Identification and characterization of lactic acid bacteria isolated from rainbow trout, Oncorhynchus mykiss (Walbaum), with inhibitory activity against Lactococcus garvieae

A study was conducted to evaluate the probiotic properties of endogenous rainbow trout microbiota against pathogenic Lactococcus garvieae. A total of 335 bacterial strains were isolated from rainbow trout and screened for antagonistic activity against L. garvieae using an agar spot assay. Antagonistic strains were grouped by PCR amplification of repetitive bacterial DNA elements (rep‐PCR) and identified by 16S rRNA gene sequence analysis. The results revealed that the antagonistic strains belonged to the genera Lactobacillus, Lactococcus and Leuconostoc. Further probiotic characteristics, such as specific growth rate, doubling time, resistance to biological barriers, antibiotic resistance, hydrophobicity and production of antimicrobial substances, were also studied. These strains were able to survive low pH and high bile concentrations, showed good adherence characteristics and a broad spectrum of antibiotic resistance. The antagonistic efficacy was maintained after sterile filtration and was sensitive to proteinase K, indicating that proteinaceous extracellular inhibitory compounds were at least partially responsible for pathogen antagonism. Based on these results, these strains should be further studied to explore their probiotic effects in challenge experiments in vivo. This study shows clear evidence that the indigenous trout‐associated microbiota may provide a defensive barrier against L. garvieae.     

Production of bacteriocin by Leuconostoc mesenteroides 406 isolated from Mongolian fermented mare's milk,airag

The purification and characterization of a bacteriocin produced by Leuconostoc mesenteroides strain 406 that was isolated from traditional Mongolian fermented mare's milk, airag, were carried out. Leuconostoc mesenteroides strain 406 was identified on the basis of its morphological and biochemical characteristics and carbohydrate fermentation profile and by API 50 CH kit and 16S ribosomal DNA analyses. The neutral‐pH cell‐free supernatant of this bacterium inhibited the growth of several lactic acid bacteria and food spoilage and pathogenic organisms, including Listeria monocytogenes and Clostridium botulinum. The bacteriocin was heat‐stable and not sensitive to acid and alkaline conditions, but was sensitive to several proteolytic enzymes such as pepsin, pronase E, proteinase K, trypsin, and α‐chymotrypsin, but not catalase. Optimum bacteriocin production (4000 activity units/mL) was achieved when the strain was cultured at 25°C for 24–36 h in Man Rogosa Sharpe medium. The bacteriocin was partially purified by ammonium sulfate precipitation (80% saturation), dialysis (cut‐off MW: 1000), and gel filtration chromatography. Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis revealed that the bacteriocin had a molecular weight of approximately 3.3 kDa. To our knowledge, this is the first report of the isolation of a bacteriocin‐producing Leuconostoc strain from airag. An application to fermented milks would be desired.     

肠膜明串珠菌胞外多糖的研究进展及其在饲料业中的应用前景

综述了肠膜明串珠菌胞外多糖的存在形式、组成成分、酶促合成过程、生成影响因素及提高产量的技术,介绍了肠膜明串珠菌胞外多糖的功能及用途,探讨了专供发酵饲料使用的肠膜明串珠菌的菌株选育问题、饲用肠膜明串珠菌微生态制剂的生产问题及低聚糖益生元饲料添加剂开发问题。     

产胞外多糖的黑鲷肠道乳酸菌的分离鉴定及其生物学特性

通过常规鉴定和16S rDNA序列分析,从黑鲷(Sparus macrocephalus)肠道中分离鉴定出1株明串珠菌属(Leuconostoc)乳酸菌菌株;该分离株对酸、胆盐、蛋白酶具有良好耐受性,但对温度耐受能力较差;分离株培养上清液对哈维氏弧菌(Vibrio harveyi)、溶藻弧菌(Vibrio algnolyticus)、副溶血弧菌(Vibrio parahaemolyticus)的抑菌圈直径为1.12～1.22 cm,不同培养时间的抑菌效果差异无统计学意义(P＞0.05);分离株在培养24、32、40、48和56 h时的胞外多糖质量浓度为167.24～184.45 mg·L-1,不同取样时间的胞外多糖质量浓度差异无统计学意义(P＞0.05);灌服胞外多糖20 d后黑鲷血液的红细胞、白细胞数量和血红素浓度、淋巴细胞比率均显著升高(P＜0.05).综上,该分离株为产胞外多糖的明串珠属乳酸菌,可作为开发海水鱼用微生态制剂的候选菌株.     

发酵产葡聚糖条件的确定

[目的]研究提高葡聚糖发酵产率的条件。[方法]以蔗糖转化为葡聚糖的转化率作为参考标准,通过单因素实验和正交实验确定了肠膜明串珠菌发酵产葡聚糖的最佳条件。[结果]肠膜明串珠菌发酵产葡聚糖的最适宜培养基配方为:蔗糖100.0 g/L,蛋白胨5.0g/L;最佳发酵条件为:温度25℃,活化液接种量2.5%,发酵罐转速150 r/min,起始pH值7.5。该实验测得的最大蔗糖转化率为70.0%。[结论]蔗糖和蛋白胨是肠膜明串珠菌生长所必需的碳源和氮源,对于葡聚糖的产量有很大影响;发酵温度、发酵罐转速和发酵液pH值对蔗糖转化率的影响很大,而活化液接种量对蔗糖转化率的影响不大。     

对1株肠膜明串珠菌生长曲线和世代时间的初步探讨

用添加趋势线的分析方法,对肠膜明串珠菌LA-07在新鲜脱脂牛乳培养基和MRS肉汤培养基中的生长曲线进行了初步研究。结果表明,在2种培养基中,其生长均满足对数生长曲线规律,且世代时间分别为:G乳=114.7 min,GMRS=95.9 min。     

假肠膜明串珠菌D-乳酸脱氢酶基因的克隆与表达

利用PCR的方法从假肠膜明串珠菌(Leuconostoc pseudomesenteroides 1159)的DNA中扩增得到D-乳酸脱氢酶基因,构建重组克隆质粒(pMD19-T-DLDH),转化DH5α进行蓝白斑筛选,得到阳性克隆提取质粒双酶切验证。连接pET-32a表达质粒,构建重组表达质粒,提取质粒双酶切、测序验证,测序结果与原序列基本相符。得到重组表达质粒pET-32-DLDH转化BL21大肠杆菌IPTG诱导表达,SDS-PAGE显示有明显大小约为19 ku的特异蛋白条带。     

一种肠膜明串珠菌Leuco4发酵乳的特性

制备出一种含肠膜明串珠菌Leuco4的无任何添加剂的发酵乳,采用肠膜明串珠菌Leuco4发酵乳与常规发酵乳按质量比1∶4混合,并对所得发酵乳产品进行黏度、脱水收缩敏感性、质构及感官测试.结果表明:21d保质期内,与对照组相比,含肠膜明串珠菌Leuco4的发酵乳,持水性佳,黏度、口感、稳定性均能达到理想状态,且不含任何添加剂,符合清洁标签产品的要求.     

一种通过肠膜明串珠菌发酵的花样奶布丁的研制

目前市售布丁主要是调制型奶布丁,是根据口味差异调制所需配料,加入明胶等凝固而成,虽有一些"半发酵型"的布丁产品,主要是以酸奶为原料进行调制而成,但其凝固成型过程主要依赖于添加的各种稳定剂,无法兼顾到美味、营养和健康.为此,本文研究了一种以脱脂乳和番茄汁为介质、基于肠膜明串珠菌发酵的花样奶布丁,其保留了牛乳中的各种营养物...     

乳与乳制品中明串珠菌的分离鉴定

从内蒙古通辽市科左后旗和扎鲁特旗牧民家庭乳样中分离到61株乳酸菌,并进行乳酸菌的分离鉴定。结果显示,其中有肠膜明串珠菌葡聚糖亚种2株,假肠膜明串珠菌1株,明串珠菌分离率为4．9％。