Survival of Listeria monocytogenes in cheese made of unpasteurized goat milk

Food-born infections with Listeria monocytogenes have been reported during recent years, cheese being mentioned as one of the foods responsible. A classical opinion is that cheese represents a very inhospitable environment for pathogens due to antagonism by the starter culture of lactic-acid-producing organisms. In order to study the survival of L. monocytogenes in goat cheese, cheeses were made with the addition of L. monocytogenes cultures. The maximum survival time for L. monocytogenes was 18 weeks in two of the cheeses. It is concluded that L. monocytogenes has the ability to survive in semi-soft cheese made of unpasteurized goat milk during normal curing (2–3 months).     

混合果肉羊乳扣碗酪的加工工艺研究

研制全新的具有民族特色并且适合大多数人口味的奶酪食品。采用单因素多水平试验及正交试验方法,研究出混合果肉羊乳扣碗酪的加工工艺。为:白砂糖、琼脂熬汁→过滤→杀菌→添加到过滤杀菌的羊奶中调配→冷却→加江米酒→分装→冷凝→纯化→成品。产品配方为:新鲜山羊奶400g,8%桃果肉,8%梨果肉,9%葡萄干,果肉用30%的砂糖液煮制8min最佳,7.5%白砂糖,0.5%琼脂以及1.5%江米酒。该果肉扣碗酪具有水果的保健功效,营养全面,丰富我国的乳品市场和促进羊奶产业的发展。     

Predominance and Persistence of a Single Clone of Listeria ivanovii in a Manchego Cheese Factory Over 6 Months

In an attempt to study the diversity and persistence of molecular subtypes of pathogenic Listeria spp. in a cheese factory at the La Mancha region of Spain, 43 samples were taken from incoming raw milk (cow’s, ewe’s, goat’s and mixed species) and from certain food‐contact and environmental surfaces before and/or after sanitation. Of these samples, 12 contained pathogenic Listeria. From the chromogenic agar plates corresponding to those, 46 phosphatidylinositol‐specific phospholipase C‐positive isolates were randomly taken for further analysis, including biochemical tests and pulsed‐field gel electrophoresis (PFGE). They coincided in identifying all the 46 as Listeria ivanovii subsp. ivanovii, apparently a single PFGE type. Both ewe’s and goat’s raw milk batches from asymptomatic animals tested along the 6‐month period persistently carried the same strain, which was also obtained from inner surfaces of raw milk truck tanks and the milk dump tank at the cheese factory. Biofilm‐forming abilities of this L. ivanovii clone and interference against L. monocytogenes Scott A reference strain were tested, but failed to account for the clone’s apparent pervasive presence.     

不同因素对羊奶干酪出品率和感官品质的影响

为提高羊奶干酪的出品率和感官品质,以关中奶山羊奶为原料,研究了原料乳浓度、凝乳酶、杀菌条件、酸化条件和氯化钙对羊奶干酪出品率和感官品质的影响。结果表明,原料乳浓度较高,凝乳酶选用羔羊凝乳酶,杀菌条件63℃,30min,酸化pH6.4,氯化钙添加量0.01%-0.02%时干酪出品率较高、感官品质较好。     

Survival of spray‐dried and free‐cells of potential probiotic Lactobacillus plantarum 564 in soft goat cheese

A high viability of probiotics in food product, with a living cells threshold of 10⁷/cfu/g (colony‐forming units/g) is a challenge to achieve in food production. Spray drying is an efficient and economic industrial method for probiotic bacterial preservation and its application in food products. In this study, the survival of free and spray‐dried cells of potential probiotic strain Lactobacillus plantarum 564 after production and during 8 weeks of storage of soft acid coagulated goat cheese was investigated, as well as compositional and sensory quality of cheese. Total bacterial count of spray‐dried Lb. plantarum 564 cells were maintained at the high level of 8.82 log/cfu/g in cheese after 8 weeks of storage, while free‐cell number decreased to 6.9 log/cfu/g. However, the chemical composition, pH values and sensory evaluation between control cheese (C1 sample made with commercial starter culture) and treated cheese samples (C2 and C3, made with the same starter, with the addition of free and spray‐dried Lb. plantarum 564 cells, respectively) did not significantly differ. High viability of potential probiotic bacteria and acceptable sensory properties indicate that spray‐dried Lb. plantarum 564 strain could be successfully used in the production of soft acid coagulated goat cheeses.     

Cutaneous Listeriosis in a Veterinarian with the Evidence of Zoonotic Transmission – A Case Report

A case of Listeria monocytogenes skin infection in a man is presented. A 54‐year‐old male veterinary practitioner developed pustular changes on the skin of arms and hands after assisting with the delivery of a stillborn calf. Listeria monocytogenes was isolated from the skin lesions on the arms and from the bovine placenta. Listeria monocytogenes isolates were serotyped and genotyped with pulsed‐field gel electrophoresis (PFGE) to confirm the suspected transmission of the pathogen from animal to human. All isolates were of serotype 4b with identical pulsotype. To the best of our knowledge, this is the first case of cutaneous listeriosis in which the evidence for zoonotic transmission of L. monocytogenes is supported by genotyping methods.     

Outbreak of clinical listeriosis in sheep: evaluation from possible contamination routes from feed to raw produce and humans

We report the results of clinical and microbiological investigations on Listeria monocytogenes infections in a flock of 55 sheep and describe the implications for the safety of the raw milk and raw-milk cheeses produced in the on-farm dairy. The outbreak was caused by feeding grass silage, which was contaminated with 5 log10 CFU L. monocytogenes/g. Clinically, although having been fed from the same batch of silage, abortive (nine ewes), encephalitic (one ewe) and septicaemic (four ewes) forms of listeriosis were observed during the outbreak phase. As the starting point of feeding the contaminated silage was known we could calculate an incubation period of 18+/-2 and 26 days for the abortive and the encephalitic form of listeriosis, respectively. Pathologically, the septicaemic cases suffered from Listeria accumulation at comparable numbers in visceral organs but not in the brain. Only a single ewe developed central nervous symptoms and a rhomb-encephalitis was immunohistologically confirmed. In this case the infection proceeded from the nasal mucosa into the brain, with no infections of the liver, spleen and other visceral organs. Sampling of the cheese production chain, the farm environment and the persons living at the farm revealed the exposure of a farm-worker to an isolate genetically indistinguishable from the outbreak clone, obviously through the consumption of faecally contaminated bovine raw milk. The cheese under processing was free of Listeria because, as a result of intensive consultations, the farmer ensured a proper acidification of the cheese. The epidemiological findings suggest that food safety matters should be assessed in any case where infection of food-producing animals with potential human pathogens is observed.     

Deletion of the oligopeptide transporter Lmo2193 decreases the virulence of Listeria monocytogenes

BackgroundListeria monocytogenes is a gram-positive bacterium that causes listeriosis mainly in immunocompromised hosts. It can also cause foodborne outbreaks and has the ability to adapt to various environments. Peptide uptake in gram-positive bacteria is enabled by oligopeptide permeases (Opp) in a process that depends on ATP hydrolysis by OppD and F. Previously a putative protein Lmo2193 was predicted to be OppD, but little is known about the role of OppD in major processes of L. monocytogenes, such as growth, virulence, and biofilm formation.ObjectivesTo determine whether the virulence traits of L. monocytogenes are related to OppD.MethodsIn this study, lmo2193 gene deletion and complementation strains of L. monocytogenes were generated and compared with a wild-type strain for the following: adhesiveness, invasion ability, intracellular survival, proliferation, 50% lethal dose (LD₅₀) to mice, and the amount bacteria in the mouse liver, spleen, and brain.ResultsThe results showed that virulence of the deletion strain was 1.34 and 0.5 orders of magnitude higher than that of the wild-type and complementation strains, respectively. The function of Lmo2193 was predicted and verified as OppD from the ATPase superfamily. Deletion of lmo2193 affected the normal growth of L. monocytogenes, reduced its virulence in cells and mice, and affected its ability to form biofilms.ConclusionsDeletion of the oligopeptide transporter Lmo2193 decreases the virulence of L. monocytogenes. These effects may be related to OppD''s function, which provides a new perspective on the regulation of oligopeptide transporters in L. monocytogenes.     

世界及我国奶山羊产业发展现状及趋势分析

近年来,世界山羊养殖数量持续增长,据联合国粮农组织(FAO)统计显示,2018年全球山羊养殖数量已超10.4亿只,其中奶山羊养殖数量超2.16亿只,约有90%以上的奶山羊和山羊奶产自亚洲和非洲。欧洲的奶山羊存栏和产奶量均在亚洲和非洲之后,但其单产水平远高于其他各大洲,在世界奶山羊每只平均年产奶量100 kg以上的国家中,前十位均为欧洲国家。我国奶山羊产业发展迅速,2018年我国奶山羊实际存栏约518万只,年产羊奶量约100万t,约占全国鲜奶产量的3.3%。本文对全球及我国奶山羊产业进行了纵向和横向比较,客观分析我国奶山羊产业的地位、发展现状以及未来发展趋势,旨在为我国奶山羊产业的发展提供参考。     

简析凝乳酶凝乳机理及羔羊凝乳酶自制方法

本文重点介绍了凝乳酶的种类和凝乳机理,以及自制羔羊凝乳酶及其活力测定的方法,对引导我国家庭牧场和小型羊乳企业突破凝乳酶自制核心技术,创新开展羊奶酪生产研发,填补国产羊奶酪市场空白与丰富羊乳制品种类,具有重要的指导意义。     

蛋花羊奶皮子配方及加工工艺研究

通过改进传统奶皮的加工工艺,研究开发出一种营养价值更加全面,外观和风味更好,更易吸收的新型鸡蛋花羊乳奶皮子。本研究以新鲜山羊奶和鸡蛋为主要原料,通过正交试验筛选出了蛋花奶皮子的最佳制作工艺以及原料配方。试验得出:(1)蛋花奶皮子最佳制作工艺:原料乳→过滤、灭菌→均质→加热翻扬搅拌(90℃,2h)→加入鸡蛋糊(2%)→轻搅混匀→保温(4-6h)→停止加热使其自然冷却(约12h)→从锅中倒出奶皮子→干燥→冷藏。(2)蛋花奶皮子最佳原料配方:新鲜羊奶98%,鸡蛋添加量2%,新鲜羊奶≥3.5 kg。研制的新型羊乳制品不仅含有人体所需的亚油酸和亚麻酸,而且还有丰富的DHA和卵磷脂,健脑益智,改善各个年龄组的记忆力,具有丰富的营养价值。     

自主筛选的植物乳杆菌对酸羊乳品质与功能特性的影响

为改善酸羊乳风味与品质,提高酸羊乳的功能价值,将自浆水中筛选的植物乳杆菌JS5和JS19用于羊乳发酵,研究其对酸羊乳理化性质、质构特性及功能特性的影响。结果表明：2 种植物乳杆菌与商业发酵剂复合发酵后,均能在贮藏期内有效提高酸羊乳持水性和表观黏度,降低其硬度与胶着性,促进乙醛和双乙酰的释放;添加植物乳杆菌JS5的酸羊乳胆固醇降解率显著高于对照组（P＜0.05）,最高可达36.62%;添加植物乳杆菌JS19的酸羊乳体外抗氧化能力更强,贮藏1 d时1,1-二苯基-2-三硝基苯肼自由基清除率高达70.58%,铁离子还原/抗氧化能力达32.03 μmol/L。2 种菌株均为适用于羊乳发酵生产的优良菌株。     

Listeria monocytogenes in Products of Animal Origin in Turkey

A study was carried out on 430 samples of different foodstuffs (soft cheese, raw chicken, minced beef, sausage, fish) and 400 carcase samples (sheep, young and adult cattle) for screening of Listeria monocytogenes. It was found that only one of the samples containedL. monocytogenes at >10³ cfu/ml in the initial examination, but another 42 samples containedL. monocytogenes following an enrichment process. L. monocytogenes was isolated most frequently from raw chicken samples (18%), but was not isolated from sausage samples. Forty-three isolates were defined as serotypes by using Bacto-Listeria- O-antisera Type 1 (Difco 2300-50-2) and Type 4 (Difco 2301-50-1) except that Type poly was not used. For these reasons, all isolates were classified as type 1 or type 4 and the other was termed untypeable. Twenty-one samples were type 1, 17 were untypeable, and 5 were both serotype 4 and untypeable. This revised version was published online in July 2006 with corrections to the Cover Date.     

奶山羊养殖与其他养殖项目的比较优势

奶山羊养殖是一项投资小、设备及技术要求低、资金周转快、收益相对稳定的养殖产业项目,很适应农村发展.奶山羊以产奶为主,奶肉兼用,可提供营养丰富、适口性好的生鲜乳和鲜羊肉,市场需求量大;近年来,活羊出栏价相对稳定,在中小城市,羊肉价格保持在80元/kg左右,鲜羊奶市场价格在14元/kg左右.奶山羊体格健壮、活泼好动,适应性...     

Occurrence of Listeria Species in an Abattoir for Cattle and Pigs in Bosnia and Hercegovina

Altogether 496 samples of meat, lymph nodes, process water and swabs from different places in the abattoir were examined for the presence of Listeria spp. L. monocytogenes was isolated from 31 (6%) and other Listeria spp. from 65 (13%) samples. L. monocytogenes was isolated from 2 of 10 beef meat samples, 4 of 50 pig meat samples and 1 of 21 lymph nodes of pigs. No Listeria bacteria were isolated from lymph nodes of cattle. The highest percentage of Listeria was recovered from the unclean sections (cattle 22% and pigs 27% ) and the highest frequency was observed during the winter months.     

黄金伴侣对关中奶山羊生产性能的影响

[目的]探讨黄金伴侣对关中奶山羊生产性能的影响,[方法]在富平县流曲镇双杨村向忠奶山羊场选取月龄、体重相近的健康关中奶山羊产奶羊60只,采用配对试验设计方法,试验组日粮中添加黄金伴侣,对照组不添加,两组饲养管理条件完全相同。[结果]试验组奶山羊日均产奶量提高0.4 kg,提高22.22%(P0.05),饲料转化率提高19.38%(P0.05)。日增重增加0.90 kg(P0.05);平均日增重增加0.15 kg(P0.05)。日纯收入增加2.06元。经济效益提高33.40%(P0.05)。[结论]在关中奶山羊日粮中添加黄金伴侣,奶山羊产奶量、饲料转化率和日增重均增加,经济效益提高。     

Host-Parasite Relations In Initiation Of Infection: I. Occurrence Of Listeriosis In Arctic Mammals, With A Note On Its Possible Pathogenesis

A lemming colony maintained at Fort Churchill was examined for the possibility of the presence of L. monocytogenes in latent form, but the organism was not isolated. Following transfer of the lemmings from Churchill to Kingston, L. monocytogens was isolated. In speculation on the pathogenesis of Listerosis, the author suggests that an upset carbohydrate metabolism may be involved in the trigger mechanism.

The isolation of L. monocytogenes from a seemingly ill Arctic fox caught at Fort Churchill is reported for the first time.

     

The Occurrence of Pathogenic Listeria monocytogenes and Antibodies against Listeriolysin‐O in Buffaloes

The occurrence of Listeria monocytogenes in meat and milk samples, and antilisteriolysin O (ALLO) antibodies in sera of buffaloes were studied. Isolation of the pathogen was attempted from the samples by selective enrichment in University of Vermont Medium and plating onto Dominguez–Rodriguez isolation agar. The pathogenicity of the isolates was tested by Christie, Atkins, Munch Petersen test and mouse inoculation test. Of 167 meat samples 2.4 and 10.17% were positive for L. monocytogenes and Listeria sp., respectively. Of the 64 milk samples 6.25 and 26.13% were positive for L. monocytogenes and Listeria sp., respectively. A total of 284 serum samples were tested by listeriolysin O (LLO)‐based indirect enzyme‐linked immunosorbent assay of which 25.35% were found to be seropositive. The culture positivity for L. monocytogenes and detection of ALLO did not show any agreement (κ=0.035). The prevalence of pathogenic L.monocytogenes in milk and meat and the occurrence of anti‐LLO antibodies is of concern from the public health point of view.