Screening and Characterization of Plant-derived Probiotic Lactic Acid Bacteria

To select plant-derived lactic acid bacteria with probiotic characteristics, 1000 strains of lactic acid bacteria (LAB) isolated from traditional fermented vegetables were evaluated for acid resistance, bile salt tolerance, bacteriostasis, in vitro antioxidant capacity, drug susceptibility, hemolytic activity and amino acid decarboxylase activity. Furthermore, the selected strains were identified by 16S rDNA gene sequencing. Totally 82 LAB strains were obtained by culturing in MRS medium at pH 3.0, and out of these, 49 strains were selected by culturing in MRS medium with pH 2.5, all of which were tolerant to 0.3% bile salt. Nineteen of the 49 strains were further selected based on their microscopic morphology and plant sources to evaluate their drug sensitivity, hemolytic activity, bacteriostatic effect, amino acid decarboxylase activity and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity. Results showed that the 19 strains were susceptible to most of the 20 antibiotics tested with four of them being susceptible to all the antibiotics. All of the 19 strains had inhibitory activity against the tested pathogenic bacteria and had no hemolytic activity. As determined using a commercial amino acid decarboxylase activity kit and polymerase chain reaction (PCR), the 19 strains had no potential risk of producing bioamine, and the in vitro antioxidant capacity of five of these strains was higher than 40%, suggesting the 19 strains have probiotic properties. The results of identification showed that the 19 strains contained seven strains of Lactobacillus fermentorum, six strains of Lactobacillus plantarum, and one strain of Bacillus eneniensis, one strain of Lactococcus pentosus, one strain of Limoxibacter, one strain of Lactobacillus pentosus, one strain of Enterococcus faecium and one strain of Lactobacillus brevis.