戊糖乳杆菌素pentocin LPEM818的初步纯化及特性研究

对戊糖乳杆菌(Lactobacillus pentosus)LPEM818所产戊糖乳杆菌素(pentocin)LPEM818进行了初步纯化,并对其生物学特性进行了研究。结果表明,采用80%硫酸铵沉淀和Sephadex G-25凝胶层析分离纯化后,细菌素的纯化倍数为11.09倍,回收率为6.4%;该细菌素在pH 2.0～8.0条件下稳定,121℃加热15 min保留84.52%的抑菌活性;对胰蛋白酶和蛋白酶K敏感;该细菌素的作用方式为杀菌;对供试的部分革兰氏阳性菌(G+)和革兰氏阴性菌(G-)具有较强抑制作用,因其抑菌谱较广,对多数致病菌和食品腐败菌有较好抑菌作用,所以具有作为食品生物防腐剂的潜在应用价值。     

泡菜中产细菌素菌株的分离及细菌素性质的初步研究

从四川泡菜中分离得到一株产细菌素的菌株,经形态学、生理生化鉴定等试验,初步鉴定此菌株为乳酸菌。对其所产细菌素做温度、pH、蛋白酶的敏感性试验,实验结果表明,发酵上清液中的抑菌物质对胃蛋白酶、木瓜蛋白酶较敏感,菌株所产细菌素在高温(121℃20min)和酸性条件(pH 3.0～5.0)下均有较强的抑菌活性,可以较好地抑制革兰氏阳性、阴性菌,筛选得到的菌株所产细菌素是一类具有广谱抑菌活性的细菌素。     

产细菌素屎肠球菌的筛选鉴定及其抑菌特性

从采自四川红原的传统发酵酸乳中分离得到308 株疑似乳酸菌,通过96 孔板法初筛和平板打孔法复筛,筛选出1 株具有明显抑菌作用的菌株SC-Y112。通过形态学观察、16S rDNA序列同源性分析和ropA管家基因序列同源性分析结合生理生化实验,鉴定该菌株为屎肠球菌（Enterococcus faecium）。通过排酸及排除H2O2影响后,该菌株的发酵上清液仍具有明显抑菌活性,经蛋白酶处理后,抑菌效果明显消失或下降,说明发酵上清液中的抑菌成分具有蛋白质性质。进一步探究该菌株所产细菌素的生物学特性、遗传稳定性及抑菌特性表明,该细菌素在菌株接种后6 h产生,12 h达到最高;菌株在连续传代86 代内,产细菌素能力较为稳定;细菌素在 pH 3.0～7.0的条件下稳定,在100 ℃处理30 min后仍具有抑菌活性;SC-Y112所产细菌素具有广谱抗菌性,对单核细胞性李斯特菌有明显的抑菌活性。     

产细菌素植物乳杆菌菌株的筛选及其细菌素生物学特征研究

从甘蓝泡菜中分离到６９株乳酸杆菌,通过琼脂点扩散交叉拮抗试验,筛选出３株有明显抑菌活性代谢产物的植物乳杆菌。排除酸、过氧化氢等干扰因素后,离心发酵液对指示菌Ｌａｃｔｏｂａｃｉｌｕｓｐｌａｎｔａｒｕｍ９６Ｄ仍有抑菌作用,用胰蛋白酶对其透析液处理后活性丧失,说明它们产生的抑菌物质是细菌素。以Ｇ８菌株为试材,对其细菌素类物质的产生及细菌素粗提物进一步研究,发现在对数末期其抑菌活性最高,对热相对稳定（１００℃,２０ｍｉｎ）,易被胰蛋白酶、蛋白酶Ｋ和胃蛋白酶失活,显示活性的ｐＨ值范围为４．０～５．５,粗提液表现为不仅抗明串株菌属、片球菌属、乳杆菌属的一些菌株,而且抗一些非乳酸菌的革兰氏阳性菌,但对大肠杆菌（Ｅ．ｃｏｌｉ）等革兰氏阴性菌没有任何抑制作用。说明Ｇ８菌株产生的是一类抗广谱革兰氏阳性菌的细菌素     

Probiogenomic In-Silico Analysis and Safety Assessment of Lactiplantibacillus plantarum DJF10 Strain Isolated from Korean Raw Milk

The whole genome sequence of Lactiplantibacillus plantarum DJF10, isolated from Korean raw milk, is reported, along with its genomic analysis of probiotics and safety features. The genome consists of 29 contigs with a total length of 3,385,113 bp and a GC content of 44.3%. The average nucleotide identity and whole genome phylogenetic analysis showed the strain belongs to Lactiplantibacillus plantarum with 99% identity. Genome annotation using Prokka predicted a total of 3235 genes, including 3168 protein-coding sequences (CDS), 59 tRNAs, 7 rRNAs and 1 tmRNA. The functional annotation results by EggNOG and KEGG showed a high number of genes associated with genetic information and processing, transport and metabolism, suggesting the strain’s ability to adapt to several environments. Various genes conferring probiotic characteristics, including genes related to stress adaptation to the gastrointestinal tract, biosynthesis of vitamins, cell adhesion and production of bacteriocins, were identified. The CAZyme analysis detected 98 genes distributed under five CAZymes classes. In addition, several genes encoding carbohydrate transport and metabolism were identified. The genome also revealed the presence of insertion sequences, genomic islands, phage regions, CRISPR-cas regions, and the absence of virulence and toxin genes. However, the presence of hemolysin and antibiotic-resistance-related genes detected in the KEGG search needs further experimental validation to confirm the safety of the strain. The presence of two bacteriocin clusters, sactipeptide and plantaricin J, as detected by the BAGEL 4 webserver, confer the higher antimicrobial potential of DJF10. Altogether, the analyses in this study performed highlight this strain’s functional characteristics. However, further in vitro and in vivo studies are required on the safety assurance and potential application of L. plantarum DJF10 as a probiotic agent.     

Bio-Engineered Nisin with Increased Anti-Staphylococcus and Selectively Reduced Anti-Lactococcus Activity for Treatment of Bovine Mastitis

Bovine mastitis is a significant economic burden for dairy enterprises, responsible for premature culling, prophylactic and therapeutic antibiotic use, reduced milk production and the withholding (and thus wastage) of milk. There is a desire to identify novel antimicrobials that are expressly directed to veterinary applications, do not require a lengthy milk withholding period and that will not have a negative impact on the growth of lactic acid bacteria involved in downstream dairy fermentations. Nisin is the prototypical lantibiotic, a family of highly modified antimicrobial peptides that exhibit potent antimicrobial activity against many Gram-positive microbes, including human and animal pathogens including species of Staphylococcus and Streptococcus. Although not yet utilized in the area of human medicine, nisin is currently applied as the active agent in products designed to prevent bovine mastitis. Over the last decade, we have harnessed bioengineering strategies to boost the specific activity and target spectrum of nisin against several problematic microorganisms. Here, we screen a large bank of engineered nisin derivatives to identify novel derivatives that exhibit improved specific activity against a selection of staphylococci, including mastitis-associated strains, but have unchanged or reduced activity against dairy lactococci. Three such peptides were identified; nisin A M17Q, nisin A T2L and nisin A HTK.     

绿原酸与Ⅲ型细菌素复配对鸡肉中假单胞菌的抑菌机制

荧光假单胞菌是引起冷鲜鸡肉腐败变质的优势腐败菌,可降解肉品中的蛋白质、脂肪等物质,产生多种 腐败代谢产物,进而使肉类食品风味和品质发生劣变。采用体外抑菌实验研究绿原酸（chlorogenic acid,CA）、 Ⅲ型细菌素Helveticin-M及二者复配对荧光假单胞菌的抑菌效果;通过扫描电子显微镜观察不同处理对荧光假单 胞菌外部形态结构的影响,通过激光共聚焦显微镜观察、测定胞外ATP含量、胞外蛋白和核酸外渗,研究CA或 Helveticin-M对指示菌细胞膜渗透性的影响。结果表明：与CA或Helveticin-M单独作用相比,二者复配后抑菌作用 显著增强（P＜0.05）;绿原酸与Helveticin-M复配处理可显著破坏荧光假单胞菌形态,增强细胞膜渗透性,加剧胞 内物质外泄,最终加速荧光假单胞菌死亡。     

干酪乳杆菌细菌素的抗菌机制分析

目的：分析和预测干酪乳杆菌细菌素基因及其编码蛋白的分子结构和理化性质,明确细菌素的抗菌机制。方法：利用生物信息学软件进行细菌素编码蛋白的结构预测和功能分析,采用氨基酸定点突变技术对预测的氨基酸位点进行点突变,检测突变体的抗菌活性。结果：干酪乳杆菌细菌素（LacA和LacB）属于热稳定、分泌信号肽的跨膜蛋白,LacA蛋白存在典型的抗菌结构域GxxxG,构建LacA蛋白中第40位V和第57位I的突变载体,两个位点中任何一个发生突变都明显影响细菌素的抗菌活性。结论：推测V40和I57是干酪乳杆菌细菌素发挥抑菌活性的关键氨基酸位点,为今后探索干酪乳杆菌细菌素（class IIb）抗菌机制提供理论依据。     

乳酸菌细菌素和超高压联合处理对低温切片火腿的防腐保鲜效果

为了揭示乳酸菌细菌素和超高压联合处理对低温切片火腿的防腐保鲜效果,并探讨乳酸菌细菌素和超高压联合处理在低温肉制品防腐保鲜应用中的可行性,在不添加任何化学防腐剂的情况下,分别以乳酸菌细菌素(enterocin LM-2)添加量320AU/g、600MPa超高压处理5min以及两者联合处理低温切片火腿,考察联合处理对样品中微生物数量、理化指标以及感官特性的影响。结果表明：enterocin LM-2和超高压技术的联合使用可明显延长低温切片火腿的货架期,有效减少贮藏过程中挥发性盐基氮的生成及脂肪氧化,并保持产品原有色泽、气味、质构等感官特性。综合微生物和理化特性分析结果,联合处理组的防腐效果最好,可将低温切片火腿的货架期延长至100d。     

天然食品防腐剂——细菌素

细菌素是一类安全、高效、无毒的天然食品防腐剂。本文介绍了细菌素的分类,以及细菌素与抗生素的区别,以尼生素,纳他霉素为重点阐述了细菌素的抑菌机理及在肉制品中的应用。