Laboratory-confirmed non-O157 Shiga toxin-producing Escherichia coli--Connecticut, 2000-2005

Shiga toxin-producing Escherichia coli (STEC) infection causes diarrhea that is often bloody and can result in potentially life-threatening hemolytic uremic syndrome (HUS). Escherichia coli O157:H7 is the most common cause of STEC infection in the United States, producing 73,000 illnesses annually, according to the last estimate in 1999. Unlike O157, however, little is known about the incidence of non-O157 strains. Because STEC other than O157 are not commonly identified, the incidence, trends, and epidemiology of non-O157 STEC are not well understood. To assess trends in Shiga toxin enzyme immunoassay (Stx EIA) testing by local clinical laboratories, the Connecticut Department of Public Health (CTDPH) analyzed results of confirmatory testing conducted in the state laboratory during 2000--2005. The findings indicated that a total of 403 STEC infections were reported by clinical laboratories in Connecticut, including 207 identified as STEC by Stx EIA testing alone, and that the use of Stx EIA increased from 2000 to 2005. Use of Stx EIA without prompt culture confirmation can delay or prevent serotyping and subtyping of isolates and detection of both O157 and non-O157 STEC outbreaks. Public health authorities in all states should ensure that clinical laboratories forward Stx EIA-positive specimens to the state laboratory for isolation and identification of STEC, as recommended by the Association of Public Health Laboratories and CDC.     

Identifying Shiga toxin-producing Escherichia coli: results of a laboratory evaluation

Laboratory procedures for identifying Escherichia coli O157 and other Shiga toxin-producing E. coli (STEC) strains vary considerably, causing concern that these infections may be underdiagnosed. E. coli O157 may be screened for by culture on sorbitol-containing selective media; however, no selective medium is available for isolation of non-O157 STEC. Shiga toxins may be detected using enzyme immunoassay or real-time polymerase chain reaction; however, the organism is not isolated for subsequent characterization. The Centers for Disease Control and Prevention (CDC) recommends using both routine bacterial culture on sorbitol-containing medium and an assay for Shiga toxins to identify STEC. An evaluation of laboratories revealed limited compliance with these recommendations. Enhancing laboratory procedures to comply with the CDC guidelines is essential for public health surveillance.     

Laboratory practices and incidence of non-O157 shiga toxin-producing Escherichia coli infections

We surveyed laboratories in Washington State, USA, and found that increased use of Shiga toxin assays correlated with increased reported incidence of non-O157 Shiga toxin-producing Escherichia coli (STEC) infections during 2005-2010. Despite increased assay use, only half of processed stool specimens underwent Shiga toxin testing during 2010, suggesting substantial underdetection of non-O157 STEC infections.     

Laboratory practices for the identification of Shiga toxin-producing Escherichia coli in the United States, FoodNet sites, 2007

Clinical laboratory practices affect patient care and disease surveillance. It is recommended that laboratories routinely use both culture for Escherichia coli O157 and a method that detects Shiga toxins (Stx) to identify all Stx-producing E. coli (STEC) and that labs send broths or isolates to a public health laboratory. In 2007, we surveyed laboratories serving Foodborne Diseases Active Surveillance Network sites that performed on-site enteric disease diagnostic testing to determine their culture and nonculture-based testing practices for STEC identification. Our goals were to measure changes over time in laboratory practices and to compare reported practices with published recommendations. Overall, 89% of laboratories used only culture-based methods, 7% used only Stx enzyme immunoassay (EIA), and 4% used both Stx EIA and culture-based methods. Only 2% of laboratories reported simultaneous culture for O157 STEC and use of Stx EIA. The proportion that ever used Stx EIA increased from 6% in 2003 to 11% in 2007. The proportion that routinely tested all specimens with at least one method was 66% in 2003 versus 71% in 2007. Reference laboratories were less likely than others to test all specimens routinely by one or more of these methods (48% vs. 73%, p=0.03). As of 2007, most laboratories complied with recommendations for O157 STEC testing by culture but not with recommendations for detection of non-O157 STEC. The proportion of laboratories that culture stools for O157 STEC has changed little since 2003, whereas testing for Stx has increased.     

不同来源产志贺毒素大肠埃希菌分布特征

目的探讨不同标本中产志贺样毒素大肠埃希菌（STEC）的分布特征。方法采集动物粪便、肉类食品和排污口污泥样品，常规分离大肠埃希菌，血清学分型，PCR鉴定产志贺样毒素（stx1，stx2）菌株。结果293份标本中鉴定出8株STEC，1株为产志贺毒素O157：H7型，2株为不产志贺毒素O157：H7型，5株为产志贺毒素非O157：H7型。结论STEC存在于不同来源的标本中，菌株表型与毒力因子存在一定差异。     

Continuous surveillance of Shiga toxin-producing Escherichia coli infections by pulsed-field gel electrophoresis shows that most infections are sporadic

The purpose of this study was to evaluate the value of real-time molecular typing of Shiga toxin (Verocytotoxin)-producing Escherichia coli (STEC) infections in order to detect possible outbreaks of infections. All laboratory confirmed STEC infections in Denmark from 2003 to mid 2005 were routinely characterized by serotyping, virulence genes characterization, and subtyping by pulsed-field gel electrophoresis (PFGE) using the PulseNet protocol for STEC O157. The study included 312 STEC isolates representing 50 different O groups and 75 O:H-serotypes, and 68% of the isolates belonged to the eight most common O-groups: O157 (26%), O103 (13%), O146 (8%), O26 (8%), O117 (4%), O145 (3%), O128 (3%), and O111 (2%). The remaining O-groups constituted less than 2% each, and 8.1% of the isolates were O-rough. The eae gene was found in 60% of all isolates, and detection of the two main Shiga toxin genes showed that 40% had stx1 only, 31% had stx2 only, and 29% had both stx1 and stx2. A high diversity was seen within all O groups, and for most of the rare O groups, the number of PFGE profiles equaled the number of isolates. However, one outbreak of E. coli O157 was detected by the routine PFGE typing. The value of "real-time' PFGE typing of the infrequent serotypes is limited if the full scheme for O-grouping or O:H-serotyping is used routinely for all STEC isolates. Possible outbreaks can then be detected by the increased number of isolates within a particular serotype. PFGE typing would then be valuable in subsequent steps of the outbreak investigation. However, routine PFGE typing of the three to five most common O groups will enable early recognition of possible outbreaks.     

Public health approach to detection of non-O157 Shiga toxin-producing Escherichia coli: summary of two outbreaks and laboratory procedures

Routine laboratory testing may not detect non-O157 Shiga toxin-producing Escherichia coli (STEC) reliably. Active clinical, epidemiological, environmental health, and laboratory collaboration probably influence successful detection and study of non-O157 STEC infection. We summarized two outbreak investigations in which such coordinated efforts identified non-O157 STEC disease and led to effective control measures. Outbreak 1 involved illness associated with consuming unpasteurized apple cider from a local orchard. Public health personnel were notified by a local hospital; stool specimens from ill persons contained O111 STEC. Outbreak 2 involved bloody diarrhoea at a correctional facility. Public health personnel were notified by the facility infection control officer; O45 STEC was the implicated agent. These reports highlight the ability of non-O157 STEC to cause outbreaks and demonstrate that a coordinated effort by clinicians, infection-control practitioners, clinical diagnostic laboratorians, and public health personnel can lead to effective identification, investigation, and prevention of non-O157 STEC disease.     

Comparison of Escherichia coli Isolates from humans, food, and farm and companion animals for presence of Shiga toxin-producing E. coli virulence markers

The objective of this study was to characterize Escherichia coli isolates from dairy cows/feedlots, calves, mastitis, pigs, dogs, parrot, iguana, human disease, and food products for prevalence of Shiga toxin-producing E. coli (STEC) virulence markers. The rationale of the study was that, isolates of the same serotypes that were obtained from different sources and possessed the same marker profiles, could be cross-species transmissible. Multiplex polymerase chain reaction (PCR) was used to detect presence of genes encoding Shiga toxin 1 and 2 (stx1 and stx2), H7 flagella (flicC), enterohemolysin (hly) and intimin (eaeA) in E. coli isolates (n = 400). Shiga toxin-producing isolates were tested for production of Shiga toxins (Stx1 and Stx2 and enterohemolysin. Of the E. coli O157:H7/H- strains, 150 of 164 (mostly human, cattle, and food) isolates were stx+. Sixty-five percent of O157 STEC produced both Stx1 and Stx2; 32% and 0.7% produced Stx2 or Stx1, respectively. Ninety-eight percent of O157 STEC had sequences for genes encoding intimin and enterohemolysin. Five of 20 E. coli O111, 4 of 14 O128 and 4 of 10 O26 were stx+ . Five of 6 stx+ O26 and O111 produced Stx1, however, stx+ O128 were Stx-negative. Acid resistance (93.3%) and tellurite resistance (87.3%) were common attributes of O157 STEC, whereas, non-O157 stx+ strains exhibited 38.5% and 30.8% of the respective resistances. stx-positive isolates were mostly associated with humans and cattle, whereas, all isolates from mastitis (n = 105), and pigs, dogs, parrot and iguanas (n = 48) were stx-negative. Multiplex PCR was an effective tool for characterizing STEC pathogenic profiles and distinguished STEC O157:H7 from other STEC. Isolates from cattle and human disease shared similar toxigenic profiles, whereas isolates from other disease sources had few characteristics in common with the former isolates. These data suggest interspecies transmissibility of certain serotypes, in particular, STEC O157:H7, between humans and cattle.     

Prevalence of non-O157:H7 shiga toxin-producing Escherichia coli in diarrheal stool samples from Nebraska

We determined the prevalence of Shiga toxin-producing Escherichia coli (STEC) in diarrheal stool samples from Nebraska by three methods: cefixime-tellurite sorbitol MacConkey (CT- SMAC) culture, enterohemorrhagic E. coli (EHEC) enzyme immunoassay, and stx1,2 polymerase chain reaction (PCR). Fourteen (4.2%) of 335 specimens were positive by at least one method (CT-SMAC culture [6 of 14], EHEC enzyme immunoassay [13 of 14], stx1,2 PCR [14 of 14]). Six contained serogroup O157, while non-O157 were as prevalent as O157 serogroups.     

A cluster of Escherichia coli O157: nonmotile infections associated with recreational exposure to lake water

OBJECTIVES: To identify cases and determine risk factors for an outbreak of Escherichia coli (E. coli) O157: nonmotile (NM) infections in children attending a summer day care program in California. METHODS: The authors conducted a retrospective cohort study; the cohort comprised first and second graders who attended the day care program during the last week in August 1999. Shiga toxin testing and molecular subtyping using pulsed-field gel electrophoresis were performed on isolates. Lake water, lake bottom sediment samples, and waterfowl feces from the lake environs were cultured for E. coli O157. RESULTS: Three cases of Shiga toxin-producing E. coli O157: NM infections with matching pulsed-field gel electrophoresis patterns and four probable cases were found. Children who swallowed more than a mouthful of water had a higher attack rate than those who swallowed less than a mouthful or none at all (43% vs. 10%, relative risk = 4.43, 95% confidence interval 1.12, 17.50). CONCLUSIONS: E. coli O157: NM infections were associated with swallowing water from a freshwater lake. Potential sources of contamination include feces from humans, cattle, or deer. This outbreak illustrates the value in screening patients with diarrhea for E. coli O157, submitting isolates to public health laboratories, and using molecular techniques to identify related cases. Outbreaks associated with contaminated freshwater could be averted by prevention and early detection of contamination.     

Quantitative detection of E. coli, E. coli O157 and other shiga toxin producing E. coli in water samples using a culture method combined with real-time PCR

Recent water related outbreaks of shiga toxin producing E. coli O157 have resulted in increased attention of the water industry to this potentially deadly pathogen. Current methods to detect E. coli O157 and its virulence genes are laborious and time-consuming. Specificity, sensitivity and simple use of a real-time PCR method makes it an attractive alternative for the detection of STEC E. coli O157. This study describes the development and application of real-time PCR methods for the detection of E. coli O157, shiga toxin genes (Stx1 and Stx2) and E. coli. The specificity of the methods was confirmed by performing colony-PCR assays on characterized bacterial isolates, demonstrating the applicability of these assays as rapid tests to confirm the presence of E. coli or E. coli O157 colonies on culture plates. Sensitive culture-PCR methods were developed by combining culture enrichment with real-time PCR detection. This rapid method allowed detection of low concentrations of E. coli O157 in the presence of high concentrations of non-O157-E. coli (1:104). Culture-PCR methods were applied to 27 surface water and 4 wastewater samples. E. coli O157 and both Stx genes were detected in two wastewater samples, whereas only E. coli O157 was detected in two surface water samples. Culture-PCR methods were not influenced by matrix effects and also enabled quantitative (MPN) detection of E. coli in these samples.     

Phenotypic and genetic markers for serotype-specific detection of Shiga toxin-producing Escherichia coli O26 strains from North America

Phenotypic and genetic markers of Shiga toxin-producing Escherichia coli (STEC) O26 from North America were used to develop serotype-specific protocols for detection of this pathogen. Carbohydrate fermentation profiles and prevalence of gene sequences associated with STEC O26 (n = 20) were examined. Non-STEC O26 (n = 17), E. coli O157 (n = 20), E. coli O111 (n = 22), and generic E. coli (n = 21) were used as comparison strains. Effects of supplements: cefixime-tellurite, 4-methylumbelliferyl-beta-D-glucuronide (MUG) and chromogenic additives (5-bromo4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal), 5-bromo-4-chloro-3-indolyl-beta-D-glucuronide (X-GlcA) and o-nitrophenyl-beta-D-galactopyranoside (ONPG), added to isolation agar media were examined. Tests for presence of gene sequences encoding beta intimin (eae beta), Shiga toxin 1 and 2 (stx1 and stx2), H7 flagella (flicCh7), enterohemolysin (ehlyA), O26 somatic antigen (wzx), and high pathogenicity island genes (irp2 and fyuA) were conducted using multiplex polymerase chain reaction. Pulsed-field gel electrophoresis (PFGE) of XbaI restriction endonuclease genomic DNA digests was used to establish clonality among E. coli O26 strains. Of the 26 carbohydrates tested, only rhamnose had diagnostic value. Rhamnose non-fermenters included STEC O26 (100%), non-STEC O26 (40%), generic E. coli (29%), E. coli O111 (23%), and E. coli O157 (0%). Rhamnose non-fermenting colonies growing on Rhamnose-McConkey agar supplemented with X-GlcA, X-Gal, or ONPG, respectively, were blue, white, or faint yellow, whereas rhamnose-fermenters were red. Blue colonies from X-GlcA-containing media were the most well-defined and easiest to pick for further tests. All STEC O26 were MUG-fluorescent, while STEC O157 (n = 18) were non-fluorescent. E. coli O111 and generic E. coli strains were either MUG-positive or-negative. Serotype-specific detection of STEC O26 was achieved by selecting cefixime-tellurite-resistant, MUG-fluorescent, rhamnose-nonfermenting colonies, which carried stx1, eae beta, irp2, and wzx gene sequences. STEC O26 prevalence in dairy farm environmental samples determined using the developed isolation and genetic detection protocols was 4%. PFGE indicated the presence of one major cluster of E. coli O26 with 72-100% DNA fragment-length digest similarity among test strains. The serotype-specific detection methods described herein have potential for routine application in STEC O26 diagnosis.     

Molecular epidemiology of Escherichia coli isolated from young South African children with diarrhoeal diseases

Molecular techniques were used for studying the epidemiology of diarrhoeal infections due to Escherichia coli in the Gauteng region in South Africa. In total, 151 E. coli strains isolated from stools of patients with diarrhoea and 30 strains isolated from stools of healthy individuals were collected between March 1996 and May 1997. The E. coli isolates were characterized by serotyping, antimicrobial susceptibility testing, and adherence patterns. Polymerase chain reaction (PCR) was performed to determine the presence of the genes-encoding virulence factors. PCR showed that 59 (32.6%) of the E. coli isolates carried eaeA genes, 6 (3.3%) possessed bfpA genes, 4 (2.2%) CNF1, and 2 (1.1%) carried labile toxin and Stx2 genes. The eae genes were more prevalent in strains isolated from patients than in those from the control group (p < 0.001). Forty-eight (26.5%) strains belonged to enteropathogenic E. coli (EPEC) O serogroups and 14 (7.7%) to Shiga toxin-producing E. coli (STEC) O157 serotype. A high percentage (28.2%) of atypical EPEC strains possessing the eaeA but not the bfpA genes was isolated. Most isolates were susceptible to commonly-used antimicrobial agents. The adherence of the E. coli strains to HeLa cells was identified more in patients (69.4%) than in the control group (60%) and was more dominant in infants than in adults. PCR and tissue culture assays were shown to be useful techniques for the epidemiological study of E. coli where this organism is a major cause of diarrhoea.     

Prevalence and growth kinetics of Shiga toxin-producing Escherichia coli (STEC) in bovine offal products in Japan

Recent epidemiological data suggest a link between the consumption of bovine offal products and Shiga toxin-producing Escherichia coli (STEC) infection in Japan. This study thus examined the prevalence of STEC in various types of these foods. PCR screened 229 bovine offal products for the presence of Shiga toxin (stx) gene. Thirty-eight (16·6%) samples were stx positive, of which eight were positive for rfbE(O157) and three were positive for wzy(O26). Four O157 and one O26 STEC isolates were finally obtained from small-intestine and omasum products. Notably, homogenates of bovine intestinal products significantly reduced the extent of growth of O157 in the enrichment process compared to homogenates of beef carcass. As co-incubation of O157 with background microbiota complex from bovine intestinal products in buffered peptone water, in the absence of meat samples, tended to reduce the extent of growth of O157, we reasoned that certain microbiota present in offal products played a role. In support of this, inoculation of generic E. coli from bovine intestinal products into the homogenates significantly reduced the extent of growth of O157 in the homogenates of bovine intestinal and loin-beef products, and this effect was markedly increased when these homogenates were heat-treated prior to inoculation. Together, this report provides first evidence of the prevalence of STEC in a variety of bovine offal products in Japan. The prevalence data herein may be useful for risk assessment of those products as a potential source of human STEC infection beyond the epidemiological background. The growth characteristic of STEC O157 in offal products also indicates the importance of being aware when to test these food products.     

Escherichia coli O157 infection associated with a petting zoo

A young child was admitted to hospital with haemolytic-uraemic syndrome caused by infection with a Shiga toxin 2-producing strain of Escherichia coli (STEC) O157. Five days before he became ill, the child had visited a small petting zoo. STEC O157 strains were isolated from faecal samples from goats and sheep housed on the farm. The human and the animal isolates were indistinguishable by molecular subtyping. The petting zoo voluntarily closed temporarily to prevent further cases of infection. Two out of 11 other, randomly selected petting zoos (including one deer park) visited subsequently, tested positive. Furthermore, during the study period there was one more notification of STEC O157 infection possibly linked with a farm visit. Although STEC O157 was indeed found in the petting zoo associated with this patient, transmission through animal contact could not be confirmed because the human isolate was not available for subtyping. The case study and the results of the other on-farm investigations highlight the risk of acquiring severe zoonotic infections during visits to petting zoos.     

Expression and putative roles in attachment of outer membrane proteins of Escherichia coli O157 from planktonic and sessile culture

Many strains of Shiga toxigenic Escherichia coli (STEC), particularly the serotype O157:H7, are foodborne pathogens causing disease in many countries throughout the world. E. coli O157:H7 is able to attach and survive on various surfaces such as stainless steel (SS) found within the food processing environment. We examined the outer membrane protein (OMP) profiles of four E. coli O157 (three toxigenic O157:H7 and one nontoxigenic O157:HR) and one non-STEC strain (O1:H7), previously reported to have different abilities to attach to SS following growth in planktonic (nutrient broth) and sessile (nutrient agar) culture. The OMPs of the five E. coli strains grown in planktonic and sessile culture were extracted using N-lauroyl sarcosine and the OMP profiles were separated using two-dimensional (2D) gel electrophoresis. Qualitative and quantitative variations in the total number of OMPs expressed between planktonic and sessile cultures were found for all E. coli isolates tested. A number of differentially expressed protein spots were selected from 2D gels and were identified. FlgE was found to be expressed in planktonic culture but not sessile culture. MipA and OmpX had higher expression in sessile culture than planktonic culture, while expression of OmpA did not differ between E. coli strains or between the two modes of growth. Although differential expression of OMPs was found between isolates grown in planktonic and sessile culture, further investigations are required to determine a role of some of these identified proteins during growth of E. coli in planktonic and sessile culture and their influence during the attachment process.     

Characterization and epidemiologic subtyping of Shiga toxin-producing Escherichia coli strains isolated from hemolytic uremic syndrome and diarrhea cases in Argentina

Argentina has a high incidence of hemolytic uremic syndrome (HUS); 12.2 cases per 100,000 children younger than 5 years old were reported in 2002. Shiga toxin (Stx)-producing Escherichia coli (STEC) is the primary etiologic agent of HUS, and STEC O157 is the predominant serogroup isolated. The main objective of the present work was to establish the phenotypic and genotypic characteristics of the STEC strains in general isolated from Argentine children during a prospective study and the clonal relatedness of STEC O157:H7 strains using subtyping techniques. One hundred and three STEC strains isolated from 99 children were included. The phenotypic and genotypic features were established, and a polymerase chain reaction-restriction fragment length polymorphism (PCRRFLP) was performed to determine stx2 variants. The clonal relatedness of E. coli O157 isolates was established by phage typing and pulsed-field gel electrophoresis (PFGE). The 103 STEC strains belonged to 18 different serotypes, and 59% were of serotype O157:H7. Stx2 was identified in 90.3%, and stx1 in 9.7%. Among the 61 STEC O157 strains, 93.4% harbored the stx2/stx2vh-a genes; PT4 (39.3%) and PT2 (29.5%) were the predominant phage types. Using PFGE with the enzyme XbaI, a total of 41 patterns with at least 80% similarity were identified, and seven clusters with identical profiles were established. Some of the clusters were further split by PFGE using BlnI as the second enzyme. Isolates with indistinguishable PFGE patterns were with one exception also indistinguishable by phage typing and stx genotyping. These findings confirmed that some isolates were genetically related. However, no epidemiological linkages were identified. STEC strains with different genotypes and belonging to diverse serotypes were isolated in Argentina. Some STEC O157 strains could not be distinguished by applying subtyping techniques such as PFGE and phage typing.     

Environmental isolates of Citrobacter braakii that agglutinate with Escherichia coli O157 antiserum but do not possess the genes responsible for the biosynthesis of O157 somatic antigen

While searching for Escherichia coli O157 in the aquatic environment of Calcutta using an immunodetection procedure, we fortuitously detected five strains of Citrobacter braakii, which cross-reacted with the commercially available O157 polyvalent antiserum. The five C. braakii isolates gave positive results when a sensitive dot-ELISA was performed with E. coli O157 monoclonal antibody. Further, the O157 monoclonal antibody recognized the bands of proteinase K treated whole cells of lipopolysaccharide of all the C. braakii isolates. Apart from weak reactions with two or three of the DNA probes, all the C. braakii strains did not hybridize with the other probes spanning the minimum region required for O157 O-antigen biosynthesis. These strains did not possess any of the virulence genes that are commonly found in the Shiga toxin-producing E. coli (STEC) specially the serotype O157: H7. Therefore, it appears that the serological cross-reaction between C. braakii and E. coli O157 antiserum is based on structural mimicry between the O-polysaccharide of C. braakii and E. coli O157.     

徐州市2000年肠出血性大肠埃希菌O157：H7感染性腹泻的调查

目的 了解徐州市丰县和铜山县肠出血性大肠埃希菌（EHEC）O157：H7引起的出血性结肠炎（HC）在腹泻病患者中所占的比例，以及临床症状和肾功能变化的情况。方法 使用EHECO157胶体金快速检测试剂筛选粪便标本，阳性者使用免疫磁珠方法分离病原菌。对经过细菌学证实的EHECO157：H7引起的HC患者，进行临床症状的观察和生化检验指标分析。结果 2000年5月份，丰县由EHECO157：H7引起的HC占腹泻病患者0.98%，6月份铜山县的HC患者占腹泻病患者5.89%。在出现腹泻病症状的同时，18.5%患者的肾功能已经出现异常，表现为尿蛋白，血清肌苷或血尿素氮等指标的升高，在27例HC患者中，有14和13例分别分离到不产生志贺毒素和产生志贺毒素的EHECO157：H7菌株，根据分离菌株是否产生志贺毒素将患者分为两组进行比较，尿蛋白阳性患者的比例分别为4/13和1/14，血小板减少患者的比例分别为6/13和3/14，统计学分析有显著意义。提示分离到产生志贺毒素的EHECO157：H7菌株的患者，发生肾功能异常的可能性较大，结论 此次调查证实了EHECO157：H7感染所引起的HC在整个腹泻病患者中所占的比例随季节的变化而不同，感染产生志贺毒素EHECO157：H7菌株的患者，发生肾功能异常的可能性要比不产生志贺毒素的大，还证实了在该菌感染的初期，患者的肾功能就已经出现了异常。     

Detection and characterization of Shiga toxin-producing Escherichia coli from seagulls

Shiga toxin (Stx)-producing Escherichia coli (STEC) strains isolated from a seagull in Japan were examined. A total of 50 faecal samples was collected on a harbour bank in Hokkaido, Japan, in July 1998. Two different STEC strains, whose serotypes were O136:H16 and O153:H-, were isolated from the same individual by PCR screening; both of them were confirmed by ELISA and Vero cell cytotoxicity assay to be producing active Stx2 and Stx1, respectively. They harboured large plasmids, but did not carry the haemolysin or eaeA genes of STEC O157:H7. Based on their plasmid profiles, antibiotic resistance patterns, pulsed-field gel electrophoresis analysis (PFGE), and the stx genes sequences, the isolates were different. Phylogenic analysis of the deduced Stx amino acid sequences demonstrated that the Stx toxins of seagull-origin STEC were closely associated with those of the human-origin, but not those of other animal-origin STEC. In addition, Stx2phi-K7 phage purified from O136 STEC resembled Stx2phi-II from human-origin O157:H7, and was able to convert non-toxigenic E. coli to STEC. These results suggest that birds may be one of the important carriers in terms of the distribution of STEC.