Escherichia coli O157:H7 infection in cows and calves in a beef cattle herd in Alberta,Canada

Escherichia coli O157:H7 infection of cows and calves in a naturally-infected beef cattle herd in Alberta, Canada, was investigated over 2 years, encompassing two calf production cycles. In both years of the study, E. coli O157:H7 was isolated from the faeces of cows shortly after but not before parturition in late winter: 6/38 (16%) in 1996 and 13/50 (26%) in 1997. At < 1 week post-partum, 13/52 (25%) calves born in 1997 were shedding the organism. Faecal shedding of E. coli O157:H7 by cows and calves continued over the 7 weeks that they were in the calving pens, with the organism being isolated from the faeces of 2-18% of cows and 23-26% of calves during this period. Five weeks after they were moved onto a native grass pasture, all the calves and all but one cow in 1997 had ceased shedding the organism. When the calves were weaned in the fall, E. coli O157:H7 was isolated from the faeces of 0-1.5% of the calves 1 week prior to weaning and from 6-14% of the calves within 2 weeks after weaning. Parturition, calving pens and weaning appear to be important factors in maintaining E. coli O157:H7 infections in this beef cattle herd. Isolates from cows and calves during the immediate post-partum period were mostly of the same pulsed-field gel electrophoresis (PFGE) type of E. coli O157:H7. Similarly, at weaning a common PFGE type of E. coli O157:H7, which differed slightly from the post-partum PFGE type, was isolated from the calves. These typing data suggest a common source of infection for the animals as well as demonstrate clonal turnover of resident populations of this pathogen.     

Swimming-associated outbreak of Escherichia coli O157:H7

In 1997 the first outbreak of Escherichia coli O157:H7 infections involving 14 cases occurred in Finland. A case was defined as a resident of Alavus with an episode of diarrhoea between 5 and 17 July 1997, and from whom E. coli O157:H7 was isolated from stool. The investigation included case searching and a population-based case control study. Five primary and eight symptomatic secondary cases of E. coli O157:H7 illness were detected. In the 10 days before the outbreak, all 5 primary patients (aged 3-8 years), but only 6 of 32 population controls from the same age range (Fisher's test, P < 0.001) and 4 of 10 sibling controls (P < 0.05) had visited (but had not necessarily bathed in) a shallow beach popular among young children. Four out of 5 primary cases had remained within 5 m of the beach while swimming and had swallowed lake water compared to 1 of 5 population controls. These analytical epidemiologic findings incriminated fresh lake water as the vehicle of E. coli O157:H7 transmission.     

Estimation of the basic reproduction ratio (R0) for Shiga toxin-producing Escherichia coli O157:H7 (STEC O157) in beef calves

To understand the dynamics of transmission of Shiga toxin-producing Escherichia coli O157:H7 (STEC O157) in beef calves, serum samples were obtained from calves in a beef cow-calf herd approximately every 6 weeks from birth until weaning for three consecutive years. The presence of specific anti-O157 antibodies in these serum samples was detected using a blocking ELISA assay incorporating an anti-O157 monoclonal antibody. Using seroconversion data, the basic reproduction ratio (R0) was estimated for each of the three years as well as in aggregate using both deterministic and Martingale methods. R0 for STEC O157 infection in range beef calves by deterministic methods varied from 2.9-5.6, with an average of 4.3 (95% CI 2.8-5.9). Martingale estimates of R0 ranged from 3.5-7.4, or 5.3 (95% CI 3.9-6.6), for data from all three years. Given the above estimate of R0, it is predicted that 65-86% of a herd of calves must be effectively vaccinated, or must be rendered non-susceptible through other means, to eliminate STEC O157 infection from a herd.     

Community-wide outbreak of Escherichia coli O157:H7 associated with consumption of frozen beef burgers

On 24-25 October 2005 a cluster of five haemolytic uraemic syndrome (HUS) cases was reported in southwest France. An investigation was undertaken to identify the outbreak source and implement control measures. Cases were defined as individuals with HUS or diarrhoea with isolation of Escherichia coli O157:H7 in stools or a positive antibody response to E. coli O157 lipopolysaccharide, resident in southwest France with symptom onset after 19 September 2005. Sixty-nine identified patients had symptom onset between 5 October and 3 November 2005, including 17 cases of HUS. One brand of frozen beef burgers produced on 22 August 2005 was consumed by all patients in the week before symptom onset. E. coli O157:H7 strains from patients, patients' burgers and the manufacturing plant were genetically related. This is the largest community-wide outbreak of E. coli O157:H7 in France to date and the first associated with consumption of contaminated frozen beef burgers.     

Escherichia coli O157:H7 outbreak associated with consumption of ground beef, June-July 2002

OBJECTIVE: A case-control and environmental study tested the hypothesis that purchasing and eating ground beef from a specific source was the cause of a cluster of cases of hemolytic uremic syndrome (HUS) and Escherichia coli (E. coli) O157:H7 gastroenteritis. METHODS: A case-control study comparing risk factors was conducted over the telephone on nine case-patients with 23 selected controls. An environmental investigation was conducted that consisted of reviewing beef handling practices at a specific local supermarket and obtaining ground beef samples from the store and two households with case-patients. RESULTS: The analysis of the case-control study showed that eight case-patients (89%) purchased ground beef at Grocery Chain A compared with four controls who did not develop illness (17%) (matched odds ratio=undefined; 95% confidence interval 2.8, infinity; p=0.006). The environmental investigation showed that Grocery Chain A received meat from Meatpacker A. Laboratory analysis of meat samples from Meatpacker A and Grocery Chain A and stool samples from some patients recovered an identical strain of E. coli O157:H7 according to pulse-field gel electrophoresis. CONCLUSIONS: Both the case-control and environmental studies showed that purchasing ground beef at Grocery Chain A, which received ground beef from Meatpacker A, was the major risk factor for illness in eight case-patients; the ninth case-patient was found to be unrelated to the outbreak. Furthermore, meat from Meatpacker A was associated with a nationwide outbreak of E. coli O157:H7 illness that resulted in the second largest recall of beef in U.S. history at the time.     

Chlorine inactivation of Escherichia coli O157:H7.

We analyzed isolates of Escherichia coli O157:H7 (which has recently caused waterborne outbreaks) and wild-type E. coli to determine their sensitivity to chlorination. Both pathogenic and nonpathogenic strains were significantly reduced within 1 minute of exposure to free chlorine. Results indicate that chlorine levels typically maintained in water systems are sufficient to inactivate these organisms.     

Escherichia coli O157:H7 infection of calves: infectious dose and direct contact transmission.

Cattle are considered to be a reservoir host of Escherichia coli O157:H7 and contaminated foods of bovine origin are important vehicles of human infection. In this study, the susceptibility of calves to experimental E. coli O157:H7 infection following low oral exposures was determined. Two of 17 calves exposed to very low (< 300 c.f.u.) doses, and 3 of 4 calves exposed to low (< 10,000 c.f.u.) doses, subsequently excreted the challenge strains in their faeces. All calves (n = 12) sharing isolation rooms with calves that excreted the challenge strain in their faeces similarly began faecal excretion of the same strains within 21 days or less. The identity between the challenge strains and the strains excreted in calf faeces was confirmed by restriction digestion electrophoretic patterns using pulsed field gel electrophoresis. Calves shed E. coli O157:H7 in their faeces after very low dose exposures at concentrations ranging from < 30 to > 10(7) c.f.u./g, and for durations similar to the values previously reported for calves challenged by larger doses. The susceptibility of calves to infection following very low exposures or direct contact with infected calves has important implications for programmes for pre-harvest control of this agent.     

2004-2007年云南省肠出血性大肠埃希菌0157:H7监测分析

肠出血性大肠埃希菌O157:H7(O157:H7)是近年来新发现的危害严重的肠道致病菌.自1982年美国首次暴发O157:H7,感染性腹泻以来,世界各地陆续有疫情出现[1,2].     

Extended phage-typing scheme for Escherichia coli O157:H7

In Canada, the number of human isolates of verotoxigenic (VT + ve) Escherichia coli O157:H7 from diarrhoeal cases and haemolytic uraemic syndrome and haemorrhagic colitis has increased from 25 in 1982 to 2384 in 1989. A total of 3273 VT + ve E. coli O157:H7 strains (3255 strains isolated in Canada and 18 isolates from other countries) were phage typed. The phage typing scheme has been extended from 14 to 62 phage types. Of these, five types occurred exclusively in other countries (type 47 in Japan; and types 49, 50, 51 and 52 in the U.K.). Thirty-five different phage types were identified in Canada; only nine of these (1, 2, 4, 8, 14, 21, 23, 31 and 32), each accounted for more than 1% of the cases from human sources. The same nine types were the only ones observed among the isolates from non-human sources (meat and slaughter houses) suggesting a food-borne transmission in most of the human cases. Phage types 1 (30.5%); 4 (21%); 8 (13.5%); 31 (8.9%) and 14 (8%) were encountered in varying frequencies in most of the provinces; infrequently occurring phage types also showed regional variation. Thirteen different phage types were identified among 151 outbreaks representing 556 isolates of E. coli O157:H7. More than one phage type were encountered in 12 outbreaks whereas in 141 outbreaks, all strains in each, had the same phage type.     

Hemolytic uremic syndrome risk and Escherichia coli O157:H7

We reviewed medical records of 238 hospitalized patients with Escherichia coli O157:H7 diarrhea to identify risk factors for progression to diarrhea-associated hemolytic uremic syndrome (HUS). Data indicated that young age, long duration of diarrhea, elevated leukocyte count, and proteinuria were associated with HUS.     

大肠埃希菌O157：H7家蝇实验带菌消长的研究

目的采用大肠埃希菌O157∶H7-EDL933株,实验感染家蝇,观察家蝇体内外感染和带菌消长情况。方法点滴法体外定量染菌,剂量为1μ（l菌悬液浓度为8.0×10^5～1.9×10^7cfu/ml）,并采用昆虫单虫单管方法饲养观察。结果家蝇经体外染菌,获得体内外带菌,体外带菌时间中位数为（96.0±15.3）h（95%CI：66.0～126.0h）;体内中位数为（144.0±17.3）h（95%CI：110.2～177.8h）;家蝇体内外带菌消长差异无统计学意义（χ^2=0.74,P=0.388）,家蝇最长带菌时间至少216h（9d）。结论研究结果提示,家蝇不仅是O157∶H7疾病传播的媒介,更重要的可能是人类感染潜在的贮存宿主。     

我市首次分离到O157:H7大肠杆菌分离株的生化特征、毒力因子与耐药性的探讨

目的：了解金华市外环境中O157：H7大肠杆菌分离株中生化特征、毒力因子的携带与耐药情况。方法：直接分离接种于O157显色培养基。结果：从51份样品中分离出2株O157：H7大肠杆菌,对这2株O157：H7大肠杆菌分离株进行PCR毒力因子的测定,携带eaeA、stx2毒力因子。结论：药敏试验结果显示,这两株O157：H7大肠杆菌分离株对利福平类、四环素耐药。     

Detection of Escherichia coli O157:H7 and Listeria monocytogenes in beef products by real-time polymerase chain reaction

Rapid methods for the detection of Escherichia coli O157:H7 and Listeria monocytogenes in food products are important to the food industry and for public health. Conventional microbiological methods and newly developed molecular-based techniques such as polymerase chain reaction (PCR)-based methods are time consuming. In this study, a faster method based on utilization of a hybridization probe with real-time PCR, was developed and applied for detection of E. coli O157:H7 and L. monocytogenes from artificially contaminated raw ground beef and fully cooked beef hotdogs. Target genes for E. coli O157:H7 and L. monocytogenes were rfbE and hylA, respectively. An analysis of 169 bacterial strains showed that the chosen primers and probes were specific for detection of E. coli O157:H7 and L. monocytogenes by real-time PCR. The assay was positive for nine of 10. E. coli O157:H7 strains, and all L. monocytogenes (7/7) strains evaluated. Bacterial strains lacking these genes were not detected by these assays. Detection limits of real-time PCR assays ranged from 10(3) to 10(8) colony forming units (CFU)/ml for E. coli O157:H7 in modified tryptic soy broth and 10(4) to 10(8) CFU/mL for L. monocytogenes in Fraser Broth. Detection sensitivity ranged from 10(3) to 10(4) CFU/g of raw ground beef or hotdog without enrichment for E. coli and L. monocytogenes. Approximately 1.4-2.2 CFU/g of E. coli O157:H7 in raw ground beef were detected following an enrichment step of 4 h. Approximately 1.2-6.0 CFU/g of L. monocytogenes in beef hotdogs were detected following an enrichment step of 30 h. The real-time PCR assays for detection of E. coli O157:H7 and L. monocytogenes in raw ground beef and beef hotdogs were specific, sensitive and rapid.     

Thermal tolerance of acid-adapted and non-adapted Escherichia coli O157:H7 and Salmonella in ground beef during storage

Thermal tolerance of acid-adapted Escherichia coli O157:H7 or Salmonella in ground beef was evaluated during storage at 4 degrees C or -20 degrees C. Both pathogens were adapted to acidic conditions (pH approximately 4.6) by growing in tryptic soy broth supplemented with 1% glucose. A five-strain cocktail of E. coli O157:H7 or Salmonella was grown separately in TSB (pH approximately 6.6) and TSB + 1% glucose for 24 h at 37 degrees C to provide cells with or without acid adaptation. Irradiated ground beef was inoculated with either acid-adapted or non-adapted E. coli O157:H7 or Salmonella; the samples stored at 4 degrees C were subjected to heat treatment at 62 degrees C or 65 degrees C on days 1, 7, 14, 21, and 28, and the samples stored at -20 degrees C were subjected to heat treatment at 62 degrees C or 65 degrees C on days 1, 30, 60, 90, and 120. Decimal reduction time (D values) of the pathogens was determined as an indicator of thermal tolerance. Significantly higher D(62) values were observed on days 21 and 28 for non-adapted E. coli O157:H7 stored at 4 degrees C and on days 90 and 120 for non-adapted E. coli O157:H7 stored at -20 degrees C (P < 0.05). Higher D(62) values were observed on days 21 and 28 among non-adapted Salmonella strains stored at 4 degrees C and on day 28 for acid-adapted strains of Salmonella stored at 4 degrees C (P < 0.05). Higher D(62) values for acid-adapted strains of Salmonella stored at -20 degrees C were observed on days 30, 60, and 90 (P < 0.05), when while no differences were observed in the D(65) values of acid-adapted and non-adapted strains of E. coli O157:H7 and Salmonella throughout storage at both temperatures (P > 0.05). This suggests that acid adaptation of foodborne pathogens provides a certain level of protection against heat treatment at lower cooking temperatures, while at higher temperatures there were no observed differences between the sensitivity of acid-adapted and non-adapted strains in an actual food system over an extended period of refrigerated and frozen storage.     

The prevalence of Escherichia coli O157.H7 in dairy and beef cattle in Washington State.

Escherichia coli O157.H7 was found in 10 of 3570 (0.28%) faecal samples from dairy cattle in 5 of 60 herds (8.3%). Several tentative associations with manure handling and feeding management practices on dairy farms were identified. Faecal/urine slurry samples, bulk milk samples, and milk filters from dairy herds were negative for E. coli O157.H7. E. coli O157.H7 was also isolated from 10 of 1412 (0.71%) faecal samples from pastured beef cattle in 4 of 25 (16%) herds. The prevalence of E. coli O157.H7 excretion in feedlot beef cattle was 2 of 600 (0.33%). The identification of cattle management practices associated with colonization of cattle by E. coli O157.H7 suggests the possibility that human E. coli O157.H7 exposure may be reduced by cattle management procedures.     

大肠杆菌O157:H7实验室诊断方法研究进展

肠出血性大肠杆菌(EHEC)O157:H7是近年来新发现的危害严重的肠道致病菌,主要通过食源传播,污染的牛肉、牛奶、鸡肉、蔬菜、水果饮料等均可成为传播媒介[1].肠出血性大肠杆菌O157:H7感染性腹泻已成为威胁人群健康的全球性的公共卫生问题,O157:H7的快速、特异检测对于该病的早期发现及疫情有效控制至关重要.生物技术的发展为大肠杆菌O157:H7的实验室诊断提供了许多有效的手段和方法,本文就这些方法的最新研究进展进行综述.1常规鉴定方法菌株的分离和筛选常规使用山梨醇麦康凯琼脂(SMAC),在正常条件下,O157:H7不能发酵山梨醇,在SMAG琼脂上为无色菌落,而其他大肠杆菌则呈粉红色菌落.分离培养法简单、直观、费用低,虽经不断改进,但敏感性、特异性仍不理想.