乳制品中嗜热链球菌的快速检测

利用血清学方法检测乳制品中的嗜热链球菌。首先，通过动物免疫方法制备了小鼠及家兔抗嗜热链球菌(Streptococcus thermophilus)的免疫血清。然后，用此血清经酶联免疫吸附测定法(ELISA法)对乳制品中嗜热链球菌进行检测。用间接ELISA法及双夹心ELISA法对乳制品中的嗜热链球菌进行检测。结果表明，两种方法均可测出乳制品中嗜热链球菌，其最低检测量可达10^7mE^-1。这一结果为乳制品中嗜热链球菌的血清学快速检测提供了参考。     

嗜热链球菌产SOD的培养条件

以嗜热链球菌为实验菌株,利用摇床液体发酵,采用完全随机化设计研究不同培养温度、不同培养时间和植物(枸杞和刺五加)提取液不同添加量对嗜热链球菌产超氧化物歧化酶(SOD)的影响,并用方差分析和回归分析对不同处理的实验结果进行比较。方差分析表明：不同培养温度对嗜热链球菌产SOD的影响差异极显著(P＜0.01),当培养温度达到41℃时,SOD平均产量达到最高(901.667U/g);不同培养时间对嗜热链球菌产SOD的影响差异极显著(P＜0.01),当培养时间为48h时,SOD平均产量达到最高(932.6667U/g);不同植物提取液添加量对嗜热链球菌产SOD的影响差异极显著(P＜0.01),植物提取液添加量为8%时,SOD平均产量达到最高(1347.0000U/g)。综合考虑降低成本,提高效益等因素,确定最优方案为：培养温度41℃、培养时间24h、植物提取液添加量为8%,此时获得较高的SOD产量,且投入与产出比较高。回归分析表明：SOD产量与培养温度之间回归关系不显著(P＞0.05);SOD产量与植物提取液添加量之间存在极显著的线性回归关系：Y=865.033+52.383X(P＜0.01);SOD产量与培养时间之间存在极显著的线性回归关系：Y=238.757+17.346X(P＜0.01)。     

嗜热链球菌蔬菜汁培养基及培养条件的优化

研究了蔬菜汁培养基的组成(蔬菜汁、碳源、氮源)和培养条件(温度、接种量、起始pH、培养时间等)对嗜热链球菌生长的影响,优化了蔬菜汁培养基的组成。结果表明:用于嗜热链球菌生长的最优的蔬菜汁组分为番茄汁10%、豆浆2%、乳糖2%,在接种量为5%,起始pH为7.0,生长温度37℃的条件下,培养时间30h,嗜热链球菌的细胞密度达到3.85×1010CFU/mL。      

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。     

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%。     

嗜热链球菌937增殖培养基及发酵条件的优化

该研究以化学限定培养基为基础,通过单因素实验、响应面实验和正交优化实验对嗜热链球菌937的培养基、培养条件进行优化。通过实验确定嗜热链球菌937最适培养基：乳糖20 g/L,酶解脱脂乳16.60%,大豆低聚肽18.88 g/L,乳清蛋白粉1.69%,10 mmol/L组氨酸、10 mmol/L异亮氨酸、5 mmol/L酪氨酸、1 mmol/L半胱氨酸和1 mmol/L谷氨酸、2 mg/L烟酸、0.5 g/L抗坏血酸、40 mg/L氯化镁、2 mg/L泛酸钙、4 mg/L盐酸硫胺素、0.4 g/L氯化钙。初始pH值6.5,接种量2%,39 ℃发酵,嗜热链球菌937活菌数高达1.75×109 CFU/mL。由此可见,该研究实现嗜热链球菌937低成本、高效率的培养技术,为高活菌数的嗜热链球菌商业产品的开发生产奠定基础。     

保加利亚乳杆菌和嗜热链球菌冻干工艺条件的研究

试验对保加利亚乳杆菌和嗜热链球菌的冻干工艺进行了研究,结果表明：两菌的最佳离心条件为：转速4000r／min,时间10min;最佳预冻温度和预冻时间为在一20℃预冻3h;冻干保护剂的最佳pH为6．5;保护剂与菌泥的最佳平衡时间为30min;保护剂与菌泥的最佳配比为4：1;最佳装液厚度为7mm;冻干菌粉的最佳含水量为2％-3％。     

嗜热链球菌冻干保护剂保护作用的研究

冷冻干燥前在菌液中加入保护剂,可提高乳酸菌的冻干存活率。对多种保护剂的保护作用做了比较,其中海藻糖的保护效果最好;在扫描电镜下观察了冻干后的嗜热链球菌,加海藻糖保护的菌体细胞饱满、完整,对照则有变形和塌缩,该结果较为直观地揭示了海藻糖对菌体细胞的保护作用。     

嗜热链球菌增菌缓冲剂的研究

为制备高浓度的嗜热链球菌(S.t)菌悬液,采用正交试验和均匀试验,对嗜热链球菌的缓冲剂进行了研究。结果表明,以NaAC和CaCO3为缓冲体系效果较佳。嗜热链球菌质量浓度在以0.5g／100mL的NaAC和0.04g／100mL的CaCO3为缓冲体系的脱脂乳复原中发酵,发酵液的活菌数最高,可达6.5×109mL-1。     

嗜热链球菌分批发酵工艺放大研究

近年来,随着国内消费者对酸奶制品需求量的激增,使得乳酸菌浓缩培养成为亟待解决的难题。针对这种情况,在确定嗜热链球菌适宜的碳、氮源分别为乳糖和蛋白胨、适宜的碳氮比例为2∶1的基础上,将嗜热链球菌从小试培养放大到10L发酵罐。试验结果初步证实,三颈瓶比三角瓶更适于将实验室成果向小规模工业发酵过渡,只要保证关键参数与发酵罐相同或接近,嗜热链球菌经三颈瓶培养6h的最大活细胞数可达到3.81×109cfu/mL,与10L发酵罐的3.78×109cfu/mL菌体产量相似。     

Streptococcus thermophilus bacteriophages

At least 345 bacteriophages infecting Streptococcus thermophilus starter cultures have been isolated; general characteristics include high thermal resistance, short latent periods and large burst size. Phages with such characteristics are primed to thrive in the cheese making environment, lysing bacterial cultures and generating low-quality fermented products. All S. thermophilus phages isolated to date are members of the Siphoviridae family and the Caudovirales order and appear to constitute a polythetic phage species comprising two large groups, cos- and pac-types, based on the mode of DNA packaging. Comparative analyses have shown that S. thermophilus phage genomes are similarly organized into distinct modular regions and allow the detection of a core genome region. Several PCR-based techniques have been designed to detect them in cheese whey and milk samples. Similar S. thermophilus phages are globally distributed and endemic in specific dairy environments. The biogeography of S. thermophilus phages reinforces their current classification.     

嗜热链球菌胞外多糖的结构生物合成与遗传调控

介绍了嗜热链球菌胞外多糖的组成结构、生物合成、代谢途径和针对途径中关键酶的遗传调控,为胞外多糖研究提供参考.     

Urease production by Streptococcus thermophilus

In order to identify potential alternative sources of urease for the removal of urea from alcoholic beverages, 205 strains of lactic acid bacteria belonging to 27 different species were screened for urease production. Only Streptococcus thermophilus produced urease. Cell permeabilization with toluene allowed to increase activity significantly. Optimal pH for urease activity in whole and permeabilized cells and of cell free extracts differed slightly, but was in the range 6.0-7.0. Significant activity was retained at pH 3.0 and 8.0, and, for cell free extracts, at pH 4.0 in the presence of ethanol. Urease production was evaluated in fermentations with pH control (5.25-6.5) and without pH control. Very little urease was produced in absence of urea, which at 5g/l slowed growth significantly in fermentations without pH control, but prevented a decrease in pH below 5.1 and resulted in higher final biomass. Optimal pH for growth was between 6.0 and 6.5 but specific urease activity was higher for fermentations at low pH at the beginning of the exponential phase. However, a higher total urease activity was obtained at pH 6.0 and 6.5 because of higher biomass. Potential technological applications of urease production by S. thermophilus are discussed.     

嗜热链球菌抗噬菌体菌株的选育

研究以酸奶生产菌株嗜热链球菌S2为出发菌株。采用自然选育的方法筛选出其抗噬菌体突变株。获得4株生产性能较好的抗噬菌株KS21、KS22、KS23、KS24,溶源性检测其为非溶源菌。对4株抗性菌株进行20次传代和酸奶发酵实验,结果表明抗性稳定,其中KS23发酵酸奶产酸达109°T,凝乳时间与出发菌株相当。细胞全蛋白SDS-PAGE电泳分析显示突变菌株与出发菌株在某些蛋白表达上有所差异,可能是抗性产生的原因。     

五株嗜热链球菌抗药性研究

采用药敏纸片法研究了五株高产粘嗜热链球菌（KLDS3.1012、KLDS3.1014、KLDS-SM、KLDS3.0206、KLDS3.0207）对15种抗生素的敏感性,结果发现,KLDS3.1014对两种抗生素有抗性,KLDS3.1012、KLDS-SM、KLDS3.0206对3种抗生素有抗性,KLDS3.0207则表现出多重抗药性。对五株嗜热链球菌耐四环素基因（tet M,tet S,tet L）、耐红霉素基因（erm A,erm B,msr A/B）和耐氯霉素基因（cat）的初步研究表明,四环素耐受基因、红霉素耐受基因以及氯霉素耐受基因不位于基因组DNA上,同时,受试菌株均无质粒,因此可以初步判断受试菌株抗药性不会进行传递。      

嗜热链球菌噬菌体的分离纯化与鉴定

噬菌体颗粒的分离纯化是研究噬菌体生物学特性、基因分析的基础工作。本研究采用聚乙二醇浓缩噬菌体增殖液、缓冲液透析去除聚乙二醇、氯化铯密度梯度离心纯化,得到了纯度较高的嗜热链球菌噬菌体样品。多重PCR鉴定和SDS-PAGE蛋白组成分析结果表明,该嗜热链球菌噬菌体的包装机制为pac-型。      

Hyaluronic acid production by recombinant Streptococcus thermophilus

Generally recognized as safe, Streptococcus thermophilus was transformed using a plasmid expressing endogenous hyaluronic acid (HA) synthase genes. A single expression of hyaluronic acid synthase (hasA), uridine diphosphate-glucose dehydrogenase gene (hasB), or pyrophosphorylase gene (glmU) and double expression of hasA and hasB were attempted. A streptococcus-Escherichia coli shuttle vector, pBE31, was successfully transfected in S. thermophilus. The single expression of hasA or hasB allowed S. thermophilus to produce about 0.5-1.0 g/l HA. The strains coexpressing of hasA and hasB showed a markedly increased HA production (1.2g/l) which was six-fold increase compared with the wild-type strain. The maximum cell concentration and specific growth rate of each recombinant strain were lower than those of the wild-type strain; however, the specific production rate was more than 100-fold higher. Galactose concentration decreased in the coexpressing strain after depletion of lactose. The bacterial metabolism would be altered in order to achieve a higher production by changing the intracellular metabolism. The average molecular weight of HA (1.0 × 10(6) Da) was not affected by the expression of hasA and hasB. HA produced from recombinant strain could be an alternative material for medical, cosmetic and food utilization instead of HA from conventional pathogenic streptococci.