Identification of the O-antigen biosynthesis genes of Escherichia coli O91 and development of a O91 PCR serotyping test

AIMS: The aims of the study were to characterize the O91 O-antigen gene cluster from Shiga toxin-producing Escherichia coli (STEC) O91 and to provide the basis for a specific PCR test for rapid detection of E. coli O91. METHODS AND RESULTS: The published primers complementary to JUMPstart and gnd gene, the conserved flanking sequences of O-antigen genes clusters in E. coli and related species were used to amplify the 10-kbp O91 O-antigen biosynthesis locus of STEC O91. A DNA library representative of this cluster allowed two O91 specific probes to be identified, and two specific PCR O91 serotyping tests to be successfully developed. CONCLUSIONS: These results confirm that the O-antigen gene cluster sequences of E. coli allow rapidly a specific O-antigen PCR assay to be designed. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings increase the number of PCR-assays available to replace the classical O-serotyping among E. coli O-antigen.     

Identification of Escherichia coli O172 O-antigen gene cluster and development of a serogroup-specific PCR assay

AIM: To characterize the locus for O-antigen biosynthesis from Escherichia coli O172 type strain and to develop a rapid, specific and sensitive PCR-based method for identification and detection of E. coli O172. METHODS AND RESULTS: DNA of O-antigen gene cluster of E. coli O172 was amplified by long-range PCR method using primers based on housekeeping genes galF and gnd Shot gun bank was constructed and high quality sequencing was performed. The putative genes for synthesis of UDP-FucNAc, O-unit flippase, O-antigen polymerase and glycosyltransferases were assigned by the homology search. The evolutionary relationship between O-antigen gene clusters of E. coli O172 and E. coli O26 is shown by sequence comparison. Genes specific to E. coli O172 strains were identified by PCR assays using primers based on genes for O-unit flippase, O-antigen polymerase and glycosyltransferases. The specificity of PCR assays was tested using all E. coli and Shigella O-antigen type strains, as well as 24 clinical E. coli isolates. The sensitivity of PCR assays was determined, and the detection limits were 1 pg microl(-1) chromosomal DNA, 0.2 CFU g(-1) pork and 0.2 CFU ml(-1) water. The total time required from beginning to end of the procedure was within 16 h. CONCLUSION: The O-antigen gene cluster of E. coli O172 was identified and PCR assays based on O-antigen specific genes showed high specificity and sensitivity. SIGNIFICANCE AND IMPACT OF THE STUDY: An O-antigen gene cluster was identified by sequencing. The specific genes were determined for E. coli O172. The sensitivity of O-antigen specific PCR assay was tested. Although Shiga toxin-producing O172 strains were not yet isolated from clinical specimens, they may emerge as pathogens.     

大肠杆菌O11 O-抗原基因簇序列的破译及特异分子标识的鉴定

大肠杆菌O11是一种可在人畜间交叉传染的强致病菌,具有潜在流行性爆发的危险。现完成了O11 O-抗原基因簇的破译,筛选和鉴定了多种特异分子标识,并实现了对大肠杆菌O11的快速、灵敏和准确的分子分型检测。利用鸟枪法测定大肠杆菌O11 O-抗原基因簇的序列全长为14180bp,生物信息学方法分析序列结构,共发现12个基因:GDP-L型岩藻糖合成途径基因(gmd,fcl,gmm,manC,manB)、UDP-N乙酰葡萄糖C4异构酶基因(gne)、O-抗原转运酶基因(wzx)、O-抗原聚合酶基因(wzy)和4个糖基转移酶基因;用PCR方法筛选出2个针对大肠杆菌O11的特异基因和4对特异引物,并进行环境样品检测实验鉴定了该PCR检测方法的灵敏度;设计并筛选出8条针对大肠杆菌O11的特异探针。     

Development of PCR assays targeting genes in O-antigen gene clusters for detection and identification of Escherichia coli O45 and O55 serogroups

The Escherichia coli O45 O-antigen gene cluster of strain O45:H2 96-3285 was sequenced, and conventional (singleplex), multiplex, and real-time PCR assays were designed to amplify regions in the wzx (O-antigen flippase) and wzy (O-antigen polymerase) genes. In addition, PCR assays targeting the E. coli O55 wzx and wzy genes were designed based on previously published sequences. PCR assays targeting E. coli O45 showed 100% specificity for this serogroup, whereas by PCR assays specific for E. coli O55, 97/102 strains serotyped as E. coli O55 were positive for wzx and 98/102 for wzy. Multiplex PCR assays targeting the E. coli O45 and the E. coli O55 wzx and wzy genes were used to detect the organisms in fecal samples spiked at levels of 10(6) and 10(8) CFU/0.2 g feces. Thus, the PCR assays can be used to detect and identify E. coli serogroups O45 and O55.     

Development of a multiplex PCR approach for the identification of Shiga toxin-producing Escherichia coli strains and their major virulence factor genes

AIMS: To develop and evaluate a multiplex PCR (mPCR) system for rapid and specific identification of Shiga toxin-producing Escherichia coli (STEC) and their main virulence marker genes. METHODS AND RESULTS: A series of mPCR assays were developed using primer pairs that identify the sequences of Shiga toxins 1 and 2 (stx1 and stx2, including the stx2c, stx2d, stx2e and stx2f variants), intimin (eaeA), and enterohaemorrhagic E. coli enterohaemolysin (ehlyA). Moreover, two additional genes (rfb O157 and fliC H7), providing the genotypic identification of the O157:H7 E. coli serotype, were detected. As an internal positive control, primers designated to amplify the E. coli 16S rRNA were included in each mPCR. All the amplified genes in the E. coli reference strains were sucessfully identified by this procedure. The method was then used for the examination of 202 E. coli isolates recovered from cattle and children. Among them, 25 (12.4%) were stx positive including the strains of O157:H7 serotype (six isolates) and O157:NM serogroup (four strains). Moreover, 20 STEC strains possessed the eaeA (intimin) and ehlyA (enterohaemolysin) genes. CONCLUSIONS: The developed mPCR-based system enabled specific detection of STEC bacteria and identification of their main virulence marker genes. SIGNIFICANCE AND IMPACT OF THE STUDY: The ability to identify STEC bacteria and the majority of their virulence gene markers, including four variants of Shiga toxin, as well as the differentiation of O157:H7 from non-O157 isolates represents a considerable advancement over other PCR-based methods for rapid characterization of STEC.     

大肠杆菌O141 O-抗原基因簇的破译及进化分析

对大肠杆菌O141 O-抗原基因簇进行测序,序列全长15601bp,用生物信息学的方法进行序列分析,共发现12个基因：鼠李糖合成酶基因(rmlB,rmlD,rmlA,rmlC)、甘露糖合成酶基因(manB,manC),糖基转移酶基因(orf6,orf7,orf9,orf10)、O-抗原转运酶基因(wzx)和O-抗原聚合酶基因(wzy)。用PCR的方法筛选出了针对大肠杆菌O141的特异基因,可以用于基因芯片或PCR方法对大肠杆菌O141的快速检测。通过对大肠杆菌O141的O-抗原基因簇及甘露糖和鼠李糖合成酶基因的进化分析发现：大肠杆菌O141 O-抗原基因簇是低GC含量的片段,仅O-抗原特异的基因才出现在O-抗原基因簇;并且这些基因可能介导了O-抗原基因簇间的重组及以O141 O-抗原基因簇的形成。     

Detection, isolation and characterization of Shiga toxin-producing Escherichia coli in retail-minced beef using PCR-based techniques, immunoassays and colony hybridization

AIMS: To provide information on detection of Shiga toxin-producing Escherichia coli (STEC) in retail-minced beef using an approach combining (i) PCR-based techniques and automated immunoassay for stx screening and detection of the five major serogroups associated with human infection, and (ii) immunomagnetic separation (IMS) and colony hybridization assays for bacterial strain isolation. METHODS AND RESULTS: Twenty-seven out of 164 minced beef samples were stx-positive by PCR-ELISA, nine of which were also positive by real-time PCR for at least one marker of the five main serogroups tested (O26, O103, O111, O145 and O157). Two E. coli O103 stx-negative strains were isolated from two out of 10 IMS and nine STEC strains that did not belong to the five main serogroups were isolated by colony hybridization. CONCLUSIONS: PCR techniques are applicable for rapid screening of samples containing both an stx gene and an O-group marker of the five main pathogenic STEC serogroups. Isolation of STEC strains belonging to the main non-O157 serogroups remains difficult. SIGNIFICANCE AND IMPACT OF THE STUDY: This study presents an evaluation of a multi-faceted approach for the detection of the most frequently reported human pathogenic STEC serogroups. The advantages and limits of this strategy are presented.     

Characterization of the Escherichia coli O59 and O155 O-antigen gene clusters: the atypical wzx genes are evolutionary related

O-antigens are highly polymorphic. The genes specifically involved in O-antigen synthesis are generally grouped together on the chromosome as a gene cluster. In Escherichia coli, the O-antigen gene clusters are characteristically located between the housekeeping genes galF and gnd. In this study, the O-antigen gene clusters of E. coli O59 and E. coli O155 were sequenced. The former was found to contain genes for GDP-mannose synthesis, glycosyltransferase genes and the O-antigen polymerase gene (wzy), while the latter contained only glycosyltransferase genes and wzy. O unit flippase genes (wzx) were found immediately downstream of the gnd gene, in the region between the gnd and hisI genes in these two strains. This atypical location of wzx has not been reported before, and furthermore these two genes complemented in trans despite the fact that different O-antigen structures are present in E. coli O59 and O155. A putative acetyltransferase gene was found downstream of wzx in both strains. Comparison of the region between gnd and hisI revealed that the wzx and acetyltransferase genes are closely related between E. coli O59 and O155, indicating that the two gene clusters arose recently from a common ancestor. This work provides further evidence for the O-antigen gene cluster having formed gradually, and selection pressure will eventually bring O-antigen genes into a single cluster. Genes specific for E. coli O59 and O155, respectively, were also identified.     

Molecular analysis of Shigella boydii O1 O-antigen gene cluster and its PCR typing

Shigella is an important human pathogen and is closely related to Escherichia coli. O-antigen is the most variable part of the lipopolysaccharide on the cell surface of Gram-negative bacteria and plays an important role in pathogenicity. The O-antigen gene cluster of S. boydii O1 was sequenced. The putative genes encoding enzymes for rhamnose synthesis, transferases, O-unit flippase, and O-unit polymerase were identified on the basis of homology. The O-antigen gene clusters of S. boydii O1 and E. coli O149, which share the same O-antigen form, were found to have the same genes and organization by adjacent gene PCR assay. Two genes specific for S. boydii O1 and E. coli O149 were identified by PCR screening against E. coli- and Shigella-type strains of the 186 known O-antigen forms and 39 E. coli clinical isolates. A PCR sensitivity of 103 to 104 CFU/mL overnight culture of S. boydii O1 and E. coli O149 was obtained. S. boydii O1 and E. coli O149 were differentiated by PCR using lacZ- and cadA-based primers.     

Relationships of the Escherichia coli O157, O111, and O55 O-antigen gene clusters with those of Salmonella enterica and Citrobacter freundii, which express identical O antigens

Escherichia coli O157, Salmonella enterica O30, and Citrobacter freundii F90 have identical O-antigen structures, as do E. coli O55 and S. enterica O50. The O-antigen gene cluster sequences for E. coli O157 and E. coli O55 have been published, and the genes necessary for O-antigen biosynthesis have been identified, although transferase genes for glycosidic linkages are only generic and have not been allocated to specific linkages. We determined sequences for S. enterica O30 and C. freundii F90 O-antigen gene clusters and compared them to the sequence of the previously described E. coli O157 cluster. We also determined the sequence of the S. enterica O50 O-antigen gene cluster and compared it to the sequence of the previously described E. coli O55 cluster. For both the S. enterica O30-C. freundii F90-E. coli O157 group and the S. enterica O50-E. coli O55 group of O antigens, the gene clusters have identical or nearly identical organizations. The two sets of gene clusters had comparable overall levels of similarity in their genes, which were lower than the levels determined for housekeeping genes for these species, which were 55 to 65% for the genes encoding glycosyltransferases and O-antigen processing proteins and 75 to 93% for the nucleotide-sugar pathway genes. Nonetheless, the similarity of the levels of divergence in the five gene clusters required us to consider the possibility that the parent gene cluster for each structure was in the common ancestor of the species and that divergence is faster than expected for the common ancestor hypothesis. We propose that the identical O-antigen gene clusters originated from a common ancestor, and we discuss some possible explanations for the increased rate of divergence that is seen in these genes.     

Association of Nucleotide Polymorphisms within the O-Antigen Gene Cluster of Escherichia coli O26, O45, O103, O111, O121, and O145 with Serogroups and Genetic Subtypes

Shiga toxin-producing Escherichia coli (STEC) strains are important food-borne pathogens capable of causing hemolytic-uremic syndrome. STEC O157:H7 strains cause the majority of severe disease in the United States; however, there is a growing concern for the amount and severity of illness attributable to non-O157 STEC. Recently, the Food Safety and Inspection Service (FSIS) published the intent to regulate the presence of STEC belonging to serogroups O26, O45, O103, O111, O121, and O145 in nonintact beef products. To ensure the effective control of these bacteria, sensitive and specific tests for their detection will be needed. In this study, we identified single nucleotide polymorphisms (SNPs) in the O-antigen gene cluster that could be used to detect STEC strains of the above-described serogroups. Using comparative DNA sequence analysis, we identified 22 potentially informative SNPs among 164 STEC and non-STEC strains of the above-described serogroups and designed matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF) assays to test the STEC allele frequencies in an independent panel of bacterial strains. We found at least one SNP that was specific to each serogroup and also differentiated between STEC and non-STEC strains. Differences in the DNA sequence of the O-antigen gene cluster corresponded well with differences in the virulence gene profiles and provided evidence of different lineages for STEC and non-STEC strains. The SNPs discovered in this study can be used to develop tests that will not only accurately identify O26, O45, O103, O111, O121, and O145 strains but also predict whether strains detected in the above-described serogroups contain Shiga toxin-encoding genes.     

First isolation of Shiga toxin 1d producing Escherichia coli variant strains in shellfish from coastal areas in France

AIMS: This study was carried out to evaluate the presence of Shiga toxin-producing Escherichia coli (STEC) and E. coli O157:H7 in shellfish from French coastal environments. METHODS AND RESULTS: Shellfish were collected in six growing areas or natural beds (B category) and nonfarming areas (D category) from July 2002 to August 2004. PCR detection of stx genes was performed on homogenized whole shellfish and digestive gland tissues enrichments. STEC strains were detected by colony DNA hybridization using a stx-specific gene probe and E. coli O157 strains were additionally searched by immunomagnetic separation with O157-specific magnetic beads. Stx genes were detected in 40 of 144 (27.8%) sample enrichments from mussels, oysters or cockles, 32 of 130 enrichments (24.6%) were from B-category areas and eight of 14 (57.1%) from the D-category area. Five strains carrying stx(1) or stx(1d) genes and one stx negative, eae and ehxA positive E. coli O157:H7 were isolated from six of 40 stx-positive enrichments. No relation was found between the total E. coli counts in shellfish and the presence of STEC strains in the samples. CONCLUSIONS: The STEC strains of different serotypes and stx types are present in shellfish from French coastal environments. It is the first isolation of STEC stx1d strains in France. SIGNIFICANCE AND IMPACT OF THE STUDY: Shellfish collected in coastal environments can serve as a vehicle for STEC transmission.     

Genetic characterization of the Escherichia coli O66 antigen and functional identification of its wzy gene

Escherichia coli is a clonal species, and occurs as both commensal and pathogenic strains, which are normally classified on the basis of their O, H, and K antigens. The O-antigen (O-specific polysaccharide), which consists of a series of oligosaccharide (O-unit) repeats, contributes major antigenic variability to the cell surface. The O-antigen gene cluster of E. coli O66 was sequenced in this study. The genes putatively responsible for the biosynthesis of dTDP-6-deoxy-L-talose and GDP-mannose, as well as those responsible for the transfer of sugars and for O-unit processing were identified based on their homology. The function of the wzy gene was confirmed by the results of a mutation test. Genes specific for E. coli O66 were identified via PCR screening against representatives of 186 E. coli and Shigella O type strains. The comparison of intergenic sequences located between galF and the O-antigen gene cluster in a range of E. coli and Shigella showed that this region may perform an important function in the homologous recombination of the O-antigen gene clusters.     

大肠杆菌O23 O-抗原基因簇序列的破译及UDP-N-乙酰葡萄糖-C4异构酶的鉴定

采用鸟枪法破译大肠杆菌O23标准株的O-抗原基因簇序列,并用生物信息学的方法进行了基因注释和分析;采用基因缺失和互补的方法鉴定了O23的UDP-GlcNAc C4异构酶(Gne);用同源建模的方法构建了O23 Gne的高级结构并对其活性位点进行了分析;分析了不同血清型大肠杆菌O-抗原基因簇中gne基因的多样性;根据O23O-抗原基因簇中的特异基因筛选出了可用于大肠杆菌O23快速检测的特异DNA序列。     

The Yersinia kristensenii O11 O-antigen gene cluster was acquired by lateral gene transfer and incorporated at a novel chromosomal locus

We have sequenced the O-antigen gene clusters for the Escherichia coli O98 and Yersinia kristensenii O11 O antigens. The basic structures of these O antigens are identical, and the sequence data indicate that Y. kristensenii O11 gained its O-antigen gene cluster by lateral gene transfer (LGT). Escherichia coli O98 has a typical O-antigen gene cluster between galF and gnd as is usual in E. coli. However, the O-antigen gene cluster of Y. kristensenii O11 is not located at the traditional Yersinia O-antigen gene cluster locus, between hemH and gsk, but at a novel chromosomal locus between aroA and cmk where it is flanked by remnant galF and gnd genes that indicate the probable source of the gene cluster. Phylogenetic analysis indicated that the source was not E. coli itself but a species in the Escherichia, Salmonella, and Klebsiella group of genera. Although other O-antigen studies imply LGT on the basis of the hypervariability of the loci and GC content, this report also identifies a potential donor and provides evidence for the mechanism involved. Remnant insertion sequence (IS) sequences flank the galF and gnd remnants and suggest that LGT of the gene cluster was IS mediated.     

RAPID detection and quantification of E. coli O157/O26/O111 in minced beef by real-time PCR

AIM: To develop a real-time PCR detection procedure for Escherichia coli O111, O26 and O157 from minced meat. METHODS AND RESULTS: Strains (n = 8) of each of E. coli O26, E. coli O111 and E. coli O157 were inoculated at ca 10-20 CFU g(-1) into minced retail meat and enriched for 6 h at 41.5 degrees C as follows: E. coli O26 in tryptone soya broth (TSB) supplemented with cefixime (50 microg l(-1)), vancomycin (40 mg l(-1)) and potassium tellurite (2.5 mg l(-1)); E. coli O111 in TSB supplemented with cefixime (50 microg l(-1)) and vancomycin (40 mg l(-1)); E. coli O157 in E. coli broth supplemented with novobiocin (20 mg l(-1)). DNA was extracted from the enriched cultures, and detected and quantified by real-time PCR using verotoxin (vt1 and vt2) and serogroup (O157 per gene; O26 fliC-fliA genes and O111 wzy gene) specific primers. CONCLUSIONS: The methods outlined were found to be sensitive and specific for the routine detection of E. coli O111, O26 and O157 in minced beef. SIGNIFICANCE AND IMPACT OF THE STUDY: The enrichment, isolation and detection procedures used in this study provide a rapid routine-based molecular method for the detection and differentiation of E. coli O26, O111 and O157 from minced meat.     

大肠杆菌O138 O-抗原基因簇的破译及Gne的生物信息学鉴定

利用鸟枪法对大肠杆菌E .coliO138O 抗原基因簇进行测序 ,序列全长 14 139bp ,用生物信息学的方法进行序列分析 ,共发现 11个基因 ,分别为鼠李糖合成酶基因 (rmlB ,rmlD ,rmlA ,rmlC)、UDP GalNAcA合成酶基因 (gne ,gna)、糖基转移酶基因 (3个 )、O 抗原转运酶基因 (wzx)和O 抗原聚合酶基因 (wzy)。发现一种稀有单糖UDP Gal NAcA的合成途径 ,对合成该糖的第一种酶Gne进行了生物信息学鉴定 ,另外用PCR方法筛选出了针对大肠杆菌O138的特异基因     

猪源大肠杆菌(ETEC、STEC、AEEC)毒力基因及其与O抗原型的关系

[目的]揭示从我国部分地区仔猪腹泻或水肿病病猪体内分离到的300个大肠杆菌分离株所属病原型(pathotype)、毒力基因及其与O血清型的关系.[方法]O血清型采用常规的凝集试验进行测定,毒力基因采用PCR方法检测.[结果]通过对这300个分离株的O血清型及其毒素、紧密素和黏附素基因进行鉴定,结果显示除50株未定型、17株自凝外,测定出233个分离株的血清型,这些分离株覆盖了45个血清型,其中以0149、0107、0139、093和091为主,共133株,占定型菌株的57.1%;拥有est Ⅰ、estⅡ、elt、stx2e和eae A基因的菌株分别为102(34.0%)、190(63.3%)、81(27.0%)、57(19.0%)和54(18.0%)株;分离株中有51株K88基因阳性(其中菌毛表达率为100%),75株F18基因阳性(其中菌毛表达率为50.7%),在K88菌株中,0149血清型与est Ⅰ或estⅡ elt密切相关,在F18菌株中,0107血清型与est Ⅰ或estⅡ、0139血清型与stx2e紧密相关.依其毒力特征可将这些分离株分为以下6种类型:ETEC、STEC、AEEC、ETEC/STEC、AEEC/ETEC和AEEC/ETEC/STEC,分别拥有190、24、36、32、17和1个菌株,占分离株的63.3%、8.0%、12.0%、10.7%、5.7%和0.3%.通过分析这些分离株的O血清型、毒素类型和黏附素型之间的相关性:猪源ETEC以0149、0107、093和098等血清型为主,0149:K88菌株主要与estⅡ或estⅡ elt肠毒素相关,0107:F18菌株主要与estⅡ相关,093和098血清型菌株主要与estⅡ肠毒素相关;STEC菌株以0139:F18血清型为主,拥有stx2e;AEEC菌株拥有紧密素,无明显优势血清型;ETEC/STEC菌株以0107:F18和0116:F18血清型为主,主要与est Ⅰ stx2e或estⅡ stx2e密切相关,ETEC/AEEC菌株以091和0107血清型为主,全部拥有肠毒素est Ⅰ和紧密素基因.[结论]我国至少存在6种病原型的猪肠道致病性大肠杆菌,其中ETEC为我国部分地区猪大肠杆菌病的主要病原,同时其病原型日益复杂.     

Comparison of different PCR tests for detecting Shiga toxin-producing Escherichia coli O157 and development of an ELISA-PCR assay for specific identification of the bacteria

In an attempt to develop a standard for ELISA-PCR detection of Shiga toxin producing Escherichia coli (STEC) O157, six published PCR tests were tested in a comparative study on a panel of 277 bacterial strains isolated from foods, animals and humans. These tests were based on the detection of the genes rfbE [J. Clin. Microbiol. 36 (1998) 1801] and rfbB [Appl. Environ. Microbiol. 65 (1999) 2954], the 3' end of the eae gene [Epidemiol. Infect. 112 (1994) 449], the region immediately flanking the 5' end of the eae gene [Int. J. Food. Microbiol. 32 (1996) 103], the flicH7 gene [J. Clin. Microbiol. 35 (1997) 656], or a part of the recently described 2634-bp Small Inserted Locus (SILO(157) locus) of STEC O157 [J. Appl. Microbiol. 93 (2002) 250]. Unlike the other PCR assays, those amplifying the rfb sequences were unable to distinguish toxigenic from nontoxigenic O157. These assays were relatively specific to STEC O157, giving essentially a cross reaction with clonally related E. coli O55 and to a lesser extent with E. coli O145, O125, O126. They also detected the Shiga toxin (stx)-negative derivatives of STEC O157. Based on these results, an ELISA-PCR assay consisting of the solution hybridization of amplicons with two probes that ensured the specificity of the amplification was developed. The ELISA-PCR assay, which used an internal control (IC) of inhibition, was able to detect 1 to 10 copies of STEC O157 in the PCR tube. Adaptation of PCR into ELISA-PCR assay format facilitates specific and sensitive detection of PCR amplification products and constitutes a method of choice for screening STEC O157.     

Genetic Characterization of Escherichia coli O157:H7 Strains Isolated from the One-Humped Camel (Camelus dromedarius) by Using Microarray DNA Technology

From the Camelidae family members, several serotypes of Escherichia coli (E. coli) have recently been isolated from diarrhoeic and non-diarrhoeic faecal samples. To date Shiga toxin-producing E. coli (STEC) strains have never been typed in one-humped camel (Camelus dromedarius). In the present study, two E. coli O157:H7 strains isolated from sick dromedaries were investigated. Virulence gene profiles were determined using a custom E. coli virulence DNA microarray, composed of 70-mer oligonucleotide probes targeting 264 virulence or related genes of known E. coli pathotypes. Both strains displayed positive hybridization signals for the Locus of enterocyte effacement (LEE) gene probes (ler, eae, espA, espB, tir genes), two Shiga toxin probes (stx1 and stx2), the O157 O-antigen specific probe, various virulence plasmid (pO157) probes like katP in addition to other accessory virulence genes characterized in STEC.