Nisin抗性嗜热链球菌的筛选

采用两倍稀释法在脱脂乳培养基和乳清培养基中测定了nisin对嗜热链球菌9的最小抑菌浓度(MIC)。在脱脂乳培养基中逐渐增加nisin的浓度，驯化嗜热链球菌9，直到其抗性达到300IU／ml。经生产性能鉴定和遗传性状实验，获得两株适宜做酸奶发酵剂的nisin抗性嗜热链球菌9.31和9．4。     

Structural characterization of the exopolysaccharide produced by Streptococcus thermophilus 05-34 and its in situ application in yogurt

An exopolysaccharide (EPS) producing strain was isolated from Tibetan kefir grains in China, which was identified by 16S rDNA tests and designated as Streptococcus thermophilus 05-34. The high-performance liquid chromatography analysis showed that it was composed of galactose and glucose in a molar ratio of 1.0:0.8 with a molecular mass of 2.5 × 10(4) Da. EPS was further revealed to have α-d-glucose, α-d-galactose, β-d-glucose, and β-d-galactose by Fourier transform infrared spectroscopy combined with 1D (1) H nuclear magnetic resonance spectroscopy. The length of EPS ranged from 10 to 100 nm and the maximal height of lumps was 2.5 nm through atomic force micrograph analysis. Furthermore, yogurt fermented with EPS-producing S. thermophilus 05-34 exhibited lower susceptibility to whey separation, higher viscosity, and sensory scores than those made with non-EPS-producing strain in yogurt production. These results suggested that EPS-producing Streptococcus thermophilus 05-34 provided a potential application in the fermented dairy industry.     

嗜热链球菌固态培养的研究

该文研究了在豆渣粉中添加不同营养基质、生长促进剂、缓冲剂对嗜热链球菌ST-1001(StreptococcusthermophilusST-1001)生长特性的影响。结果表明,固态培养基的最佳组合为豆渣粉13%,脱脂奶粉10%,CaCO31%,西红柿汁10%,磷酸氢二钠-磷酸二氢钠缓冲液(pH6.8)66%。     

乳链菌肽发酵条件的研究

利用分批培养，对乳酸链球菌ＳＭ５２６产生乳链菌肽（ｎｉｓｉｎ）的代谢调控及发酵条件进行研究，代谢动力学分析表明，ｎｉｓｉｎ在ＳＭ５２６指数生长期产生，到指数生长后期达到高峰，进入稳定期ｎｉｓｉｎ逐渐停止产生，表现出一种初级代谢动力学特征。ｎｉｓｉｎ的生物合成主要受碳源、氮源和磷源的调控，试验了各种不同的碳源，发现以二糖为碳源要比以单糖为碳源效果好；在基本发酵培养基中提高碳源（蔗糖）浓度，可使菌体得率和ｎｉｓｉｎ产率同时得以提高，其中以４％（Ｗ／Ｖ）蔗糖浓度较理想。此处碳源的调控主要是通过提高菌体生物量以达到提高ｎｉｓｉｎ效价。磷源则对ｎｉｓｉｎ的生物合成起极大的促进作用，试验了不同的磷源，其中以ＫＨ２ＰＯ４效果最好，在基本发酵培养基中提高ＫＨ２ＰＯ４浓度，可使得在菌体生物量基本不变的情况下，ｎｉｓｉｎ效价大幅度提高。     

保加利亚乳杆菌和嗜热链球菌的产香特性研究

通过分析凝固型酸奶后发酵过程中香气物质乙醛和丁二酮的含量,研究了保加利亚乳杆菌(LBZ)和嗜热链球菌(STZ)单一及混合菌种(LSZ、GST)后发酵过程中产香特性。结果表明香气物质丁二酮:LBZ菌种基本上保持在0.09mg/L左右;STZ菌种在34h和154h分别有个峰值,但波动较大;LSZ菌种基本较为稳定,且保持在0.23~0.31mg/L之间;GST菌种在0.73~0.92mg/L之间,是LBZ菌种的10倍左右,但总的来说呈下降趋势。香气物质乙醛:LBZ在10h为高11.68mg/L;STZ出现了两个峰值(分别34h和154h);GST在34h有个峰值,其后逐渐下降;LSZ在154h有个峰值,在16.26~19.54mg/L之间波动,总的来说较稳定,因此LSZ为最佳凝固型酸奶菌种。     

Short communication: Conservation of Streptococcus uberis adhesion molecule and the sua gene in strains of Streptococcus uberis isolated from geographically diverse areas

The objective was to identify and sequence the sua gene (GenBank no. DQ232760; http://www.ncbi.nlm.nih.gov/genbank/) and detect Streptococcus uberis adhesion molecule (SUAM) expression by Western blot using serum from naturally S. uberis-infected cows in strains of S. uberis isolated in milk from cows with mastitis from geographically diverse areas of the world. All strains evaluated yielded a 4.4-kb sua-containing PCR fragment that was subsequently sequenced. Deduced SUAM AA sequences from those S. uberis strains evaluated shared >97% identity. The pepSUAM sequence located at the N terminus of SUAM was >99% identical among strains of S. uberis. Streptococcus uberis adhesion molecule expression was detected in all strains of S. uberis tested. These results suggest that sua is ubiquitous among strains of S. uberis isolated from diverse geographic locations and that SUAM is immunogenic.     

Streptococcus dysgalactiae isolates at calving and lactation performance within the same lactation

The objective of the study was to investigate the association between early lactation Streptococcus dysgalactiae isolates and milk yield, somatic cell count (SCC), clinical mastitis, and culling in the same lactation. The 178 commercial dairy herds were randomly placed into 3 penicillin- or penicillin-dihydrostreptomycin-based dry-cow treatments and 3 different postmilking teat disinfection groups—negative control, iodine, or external teat sealant. All cows were sampled in early lactation, and Strep. dysgalactiae-positive and culture-negative cows were followed throughout the remainder of the lactation. Mixed models, including repeated measurements, with test-day observation as dependent variable, were used to compare milk yield, SCC, and available milk quality variables throughout the remaining lactation. Survival analyses, using a positive frailty model to account for any herd random effects, were used to estimate the hazard ratio for clinical mastitis and culling. Streptococcus dysgalactiae-positive cows had a significantly higher SCC throughout the lactation compared to culture-negative cows. For primiparous or multiparous cows, respectively, the differences in the geometric mean SCC between Strep. dysgalactiae-positive and culture-negative cows was 197,000 or 280,000 cells/mL at the beginning of the lactation, 24,000 or 46,000 cells/mL in mid lactation, and 39,000 or 111,000 cells/mL at the end of the lactation. Streptococcus dysgalactiae-positive primiparous or multiparous cows produced 334 or 246 kg less milk, respectively, during a 305-d lactation compared with culture-negative cows. Compared with culture-negative cows, the hazard ratios for clinical mastitis in Strep. dysgalactiae-positive cows were 2.3 (1.9 to 2.9) and 1.6 (1.3 to 2.0) for culling. For cows with both Strep. dysgalactiae and Staphylococcus aureus isolates, the hazard ratio for culling significantly increased to 2.5 (1.9 to 3.2).     

芦荟发酵乳饮料的研制

以芦荟汁调配适量的乳粉为发酵原液,经乳酸菌发酵制成具有芦荟营养和保健功能的乳饮料。通过正交试验得到发酵乳饮料的最佳工艺条件,即发酵原液芦荟汁浓度20%、蔗糖添加量8%、发酵剂混合菌种保加利亚乳杆菌和嗜热链球菌的比例为1:1。     

Production of hyaluronic acid from Streptococcus zooepidemicus MTCC 3523 and its wound healing activity

Exopolysaccharide produced and purified from Streptococcus zooepidemicus MTCC 3523 was identified as hyaluronic acid (HA) based on IR and NMR spectroscopy while its Mw was found to be 5.38 × 10(5)Da. HA produced passed bacterial endotoxin test and showed significant wound healing activity in Wistar rats on 12th and 16th day.