Thermal Inactivation of Acid-Adapted Escherichia coli O157:H7 in Dairy Compost

Abstract It is well documented that stress-adapted microorganisms can develop cross-resistance to other unrelated stress. This study was designed to evaluate the thermal resistance of acid-adapted Escherichia coli O157:H7 in both fresh and finished dairy composts. A three-strain mixture of E. coli O157:H7, either acid-adapted or non-adapted (control), was inoculated into dairy compost to a final concentration of approximately 10(7) CFU/g. The inoculated compost was kept in an environmental chamber which was programmed to raise temperature from room to target temperatures (50°C, 55°C, and 60°C) in 2 days, simulating the early phase of composting. In fresh dairy compost with 2 days of come-up time, acid-adapted and control E. coli O157:H7 survived for 19 and 17 days at 50°C, respectively, and 6 and 4 days for both types of culture at 55°C and 60°C, respectively. Overall, pathogen survival was non-significant (p>0.05) between control and acid-adapted cultures at all tested temperatures. In finished compost, the same trend in pathogen survival between control and acid-adapted cultures was observed at 55°C. However, the duration of survival for both cultures was short in comparison to that in fresh compost. In fresh compost with short come-up time (15?min), acid-adaptation provided E. coli O157:H7 some cross-protection to heat at 55°C up to 30?min of exposure. The effect of heating medium on thermal resistance of acid-adapted E. coli O157:H7 revealed that in saline, acid-adapted E. coli O157:H7 was inactivated slower (p<0.05) with 0.5 and 1?h of heat exposure at 55°C as compared to control culture. Our results revealed that cross-protection against heat in E. coli O157:H7 due to acid-adaptation was demonstrated in saline but lost in fresh dairy compost with 2 days of come-up time during composting. Additionally, the type of compost and heating medium can influence the rate of pathogen inactivation at composting temperatures.     

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.     

Role of curli and cellulose expression in adherence of Escherichia coli O157:H7 to spinach leaves

Shiga-toxigenic Escherichia coli O157:H7 outbreaks have been linked to consumption of fresh produce. It is generally recognized that bacterial attachment to vegetal matrices constitutes the first step in contamination of fresh produce. Cellular appendages, such as curli fibers, and cellulose, a constituent of extracellular matrix, have been suggested to be involved in E. coli attachment and persistence in fresh produce. A comparative evaluation was conducted on the ability of Shiga toxin-producing E. coli O157:H7 strains EDL933 and 86-24, linked to two independent foodborne disease outbreaks in humans, and their mutants deficient in curli and/or cellulose expression to colonize and to firmly attach to spinach leaf. Inoculated spinach leaves were incubated at 22°C, and at 0, 24, and 48?h after incubation loosely and strongly attached E. coli O157:H7 populations were determined. Curli-expressing E. coli O157:H7 strains developed stronger association with leaf surface, whereas curli-deficient mutants attached to spinach at significantly (p<0.01) lower numbers. Attachment of cellulose-impaired mutants to spinach leaves was not significantly different from that of curliated strains. The relative attachment strength of E. coli O157:H7 to spinach increased with incubation time for the curli-expressing strains. Laser scanning confocal microscopy (LSCM) analysis of inoculated leaves revealed that curli-expressing E. coli O157:H7 were surrounded by extracellular structures strongly immunostained with anti-curli antibodies. Production of cellulose was not required to develop strong attachment to spinach leaf. These results indicate that curli fibers are essential for strong attachment of E. coli O157:H7 to spinach whereas cellulose is dispensable.     

Inactivation of Escherichia coli O157:H7 by high-intensity ultrasonication in the presence of salts

Inactivation of Escherichia coli O157:H7 suspended in salt solutions (Na(2)PO(4), NaCl, NaNO(3), NH(4)Cl, CaCl(2), and AlCl(3)) at concentrations ranging from 0 to 5% (w/v) by high-intensity ultrasound at two different temperature conditions (ice water bath, 40 degrees C water bath) and three ultrasonic intensity levels (9.5, 21.8, 49.2 W/cm(2)) was determined. Increases in sonication treatment time, intensity, and temperature led to increased lethality of E. coli O157:H7. However, cell lethality, as a function of solute concentration, varied depending upon type of salt. CaCl(2), NaCl, NaNO(3), Na(2)PO(4), and NH(4)Cl had little or no effect on survival of E. coli O157:H7 (<1-log reduction) regardless of other treatment conditions at 9.5 W/cm(2). Concentrations of >0.5% of CaCl(2), NaNO(3), Na(2)PO(4), and NH(4)Cl adversely affected survival (1.0- to 1.6-log reduction) with treatment of 21.8 W/cm(2) in an ice bath and showed greater inactivation (1.2-4.0-log reduction) in the 40 degrees C water bath. Treatment of 49.2 W/cm(2) showed the greatest impact regardless of other parameters. In the 40 degrees C water bath, treatment for 10 min at 49.22 W/cm(2) led to total inactivation for cells suspended in 0.5% NH(4)Cl, 1% CaCl(2), 2% NaCl, 5% Na(2)PO(4), and all concentrations of AlCl(3). Complete inactivation also occurred in an ice bath for 5% AlCl(3), which was shown to be the most effective salt. The most efficient treatment combination was in the 40 degrees C water bath for 10 min at 49.2 W/cm(2) with 5% AlCl(3). Inactivation of E. coli O157:H7 is attributed to cavitation-induced shear forces, reaction of cavitation-generated hydrogen peroxide with microbial cell wall constituents and electrostatic interactions of dissociated salts with cell membranes.     

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.     

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.     

Escherichia coli O157:H7 in feral swine near spinach fields and cattle, central California coast

We investigated involvement of feral swine in contamination of agricultural fields and surface waterways with Escherichia coli O157:H7 after a nationwide outbreak traced to bagged spinach from California. Isolates from feral swine, cattle, surface water, sediment, and soil at 1 ranch were matched to the outbreak strain.     

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.     

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。     

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。     

Strategies to reduce person-to-person transmission during widespread Escherichia coli O157:H7 outbreak

During the Escherichia coli O157:H7 outbreak in 2006 in the United States, the primary strategy to prevent illness was to advise consumers not to eat spinach. No widespread warnings were issued about preventing person-to-person (secondary) transmission. A disease transmission model, fitted to the current data, was used to investigate likely reductions in illnesses that could result from interventions to prevent secondary transmission. The model indicates that exposure to contaminated spinach occurred early in the outbreak and that secondary transmission was similar to that in previous E. coli outbreaks ( 12%). The model also suggests that even a modestly effective strategy to interrupt secondary transmission (prevention of only 2%-3% of secondary illnesses) could result in a reduction of 5%-11% of symptomatic cases. This analysis supports the use of widespread public health messages during outbreaks of E. coli O157:H7 with specific advice on how to interrupt secondary transmission.     

Factory outbreak of Escherichia coli O157:H7 infection in Japan.

To determine the cause of a July 1996 outbreak of Escherichia coli O157:H7 among factory workers in Kyoto, Japan, we conducted cohort and case-control studies. Eating radish sprout salad during lunch at the factory cafeteria had been linked to illness. The sprouts were traced to four growers in Japan; one had been associated with an outbreak of E. coli O157:H7 among 6,000 schoolchildren in Sakai earlier in July.     

Reduction of Escherichia coli O157:H7 in cattle drinking-water by trans-cinnamaldehyde

Cattle serve as a major reservoir of E. coli O157:H7 and excrete the pathogen in feces. Environmental persistence of E. coli O157:H7 plays a vital role in its epidemiology on farms, and cattle water troughs are a demonstrated long-term reservoir of E. coli O157:H7 for animals. The objective of this study was to investigate the potential of low concentrations of trans-cinnamaldehyde for killing E. coli O157:H7 in cattle drinking-water. A five-strain mixture of E. coli O157:H7 was inoculated (at approximately 8.0 log colony-forming units [CFU]/mL) into 100 mL samples of well water containing 0, 0.03, 0.05, 0.07, or 0.1% trans-cinnamaldehyde. Additionally, water samples containing (1% w/v) bovine feces or feed were also included. The samples were incubated at 21 degrees , 8 degrees , or 4 degrees C for 7 days and tested for viable E. coli O157:H7 on days 0, 1, 3, 5, and 7. Triplicate samples of each treatment and control were included and the study was replicated twice. All concentrations of trans-cinnamaldehyde were effective in killing E. coli O157:H7 in water, but the magnitude of killing significantly increased with increase in trans-cinnamaldehyde concentration and storage temperature (p < 0.05). The presence of feed or feces in water decreased the antibacterial effect of trans-cinnamaldehyde on E. coli O157:H7 (p < 0.05). This study indicated that trans-cinnamaldehyde is effective in killing E. coli O157:H7 in cattle drinking-water, but detailed palatability studies on cattle intake of water containing the antimicrobial are needed.     

肠出血性大肠埃希菌O157:H7疫苗的研究进展

O157:H7是肠出血性大肠埃希菌(EHEC)最常见的血清型.目前国内外尚无EHEC O157:H7疫苗问世,因此疫苗研究对防治EHEC O157:H7有着重大意义.外膜蛋白A(OmpA)作为抗EHEC O157:H7基础疫苗为疫苗研究提供了新的思路,此文对EHEC O157:H7疫苗研究的有关进展作了综述.