Three hundred and forty-seven strains of Lactobacillus plantarum previously isolated from Chinese and Mongolian traditionally fermented foods were preliminary evaluated for their probiotic properties, including their resistance to simulated gastrointestinal fluids and bile salts, and their antibacterial activity. Fifteen strains showed broad-spectrum inhibitory activity against five indicator enteric pathogens. Seven out of these 15 strains showed high tolerance to both simulated gastrointestinal fluids and bile salts. Further preliminary experiments (by pH adjustment, treatment with catalase, pepsin, and trypsin or heat) were performed to characterize the nature of antibacterial materials in the cell-free supernatants. The antibacterial property was suppressed by the adjustment to pH 6.0 except for strain IMAU80087, suggesting that such activity was pH-dependent for most of the characterized strains. The antibacterial activity of IMAU70104 and IMAU80184 was largely hydrogen peroxide-based, whereas the antibacterial property of IMAU70010 and IMAU80171 was possibly peptide/protein in nature. The antibacterial materials of IMAU80076 and IMAU70088 were partially sensitive to pepsin treatment. Finally, the antibacterial material in the cell-free supernatant of IMAU80087 was strongly resistant to pH change and most treatments used in this study, which makes it particularly desirable for application in neutral food. The current study has identified novel L. plantarum strains and valuable microbial resources, which are of good potential to be applied in controlling the growth of pathogenic food bacteria.
Based upon morphological, physiological and biochemical analysis, 33 strains of lactic acid bacteria were isolated and identified from 11 samples of traditional natural fermented goat milk collected from different individual households in Haixi region of Qinghai. The counts of lactic acid bacteria were 2.5 x 108ෂ3.0 x 10 9 CFU/mL, while yeasts were 2.6 x 10 6 ෂ1.6 x 10 8 CFU/mL. Strains were identified as follows: 7 strains of Lactobacillus delbrueckii subsp. lactis, 4 strains of Lactobacillus delbrueckii subsp. bulgaricus, 3 strains of Lactobacillus acidophilus, 1 strain of Lactobacillus coryniformis subsp. coryniformis, 12 strains of Streptococcus thermophilus, 1 strain of Leuconostoc mesenteroides subsp.mesenteroides, 3 strains of Pediococcus acidilactici, and 2 strains of Aerococcus urinaeequi comb. nov.
Bile salt hydrolase (BSH) is one of the genes relevant to bile tolerance. Biochemical assay showed that Lactobacillus casei Zhang was able to deconjugate sodium taurocholate during growth. To explore the possible relationship between BSH activity and bile tolerant ability, we cloned and determined full-length DNA sequence of the BSH gene in L. casei Zhang, and monitored its expression pattern under the stress of bile salts. The DNA sequence consists of 1181 nucleotides; the putative protein includes 338 amino acids. The sequences alignment and homology studies illustrated a great diversity between species. Further real-time PCR analysis revealed that expression of the BSH gene was up-regulated when there presented bile salts in the growth medium.
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