不同pH、温度、金属离子对溶菌酶抗菌稳定性的初步研究

本文选择金黄色葡萄球菌(Staphylococcus aureus)与大肠杆菌O157:H7(Escherichia coli O157:H7)为受试菌,以活菌抑制率为评价指标,评价不同pH、温度、金属离子条件对溶菌酶抗菌稳定性的影响。结果表明:溶菌酶对金黄色葡萄球菌与大肠杆菌O157:H7的最小抑菌浓度分别为1.3×10-3 g/mL与2.6×10-3 g/mL。溶菌酶在酸性条件(pH4~6),其对两种菌均能表现很好的抑菌效果。经过4~121 ℃处理后,溶菌酶的抗菌活性不受处理温度的影响。不同金属离子对溶菌酶抗菌活性影响较大,Zn2+、Mn2+与溶菌酶具有较强的协同抑菌效应,其中Zn2+效果最为明显,而Mg2+、Ca2+具有一定的拮抗抑菌效应,可降低溶菌酶的抑菌效果。     

植物源香辛料对E.coli O157：H7的杀菌效果比较

以常见植物源香辛料包括八角、丁香、桂皮、茴香、芥末、花椒、麻椒、香叶为材料,研究其醇提取物在不同浓度和作用时间下对E.coli O157：H7的杀菌效果,并分析不同产地对香辛料杀菌效果的影响。结果表明：试验用香辛料对E.coli O157：H7均具有一定的杀菌作用,杀菌能力差异显著（p＜0.05）,杀菌效果最好的香辛料为丁香,体积分数为9.1%的丁香提取物作用1 h可杀灭E.coli O157：H7 5 lg（CFU/mL）以上,其次为八角;相比其它香辛料,芥末提取物杀灭E.coli O157：H7的效果不理想,体积分数为50%的3个不同芥末产品提取物处理1 h平均杀灭2.47 lg（CFU/mL）E.coli O157：H7;产地来源对某些香辛料的杀菌能力有影响,如茴香、桂皮、八角（p＜0.05）。     

不同粒径纳米金标记二抗增强表面等离子共振检测E. coli O157:H7

基于双通道表面等离子共振（surface plasmon resonance,SPR）传感器,结合不同粒径的金纳米粒子（Aunanoparticle,AuNPs）标记多克隆抗体（polyclonal antibody,PAb）作为第二抗体,采用氨基偶联的方法将PAb固定在传感器表面作为第一抗体,采用三明治夹心法进行了检测大肠杆菌O157∶H7（E. coli O157∶H7）的研究。考察3 种粒径的AuNPs作为标记物,增强SPR响应信号检测E. coli O157∶H7的能力。结果表明,增强效果最佳的AuNPs粒径为17.79 nm,其可检测到的E. coli O157∶H7的最低浓度为10 CFU/mL。     

甘草提取液对大肠杆菌O157∶H7抑菌作用及豆腐干的保鲜研究

研究了甘草提取液对豆腐干中大肠杆菌(E.coli)O157∶H7的抑菌作用以及对豆腐干在10℃下的贮藏保鲜作用。根据响应面法优化的最佳工艺条件得到甘草提取液,用于大肠杆菌O157∶H7的抑菌研究,通过理化指标和感官评价研究对豆腐干的保鲜作用。结果表明提取的最佳条件为提取温度77.80℃,提取时间7.58 h,料液比1∶9.61(g/mL),5%甘草提取液使大肠杆菌O157∶H7在豆腐干中的停滞期达5.8 d,同时能延缓豆腐干的pH值和可滴定酸度、失水率、感官品质等变化。甘草提取液对大肠杆菌O157∶H7有较好的抑制作用,对豆腐干有一定的保鲜作用。     

致病菌快速检测管联合基质辅助激光解吸电离飞行时间质谱法鉴定即食食品中的大肠埃希氏菌O157:H7

目的 建立基于致病菌快速检测管技术联合基质辅助激光解吸电离飞行时间质谱法(matrix-assisted laser desorption ionization-time of flight mass spectrometry, MALDI-TOF MS)快速、高效、准确鉴定即时食品中大肠埃希氏菌(Escherichia coli, E. coli) O157:H7的方法。方法 选取改良胰蛋白胨大豆肉汤(modified tryptone soya broth, mTSB)为初筛培养基, 制作出针对即时食品中E. coli O157:H7的致病菌快速检测管, 初筛阳性结果采用MALDI-TOF MS技术鉴定。结果 5株常见E. coli O157:H7菌株均能特异检出, 而其他非E. coli O157:H7均未检出, 灵敏度可达51 CFU/mL; 通过对人工污染样品和自然样品检测, 鉴定结果和GB 4789.36—2016《食品安全国家标准 食品微生物学检验 大肠埃希氏菌O157:H7/NM检验》方法完全一致, 且检测效率提高了30%。结论 两种技术联合应用建立的鉴定即时食品中E. coli O157:H7的新方法, 操作简便、成本低廉, 适合推广, 为快速、准确鉴定即时食品中E. coli O157:H7打开了新思路。     

UVC-GA抑菌液对罗非鱼皮在0℃贮藏下微生物区系及品质的影响

紫外短波(UV-C)辐照没食子酸(GA)溶液12 h形成一种新的抑菌液(UVC-GA),与GA和去离子无菌水(DI)分别处理鱼皮后在0℃贮藏,DI组、GA组和UVC-GA组的贮藏期感官评价货架期分别为5 d、7 d和8 d。对优势菌属测定结果发现,1D组5 d(以下简称DI5)的优势菌属是Pseudoalteromonas(31.31%)、Candidatus-Bacilloplama(21.50%)和Litorimicrobium(17.11%),GA组7d(以下简称GA7)的优势菌是Aliivibrio(42.40%)、Pseudoalteromonas(20.51%)和Psychrobater(10.32%),UVC-GA组8d(以下简称UVC-GA8)的优势菌属Aliivibrio(29.81%)、C.Bacilloplama(20.90%)和Moritella(11.11%),UVC-GA8的Vibrio和Pseudoalteromonas相对含量均较低。对鱼皮品质相关指标检测发现,UVC-GA组的TVB-N、TVC、腐胺、尸胺、次黄嘌呤核苷(Hx R)和次黄嘌呤(Hx)的含量均比较DI组和GA组低,但5′-单磷酸肌苷(IMP)含量高于其它组;UVC-GA8的K值显著低于DI5和GA7,随着贮藏时间延长UVC-GA组的p H值呈下降线性趋势,而DI组和GA组则呈"V"形。以上结果表明,UVC-GA组影响了罗非鱼皮在0℃贮藏下的微生物区系、TVB-N、TVC、生物胺、ATP复合物、K值等变化,应用UVC-GA抑菌液保鲜使得鱼皮货架期变长。     

基于内参的大肠埃希氏菌O157∶H7实时荧光定量PCR快速检测方法的建立

针对大肠埃希氏菌O157∶H7 rfbE和Flic靶基因保守序列,设计特异性引物和探针,优化反应体系,并加入内参（internal amplification control,IAC）,建立能够实时监控反应过程的荧光定量聚合酶链式反应（polymeasechain reaction,PCR）检测方法。结果表明,该方法对E. coli O157∶H7基因组DNA的最低检测限为1 pg/μL;对含有靶基因质粒的最低检测限为103 copies/μL;对细菌的最低检测限为5×103 CFM/mL;Ct值与模板拷贝数均呈良好的线性关系（R2=0.999）。人工污染实验结果表明,在初始菌量为7 CFM/25 g时,采用水洗加试剂盒法提取DNA,E. coli O157∶H7在增菌6 h后即可检出;而采用水煮法提取DNA,则在增菌10 h后方可检出。建立的E. coli O157∶H7实时荧光定量PCR方法,既能有效检测食品中O157∶H7,又能实时监测PCR反应过程,有效防止“假阴性”的发生。     

ε-聚赖氨酸对大肠杆菌O157:H7和金黄色葡萄球菌的抗菌稳定性

大肠杆菌O157:H7和金黄色葡萄球菌是常见的引起食物中毒的食源性致病菌,ε-聚赖氨酸(ε-PL)是一种安全、无毒、天然的食品防腐剂。食品的加工温度、pH值、金属离子是影响食品品质的三大要素。研究ε-PL在不同的温度、p H值、金属离子条件下,对食源性病原菌的杀菌稳定性,是指导ε-PL应用防治此类食源性致病菌的理论基础。结果表明:ε-PL对大肠杆菌O157:H7和金黄色葡萄球菌的最小抑菌质量浓度均为2.60 mg/mL。在4～121℃下,ε-PL抗菌活性不受温度影响,抑菌效果稳定,对大肠杆菌O157:H7和金黄色葡萄球菌有良好的抑菌效果。当p H值为4～6时,ε-PL对大肠杆菌O157:H7和金黄色葡萄球菌的抑菌效果最佳。Mn~(2+)、Zn~(2+)与LYS具有较高的协同作用;Mg~(2+)在很大程度上消除了ε-PL的抑菌效果,且呈剂量效应关系。     

LED蓝光与柠檬酸对大肠杆菌的协同抗菌作用

为了开发新型食品抗菌方法,研究了LED蓝光辐照强度、柠檬酸质量浓度和温度3个因素对营养肉汤中大肠杆菌O157:H7抗菌性能的影响。结果表明:LED蓝光在低温(12℃)下对大肠杆菌O157:H7的抗菌效果优于室温(25℃),且抗菌效果随着光照剂量的增加而增强;柠檬酸在低温下对大肠杆菌O157:H7的影响较弱,但在室温下可明显减缓其生长速率;与空白对照组相比,在使用4 072.3J/cm~2光照剂量的LED蓝光照射后,大肠杆菌O157:H7的数量在低温下可减少(2.60±0.19)lg CFU/mL,而在室温下仅减少(0.67±0.12)lg CFU/mL;加入柠檬酸后,显著增强了LED蓝光的抗菌效果,在使用2 471.0J/cm~2光照剂量的LED蓝光照射后,大肠杆菌O157:H7的数量在低温下可减少(5.13±0.11)lg CFU/mL,在室温下可减少(3.08±0.11)lg CFU/mL。     

乳酸菌对肠出血性大肠杆菌O157:H7抑制作用的研究

为探讨乳酸菌对肠出血性大肠杆菌O157：H7 ATCC43895(E．Coli O157：H7)的抑制作用，在培养基上进行了研究。将E．Coli O157：H7与干酪乳杆菌干酪亚种、植物乳杆菌、发酵乳杆菌、乳酸乳球菌和瑞士乳杆菌同时接种在培养基中，E．Coli O157：H7的活性不受影响；将E．Coli O157：H7接种到培养了24h的乳酸茵培养液中，E．Coli O157：H7活性显下降。以乳酸调整的低pH值对E．Coli O157：H7有一定的杀灭作用。本研究表明：乳酸菌的代谢产物乳酸对E．Coli O157：H7有杀灭作用。     

Survival of Escherichia coli O157:H7 in dry fermented sausages containing micro-encapsulated probiotic lactic acid bacteria

Escherichia coli O157:H7 is capable of surviving the rigorous processing steps during the manufacture of dry fermented sausages. The effect of adding two probiotic organisms, Lactobacillus reuteri and Bifidobacterium longum as co-cultures with the meat starter cultures Pediococcus pentosaceus and Staphylococcus carnosus on the viability of E. coli O157:H7 in dry fermented sausages was studied. A 5 strain cocktail of E. coli O157:H7 was added at 7.4 log cfu/g to the sausage batter and challenged with either or both Lb. reuteri or B. longum before or after they were micro-encapsulated. Sausages were fermented at < or = 26 degrees C and 88% relative humidity (RH) followed by drying at 75% RH and 13 degrees C for 25 d. The pH, water activity (aw), protein, moisture, and numbers of all inoculated organisms were monitored during processing. The pH and aw decreased from 5.7 and 0.98 to 4.9 and 0.88 at the end of fermentation and drying, respectively. These processes reduced E. coli O157:H7 by 1.0 and 0.7 log cfu/g at the end of fermentation and drying, respectively. Unencapsulated Lb. reuteri with or without B. longum reduced E. coli O157:H7 by 3.0 log cfu/g and B. longum caused a 1.9 log cfu/g reduction. While micro-encapsulation increased survival of Lb. reuteri and B. longum, it reduced their inhibitory action against E. coli O157:H7.     

Use of deodorized yellow mustard powder to control Escherichia coli O157:H7 in dry cured Westphalian ham

Dry cured (uncooked) hams with low water activity and pH ≥5.6 seem a likely food vehicle for Escherichia coli O157:H7. In previous work, isothiocyanates produced from mustard glucosinolates by bacterial myrosinase-like activity converted deodorized mustard into a potent antimicrobial in dry sausage. In this study its value in controlling E. coli O157:H7 survival in Westphalian ham was investigated. Hams were inoculated with a 7.5 log cfu g(-1) cocktail of E. coli O157:H7, 4% or 6% (w/w) deodorized yellow mustard powder was surface applied and monitored 80 d for pathogen survival. In one trial to accelerate formation of isothiocyanate, a Staphylococcus (S.) carnosus meat starter culture was added to hams at 45 d (after salt equilibration). At 21 d, E. coli O157:H7 was reduced by 3 log cfu g(-1) on hams treated with mustard powder compared to only a 1 log cfu g(-1) reduction in the control. By 45 d, mustard powder caused a reduction of >5 log cfu g(-1)E. coli O157:H7, whereas it took 80 d for numbers in control hams to be similarly reduced. Although the commercial process used caused a 5 log cfu g(-1) reduction of E. coli O157:H7 in 80 d, 4% or 6% deodorized mustard accelerated this reduction and the S. carnosus starter culture may have contributed to the maintenance of this effect.     

Antibacterial effect of lactoferricin B on Escherichia coli O157:H7 in ground beef.

The antibacterial activity of lactoferricin B on enterohemorrhagic Escherichia coli O157:H7 in 1% peptone medium and ground beef was studied at 4 and 10 degrees C. In 1% peptone medium, 50 and 100 microg of lactoferricin B per ml reduced E. coli O157:H7 populations by approximately 0.7 and 2.0 log CFU/ml, respectively. Studies comparing the antibacterial effect of lactoferricin B on E. coli O157:H7 in 1% peptone at pH 5.5 and 7.2 did not reveal any significant difference (P > 0.5) at the two pH values. Lactoferricin B (100 microg/g) reduced E. coli O157:H7 population in ground beef by about 0.8 log CFU/g (P < 0.05). No significant difference (P > 0.5) was observed in the total plate count between treatment and control ground beef samples stored at 4 and 10 degrees C. The antibacterial effect of lactoferricin B on E. coli O157:H7 observed in this study is not of sufficient magnitude to merit its use in ground beef for controlling the pathogen.     

Cell age, suspending medium and metal ion influence the susceptibility of Escherichia coli O157:H7 to water-soluble maltose chitosan derivative

The effects of cell age, suspending medium and metal ions on the susceptibility of Escherichia coli O157:H7 to the water-soluble maltose chitosan derivative were investigated. In addition, the leakage of glucose, protein (absorbance at 280 nm) and lactate dehydrogenase (LDH) induced by maltose chitosan derivative in saline solution and deionized water, was examined. Cells of E. coli O157:H7 in the mid-exponential phase (6 h) were most susceptible to the chitosan derivative followed by cells in the late-exponential phase (12 h) and stationary phase (24 h). In addition, it was found that the susceptibility of the test organism to the maltose chitosan derivative was less in saline solution than in deionized water. The viable population of E. coli O157:H7 in deionized water containing the maltose chitosan derivative (500 ppm), was reduced from ca 7.6 log cfu/ml to a non-detectable level after 10 h of incubation at 37 degrees C compared to a viable population of ca 6.2 log cfu/ml noted in the chitosan derivative-containing-saline solution. After cells of E. coli O157:H7 were exposed to the chitosan derivative in deionized water, a marked increase in the levels of glucose, protein and LDH activity was observed in the supernatant of cell suspension compared to cells of test organism exposed to the saline solution containing chitosan derivative. Metal ions were also found to reduce the antibacterial activity of chitosan derivative. Their effectiveness increased at greater concentrations and varied with the kinds of metal ions with Ba(2+) the most effective and Mg(2+) the least effective.     

Growth and survival of Escherichia coli O157:H7 during the manufacture and ripening of raw goat milk lactic cheeses

The behaviour of Escherichia coli O157:H7 was studied during the manufacture and ripening of raw goat milk lactic cheeses. Cheese was manufactured from raw milk in the laboratory and inoculated with E. coli O157:H7 to a final concentration of 10, 100 and 1000 cfu ml(-1). E. coli O157:H7 was counted by CT-SMAC (Mac Conkey Sorbitol Agar with cefixim and tellurite) and O157:H7 ID throughout the manufacturing and ripening processes. When the milk was inoculated with 10, 100 or 1000 cfu ml(-1), counts decreased to less than 1 log(10) g(-1) in curds just prior to moulding. However, viable E. coli O157:H7 were found in cheeses throughout processing, and even after 42 days of ripening. Results indicate that E. coli O157:H7 survives the lactic cheese manufacturing process. Thus, the presence of low numbers of E. coli O157:H7 in milk destined for the production of raw milk lactic cheeses can constitute a threat to the consumer.     

等离子体活化水-苯乳酸协同杀灭大肠杆菌O157:H7作用及机制研究

拟研究等离子体活化水（Plasma-activated water,PAW）与苯乳酸（Phenyllactic acid,PLA）协同处理对大肠杆菌O157:H7的杀灭效果及其作用机制。采用平板计数、扫描电镜、荧光染色等方法研究PAW与PLA协同处理对大肠杆菌O157:H7的杀灭作用及其对细胞形态、细胞膜完整性和胞内活性氧水平等的影响。结果表明,经终浓度为0.125～1.0 mg/mL的PLA处理8 min后,大肠杆菌O157:H7活细胞数未发生显著变化（P>0.05）。经PAW与PLA（终浓度为1.0 mg/mL）协同处理8 min后,大肠杆菌O157:H7降低了5.65 lg CFU/mL,显著高于PAW单独处理组（降低了1.06 lg CFU/mL） （P<0.05）。扫描电镜结果表明,PAW与PLA协同处理可造成细胞形态发生明显变化。与对照组细胞相比,经PAW-PLA（1.0 mg/mL）协同处理8 min后,胞外蛋白含量、细胞膜电位和胞内活性氧分别升高了25.6、0.75和9.53倍（P<0.05）。综上所述,PAW与PLA协同处理能够有效杀灭大肠杆菌O157:H7,这可能与其破坏细胞膜及诱导氧化损伤等有关。本研究为PAW与PLA协同处理在食品保鲜中的应用提供了理论依据。     

Comparison of aqueous commercial cleaners for effectiveness in removing Escherichia coli O157:H7 and Salmonella muenchen from the surface of apples

Unpasteurized fruit juice and cider have been implicated in outbreaks of Escherichia coli O157:H7 and Salmonella infections, yet various processes used to clean and sanitize fruits before producing juice have not been thoroughly studied for their effectiveness in removing pathogens. The objective of this study was to evaluate cleaners used in the apple industry for their efficacy in removing E. coli O157:H7 and Salmonella from the surface of apples. E. coli O157:H7 was transformed with green fluorescent protein plasmid (pGFP). In addition to encoding for the production of GFP, the plasmid also encodes for ampicillin resistance. S. muenchen was adapted to grow in media containing 50 microg/ml nalidixic acid. The use of ampicillin and nalidixic acid resistant strains enabled enumeration of the pathogen without interference by microflora naturally present on apples. Unwaxed Red Delicious cv. apples were surface inoculated with 8.58 log10 cfu of E. coli O157:H7 and 8.11 log10 cfu of S. muenchen. Five commercial apple cleaners were applied at concentrations and exposure times recommended by manufacturers. Populations of E. coli O157:H7, S. muenchen, aerobic mesophiles, and yeasts and molds on apples treated with cleaners and water (control) were determined. Compared to washing with water, treatment with cleaners removed or killed up to 2.86, 3.11, 2.48, and 0.73 log10 cfu of E. coli O157:H7, S. muenchen, aerobic mesophiles, and yeasts and molds per apple, respectively. There were differences in the effectiveness of cleaners in removing pathogens, but pH (2.0 and 12.0) and concentration (1% and 5%) of cleaner, and time of exposure (0.5-2 min) were not correlated with magnitude of reduction in population. The use of some types of cleaners commercially formulated for apples may contribute significantly in attaining target 5-log10 reductions of pathogens on the fruit intended for unpasteurized juice production or the fresh produce market.     

Inhibitory effects of microencapsulated allyl isothiocyanate (AIT) against Escherichia coli O157:H7 in refrigerated, nitrogen packed, finely chopped beef

Allyl isothiocyanate (AIT) is an effective inhibitor of various pathogens, but its use in the food industry is limited by its volatility and pungency. The objective of this study was to overcome the volatility of AIT by microencapsulation and evaluate its antimicrobial effectiveness against Escherichia coli O157:H7 in chopped beef. Chopped beef was aseptically prepared and inoculated with a five-strain cocktail of E. coli O157:H7 to yield 4 or 8 log10 cfu/g. AIT was microencapsulated in gum acacia to yield 3.7-54.8 mg AIT/g at a ratio of 1:4 and freeze dried. Microcapsules at 5% or 10% (w/w) were then added to experimental samples that were packed under nitrogen, and stored at 4 degrees C for 18 days. Samples were analyzed for numbers of E. coli O157:H7 and the aerobic mesophilic bacteria (TAC) at 3-day intervals. AIT at 4980 ppm eliminated both low and high levels of inoculated E. coli O157:H7 after 15 and 18 days of storage, respectively. AIT at 2828 ppm reduced E. coli by 2.7 log10 cfu/g by 18 days of storage. AIT levels <1000 ppm were not more effective in reducing E. coli survival than the control treatment without AIT addition. AIT at 170-1480 ppm had negligible effects on the TAC, and while 4980 ppm kept TAC levels 相似文献   

Antimicrobial Activity and Synergistic Effect of Cinnamon with Sodium Benzoate or Potassium Sorbate in Controlling Escherichia coli O157:H7 in Apple Juice

ABSTRACT: Antimicrobial effects of cinnamon, sodium benzoate, potassium sorbate, and combinations were examined against Escherichia coli O157:H7 in apple juice at 8°C and 25°C. E. coli O157:H7 was reduced by 1.6 log colony-forming units (CFU)/mL at 8°C and 2.0 log CFU/mL at 25°C by 0.3% cinnamon. At 8°C, 5.2 log CFU/mL of E. coli O157:H7 was eliminated in 11 d by 0.3% cinnamon with 0.1% sodium benzoate, and in 14 d by 0.3% cinnamon with 0.1% potassium sorbate. At 25°C, 5.3 log CFU/mL E. coli O157:H7 was eliminated in 3 d by the same combinations. A synergistic effect was observed between cinnamon and preservatives against E. coli O157:H7 at 8°C and 25°C.     

In vitro inactivation of Escherichia coli O157:H7 in bovine rumen fluid by caprylic acid

The antibacterial effect of caprylic acid (35 and 50 mM) on Escherichia coli O157:H7 and total anaerobic bacteria at 39 degrees C in rumen fluid (pH 5.6 and 6.8) from 12 beef cattle was investigated. The treatments containing caprylic acid at both pHs significantly reduced (P < 0.05) the population of E. coli O157:H7 compared with that in the control samples. At pH 5.6, both levels of caprylic acid killed E. coli O157:H7 rapidly, reducing the pathogen population to undetectable levels at 1 min of incubation (a more than 6.0-log CFU/ml reduction). In buffered rumen fluid at pH 6.8, 50 mM caprylic acid reduced the E. coli O157:H7 population to undetectable levels at 1 min of incubation, whereas 35 mM caprylic acid reduced the pathogen by approximately 3.0 and 5.0 log CFU/ml at 8 and 24 h of incubation, respectively. At both pHs, caprylic acid had a significantly lesser (P < 0.05) and minimal inhibitory effect on the population of total anaerobic bacteria in rumen compared with that on E. coli O157:H7. At 24 h of incubation, caprylic acid (35 and 50 mM) reduced the population of total anaerobic bacteria by approximately 2.0 log CFU/ml at pH 5.6, whereas at pH 6.8, caprylic acid (35 mM) did not have any significant (P > 0.05) inhibitory effect on total bacterial load. Results of this study revealed that caprylic acid was effective in inactivating E. coli O157:H7 in bovine rumen fluid, thereby justifying its potential as a preslaughter dietary supplement for reducing pathogen carriage in cattle.