainable probiotics in goats’ industry. Successful use of probiotics in animals depends upon availability of appropriate isolates originating from the specific host animal. This study is a positive contribution towards identification of isolates with potential for formulation as direct-fed microbials for South African Saanen goats.

Plant-derived lactic acid bacteria are major fermentation organisms that can grow in medicinal herb extracts enriched with phytochemicals like glycosides, phenolic acids, flavonoids, and tannins. Fermentation with strain-specific Lactobacilli harboring metabolic enzymes can increase the bioactivity and bioavailability of medicinal herbs. Fermentation of extracts of Artemisia princeps and Paeonia lactiflora has been previously found to increase their bioactivities. Therefore, this study explores the possibility of increasing the bioactivity of Mentha arvensis (Mentha) extract against lipopolysaccharide (LPS)-induced RAW 264.7 macrophage cells by fermenting with plant-derived probiotic strains Lactobacillus (Lact.) plantarum SN13T and Pediococcus (Ped.) pentosaceus LP28. As a result, fermentation with SN13T significantly increased the bioactivity of Mentha extract as compared to unfermented or LP28-fermented extracts. This higher bioactivity was associated with the metabolism of rosmarinic acid (RA) and caffeic acid (CA), the major bioactive phenolic acids reported in Mentha, along with the production of the metabolite dihydrocaffeic acid (DHCA). DHCA was found to be a more potent LPS-induced nitric oxide (NO) inhibitor than its precursor phenolic acids. The metabolism of RA to DHCA via CA could be mediated by the enzymes cinnamoyl ester hydrolase and hydroxycinnamate reductases, encoded by the ceh gene and the hcrRABC gene operon, respectively, which were identified in the complete genome sequence of Lact. plantarum SN13T but were absent in Ped. pentosaceus LP28. The genes hcrA, hcrB, and hcrC were significantly and time-dependently overexpressed in Lact. plantarum SN13T when grown in the Mentha extract, suggesting the role of phenolic acid metabolism in enhancing its bioactivity.

The objective of this study was to characterise the antagonistic activity of cellular components of potential probiotic bacteria isolated from the gut of healthy rohu (Labeo rohita), a tropical freshwater fish, against the fish pathogen, Aeromonas hydrophila. Three potential probiotic strains (referred to as R1, R2, and R5) were screened using a well diffusion, and their antagonistic activity against A. hydrophila was determined. Biochemical tests and 16S rRNA gene analysis confirmed that R1, R2, and R5 were Lactobacillus plantarum VSG3, Pseudomonas aeruginosa VSG2, and Bacillus subtilis VSG1, respectively. Four different fractions of cellular components (i.e. the whole-cell product, heat-killed whole-cell product [HKWCP], intracellular product [ICP], and extracellular product) of these selected strains were effective in an in vitro sensitivity test against 6 A. hydrophila strains. Among the cellular components, the ICP of R1, HKWCP of R2, and ICP of R5 exhibited the strongest antagonistic activities, as evidenced by their inhibition zones. The antimicrobial compounds from these selected cellular components were partially purified by thin-layer and high-performance liquid chromatography, and their properties were analysed. The ranges of pH stability of the purified compounds were wide (3.0–10.0), and compounds were thermally stable up to 90 °C. Considering these results, isolated probiotic strains may find potential applications in the prevention and treatment of aquatic aeromonosis.