牛源产志贺毒素大肠杆菌分离株的毒力基因分布和遗传进化分析

为了探讨牛源产志贺毒素大肠杆菌（Shiga toxin-producing Escherichia coli,STEC）分离株在毒力基因分布和遗传进化方面与人源EHEC O157菌株之间的关系,本试验选择收集来自江苏某奶牛场的STEC菌株18株以及人源、羊源、猪源、禽源STEC参考菌株9株,参照美国疾病预防控制中心PulseNet推荐的方法,运用XbaⅠ酶进行酶切并完成脉冲肠凝胶电泳（PFGE）分型和聚类分析;同时对部分STEC菌株进行毒力基因检测。结果表明,经毒力基因检测,不同来源的O157菌株毒力基因分布不尽相同,其中牛源STEC O157与参考株EHEC O157∶H7（EDL933W）的基因排谱最为相近;牛源STEC O18和O26的基因排谱与参考株EHEC O157∶H7（EDL933W）类似,但存在部分基因的缺失。对27株不同来源的STEC分离株进行PFGE,产生了22种不同的酶切图谱。总体来看,不同来源的STEC Dice相似性系数在72%~100%之间。牛源O157分离株与猪源及禽源O157菌株的相似度偏低,而与两株人源O157分离株的相似度偏高,Dice相似性系数在83%~95%之间,牛源O26（克隆群Ⅶ、Ⅷ）与人源O157的相似性系数 > 82%。显然,从牛群中分离到的部分STEC菌株与人源EHEC O157具有较近的遗传进化关系。     

产志贺毒素大肠杆菌流行病学及主要毒力因子研究进展

产志贺毒素大肠杆菌(Shiga toxin-producing Escherichia coli,STEC) 是一类能引起包括水样腹泻、出血性结肠炎、尿毒综合症等一系列人体疾病的人畜共患肠道致病菌,其感染在世界范围内包括中国都有过暴发流行。文章阐述了STEC O157血清型和非O157血清型的分布特征及流行趋势,同时还对该病的主要毒力因子进行了综述,以期为该病的防控提供科学依据。     

新疆部分地区牛羊源产志贺毒素大肠埃希菌菌株检测与分析

产志贺毒素大肠埃希菌（Shiga toxin-producing Escherichia coli，STEC）是一类携带了前噬菌体编码的一种或两种志贺毒素基因的新发高致病性食源性病原菌，已成为威胁人类健康的重要公共卫生问题。为了解新疆部分地区牛、羊源各个环节产志贺毒素大肠埃希菌的感染情况及其遗传多样性，以及分离株对17种常见抗生素的敏感性，笔者采用PCR方法对STEC分离株进行了4种毒力基因（stx1、stx2、eae、hlyA）的检测和ERIC-PCR基因分型研究。结果表明：从屠宰场、养殖场和市场共431份样品中分离出产志贺毒素的大肠埃希菌64株，其中，编码stx1+stx2的STEC有31株（48.4%），只编码stx1的STEC有29株（45.3%），只编码stx2的STEC有4株（6.3%），4种毒力基因同时存在的有1株。药物敏感性检测发现STEC菌株对麦迪霉素（61%）、头孢噻吩（4.7%）、头孢西丁（4.7%）、氨苄西林（3.1%）、哌拉西林（1.6%）、妥布霉素（1.6%）、头孢唑啉（1.6%）等7种抗生素存在耐药。ERIC-PCR检测结果呈多态性分布，分为A（36株）和B（28株）两个簇。STEC菌株在新疆部分地区牛、羊源各个环节被检出，其中一些菌株可能会增加对食物的污染，从而引起人发病。     

Detection and Analysis of Shiga Toxin-producing Escherichia coli Isolates from Cattle and Sheep Sources in Some Regions of Xinjiang,China

Shiga toxin-producing Escherichia coli(STEC) is a new class of highly pathogenic food-borne pathogens carrying a prephage encoding one or two Shiga toxin genes. It has become an important public health issue that threatens human health. The present work aimed to characterize STEC strains isolated from cattle and sheep at various stages, in parts of Xinjiang, in terms of the presence of prevalence, genetic diversity, and antimicrobial susceptibility to 17 common antibiotics. Through amplification of four virulence genes (stx1, stx2, eae, hlyA)by PCR and ERIC-PCR genotyping to detection STEC isolates. In the present study, a total of 64 STEC strains were isolated from 431 samples from slaughterhouses, farms and markets. Of these, 31 (48.4%) of the isolates harbored stx1 + stx2, and only 29 (45.3%) of the isolates possessed stx1, only 4 (6.3%) of the isolates harbored stx2, and 1 isolates harbored all the 4 virulence genes. Drug sensitivity tests found that STEC strains displayed 7 antimicrobial resistance to midecamycin(61%), cephalothin(4.7%), cefoxitin(4.7%), ampicillin(3.1%), piperacillin(1.6%), tobramycin(1.6%), cefazolin(1.6%). The ERIC-PCR results showed a polymorphic distribution, which was divided into two clusters of A (36 strains) and B (28 strains). STEC strains isolated from cattle and sheep at various stages, in parts of Xinjiang, some of which might have the potential to cause food contamination and human diseases.     

新疆牛、羊和骆驼源产志贺毒素大肠埃希菌的系统进化分群、血清群与毒力基因及耐药性分析

旨在了解新疆牛、羊和骆驼源产志贺毒素大肠埃希菌（Shiga toxin-producing Escherichia coli,STEC）的系统进化分群、血清群、毒力基因、耐药性及其遗传多样性,本研究采用PCR方法对牛、羊和骆驼源STEC进行了系统发育分群、血清群和毒力基因stx₁、stx₂（包括亚型）、eaeA、hlyA检测,通过K-B纸片法对分离株进行药物敏感性检测,并对其进行ERIC-PCR基因分型。结果表明：94株非O157 STEC以B1群为主,含9个血清群,包括O146（n=14）、O22（n=7）、O3（n=4）、O168（n=4）、O8（n=3）、O167（n=2）、O88（n=1）、O112ab （n=1）和O147（n=1）。毒力基因检测显示,46.8%（44/94）仅携带stx₁,6.4%（6/94）仅携带stx₂,46.8%（44/94）同时携带stx₁+stx₂。羊源STEC以携带stx₁+hlyA为主（68.0%）;牛源STEC以携带stx₁+stx₂+hlyA为主（57.9%）;骆驼源STEC以携带stx₁+hlyA为主（25.0%）。stx_1a主要分布于牛源STEC,stx_1c主要分布于羊源STEC。14株（14.9%）为耐药菌,对头孢他啶、四环素、头孢噻肟、氨苄西林和氨曲南的耐药率为3.2%~5.3%,对复方新诺明、头孢吡肟、哌拉西林-他唑巴坦、氨苄西林-舒巴坦、阿莫西林-克拉维酸和多黏菌素B的耐药率为1.1%~2.1%。ERIC-PCR结果显示牛、羊和骆驼源STEC亲缘关系较近。牛、羊和骆驼携带多种已知血清群STEC,贮存丰富的毒力基因,存在感染人类的风险,应在屠宰加工过程中予以预防和控制。     

产志贺毒素大肠杆菌的流行病学及致病因子的研究进展简

产志贺毒素大肠杆菌（Shiga toxin-producing Escherichia coli，STEC）是一类危害严重的食源性病原菌，能引起人类的严重疾病，如出血性结肠炎、溶血性尿毒症等，牛、羊等反刍动物是引起人类发病的主要宿主来源。作者总结了产志贺毒素大肠杆菌病的流行病学现状，就产志贺毒素大肠杆菌染色体和毒性质粒上的主要毒力因子的研究进展作一综述。     

江苏某奶牛场健康奶牛体内产志贺毒素大肠杆菌的分离鉴定及其对小鼠致病性的研究

通过对江苏省某奶牛场连续6个月的定群、定畜跟踪调查,获得产志贺毒素大肠杆菌(STEC)在该牛场分布的广泛性、持续性和血清型多样化的资料,并对一些重要血清型分离株作致病性的鉴定.基于本实验室已经建立的多重PCR方法对stx1、stx2、eaeA、ehxA共4个基因进行检测,对检测出的阳性样品,非O157 STEC采用多重PCR结合CT-SMAC平板的分离方法,而O157 STEC通过免疫磁珠结合O157显色平板的分离方法.结果表明,该奶牛场STEC的初筛率为16.1%(112/696),分离率为11.1%(77/696).分离株属于35种O血清型和60种O:H血清型.该场的优势血清型为O4、O26和O93,O157在该场存在,但并非优势血清型.77个分离株中,stx2基因的检出率为68.8%,远远高于其它毒力基因,如stx1(19.5%)、eaeA(11.7%1)和ehxA(20.8%).该场分离到一些O157和O26血清型的菌株,对小鼠具有较强的致病性.奶牛是STEC的天然宿主,可健康带菌.除了O157STEC外,非O157 STEC中一些高致病力菌株对人类的健康也存在威胁.     

牦牛产志贺毒素大肠杆菌主要黏附因子相关基因的分子流行病学调查

为了解中国牦牛产志贺毒素的大肠杆菌(Shiga toxin-producing Escherichia coli, STEC)中主要黏附因子的流行情况,采用PCR方法对来自四川甘孜阿坝等地区健康牦牛的70株STEC的eae、saa、iha 3种与黏附相关的毒力基因进行检测,并对部分含有相关黏附因子的阳性分离株的毒力基因进行了克隆及序列分析。结果显示,牦牛STEC中saa、iha的阳性率分别为71.42%(50/70)和78.57%(55/70),无eae基因序列(0/70),saa、iha的测序结果与GenBank上序列的同源性分别为100%和93%~99%。健康牦牛分离的STEC无LEE毒力岛编码eae,其他的一些与黏附相关的主要毒力基因saa、iha的携带率较高。     

川西北牦牛肉中产志贺毒素大肠杆菌的分离鉴定及stx2基因的序列分析

为了解中国川西北牦牛肉中产志贺毒素大肠杆菌(STEC)的携带情况及stx2的亚型和特征,试验将采集的204份川西北牦牛肉样品(各25g)增菌培养后,每份挑取5个可疑菌落,采用stx1、stx2双重PCR方法检测STEC,对分离株中的stx2分型并克隆测定stx2编码区序列。结果显示,在204份样品中分离出8株STEC,平均分离率为3.9%(8/204);存在4个不同的O血清型,分别为O38(4)、O50(1)、O74(2)、O150(1);在6株含有stx2的菌株中,其中有2株为stx2a型、4株为stx2c型。结果表明牦牛源分离株氨基酸序列与人源和牛源菌株同源性较高;由stx2A、B亚基的氨基酸序列系统进化树可知,牦牛源分离株与人源、牛源菌株聚为一支,表明它们之间遗传距离相对较近,牦牛源stx2各自分布在自己的小分支中,表明牦牛源STEC stx2与人源和牛源stx2相比,尽管亲缘关系较近,但仍存在一定程度的差异。     

Detection and characterisation of Shiga toxin-producing Escherichia coli other than Escherichia coli O157:H7 in wild ruminants

Shiga toxin-producing Escherichia coli (STEC) are an important group of emerging pathogens, with ruminants recognised as their main natural reservoir. The aim of this work was to establish the prevalence of non-O157 STEC in free-ranging wild ruminants in the Extremadura region of Spain and to characterise them phenogenotypically. Faecal samples were collected from 243 wild ruminants, including Cervus elaphus, Capreolus capreolus, Dama dama and Ovis musimon and were examined for STEC using both phenotypic (Vero cells) and genotypic (PCR and PFGE) methods.Shiga toxin-producing Escherichia coli were isolated from 58 (23.9%) of the samples and a total of 65 isolates were characterised. A PCR method indicated that 11 (16.9%) strains carried the stx₁ gene, 44 (67.7%) carried the stx₂ gene and 10 (15.4%) carried both these genes. The ehxA gene was detected in 37 (57%) of the isolates but none contained either the eae or saa genes. The isolates were from a total of 12 ‘O’ serogroups, although 80% were restricted to the O2, O8, O128, O146, O166 and O174 serogroups. The most commonly isolated STEC bacteria, which were from the O146 serogroup, exhibited a high degree of polymorphism as indicated by PFGE. Shiga toxin-producing Escherichia coli isolates of serogroups O20, O25, O166, O171, O174 and O176 had not previously been found in wild ruminants. This is the first study to confirm that wild ruminants in Spain are a reservoir of STEC and are thus a potential source of human infection.     

Prevalence,O-genotype and Shiga toxin (Stx) 2 subtype of Stx-producing Escherichia coli strains isolated from Argentinean beef cattle

The aims of this study were to investigate prevalence, O-genotype, and virulence gene profile including Shiga toxin (Stx) 2 gene-subtype of Stx-producing Escherichia coli (STEC) in beef cattle from the Bahía Blanca in Argentina. Rectal swabs were collected from 283 beef cattle in 2012. stx genes were detected in 90 (32%) out of the 283 rectal swabs by stx gene-specific PCR assay. The positive cases were 13 with stx1, 58 with stx2, and 19 with both stx1 and stx2. Among 90 stx gene-positive samples, 45 STEC strains were isolated, which included 3 stx1, 34 stx2, and eight stx1 and stx2 genes positive isolates. O-genotyping grouped 45 STEC strains into 19 different O-genotypes such as Og8, Og145, Og171, Og185 (4 from each), Og22, Og153, Og157 (3 from each) and others. Various stx2 gene-subtypes were identified in 42 STEC strains: 13 positive cases for stx2a, 11 for stx2c, 3 for stx2g, 10 for stx2a and stx2d, 4 for stx2a and stx2c, and 1 for stx2b, stx2c and stx2g. efaI gene, generally prevalent in clinical strains, was detected in relatively high in the STEC strains. These data suggest that stx2a and stx2c were distributed not only in O145 and O157 but also in minor O-genotypes of STEC in Argentina.     

水貂出血性肺炎大肠杆菌毒力基因测定和H基因分型

为了分离鉴定引起水貂出血性肺炎的大肠杆菌,并对其致病性、血清型和毒力基因进行鉴定.本研究主要通过细菌分离鉴定试验对具有典型肺炎症状的死亡水貂的病原体进行分离,利用16S rRNA对进行细菌鉴定,并通过PCR方法对分离细菌的血清型和毒力基因进行检测,分析分离菌对动物的致病性.结果显示:28例水貂肺炎病例中分离出8株大肠杆...     

Virulence factors and antimicrobial susceptibility of Escherichia coli isolated from calves in Turkey

Escherichia coli isolates from calves were investigated by multiplex PCR assays for the presence of genes encoding K99, F41, F17-related fimbriae, heat-stabile enterotoxin a (STa), intimin (eae) and Shiga toxins (stx1 and stx2). A total of 120 E. coli isolates, 75 isolated from diarrhoeic or septicemic calves and 45 from clinically healthy calves aged between 1 day and 2 months were tested. Each isolate was obtained from different calves in different herds. Among the isolates from diseased animals, 12 (16%) isolates from 1- to 7-day-old diarrhoeic calves were detected as enterotoxigenic E. coli which possessed K99, F41 and STa in combination; F17-related fimbriae genes were detected in 33 (44%) isolates and they were found in combination with K99 + F41 + STa in two isolates. Of 120 isolates, 16 carried eae, eight stx1 and five stx2 genes alone or in combination. None of the eae- or stx-positive strains was identified as O157:H7. However, results indicate that calves may be carrier of Shiga toxin-producing E. coli which have potential as a human pathogen. Antimicrobial susceptibility of 75 isolates from diseased calves was determined by agar disk diffusion method for 14 antimicrobial agents. In 77.3% of the isolates, multiresistance was detected. Higher resistance rates were detected for cephalothin (72%), tetracycline (69.3%), kanamycin (69.3%), ampicillin (65.3%), nalidixic acid (53.3%), trimethoprim-sulphamethoxazole (52%) and enrofloxacin (41.3%), respectively. No resistance was found for ceftiofur and cefoxitin.     

不同毒力基因型大肠杆菌的毒力测定

为确定不同毒力因子对大肠杆菌毒力的影响,选用7株不同毒力基因型(分别为Stx2e 、LEE 、LEE HPI 、Stx2e HPI 、F18 Stx2e 、F18 Stx2e LEE 和F18 Stx2e ST1 LT1 LEE )的猪源大肠杆菌为材料,以消化道为感染途径,测定了其对30日龄健康ICR小鼠的半数致死量(LD50)。结果表明,以上7株大肠杆菌的LD50分别为1.504×109,5.986×108,3.777×108,1.504×108,5.986×107,3.777×107cfu/mL和1.504×107cfu/mL;确定了不同毒力基因型的大肠杆菌之间存在毒力差异,其中S462234株(F18 Stx2e ST1 LT1 LEE )的毒力最强,S452623株(Stx2e )的毒力最弱,S462234株的毒力是S452623株的100倍。     

毛皮动物源大肠埃希菌毒力基因二重PCR检测方法的建立

为了建立一种能够快速检测毛皮动物源大肠埃希菌耶尔森菌强毒力岛(HPI)中irp2、FyuA毒力基因的二重PCR方法,根据GenBank中irp2、FyuA基因的序列,设计并合成两对引物,扩增得到irp2、FyuA基因片段,大小分别为300bp和951bp。据此建立双重PCR方法,并将反应条件进行了优化。结果表明,用所建立的二重PCR方法可同时特异性扩增出大肠埃希菌irp2、FyuA毒力基因片段,对沙门菌、金黄色葡萄球菌、铜绿假单胞菌、克雷伯菌均无特异性扩增。菌液最低检出量为2.8×105CFU/mL。在78份临床样品检测中,二重PCR检测结果与常规PCR检测结果一致。所建立的大肠埃希菌irp2、FyuA毒力基因二重PCR检测方法具有很好的特异性和灵敏度,能够提高临床样品检测的效率。     

致病性大肠杆菌携带原噬菌体的预测及耐药性与毒力研究

【目的】研究致病性大肠杆菌携带原噬菌体的比例、原噬菌体携带毒力基因及耐药基因的情况,了解致病性大肠杆菌中原噬菌体对菌株的耐药性与毒力的影响,保证噬菌体生产菌的生物安全性,为大肠杆菌噬菌体的基础研究与应用提供借鉴。【方法】从NCBI中下载大肠杆菌全基因组信息,通过在线网站预测大肠杆菌中携带的原噬菌体数目,并分析原噬菌体的GC含量、基因组大小、占细菌基因组比例等基因组特征及完整型原噬菌体的类型,对原噬菌体做初步分类,统计分析完整型原噬菌体中携带耐药基因数目、耐药表型、耐药机制与毒力基因数目、毒力基因家族分布等。【结果】112株大肠杆菌携带完整型原噬菌体1 024个,疑似型原噬菌体287个,缺陷型原噬菌体505个。1 024个完整型原噬菌体中,多数与长尾噬菌体相似,占70.21%(719/1 024);共有63种噬菌体类型,其中BP4795(登录号：NC＿004813.1)类型的占比最高,达到19.24%(197/1 024),其次是DE3(登录号：NC＿042057.1),占比11.72%(120/1 024)。大肠杆菌携带原噬菌体的GC含量在38%～57%之间,基因组大小为3.1～152...     

鸭源致病性大肠杆菌O抗原与毒力基因检测及药敏试验

【目的】探究荣昌、大足和隆昌三地鸭大肠杆菌分离株的O抗原、毒力基因及耐药性。【方法】将2014年—2021年鸭病料中分离得到的107株细菌在无菌条件下接种于麦康凯培养基中划线进行培养纯化,通过16S rDNA基因扩增测序和生化试验进行细菌鉴定,采用PCR技术对O抗原和16种毒力基因进行检测,采用Kirby-Bauer纸片扩散法进行药敏试验。【结果】107株分离株鉴定为大肠杆菌;O抗原鉴定试验鉴定出9种O抗原,其中优势抗原为O78(37.00%)、O7(25.00%),O121和O145(均为15.00%),并检测到5株O78+O145和O7+O145融合株;共检测出11种毒力因子,其中强致病性毒力基因有Tsh基因(检出率为25.23%)、fyuA基因(检出率为31.78%)、estB基因(检出率为31.78%)、Vat基因(检出率为2.80%)、iucA基因(检出率为44.56%)。3种毒力基因ompA、yijP和ibeB的携带率最高,分别为100.00%、96.26%和85.98%;药敏试验结果表明分离株对氨基糖苷类药物、米诺环素和多黏菌素最为敏感,对大环内酯类药物和克林霉素耐药,分...     

Prevalence and Genetic Relatedness of Antimicrobial‐Resistant Escherichia coli Isolated From Animals,Foods and Humans in Iceland

The prevalence of resistant bacteria in food products in Iceland is unknown, and little is known of the prevalence in production animals. The aim of this study was to investigate the prevalence and genetic relatedness of antimicrobial‐resistant Escherichia coli from healthy pigs and broiler chicken, pork, broiler meat, slaughterhouse personnel and outpatients in Iceland. A total of 419 E. coli isolates were tested for antimicrobial susceptibility using a microbroth dilution method (VetMIC), and resistant strains were compared using pulsed‐field gel electrophoresis (PFGE). All samples were screened for enrofloxacin‐resistant strains with selective agar plates. The resistance rates among E. coli isolates were moderate to high from caecal and meat samples of pigs (54.1% and 28%), broilers (33.6% and 52%) and slaughterhouse personnel (39.1%), whereas isolates from outpatients showed moderate resistance rates (23.1%). Of notice was resistance to quinolones (minimum inhibitory concentrations: nalidixic acid ≥ 32, ciprofloxacin ≥ 0.12 and enrofloxacin ≥ 0.5), particularly among broiler and broiler meat isolates (18.2% and 36%), as there is no known antimicrobial selection pressure in the broiler production in Iceland. The majority (78.6%) of the resistant E. coli isolates was genotypically different, based on PFGE fingerprint analyses and clustering was limited. However, the same resistance pattern and pulsotype were found among isolates from broiler meat and a slaughterhouse worker, indicating spread of antimicrobial‐resistant E. coli from animals to humans. Diverse resistance patterns and pulsotypes suggest the presence of a large population of resistant E. coli in production animals in Iceland. This study gives baseline information on the prevalence of antimicrobial‐resistant E. coli from production animals, and their food products in Iceland and the moderate to high resistance rates emphasize the need for continuing surveillance. Further studies on the origin of the resistant strains and the genetic relatedness of strains of different origin are needed.     

Clarification of relationship between single-nucleotide polymorphism panels of Shiga toxin-producing Escherichia coli O157:H7/H- strains

Eighty strains of enterohemorrhagic Escherichia coli O157:H7/H- were analyzed by three single-nucleotide polymorphism (SNP) panels using whole-genome sequencing data. The partial concordance of SNP types among the different SNP panels was observed on minimum spanning trees reconstructed with SNP data. As for lineage I/II strains, some of the clade 7 strains belonged to one unique SNP type as determined by three panels, suggesting that clade 7 should be divided into at least two genotypes, namely, the unique type and the rest. In addition, clade 8 contained two unique genotypes, which was consistent with the previous prediction. Similarly, for lineage II, clade 12 should be divided into three genotype strains. In contrast, many strains of several clades belonging to lineage I were clustered into the same node on each minimum spanning tree upon testing with the three SNP panels. Previous studies reported that lineage I diverged more recently than lineages I/II and II. Such low diversity in lineage I in this study may have arisen because this lineage has not accumulated SNPs because of its relatively recent divergence. Based on the concordance observed in this study, some of the previously published O157 genotype distribution data were successfully interpreted to clarify the clade distribution, which was well supported by previous literature.     

Genetic Variations in Shiga Toxin‐Producing Abilities of Bovine and Human Escherichia coli O157:H7

Cattle are a primary reservoir of Escherichia coli O157:H7, a major foodborne pathogen. The organism causes haemorrhagic colitis which can lead to serious complications, including haemolytic–uraemic syndrome. Although E. coli O157:H7 is widely prevalent in cattle and cattle environments, the number of human cases remain relatively low, suggesting possible strain diversity and differences in virulence between human and bovine strains. Shiga toxins, Stx1 and Stx2, are the major virulence factors. Differences in Stx2 production between human and bovine strains have been demonstrated previously, and isolates possessing the stx₂ gene, but not producing Stx2 [toxin non‐producing (TNP) strains] have been identified. In this study, 150 isolates (56 human, 94 bovine) were tested by PCR for stx2 upstream regions associated with TNP and the Q933 gene, which has been previously associated with toxin production. A reverse passive latex agglutination test was used to evaluate 107 isolates (50 human, 57 bovine) for Stx1 and Stx2 production. The percentages of human and bovine isolates positive for presence of the TNP regions were similar (57.1% and 53.1% respectively), while a higher percentage of human isolates was positive for Q933 gene (89.3% versus 54.3%). Stx2 production of ≥1 : 8 was found in 86.0% of human isolates compared with 26.3% of bovine isolates. Bovine isolates with the presence of the TNP regions were associated with significantly lower Stx2 production (P < 0.05), while the Q933 gene was associated with higher Stx2 production (P < 0.05). However, the presence of the TNP region was not associated (P > 0.05) with low Stx2 production in human isolates. Therefore, Q933 was a better indicator of high Stx2 production by human and bovine isolates and may be a useful screening method to assess their potential to cause human disease.