Molecular characterization of Escherichia coli O157 contamination routes in a cattle slaughterhouse

In a cattle slaughterhouse, sampling was performed over a 1-week period to examine the prevalence and possible contamination routes of Escherichia coli O157. Each sampling day, swab samples were collected from the slaughterhouse environment before onset of slaughter, from the slaughterline, and from 20 successively slaughtered animals. Isolation of E. coli O157 consisted of a 6-hour enrichment followed by immunomagnetic separation and selective plating. From the 394 samples taken, 84 (21%) were positive for E. coli O157. Pulsed-field gel electrophoresis (PFGE) of collected isolates produced 26 different profiles, from which 5 PFGE profiles carried two or more Stx genes. The combination of PFGE profiles and Stx types resulted in 32 different E. coli O157 types. E. coli O157 was found in the slaughterhouse environment before the onset of slaughter. The first two sampling days, feces and carcasses were found negative. On the third sampling day, five fecal samples and four carcasses from animals negative in the feces were positive. Hide of the anal region and the shoulder were found positive every sampling day. The shoulder hide was more than twice as contaminated as the anal region hide. Typing of different isolates from a sample showed that frequently different E. coli O157 types were presented. On sampling days 1 and 2, types present in the environment and on the hides of the slaughtered animals differed. On the third sampling day, two dominant types were found in the environment (even before the onset of slaughter), as well as on the hides, feces, and carcasses. Although examined animals originated from different farms, one (two on day 3) dominant E. coli O157 type was present on their hides each sampling day. These data indicated that (i) the progress of contamination can differ from day to day within a slaughterhouse and (ii) contact between animals after the departure from the farm can have a large effect on the spread of E. coli O157 hide contamination.     

水培生菜培育、运输、贮存各环节微生物的动态变化研究

目的探究水培生菜在培育、运输、贮存各环节中微生物数据的动态变化,分析影响水培生菜微生物风险的环节因素。方法对水培生菜在培育过程、运输阶段和贮存阶段的菌落总数、大肠菌群、霉菌等指示菌数据进行跟踪,并于培育的第1周和第7周对其致病菌进行检测。结果水培生菜在培育过程中菌落总数lg平均值为6.52,标准差0.37,大肠菌群lg平均值为4.78,标准差0.61,霉菌lg平均值为4.01,标准差0.22,基本维持稳定;经常清洗运输工具能有效抑制微生物生长;生菜贮存1 d后微生物指示菌数量显著增多(P0.05),冷藏贮存生菜有助于减缓微生物指示菌的增长;在第1周和第7周均未对水培生菜检出致病菌。结论水培生菜在生长过程中更容易控制种植环境,微生物污染风险较小。后续的运输环节和储存条件需要严格控制,以降低蔬菜中微生物的污染风险。     

Formation of pyrochlorophylls and their derivatives in spinach leaves during heating

The changes of chlorophylls and their derivatives during heating of spinach leaves were studied. Chlorophylls and their derivatives were analyzed by high performance liquid chromatography (HPLC) with photodiode-array detection or positive ion fast atom bombardment mass spectrometry (FAB–MS). No chlorophyll derivatives were detected in fresh spinach leaves. The degradations of both chlorophylls, a and b, fit the first-order model, and the rate constant (min⁻¹) by microwave cooking or blanching was greater than that by steaming or baking. The major chlorophyll derivatives formed during baking and blanching included chlorophyll epimers and pheophytins. Pyrochlorophylls a and b were detected in spinach leaves after steaming for 30 min or microwave cooking for 1 min. Pyropheophytins a and b were not formed until steaming or microwave cooking time reached 30 or 5 min, respectively. Steaming favored the formation of pheophytins a and b while microwave cooking favored that of pyrochlorophylls a and b.     

Coliphage as an indicator of fecal contamination in hydroponic cucumber (Cucumis sativus L) greenhouses

A preliminary study has been performed to evaluate the utility of somatic and F⁺‐specific coliphage as quality indicators of irrigation water used in hydroponic cucumber greenhouse operations. Samples of incoming water, waste hydroponic solution, cucumber fruit and plant roots derived from two greenhouses were screened for bacterial fecal indicators (generic Escherichia coli, fecal coliforms, total coliforms and Clostridium perfringens) and coliphage. Bacterial fecal indicators were present in incoming water and in spent hydroponic solution with coliphage only being sporadically recovered. However, both somatic and F⁺‐specific coliphage were consistently recovered from the roots of cucumber plants along with bacterial fecal indicators. Despite the heavy contamination of plant roots, the cucumber fruits were within acceptable microbiological limits. F⁺‐specific coliphage was recovered from 1 out of 25 cucumbers tested along with generic E coli. In contrast, no somatic coliphage was recovered from cucumbers despite coliforms being present on 15 out of 25 units. In conclusion, coliphage represents a poor index of hydroponic irrigation water quality but presence on cucumber fruit and roots can be used to highlight the presence of fecal indicator bacteria within greenhouse operations. Copyright © 2005 Society of Chemical Industry     

Texture,composition and anatomy of spinach leaves in relation to nitrogen fertilization

BACKGROUND: The postharvest quality and shelf life of spinach are greatly influenced by cultural practices. Reduced spinach shelf life is a common quandary in the Salinas Valley, California, where current agronomic practices depend on high nitrogen (N) rates. This study aimed to describe the postharvest fracture properties of spinach leaves in relation to N fertilization, leaf age and spinach cultivar. RESULTS: Force–displacement curves, generated by a puncture test, showed a negative correlation between N fertilization and the toughness, stiffness and strength of spinach leaves (P > 0.05). Younger leaves (leaves 12 and 16) from all N treatments were tougher than older leaves (leaves 6 and 8) (P > 0.05). Leaves from the 50 and 75 ppm total N treatments irrespective of spinach cultivar had higher fracture properties and nutritional quality than leaves from other N treatments (P > 0.05). Total alcohol‐insoluble residues (AIR) and pectins were present at higher concentrations in low‐N grown plants. These plants also had smaller cells and intercellular spaces than high‐N grown leaves (P > 0.05). CONCLUSION: Observed changes in physicochemical and mechanical properties of spinach leaves due to excess nitrogen fertilization were significantly associated with greater postharvest leaf fragility and lower nutritional quality. Copyright © 2012 Society of Chemical Industry     

乳品中腐败微生物检测及污染途径的研究进展

牛乳营养丰富,容易受到微生物的污染而引起腐败变质。该文从食品安全的角度出发,系统地介绍了乳品中主要的腐败微生物及其危害,概述了国内外乳品腐败微生物的检测方法,分析了其主要的污染途径,并提出了目前存在的问题和乳品中腐败微生物检测技术的发展方向。     

Radiosensitization of Salmonella spp. and Listeria spp. in ready-to-eat baby spinach leaves

The FDA recently approved irradiation treatment of leafy greens such as spinach up to 1 kGy; however, it is important to reduce the dose required to decontaminate the produce while maintaining its quality. Thus, the objectives of this study were: (1) to assess the radiation sensitivities of Salmonella spp. and Listeria spp. inoculated in ready-to-eat baby spinach leaves under modified atmosphere packaging (MAP) and irradiated using a 1.35-MeV Van de Graff accelerator (the leaves were irradiated both at room temperature and at -5 °C); and (2) to understand and optimize the synergistic effect of MAP and irradiation by studying the radiolysis of ozone formation under different temperatures, the effect of dose rate on its formation, and its decomposition. Results showed that increased concentrations of oxygen in the packaging significantly increased the radiation sensitivity of the test organisms, ranging from 7% up to 25% reduction in D(10)-values. In particular, radiosensitization could be effected (P < 0.05) by production of ozone, which increases with increasing dose-rate and oxygen concentration, and reducing temperatures. Radiosensitization was demonstrated for both microorganisms with irradiation of either fresh or frozen (-5 °C) baby spinach. These results suggest that low-dose (below 1 kGy) e-beam radiation under modified atmosphere packaging (100% O(2) and N(2):O(2)[1:1]) may be a viable tool for reducing microbial populations or eliminating Salmonella spp. and Listeria spp. from baby spinach. A suggested treatment to achieve a 5-log reduction of the test organisms would be irradiation at room temperature under 100% O(2) atmosphere at a dose level of 0.7 kGy. Practical Application: Decontamination of minimally processed fruits and vegetables from food-borne pathogens presents technical and economical challenges to the produce industry. Internalized microorganisms cannot be eliminated by the current procedure (water-washed or treated with 200-ppm chlorine). The only technology available commercially is ionizing radiation; however, the actual radiation dose required to inactivate pathogens is too high to be tolerated by the product without unwanted changes. This study shows a new approach in using MAP with 100% O(2), which is converted to ozone to radiosensitize pathogens while improving the shelf life of minimally processed fruits and vegetables. The process results in a high level of microorganism inactivation using lower doses than the conventional irradiation treatments.     

肉猪养殖和屠宰环节沙门菌污染状况监测分析

目的 了解开封市肉猪养殖屠宰加工过程中沙门菌的污染状况.方法 采集不同来源的养殖场猪混合粪便、成年猪肛拭子、胴体涂抹物、肠系膜淋巴结样本,共187份,按照GB 4789.4-2010进行沙门菌的分离和鉴定.结果 猪混合粪便沙门菌检出率为4.5％,肛拭子沙门菌的检出率为16.4％,胴体涂抹物沙门菌检出率为34.5％,肠系膜淋巴结沙门菌检出率为27.3％.不同季节的检出率差异有统计学意义(P＜0.05).阳性分离株分布于沙门菌的5个群,共14个血清型,以阿贡纳沙门菌和德尔卑沙门菌为主.结论 屠宰环节是沙门菌交叉污染的关键点,应采取综合措施,有效控制猪肉沙门菌污染.     

Comparison of multiple chemical sanitizers for reducing Salmonella and Escherichia coli O157:H7 on spinach (Spinacia oleracea) leaves

Effectiveness of multiple chemical sanitizers on the reduction of Salmonella spp. and Escherichia coli O157:H7 on spinach was compared. Fresh spinach (Spinacia oleracea) was inoculated with a bacterial suspension containing multiple strains of rifampin-resistant Salmonella and E. coli O157:H7. Inoculated spinach leaves were treated with a water wash or water wash followed by 2% L-lactic acid at 55 °C, peroxyacetic acid (80 mg/L), calcium hypochlorite (200 mg/L), ozonated water (mg/L) or ClO₂ gas (1.2 or 2.1 mg/L). The l-lactic acid produced a 2.7 log CFU/g reduction for E. coli O157:H7 and a 2.3 log CFU/g reduction for Salmonella, statistically significant compared to water wash alone (P < 0.05), which resulted in a reduction of 0.7 log CFU/g for both pathogens. These findings indicate that 2% l-lactic acid at 55 °C may be an effective treatment for reducing pathogens on spinach leaves.     

设施葡萄延后栽培中赤霉素处理对叶片衰老的影响

通过喷施不同浓度的赤霉素(GA3),研究其对葡萄延后栽培中叶片生理生化变化的影响。结果表明,不同浓度GA3处理均能延缓葡萄叶片中叶绿素和蛋白质含量的下降,降低过氧化物酶活性和丙二醛含量的积累,抑制叶片的黄化,其中150mg/L赤霉素的处理效果最佳。     

Microbiological profile of greenhouses in a farm producing hydroponic tomatoes

Produce, including tomatoes, has been implicated in several outbreaks of foodborne illness. A number of the sources of contamination for produce grown in open fields are known. However, as an alternative agricultural system, hydroponic greenhouses are reasonably expected to reduce some of these sources. The objective of the present study was to determine the microbiological profile of tomatoes grown in greenhouses at a Mexican hydroponic farm with a high technological level and sanitary agricultural practices (SAPs) in place. Tomatoes and other materials associated with the farm were analyzed for the presence of Salmonella enterica and populations of Escherichia coli, coliforms, and Enterobacteriaceae. Tomatoes showed median levels of 0.8 log CFU per tomato for Enterobacteriaceae, < 0.5 log CFU per tomato for coliforms, and 0.5 most probable number per tomato for E. coli. Despite the physical barriers that the facilities provide and the implemented SAPs, we found that 2.8% of tomatoes were contaminated with Salmonella and 0.7% with E. coli. Other Salmonella-positive materials were puddles, soil, cleaning cloths, and sponges. Samples from the nursery and greenhouses were positive for E. coli, whereas Salmonella was found only in the latter. Although hydroponic greenhouses provide physical barriers against some sources of enteric bacterial contamination, these results show that sporadic evidence of fecal contamination and the presence of Salmonella can occur at the studied greenhouse farm.     

Safety and quality assessment of packaged spinach treated with a novel ozone-generation system

The quality and safety of packaged salad are major concerns to consumers. Ozone gas is a non-thermal processing technology capable of treating food to reduce pathogens. The ozone generation system (PK-1) used in this study consisted of a pair of electrodes with an adjustable gap inside a package. Individual, fresh, prepackaged, whole spinach leaves inoculated with Escherichia coli O157:H7 6460 were treated in packaging with ozone generated in air and oxygen. Samples were treated for 5 min and stored at room temperature (22 °C) or refrigeration (5 °C) for 0.5, 2, and 24 h. Gas composition and relative humidity were measured. All treated samples showed reductions in E. coli O157:H7 populations with the largest reductions (3-5 log₁₀ CFU/leaf) after 24 h of storage. After 5 min of treatment, ozone concentrations were 1.6 and 4.3 mg/L for air and oxygen gas, respectively. The concentrations of ozone decreased with time and were not detectable after 24 h. A 5-point Spinach Color Quality (SCQ) scale was established (5-best, 1-worst). Treated spinach showed discoloration with SCQ-values of 3.83 and 1.00 for air and oxygen gas exposed leaves after 24 h. These results indicate that the PK-1 system is capable of reducing E. coli O157:H7 in packaged spinach; however, minimizing quality changes after treatment requires further research.     

2008—2011年广东省熟肉制品中常见食源性致病菌污染状况分析

目的 了解广东省市售熟肉制品中常见食源性致病菌的污染状况,为预防食源性疾病提供科学依据.方法 2008-2011年采用随机抽样的方法对全省8个地级市的市售熟肉制品进行连续监测,并按照国家标准进行检验和评价.结果 2008-2011年间广东省市售熟肉制品中年平均检出率最高的食源性致病菌为金黄色葡萄球菌(4.9％),其次为单核细胞增生李斯特菌(0.9％),略高于沙门菌(0.4％).以上致病菌主要集中在第二季度和第三季度检出.结论 广东省市售熟肉制品存在不同程度的食源性致病菌污染,尤其是金黄色葡萄球菌的污染最为严重,应加强卫生监督管理.     

Salmonella contamination of laying-hen flocks in two regions of Algeria

A preliminary epidemiological study of Salmonella contamination in laying-hen flocks was carried out in the regions of Annaba and Eltarf, Algeria, from March to October 2008 and March to November 2009. Our objectives were (i) to estimate the prevalence of infection by Salmonella spp. in seven pooled samples during the hens' laying period (ii) to identify the serotypes and antimicrobial resistance phenotypes of isolates, and (iii) to characterize the factors that may be related to Salmonella contamination in Algerian henhouses. For this purpose, 18 out of 22 operational laying-hen houses were sampled one to three times during these periods: once at the start of laying (pullets aged 22–31 weeks), once in the middle of laying (47–60 week) and once at the end of laying prior to depopulation (70–86 week). The flocks'Salmonella status was assessed by collecting 2754 environmental samples that were analyzed according to the ISO 6579 method. The antibiotic resistance of Salmonella strains was tested as per the guidelines of the Clinical and Laboratory Standards Institute (CLSI). The relationship between each potential risk factor and the Salmonella status of laying-hen flocks was evaluated by calculating the relative risk with 95% confidence intervals. Eight flocks tested positive for Salmonella spp., with a higher prevalence at the end of laying than at either the beginning or middle. Only 19 isolates were recovered from the 2754 samples analyzed and nine different serotypes identified. S. enteritidis (n = 4) was the most prevalent serovar, along with S. Kentucky and S. Hadar (n = 3), followed by S. Heidelberg, S. Manhattan and S. Virchow (n = 2), whereas S. Dublin, S. Typhimurium and S. Albany were found only once. Thirteen isolates were resistant to at least one antimicrobial agent. Of these, six were resistant to at least three different antimicrobial classes. Salmonella serovar Kentucky isolates were resistant to fluoroquinolones with ciprofloxacin MIC ≥ 8 mg/L. Six risk indicators were identified as potentially related to the Salmonella status of layer houses.     

2012年河南省市售生制速冻面米制品食源性致病菌污染状况监测

了解2012年河南省境内市售生制速冻面米制品中金黄色葡萄球菌和沙门菌的污染状况。方法 金黄色葡萄球菌、沙门菌检测及血清分型参照2012年《国家食品安全风险监测工作手册》,金黄色葡萄球菌肠毒素的测定参照mini-VIDAS试剂使用说明。结果 344份速冻面米制品中检出金黄色葡萄球菌和沙门菌共计55株,总检出率为15.99%,其中金黄色葡萄球菌49株(14.24%),沙门菌6株(1.74%)。金黄色葡萄球菌计数结果为0.2～110 cfu/g。49株金黄色葡萄球菌中22株金黄色葡萄球菌肠毒素阳性,阳性率为44.90%。6株沙门菌血清分型分属4个血清型:肠炎沙门菌、阿贡纳沙门菌、印第安纳沙门菌、德尔卑沙门菌。6株沙门菌对头孢唑啉、头孢替坦、阿米卡星、庆大霉素、妥布霉素均耐药,3株沙门菌对氨苄青霉素/舒巴坦、头孢曲松、氨曲南、呋喃妥因和复方新诺明的耐药率均为33.33%,对环丙沙星和左氧氟沙星的耐药率均为16.67%。结论 河南省市售生制速冻面米制品存在沙门菌和金黄色葡萄球菌的污染,其中沙门菌的检出率较低,但其安全风险较大;金黄色葡萄球菌虽未超标,但其检出率和肠毒素的阳性率均较高,应高度重视。     

Microencapsulated antimicrobial compounds as a means to enhance electron beam irradiation treatment for inactivation of pathogens on fresh spinach leaves

Abstract: Recent outbreaks associated to the consumption of raw or minimally processed vegetable products that have resulted in several illnesses and a few deaths call for urgent actions aimed at improving the safety of those products. Electron beam irradiation can extend shelf‐life and assure safety of fresh produce. However, undesirable effects on the organoleptic quality at doses required to achieve pathogen inactivation limit irradiation. Ways to increase pathogen radiation sensitivity could reduce the dose required for a certain level of microbial kill. The objective of this study was to evaluate the effectiveness of using natural antimicrobials when irradiating fresh produce. The minimum inhibitory concentration of 5 natural compounds and extracts (trans‐cinnamaldehyde, eugenol, garlic extract, propolis extract, and lysozyme with ethylenediaminetetraacetate acid (disodium salt dihydrate) was determined against Salmonella spp. and Listeria spp. In order to mask odor and off‐flavor inherent of several compounds, and to increase their solubility, complexes of these compounds and extracts with β‐cyclodextrin were prepared by the freeze‐drying method. All compounds showed bacteriostatic effect at different levels for both bacteria. The effectiveness of the microencapsulated compounds was tested by spraying them on the surface of baby spinach inoculated with Salmonella spp. The dose (D₁₀ value) required to reduce the bacterial population by 1 log was 0.190 kGy without antimicrobial addition. The increase in radiation sensitivity (up to 40%) varied with the antimicrobial compound. These results confirm that the combination of spraying microencapsulated antimicrobials with electron beam irradiation was effective in increasing the killing effect of irradiation. Practical Application: Foodborne illness outbreaks attributed to fresh produce consumption have increased and present new challenges to food safety. Current technologies (water washing or treating with 200 ppm chlorine) cannot eliminate internalized pathogens. Ionizing radiation is a viable alternative for eliminating pathogens; however, the dose required to inactivate these pathogens is often too high to be tolerated by the fresh produce without undesirable quality changes. This study uses natural antimicrobial ingredients as radiosensitizers. These ingredients were encapsulated and applied to fresh produce that was subsequently irradiated. The process results in high level of microorganism inactivation using lower doses than the conventional irradiation treatments.     

黑龙江省肉鸡养殖和屠宰加工环节中沙门菌调查

目的了解黑龙江省肉鸡养殖和屠宰加工环节中沙门菌污染状况。方法根据国家食品安全风险监测专项《肉鸡养殖及屠宰加工环节沙门氏菌专项监测工作手册》规定的操作程序,并参考国家标准GB 4789.4—2010《食品安全国家标准食品微生物学检验沙门氏菌检验》对黑龙江省4个地市3 766份肉鸡样品进行检验。结果 4大环节共检测样品3 766份,检出阳性样品339份,检出率为9.00%,孵化、养殖、屠宰到配送分销4个环节均检出沙门菌,检出率分别为2.82%(22/781)、2.14%(11/515)、13.84%(220/1 590)、9.77%(86/880)。其中,屠宰环节的8种样品中预冷池水样品沙门菌检出率最高,为35.42%(34/96)。检出的沙门菌分属于9个血清型,以肠炎沙门菌和印地安纳沙门菌的比例最高。结论黑龙江省肉鸡屠宰和配送分销环节中沙门菌污染较严重。屠宰环节阳性率最高,是重要的污染环节,其中预冷池水中沙门菌检出率最高,是屠宰过程中肉鸡污染沙门菌的主要环节。