原料乳中耐冷假单胞菌的种类及其肽酶活力

在冷藏的原料乳中,假单胞菌经常出现并成为主导菌群,其分泌的耐热酶会使原料乳变质。对从原料乳中分离的102株假单胞菌经rpoB基因测序进行菌种分析,用偶氮酪蛋白测试所有假单胞菌在2种培养条件(30℃培养2d或6℃培养8d)下胞外肽酶的蛋白水解活性和耐热性。结果表明:荧光假单胞菌(Pseudomonas fluorescens)是假单胞菌中最主要的菌种,其次是莓实假单胞菌(Pseudomonas fragi)和假单胞菌sp1 (Pseudomonas sp1)。不同假单胞菌菌种之间的产肽酶能力存在明显差异。大多数荧光假单胞菌(23/41)在不同温度(30℃和6℃)条件下培养后能产肽酶,而大多数的假单胞菌sp1不产肽酶,所有分离的莓实假单胞菌(13/13)只在6℃条件下产肽酶,大多数的假单胞菌所产肽酶都有热稳定性。在6℃培养条件下,荧光假单胞菌菌株M02有最高肽酶活力(11.78ΔA/ (h·mL)),其胞外肽酶最佳催化pH值为6.5,最佳催化温度为40℃。当M02的接种浓度为103 CFU/mL时,6℃培养5d就能使脱脂乳溶液产生沉淀。对耐冷假单胞菌的种类和产肽酶能力进行分析和考察有助于提高原料乳或乳制品的质量和安全性。     

牛乳中嗜冷假单胞菌胞外蛋白酶的研究进展

假单胞菌通常被认为是危害原料乳及其制品的主要嗜冷菌,其分泌的胞外蛋白酶具有耐热性,甚至能在超高温灭菌处理后仍有活性残留,并减短超高温灭菌乳的货架期.本文对来自牛乳中的嗜冷假单胞菌蛋白酶的研究进展做了总结,重点假单胞菌蛋白酶的催化机制研究进展,相关基因包括蛋白酶基因apr X在假单胞菌鉴别中的应用研究进展.最后讨论了嗜冷假单胞菌蛋白酶需要深入研究的方向.     

变质原料乳中假单胞菌的分离鉴定及产蛋白酶特性研究

[目的]为了解导致原料乳变质的微生物种类及其产蛋白酶活力。[方法]对广东省恒远市某规模化牧场提供的蛋白水解、脂肪上浮的变质原料乳稀释,涂布在MPC琼脂平板上。将平板于6.5 ℃恒温培养箱培养10 d,挑取形态不同的单菌落在LB液体培养基复壮增菌,提取其DNA,利用16S rDNA方法对分离的菌株进行鉴定,并对该菌株的蛋白酶活力及高温钝化后酶残留率进行测定。[结果]MPC琼脂板菌落形态单一,原料乳中分离鉴定出的两株菌均为霍氏假单胞菌,该菌株在28 ℃下对乳平板的水解圈为（15.35±0.56）mm,经135 ℃处理5 s,其蛋白酶残留率为43.63%。[结论]变质原料乳中分离到两株霍氏假单胞菌,并且该菌可产生热不敏感的蛋白酶,该酶的存在会造成原料乳中蛋白质水解,导致UHT乳在货架期内出现蛋白水解、胀包等质量问题。     

牛乳中荧光假单胞菌耐热性脂肪酶的活性影响因素

以新鲜牛乳中分离到的荧光假单胞菌为研究对象,对其分泌产生的耐热性脂肪酶进行纯化,并研究不同温度、pH值、Ca2+质量浓度对该脂肪酶活性的影响.结果表明:经过初步纯化的脂肪酶分子质量为55 kD,纯度为91.5％,并且发现该耐热性脂肪酶在50℃、30 min,63℃、30 min,72℃、20 s,90℃、10 min,121℃、0.1 MPa、20 min处理之后,相对酶活力分别为75.02％、86.21％、73.25％、17.62％、13.63％;并且该脂肪酶的最适温度为63℃,最适pH值为8.0;在荧光假单胞菌体外,Ca2+质量浓度对荧光假单胞菌脂肪酶的活力并无显著影响.     

嗜冷菌对UHT乳品质的影响研究

摘要：原料乳嗜冷菌污染是影响uHT乳保质期的重要原因之一,并且嗜冷菌分布具有地域特征性本研究对蒙牛8个牧场原料乳中的嗜冷菌进行了分离和鉴定,确定了牧场常见嗜冷菌种类及特性,并分析了其对uHT乳品质的影响．结果表明,从试验样品中分离出的嗜冷菌为假单胞菌属、微球菌属和产碱杆菌属;牧场原料乳的嗜冷菌数量与气温有关,1～3月份数量较高,6～9月份数量较低;原料乳嗜冷菌数越多,UHTqL货架期越短;原料乳中嗜冷菌数达到10^5 CFU／mL时,对uHT乳苦味值的影响显著（p〈（1．（15）;嗜冷菌脂肪酶活力达10IU／mL、蛋白酶活力为15Iu／mL、25IU／mL时对UHTSfL苦味值的影响显著（P〈0．05）;原料gLpH值为6．7和3.5％2冷藏条件下,蛋白酶、脂肪酶活性较高,不利于uHT乳长期贮存、综上研究,原料乳中嗜冷菌数过多会严重影响uHT乳品质和风味;低温贮藏条件下,嗜冷菌产生的脂肪酶和蛋白酶会破坏UHT乳品质,因此不建议长期低温保存uHT乳、     

原料乳中嗜冷菌种类及嗜冷芽孢杆菌研究进展

嗜冷菌能在原料乳冷藏条件下生长,其分泌蛋白酶和脂肪酶降解牛乳中的蛋白和脂肪,导致牛乳变质。本文归纳了原料乳中嗜冷菌的种类,总结嗜冷芽孢杆菌的危害研究进展,重点包括嗜冷菌常见种型、危害特点、分泌的蛋白酶和脂肪酶。最后探讨了嗜冷芽孢杆菌的研究方向。     

家蚕肠道产酶菌的分离与筛选

探明家蚕肠道菌在食物消化过程中的作用,有助于微生态饲用添加剂的开发研究。从家蚕肠道中分离出30株菌株,并研究了它们的胞外淀粉酶、蛋白酶、纤维素酶和脂肪酶的产酶能力。在家蚕肠道中存在着可以分泌蛋白酶、淀粉酶、脂肪酶和纤维素酶的菌株。在分离到的30株肠道菌株中,产4种酶的有1株菌,产3种酶的有4株菌,产2种酶的有2株菌,产1种酶的有11株菌,不产酶的有12株菌。在产酶菌中,有9株菌株能分泌蛋白酶,能分泌脂肪酶和纤维素酶的各有7株菌,有8株菌株能分泌淀粉酶。家蚕肠道菌中的各种产酶菌高达60%,表明了肠道菌在家蚕食物消化过程中的重要性。     

假单胞菌生物膜形成调控机制研究进展

假单胞菌是原料乳中常见的污染微生物,其会在乳品生产设备表面形成生物膜,导致设备腐蚀,且假单胞菌难以清除。同时假单胞菌形成的生物膜能促进假单胞菌耐热酶的分泌,还可以作为致病菌的生长基质,从而给乳品安全带来风险。本文总结了假单胞菌生物膜调控机制的研究进展和影响生物膜形成的环境因素,为假单胞菌生物膜的防控提供依据。     

菌酶协同发酵香菇菌糠复合制剂的筛选研究

研究旨在筛选发酵香菇菌糠的最佳菌酶复合制剂。试验采用单因素试验,设计16个不同的菌酶复合制剂加入香菇菌糠中,筛选植物乳杆菌、黑曲霉、嗜酸乳杆菌、布氏乳杆菌、产朊假丝酵母、纤维素酶和木聚糖酶等菌酶制剂。发酵30 d后,通过对发酵产物感官指标评定、pH值及营养成分含量进行测定,利用隶属函数法对相关指标进行综合评判。结果显示,经菌酶复合制剂发酵的香菇菌糠感官指标得分均属于尚好及以上,pH值较原料明显降低,营养成分有所改善。筛选出4个最佳菌酶复合制剂：布氏乳杆菌+产朊假丝酵母+嗜酸乳杆菌+黑曲霉+木聚糖酶+纤维素酶、布氏乳杆菌+产朊假丝酵母+嗜酸乳杆菌+木聚糖酶+纤维素酶、布氏乳杆菌+产朊假丝酵母+植物乳杆菌+黑曲霉+木聚糖酶+纤维素酶、布氏乳杆菌+产朊假丝酵母+植物乳杆菌+纤维素酶。研究表明,菌酶复合制剂能够改善香菇菌糠发酵饲料的品质,提升菌糠的利用价值。     

貂假单胞菌性肺炎的研究近况

假单胞菌属中对家畜有致病性的细菌主要有鼻疽杆菌、伪鼻疽杆菌和绿脓杆菌。貂假单胞菌性肺炎又称出血性肺炎、假单胞菌病或绿脓杆菌病,是由铜绿假单胞菌引起的貂的一种急性传染病。该病以出血性肺炎为主要特征,有的还伴有心内膜炎、脑膜炎及败血症等。该病多呈地方流行...     

Pseudomonas aeruginosa in raw and pasteurized milk

Eighteen strains of Pseudomonas aeruginosa, i.e. 8.87%, were isolated during a year from 203 samples of raw milk. Two Pseudomonas aeruginosa strains, i.e. 4%, were isolated from 50 samples of pasteurized milk. The strains were isolated using propagation techniques in meat-peptone broth with malachite green and on selective media--on centrimide agar (CEM) and on Pseudomonas F agar. All the isolated strains produced protease, whereas lipase was produced by only five strains. The strains were devitalized when exposed to pasteurization temperatures (72 degrees C) for 20 seconds. At cold store temperatures (4 degrees C), Pseudomonas aeruginosa strain cells propagated on average by two orders, inhibitory effects of low temperatures were recorded only with one strain. Inhibitory effects of milk cultures (cream, yogurt) on Pseudomonas aeruginosa were observed; their effects were more clear-cut at the temperature of 4 degrees C. The strains were markedly susceptible to gentamycin.     

Aerobic bacterial flora of the nasal cavity in Gulf of California sea lion (Zalophus californianus) pups

Nasal swab samples from clinically healthy California sea lions pups (Zalophus californianus) from six different reproductive rookeries in the Gulf of California were collected to determine the type and frequency of the representative aerobic bacterial microflora of their nasal mucosa. A total of 114 samples were examined and 100 bacterial isolates were identified and typified by microbiological and biochemical standard tests. Fifty four isolates corresponded to Gram positive bacteria (54%) and 46 isolates to Gram negative bacteria (46%). Fifteen bacterial genera were identified, including Micrococcus, Arcanobacterium, Corynebacterium, Moraxella, Neisseria, Escherichia, Kurthia, Acinetobacter, Staphylococcus, Brevibacillus, Bacillus, Klebsiella, Stenotrophomonas, Pseudomonas and Aeromonas. The most frequently isolated genera were Moraxella (24%), Micrococcus (18%), and Corynebacterium (15%). These results show the presence in the nasal cavity of sea lions of several microorganisms. Although considered part of the normal microflora, they may also be opportunistic pathogens for their hosts and may act as a potential natural sentinel of environmental changes.     

奶牛养殖场环境微生物群落结构及多样性研究

为了研究奶牛养殖场部分环境因素与奶牛乳房处的细菌多样性和差异性,将分别取自牛乳房擦拭样品(C1)、榨乳设备(E)、粪便(F)、冲洗和养殖饮用水(W)、生乳运输罐(E2) 5种样本的6个生物学重复共计30个样品使用基于16SrRNA (V3～V4区)的高通量测序技术,并采用生物信息学的方法分析了不同来源样本的细菌群落结构...     

Comparison of the API 20E and BBL Crystal E/NF Identification Systems for Differentiating Bacterial Isolates from Apparently Healthy Reared Sea Bass (Dicentrarchus labrax)

The ability of two commercial rapid identification systems, API 20E and BBL Crystal E/NF, to reliably identify bacterial isolates from the internal organs of reared sea bass were compared. The tests gave different results: API 20E identified bacteria as Pseudomonas spp. with 37% accuracy, while BBL Crystal E/NF identified them as Flavobacterium odoratum with 99% accuracy. Although F. odoratum is not a marine fish pathogen, conventional tests conducted with the same isolates were more indicative of them being Flavobacterium spp. than Pseudomonas spp., suggesting that BBL Crystal E/NF was more reliable in this identification. Both systems were found to be applicable for diagnostics of marine fish pathogens, but should be used with caution because of possible misinterpretation.     

Oxytetracycline treatment reduces bacterial diversity of intestinal microbiota of Atlantic salmon

The effect of oxytetracycline (OTC) treatment on intestinal bacterial populations in juvenile Atlantic salmon Salmo salar was evaluated. Oxytetracycline was administered by way of medicated feed to fish held in experimental tanks. Restriction fragment length polymorphism and sequencing of 16S rDNA from isolates were used to analyze the intestinal microbiota before, during, and after OTC administration. The microbiota from untreated fish was more diverse, consisting mainly of Pseudomonas, Acinetobacter, Bacillus, Flavobacterium, Psycrobacter, and Brevundimonas spp. In contrast, the microbiota of the OTC-treated group was characterized by lower diversity and consisted only of Aeromonas, clustering with A. sobria and A. salmonicida. Antibiotic-resistant isolates were identified as Aeromonas spp.; sequencing the resistance determinant showed it to be the tetE gene. Overall, OTC treatment changed the composition of the intestinal microbiota of Atlantic salmon, as evidenced by a reduction in bacterial diversity. These results support the current concern that antibiotic treatment can facilitate the proliferation of opportunistic bacteria by eradicating competing microorganisms.