双乙酸钠在食品中可抑制李斯特菌

介绍李斯特菌和污染引起“李斯特病”的特征和条件，双乙酸钠作为抗微生物剂在抑制李斯特菌的有效作用。     

人李斯特菌病监测和预防策略研究

目的通过分析比较李斯特菌病的流行特征、各国的监测方法及预防控制措施,为我国制定李斯特菌病的监测和防控策略提供依据。方法文献比较研究和分析。结果欧美多国已经将李斯特菌病列入法定报告疾病管理,李斯特菌病在欧洲呈上升趋势,在美国有所下降。暴发的发现依赖于病例报告和病人分离菌株的分型和比对。通过暴发调查可以获得危险食品、传播途径等流行病学资料。结论只有将李斯特菌病纳入法定报告疾病管理,将医院分离的病人菌株提交到公共卫生实验室,对实验室确诊病例进行流行病学调查,才能获得李斯特菌病流行规律的资料,采取针对性的防控措施。     

江西省首起中式凉拌菜引起一例孕妇李斯特菌病的溯源研究

目的 对江西省首起中式凉拌菜引起一例孕妇李斯特菌病进行溯源分析。方法 采用描述性研究方法对李斯特菌病患者开展流行病学调查,采用临床检测方法和国家标准GB 4789.30—2016方法对血液、食品样品中的单核细胞增生性李斯特菌进行分离,并用生化、质谱方法对分离的菌株进行鉴定,菌株的分型和溯源分析使用脉冲场凝胶电泳、全基因组测序方法。结果 流调结果显示,患者症状以发热为主,新生儿无感染,有每周进食一次中式凉拌菜的习惯。患者血培养鉴定结果为单核细胞增生性李斯特菌,现场对患者家进行的环境样本采样未检出单核细胞增生性李斯特菌,采集患者常去的熟食店销售的2份凉拌菜检出了该细菌。PFGE电泳分型显示患者分离株与食品分离株分型结果一致,全基因组测序结果菌株均为ST1型。结论 中式凉拌菜存在引起孕妇李斯特菌病的风险,应加强监测,有关部门应加强对相关餐饮店的监管。     

单增李斯特菌在生食鱼片中生长模型的建立

为研究生食鱼片中单增李斯特菌的生长规律,将单增李斯特菌接种到经冷杀菌后的3 种生食鱼片（三文鱼片、金枪鱼片、鲷鱼片）中,分别置于4、8、15、25、35 ℃环境下培养,间隔适当时间取出计数。用5 种常用的一级模型（Gompertz模型、Baranyi模型、Logistic模型、Richards模型和MMF模型）对实验数据进行拟合,通过比较相关系数R2和均方误差（mean square error,MSE）,确定最适一级模型为Gompertz模型。建立单增李斯特菌生长动力学参数（最大比生长速率μm和迟滞期λ）关于温度、pH值和水分活度的二级平方根扩展模型,并应用相关系数R2、偏差值Bf和准确值Af进行验证。结果表明,构建的二级模型能够很好地描述生食鱼片中单增李斯特菌的生长情况。     

肽核酸荧光原位杂交技术快速检测食品中的李斯特菌属及单增李斯特菌

目的建立利用肽核酸荧光原位杂交技术(PNA-FISH)快速检测食品中李斯特菌属及单增李斯特菌的方法。方法针对李斯特菌属、单增李斯特菌分别设计合成2份PNA探针lis-16S-1、lm-16S-2,并建立荧光原位杂交技术,优化杂交条件,对选取的13株李斯特菌和其他9株非李斯特菌进行检测,验证探针的特异性和灵敏度,并对118份食品样品用LB肉汤2次增菌培养后进行PNA-FISH检测。结果探针灵敏度和特异性均为100%,从118份食品中检出14株李斯特菌和8株单增李斯特菌,结果与API方法和VITEK方法鉴定结果一致。结论 PNA-FISH方法可靠易行,对从食品中检测致病性单增李斯特菌有较高的实用性。     

即食菜卷和肉汤中单增李斯特菌生长模型及控制研究

通过对单增李斯特菌在不同NaCl浓度、不同pH、不同温度下营养肉汤中生长情况的研究,确定了单增李斯特菌的最佳生长条件。建立了30℃下单增李斯特菌在营养肉汤和即食菜卷中的生长模型。以模型为依据,提出了即食菜卷加工中控制李斯特菌的措施。     

食源性单增李斯特菌与英诺克李斯特菌基因组特征比较

目的 通过全基因组测序对甘肃省市售食品中分离的单增李斯特菌和英诺克李斯特菌基因组特征进行比较分析。方法 收集2021—2022年甘肃省市售食品中分离的25株单增李斯特菌和7株英诺克李斯特菌作为研究对象,对菌株进行全基因组测序,分析其系统发育谱系、克隆复合群（CC）、序列型（ST）、毒力基因、抗性基因及泛基因组。结果 32株李斯特菌分属单增李斯特菌谱系Ⅰ和Ⅱ及英诺克李斯特菌3个群,单增李斯特菌分为10个亚群,英诺克李斯特菌分为5个亚群,与CC型保持一致,核心基因组多位点序列分型能将各谱系中不同CC型的菌株明显分开,谱系Ⅰ与英诺克李斯特菌的进化关系更近。25株单增李斯特菌均携带李斯特菌毒力岛LIPI-1和内化素基因,不携带LIPI-3,有2株ST87型菌株携带LIPI-4;7株英诺克李斯特菌均不携带LIPI-1和内化素基因,均携带LIPI-4,有5株菌携带LIPI-3。单增李斯特菌有16株携带SSI-1、3株携带SSI-2,7株英诺克李斯特菌均不携带SSI-1,有6株携带SSI-2。李斯特菌的泛基因组大小随着测序基因组数目的增加呈现线性增多,25株单增李斯特菌当菌株数量达到15后核心基因数目稳定在2 272个,占泛基因组基因数目的46.2%,25株单增李斯特菌和7株英诺克李斯特菌共同的核心基因1 487个,当菌株数量达到10后数目趋于稳定。结论 核心基因组多位点序列分型可将不同谱系不同克隆复合群的李斯特菌进行区分,英诺克李斯特菌与单增李斯特菌生化特性相似与其亲缘关系相近有关,致病性差异与英诺克李斯特菌缺失单增李斯特菌特有的毒力基因相关。     

单增李斯特菌增殖的影响因素研究

本实验研究在冷却肉中单增李斯特菌的增殖以及产溶血素情况,考查与冷却肉相关的各种理化和生物因素对单增李斯特菌增殖的影响。研究表明,单增李斯特菌在所选择的温度范围内,温度越低,增殖受到的影响越大,同时低于0.93的水分活度下或pH低于5.0,单增李斯特菌失去增殖的能力。另外,初始菌数和气体环境也对单增李斯特菌产生了影响,冷却肉中存在的腐败菌和20%以上浓度的CO2都抑制了单增李斯特菌的增殖。     

冷饮中李斯特菌的检测技术

０前言李斯特菌（Ｌｉｓｔｅｒｉａｍｏｎｏｃｙｔｏｇｅｎｅｓ）是一种病原性食物中毒菌。近年来，一些发达国家和地区常有因食用了奶酪和其他一些食物引起李斯特菌中毒的事件发生，去年１０月，在香港销售的美国ｄｒｅｙｅｒ，ｓ雪糕中发现了李斯特菌，它导致了几人死亡...     

李斯特氏菌对肉制品保存的影响

肉制品接种单核细胞增生李斯特氏菌(15~5个/g)后,经真空包装或非真空包装,在5℃,25℃条件下保存,观察其动态。25℃,非真空包装一天,菌数超过10~8个/g,真空包装5天,菌数超过10~8个/g;5℃,非真空包装10天,菌数超过10~8个/g,真空包装15天,菌数超过10~7个/g。真空包装对单核细胞增生李斯氏菌有抑制作用,5℃冰箱保存条件下,单核细胞增生李斯特氏菌仍能发育增殖。因此,肉制品加热后,如果二次污染单核细胞增生李斯特氏菌,危险性很大。     

一类带隔离项的具非线性传染率的SIQ模型的全局分析

研究了一类带有隔离项的具有非线性传染率的SIQ传染病模型的全局稳定性.得到了基本再生数R0,利用Lasalle不变集原理,证明了无病平衡点的全局稳定性.利用零点定理及方程根的分布特点.证明了地方病平衡点的存在性及唯一性.同时,借助多元函数微分学关于极值判断定理及Lyapunov函数,证明了地方病平衡点的全局稳定性.     

一类具有B-D非线性传染率的传染病模型的全局稳定性分析

对一类具有B-D非线性传染率的传染病模型的全局稳定性进行研究.利用分析计算技巧与李雅谱诺夫函数构造,得到阈值R及无病平衡点和地方病平衡点的存在条件,证明了无病平衡点和地方病平衡点的局部与全局稳定性.结果表明,具有B-D非线性传染率的传染病模型的平衡解局部稳定性与全局稳定性由含模型参数的阀值来决定.     

基于贝叶斯网络的猪肉合格率的模型构建

我国是猪肉消费大国,其卫生情况对人民关系重大。近年来肉制品的微生物污染现象不容乐观,所以建立一个行之有效的猪肉追溯系统有利于更好地控制猪肉质量。本文根据现有的猪肉卫生标准,选出猪肉的四种优势致腐菌:大肠杆菌、单增李斯特菌、沙门氏菌以及金黄色葡萄球菌,以贝叶斯网络为理论依据,利用Hugin Lite软件拟合出合格率模型。结果表明,基于贝叶斯网络可通过改变菌体数据快速求得猪肉的合格率,大大缩减检验时间,为猪肉卫生合格率的质检工作提供理论依据。     

基于层次贝叶斯法的沙门氏菌食品污染率统计分析

为系统性研究我国大陆范围内食品中沙门氏菌污染状况,基于贝叶斯估计方法,利用文献挖掘(Literature mining)所得的数据,建立层次贝叶斯模型(Hierarchical Bayesian model),对我国市售食品中沙门氏菌污染率进行可靠统计.结果表明,我国大陆地区市售食品的沙门氏菌平均污染率,2004～20...     

具有非线性发生率的SIR传染病模型的全局动力学分析

研究一类具有非线性发生率的时滞SIR传染病模型,此发生率反映了当某种严重疾病的染病者数目变大时,疾病会对人们心理上产生影响.研究表明,基本再生数(￡)0完全决定了疾病的传播动力学:当(￡)0＜l时,模型只存在一个无病平衡点,且它是全局渐近稳定的;当(￡)0＞l时,模型还有一个地方病平衡点,且此时痰病持久.通过Lyapu...     

Pathogen-specific incidence rate of clinical mastitis in Flemish dairy herds,severity, and association with herd hygiene

A one-year survey on clinical mastitis was conducted on 50 randomly selected commercial Flemish dairy herds to estimate the pathogen-specific incidence rate of clinical mastitis (IRCM). The severity of the cases and the potential associations with herd hygiene were studied. Participating producers sampled 845 cases and 692 dairy cows. The mean and median IRCM was estimated at 7.4 and 5.3 quarter cases per 10,000 cow-days at risk, respectively. A large between-herd variation was observed (range of 0–21.3). In general, the IRCM was lower in heifers compared with multiparous cows (2.9 vs. 11.0 quarter cases per 10,000 cow-days at risk). However, the overall IRCM in the first week after calving was higher in heifers compared with cows (43.4 vs. 31.6 quarter cases per 10,000 cow-days at risk). Streptococcus uberis (18.2% of the cases) and Escherichia coli (15.5%) were the most frequently isolated pathogens and no growth was observed in 19.9% of the cases. The majority of the cases (63.1%) were mild (only clots in milk). Moderate (hard quarter without general signs) and severe symptoms (systemic illness) were observed in 29.9 and 7.0% of the cases, respectively. Isolation of E. coli (vs. any other culture result) was more likely in moderate and severe cases compared with mild cases. Overall IRCM and E. coli IRCM were higher in dirty compared with clean herds based on udder hygiene scores (9.0 and 1.7 vs. 6.0 and 0.6 quarter cases per 10,000 cow-days at risk, respectively). This study broadens the knowledge on clinical mastitis in Flemish dairy herds and underlines the high risk of CM in early-lactation heifers, the role of the so-called environmental pathogens, and herd hygiene.     

具有时滞与饱和发生率的脉冲接种模型的研究

研究了一类具有时滞与饱和发生率的SIR脉冲接种模型,利用频闪映射得到了模型的无病周期解,进而利用比较原理给出了无病周期解全局稳定的条件及疾病控制的最大接种周期τmax,当接种周期τ<τmax时,理论上疾病可以被根除.该脉冲接种模型相比较传统的接种模型,所需成本更低,且更加有效.     

The influence of cow factors on the incidence of clinical mastitis in dairy cows

Many cow-specific risk factors for clinical mastitis (CM) are known. Other studies have analyzed these risk factors separately or only analyzed a limited number of risk factors simultaneously. The goal of this study was to determine the influence of cow factors on the incidence rate of CM (IRCM) with all cow factors in one multivariate model. Also, using a similar approach, the probability of whether a CM case is caused by gram-positive or gram-negative pathogens was calculated. Data were used from 274 Dutch dairy herds that recorded CM over an 18-mo period. The final dataset contained information on 28,137 lactations of 22,860 cows of different parities. In total 5,363 CM cases were recorded, but only 2,525 CM cases could be classified as gram-positive or gram-negative. The cow factors parity, lactation stage, season of the year, information on SCC from monthly test-day records, and CM history were included in the logistic regression analysis. Separate analyses were performed for heifers and multiparous cows in both the first month of lactation and from the second month of lactation onward. For investigating whether CM was caused by gram-positive or gram-negative pathogens, quarter position was included in the logistic regression analysis as well. The IRCM differed considerably among cows, ranging between 0.0002 and 0.0074 per cow-day at risk for specific cows depending on cow factors. In particular, previous CM cases, SCC in the previous month, and mean SCC in the previous lactation increased the IRCM in the current month of lactation. Results indicate that it is difficult to distinguish between gram-positive and gram-negative CM cases based on cow factors alone.     

A model of the specific growth rate inhibition by weak acids in yeasts based on energy requirements

Zygosaccharomyces bailii, a spoilage yeast, capable of metabolic activity in food environments with low pH, low a_w and in the presence of weak acid preservatives was chosen for a study on the effect of benzoic acid on growth parameters. In batch cultures, under controlled pH, this food preservative inhibited growth, decreasing the specific growth rate (μ) and the yield coefficient (Y_S) on glucose. Data obtained at pH 3.5, 4.0 and 4.5 showed that this inhibition was exclusively promoted by the undissociated form of the acid since the effect was independent of pH when the concentration of the acid was expressed in this form. Moreover, the relationship between the values for μ and Y_S, provided evidence that the specific consumption rate of glucose (q_S) was not affected by benzoic acid, indicating that the inhibition of growth should be completely explained by a decrease of Y_S. The outcome of parallel experiments performed in continuous culture was that the decrease of Y_S was due to an increase of the maintenance coefficient (m), defined as the fraction of q_S diverted from growth to cope with stress, represented in this case by the presence of the preservative. Based on these results a model was built, assuming that m increased hyperbolically with the concentration of benzoic acid, from zero in the absence of the acid up to q_S when growth was completely inhibited. The concentration of the acid, for which m=q_S/2, is a constant (K_W), and represents a measure of the tolerance for a preservative, in this case benzoic acid. The simple equation μ/μ₀=1+W/K_W predicts the value of μ for a concentration (W) of the preservative, requiring the knowledge of two parameters: the specific growth rate in the absence of the preservative (μ₀) and K_W. The equation fitted very well the data of the effect of benzoic acid on the specific growth rate of Z. bailii, having K_W=0.96 mM benzoic acid. The model was also validated with other spoilage yeasts grown in the presence of benzoic acid in microtiter plates in an automated spectrophotometer. The values obtained for K_W under these conditions confirm Z. bailii as the most tolerant (K_W=2.1 mM) followed by Pichia sp. (K_W=0.78 mM), Saccharomyces cerevisiae (K_W=0.53 mM) and Debaryomyces hansenii (K_W=0.11 mM).