Isolation, Identifition And Characterization Of Streptococcus Thermophilus

Streptococcus thermophilus is a kind of the important probiotics for the human, which have been utilized widely for a long time in food industry, pharmaceuticals and biological. The paper studied that the S. thermophilus form raw milk, including separation and purification, genetic diversity, biological properties and fermentation performance among the cultured strains. The main results were as follow:1.69 strains of S. thermophilus were isolated and identified from raw milk in Inner Mongolia, Xining, Xinjiang, Xi’an, Wuhan and from commercial products in market via streaking sugar fermentation assay, traditional phenotype identification and modern molecular biology technology specific PCR identification, determine the strains isolated from for S. thermophilus cultured.2. Through random amplified polymorphic DNA (RAPD) analysis using 33 random primers, and simple sequence repeats (SSRs)analysis using 5 specific primers, the similarity coefficient matrix and clustering analysis were achieved according to statistical analysis of fingerprinting.69 strains of S. thermophilus cultured are similarity in clustering analysis, are divided into two groups, each groups is divided into two sub-groups. STWY series and STNY series on the same sub-group, For STNT series analysis also similar, will NO.1 and NO.2 in a points together, other strains in another points together, and points belong to two groups. Another STXY series also have in two classifications have common parts of fingerprinting. The clustering results of the two technologies are subtle differences, SS series clustering with some STNN in a sub-group in the RAPD analysis, but it was divided into a separate subgroup in the SSR analysis. The STXN is only one group in the RAPD analysis, and divided in two groups labeled from 2 to 6 in a group, the other in another group in the SSR analysis. Tree graph shows that this related with grouping and milk source region and milk source quality.3. Biological properties of the results of the study indicate that:69 strains of S. thermophilus in glucose producing acid and gas, catalase, litmus milk, urease activity, proteolytic ability with the detection of experimental results consistency. The results showed glucose production acid and no gas, catalase negative, litmus milk is positive, urease active negative, proteolytic ability positive;and then there were 42 strains of 69 strains contains plasmid.4. Fermentation performance results said:by fermentation time, whey exhalation quantity, fermentation acidity, fermentation viscosity, living bacterium number, exocellular polysaccharide contents of this a few index comparison strains of fermentation performance, excellent strains elected from Inner Mongolia, commercial strains and Xi’an respectively. The result clearly showed that STNN7, STXY15 and SS2 were better than other strains.