Screening and Characterization of Lactic Acid Bacteria with Broad-Spectrum Antimicrobial Activity from Tibetan Qula, a Yak Milk Cheese

Abstract BackgroundLactic acid bacteria with natural, effective antibacterial activity, safe and reliable characteristic, gradually become one of the key technologies in food fermentation applications, food preservation and other fields. In this study, 112 presumptive lactic acid bacteria isolated from Tibetan Qula, a fermented yak cheese popular in the Tibetan plateau, were screened for potential probiotic microorganism with antimicrobial activity.Results12 lactic acid bacteria were found to have antibacterial activity, and strain QZ50 in particular showed broad-spectrum inhibition against pathogenic bacteria, which retained its antibacterial activity after sequential removal of acids and hydrogen peroxide, indicating the production of a broad-spectrum bacteriocin that could inhibite Micrococcus luteus ATCC 28001, Staphylococcus aureus ATCC 26003, Bacillus subtilis ATCC 63501, Escherichia coli ATCC 30105, Pseudomonas aeruginosa ATCC 10104, and Salmonella enterica ATCC 50094. Strain QZ50 was identified as Lactobacillus plantarum based on physicochemical characteristics and 16S rDNA sequencing. And the optimum production conditions were evaluated to obtain the highest yield of plantaricin QZ50. The optimum medium, temperature, initial pH, and inoculum amount for plantaricin QZ50 production were Man, Rogosa, and Sharpe (MRS), 30°C, 6.5, and 3%, respectively. In addition, different C source, N source and stimulating factors in medium show significant effects on plantaricin QZ50 production (P ＜ 0.05). The optimum C and N source were respectively glucose and yeast extract, and 2% Tween 80 contributed highest production of plantaricin QZ50. Plantaricin QZ50 exhibited strong heat stability and remained activity at pH 2.0–8.0. In addition, plantaricin QZ50 was inactivated by pepsin, proteinase K, trypsin, papain, and chymotrypsin.ConclusionsSome strains of Lactobacillus isolated from the Qula in the Tibetan plateau have good antibacterial activity which could be considered as potential probiotic. The strain of Lactobacillus plantarum QZ50, with a broad-spectrum, stable, safe, and natural antibiotic, has potential applications as a food biopreservative.