The assessment of probiotic properties of indigenous Lactobacillus strains with GABA-producing potential

Abstract

Lactobacillus species are used in many fermented foods, they contribute to the texture, flavor and shelf life of the fermented foods. Many Lactobacillus species produce Gamma-aminobutyric acid (GABA), a non-protein amino acid which act as a chief inhibitory neurotransmitter in brain that have a direct effect on the stress management. In the current study, a total of 20 Lactobacillus were isolated from indigenous food such as, raw milk, yogurt and vegetable pickles collected from various cities of Pakistan. Eight isolates were selected on the basis of tolerance to GIT like stress conditions including pH 2.0, 0.3 and 0.4 percent bile salts and phenol respectively. They were identified as Lactobacillus on the basis of 16S rDNA sequencing. Among them, 2 isolates; 2 and 12 were identified as L. rhamnosus, 4 isolates; 7b, 18, 19b and 20 as L. fermentum, isolate 7a as L. salivarious and isolate 17 as L. delbrueckii. These species potentially accumulated GABA in MRS medium supplemented with 1% MSG, which was indicated as per the preliminary findings on the basis of thin layer chromatography. The antibacterial activity of these strains was obtained against different gram positive and gram negative pathogens, including gut and food borne pathogens including Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumonii, Salmonella enterica and Listeria monocytogenes. The protein nature of antimicrobial substance was evaluated by using proteinase K and heat treatment, which indicates protein nature of the antibacterial substance. All of the eight selected isolates have ability to produce exopolysccharides. The strains 7a, 18, 19b and 20 resulted in maximum auto-aggregation and co-aggregation abilities, while strain 18 showed antioxidant potential of 78 percent. The maximum cholesterol assimilation of 58 percent was achieved by isolate 7a. The safety profile was confirmed by antibiotic susceptibility assay. They showed good sensitivity towards Tetracycline, Erythromycin, Ampicillin, Pencillin-G, Ciprofloxacin, Chloramphenicol and Amoxycillin/clavulanic acid. The strains are anti-hemolytic and anti-DNAse. The in-vitro evaluation during the study revealed that four potential probiotic strains including L. salivarious 7a and L. fermentum 18, 19b and 20 demonstrate good technological potential as agents to lower cholesterol levels, act as antioxidants, biopreservatives with presumable GABA producing potential. These strains may further be evaluated in animal models to confirm their probiotic potential and beneficial features.