Phenotypic and genotypic analyses of enterohemorrhagic Escherichia coli O145 strains from patients in Germany

Shiga Toxin-Producing Escherichia coli Isolated from Wild Ruminants in Liguria, North-West Italy

Wildlife may represent an important source of infectious diseases for humans and other wild and domestic animals. Wild ruminants can harbour and transmit Shiga toxin-producing Escherichia coli (STEC) to humans, and some strains even carry important antimicrobial resistance. In this study, 289 livers of wild roe deer, fallow deer, red deer and chamois collected in Liguria, north-west Italy, from 2019 to 2023 were analysed. Overall, 44 STEC strains were isolated from 28 samples. The characterisation of serogroups showed the presence of O104, O113, O145 and O146 serogroups, although for 28 colonies, the serogroup could not be determined. The most prevalent Shiga toxin gene in isolated strains was Stx2, and more specifically the subtype Stx2b. The other retrieved subtypes were Stx1a, Stx1c, Stx1d and Stx2g. The isolated strains generally proved to be susceptible to the tested antimicrobials. However, multi-drug resistances against highly critical antimicrobials were found in one strain isolated from a roe deer. This study highlights the importance of wildlife monitoring in the context of a "One Health" approach.

The Importance of Shiga Toxin-Producing Escherichia coli O145:NM[H28]/H28 Infections in Argentina, 1998–2020

Shiga toxin-producing Escherichia coli (STEC) is known as a pathogen associated with food-borne diseases. The STEC O145 serogroup has been related with acute watery diarrhea, bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome (HUS). Argentina has the highest rate of HUS worldwide with 70% of the cases associated with STEC infections. We aimed to describe the epidemiology and genetic diversity of STEC O145 strains isolated across Argentina between 1998–2020. The strains isolated from 543 cases of human disease and four cattle, were pheno-genotipically characterized. Sequencing of five strains was performed. The strains were serotyped as O145:NM[H28]/H28, O145:H25, and O145:HNT, and mainly characterized as O145:NM[H28]/stx_2a/eae/ehxA (98.1%). The results obtained by sequencing were consistent with those obtained by traditional methods and additional genes involved in different mechanisms of the pathogen were observed. In this study, we confirmed that STEC O145 strains are the second serogroup after O157 and represent 20.3% of HUS cases in Argentina. The frequency of STEC O145 and other significant serogroups is of utmost importance for public health in the country. This study encourages the improvement of the surveillance system to prevent severe cases of human disease.

Differential induction of Shiga toxin in environmental Escherichia coli O145:H28 strains carrying the same genotype as the outbreak strains

Shiga toxin-producing Escherichia coli (STEC) O145 is a major serotype associated with severe human disease. Production of Shiga toxins (Stxs), especially Stx2a, is thought to be correlated with STEC virulence. Since stx genes are located in prophages genomes, induction of prophages is required for effective Stxs production. Here, we investigated the production of Stxs in 12 environmental STEC O145:H28 strains under stresses STEC encounter in natural habitats and performed comparative analysis with two O145:H28 clinical strains, one linked to a 2010 U.S. lettuce-associated outbreak (RM13514) and the other linked to a 2007 Belgium ice cream-associated outbreak (RM13516). Similar to the outbreak strains, all environmental strains belong to Sequence Type (ST)-78 using the EcMLST typing scheme. Although all Stx1a-prophages were grouped together, variations in Stx1a production were observed prior to or following the inductions. Among all stx_2a positive environmental strains, only the Stx2a-prophage in cattle isolate RM9154-C1 was clustered with the Stx2a-prophages in RM13514, the Stx2a-phage induced from a STEC O104:H4 strain linked to the 2011 outbreak of enterohemorrhagic infection in Germany, and the Stx2a-prophage in STEC O157:H7 strain EDL933, a prototype of enterohemorrhagic E. coli. Furthermore, the Stx2a-prophage in RM9154-C1 shared the same chromosomal insertion site and carried the same antiterminator Q gene and the late promoter P_R' as the Stx2a-prophage in RM13514. Following mitomycin C or enrofloxacin treatment, the production of Stx2a in RM9154-C1 was the highest among all environmental strains tested. In contrast, following acid challenge and recovery, the production of Stx2a in RM9154-C1 was the lowest among all the environmental strains tested, at a level comparable to the clinical strains. A significant increase in Stx2a production was detected in all strains when exposed to H₂O₂, although the induction fold was much lower than those by other inducers. This low-efficiency induction of Stx-prophages by H₂O₂, a natural inducer of Stx-prophages, supports the hypothesis of bacterial altruism in controlling Stxs production, a strategy that assures the survival of the STEC population as a whole by sacrificing a small fraction of cells for Stxs production and release. Differential induction of Stxs among strains carrying nearly identical Stx-prophages suggests a role of host bacteria in regulating Stxs production. Our study revealed diverse Stx-prophages in STEC O145:H28 strains that were genotypically indistinguishable. Identification of a cattle isolate harboring a Stx2a-prophage associated with high virulence supports the premise that cattle, a natural reservoir of STEC, serve as a source of hypervirulent STEC strains.

Comparative genomic analysis of a Shiga toxin-producing Escherichia coli (STEC) O145:H25 associated with a severe pediatric case of hemolytic uremic syndrome in Davidson County, Tennessee, US

Background

Shiga toxin-producing E. coli (STECs) are foodborne pathogens associated with bloody diarrhea and hemolytic uremic syndrome (HUS). Although the STEC O157 serogroup accounts for the highest number of infections, HUS-related complications and deaths, the STEC non-O157, as a group, accounts for a larger proportion of STEC infections and lower HUS cases. There is limited information available on how to recognize non-O157 serotypes associated with severe disease. The objectives of this study were to describe a patient with STEC non-O157 infection complicated with HUS and to conduct a comparative whole genome sequence (WGS) analysis among the patient’s STEC clinical isolate and STEC O157 and non-O157 strains.

Results

The STEC O145:H25 strain EN1I-0044-2 was isolated from a pediatric patient with diarrhea, HUS and severe neurologic and cardiorespiratory complications, who was enrolled in a previously reported case-control study of acute gastroenteritis conducted in Davidson County, Tennessee in 2013. The strain EN1I-0044-2 genome sequence contained a chromosome and three plasmids. Two of the plasmids were similar to those present in O145:H25 strains whereas the third unique plasmid EN1I-0044-2_03 shared no similarity with other STEC plasmids, and it carried 23 genes of unknown function. Strain EN1I-0044-2, compared with O145:H25 and O157 serogroup strains shared chromosome- and plasmid-encoded virulence factors, including Shiga toxin, LEE type III secretion system, LEE effectors, SFP fimbriae, and additional toxins and colonization factors.

Conclusions

A STEC O145:H25 strain EN1I-0044-2 was isolated from a pediatric patient with severe disease, including HUS, in Davidson County, TN. Phylogenetic and comparison WGS analysis provided evidence that strain EN1I-0044-2 closely resembles O145:H25, and confirmed an independent evolutionary path of STEC O145:H25 and O145:H28 serotypes. The strain EN1I-0044-2 virulence make up was similar to other O145:H25 and O157 serogroups. It carried stx2 and the LEE pathogenicity island, and additional colonization factors and enterotoxin genes. A unique feature of strain EN1I-0044-2 was the presence of plasmid pEN1I-0044-2_03 carrying genes with functions to be determined. Further studies will be necessary to elucidate the role that newly acquired genes by O145:H25 strains play in pathogenesis, and to determine if they may serve as genetic markers of severe disease.

Escherichia coli Pathobionts Associated with Inflammatory Bowel Disease

Gut bacteria play a key role in initiating and maintaining the inflammatory process in the gut tissues of inflammatory bowel disease (IBD) patients, by supplying antigens or other stimulatory factors that trigger immune cell activation. Changes in the composition of the intestinal microbiota in IBD patients compared to that in healthy controls and a reduced diversity of intestinal microbial species are linked to the pathogenesis of IBD. Adherent invasive Escherichia coli (AIEC) has been linked to Crohn's disease (CD) patients, while diffusely adherent E. coli (DAEC) has been associated with ulcerative colitis (UC). Bacteriological analysis of intestinal biopsy specimens and fecal samples from IBD patients shows an increased number of E. coli strains belonging to the B2 phylogenetic group, which are typically known as extraintestinal pathogenic E. coli (ExPEC). Results from studies of both cell cultures and animal models reveal pathogenic features of these E. coli pathobionts, which may link them to IBD pathogenesis. This suggests that IBD-associated E. coli strains play a facilitative role during IBD flares. In this review, we explain IBD-associated E. coli and its role in IBD pathogenesis.

Escherichia coli H-Genotyping PCR: a Complete and Practical Platform for Molecular H Typing

In Escherichia coli, more than 180 O groups and 53 H types have been recognized. The O:H serotyping of E. coli strains is an effective method for identifying strains with pathogenic potential and classifying them into clonal groups. In particular, the serotyping of Shiga toxin-producing E. coli (STEC) strains provides valuable information to evaluate the routes, sources, and prevalence of agents in outbreak investigations and surveillance. Here, we present a complete and practical PCR-based H-typing system, E. coli H-genotyping PCR, consisting of 10 multiplex PCR kits with 51 single PCR primer pairs. Primers were designed based on a detailed comparative analysis of sequences from all H-antigen (flagellin)-encoding genes, fliC and its homologs. The specificity of this system was confirmed by using all H type reference strains. Additionally, 362 serotyped wild strains were also used to evaluate its practicality. All 277 H-type-identified isolates gave PCR products that corresponded to the results of serological H typing. Moreover, 76 nonmotile and nine untypeable strains could be successfully subtyped into any H type by the PCR system. The E. coli H-genotyping PCR developed here allows broader, rapid, and low-cost subtyping of H types and will assist epidemiological studies as well as surveillance of pathogenic E. coli.

Fate of Escherichia coli O145 present naturally in bovine slurry applied to vegetables before harvest, after washing and simulated wholesale and retail distribution

AIMS

To determine the fate of Escherichia coli on vegetables that were processed through commercial wash treatments and stored under simulated retail conditions at 4°C or wholesale at fluctuating ambient temperatures (0-25°C, dependent on season).

METHODS AND RESULTS

Bovine slurry that was naturally contaminated with E. coli O145 was applied without dilution or diluted 1:10 using borehole water to growing potatoes, leeks or carrots. Manure was applied 1 week prior to harvest to simulate a near-harvest contamination event by manure deposition or an application of contaminated water to simulate a flooding event or irrigation from a contaminated water source. At harvest, crops were contaminated at up to 2 log cfu g^-1 . Washing transferred E. coli into the water of a flotation tank used for potato washing and did not completely remove all traces of contamination from the crop. Manure-contaminated potatoes were observed to contain 0·72 cfu E. coli O145 g^-1 after processing and retail storage. Manure-contaminated leeks harboured 0·73-1·55 cfu E. coli O145 g^-1 after washing and storage. There was no cross-contamination when leeks were spray washed. Washing in an abrasive drum resulted in less than perfect decontamination for manure-contaminated carrots. There were five post-distribution isolations from carrots irrigated with contaminated water 24 h prior to harvest.

CONCLUSIONS

Standard commercial washing and distribution conditions may be insufficient to reliably control human pathogenic E. coli on fresh produce.

SIGNIFICANCE AND IMPACT

Previous speculation that the cause of a UK foodborne disease outbreak was soil from imperfectly cleaned vegetables is plausible.

Genome sequencing and comparative genomics of enterohemorrhagic Escherichia coli O145:H25 and O145:H28 reveal distinct evolutionary paths and marked variations in traits associated with virulence & colonization

Background

Enterohemorrhagic Escherichia coli (EHEC) O145 are among the top non-O157 serogroups associated with severe human disease worldwide. Two serotypes, O145:H25 and O145:H28 have been isolated from human patients but little information is available regarding the virulence repertoire, origin and evolutionary relatedness of O145:H25. Hence, we sequenced the complete genome of two O145:H25 strains associated with hemolytic uremic syndrome (HUS) and compared the genomes with those of previously sequenced O145:H28 and other EHEC strains.

Results

The genomes of the two O145:H25 strains were 5.3 Mbp in size; slightly smaller than those of O145:H28 and other EHEC strains. Both strains contained three nearly identical plasmids and several prophages and integrative elements, many of which differed significantly in size, gene content and organization as compared to those present in O145:H28 and other EHECs. Furthermore, notable variations were observed in several fimbrial gene cluster and intimin types possessed by O145:H25 and O145:H28 indicating potential adaptation to distinct areas of host colonization. Comparative genomics further revealed that O145:H25 are genetically more similar to other non-O157 EHEC strains than to O145:H28.

Conclusion

Phylogenetic analysis accompanied by comparative genomics revealed that O145:H25 and O145:H28 evolved from two separate clonal lineages and that horizontal gene transfer and gene loss played a major role in the divergence of these EHEC serotypes. The data provide further evidence that ruminants might be a possible reservoir for O145:H25 but that they might be impaired in their ability to establish a persistent colonization as compared to other EHEC strains.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-017-1094-3) contains supplementary material, which is available to authorized users.

Shiga toxin-producing Escherichia coli strains isolated from dairy products - Genetic diversity and virulence gene profiles

Shiga toxin-producing Escherichia coli (STEC) are widely recognized as pathogens causing food borne disease. Here we evaluate the genetic diversity of 197 strains, mainly STEC, from serotypes O157:H7, O26:H11, O103:H2, O111:H8 and O145:28 and compared strains recovered in dairy products against strains from human, meat and environment cases. For this purpose, we characterized a set of reference-collection STEC isolates from dairy products by PFGE DNA fingerprinting and a subset of these by virulence-gene profiling. PFGE profiles of restricted STEC total DNA showed high genomic variability (0.9976 on Simpson's discriminatory index), enabling all dairy isolates to be differentiated. High-throughput real-time PCR screening of STEC virulence genes were applied on the O157:H7 and O26:H11 STEC isolates from dairy products and human cases. The virulence gene profiles of dairy and human STEC strains were similar. Nevertheless, frequency-wise, stx1 was more prevalent among dairy O26:H11 isolates than in human cases ones (87% vs. 44%) while stx2 was more prevalent among O26:H11 human isolates (23% vs. 81%). For O157:H7 isolates, stx1 (0% vs. 39%), nleF (40% vs 94%) and Z6065 (40% vs 100%) were more prevalent among human than dairy strains. Our data point to differences between human and dairy strains but these differences were not sufficient to associate PFGE and virulence gene profiles to a putative lower pathogenicity of dairy strains based on their lower incidence in disease. Further comparison of whole-genome expression and virulence gene profiles should be investigated in cheese and intestinal tract samples.

Molecular Characterization of Human Atypical Sorbitol-Fermenting Enteropathogenic Escherichia coli O157 Reveals High Diversity

Alongside the well-characterized enterohemorrhagic Escherichia coli (EHEC) O157:H7, serogroup O157 comprises sorbitol-fermenting typical and atypical enteropathogenic E. coli (EPEC/aEPEC) strains that carry the intimin-encoding gene eae but not Shiga toxin-encoding genes (stx). Since little is known about these pathogens, we characterized 30 clinical isolates from patients with hemolytic uremic syndrome (HUS) or uncomplicated diarrhea with respect to their flagellin gene (fliC) type and multilocus sequence type (MLST). Moreover, we applied whole-genome sequencing (WGS) to determine the phylogenetic relationship with other eae-positive EHEC serotypes and the composition of the rfbO157 region. fliC typing resulted in five fliC types (H7, H16, H34, H39, and H45). Isolates of each fliC type shared a unique ST. In comparison to the 42 HUS-associated E. coli (HUSEC) strains, only the stx-negative isolates with fliCH7 shared their ST with EHEC O157:H7/H(-) strains. With the exception of one O157:H(-) fliCH16 isolate, HUS was exclusively associated with fliCH7. WGS corroborated the separation of the fliCH7 isolates, which were closely related to the EHEC O157:H7/H(-) isolates, and the diverse group of isolates exhibiting different fliC types, indicating independent evolution of the different serotypes. This was also supported by the heterogeneity within the rfbO157 region that exhibited extensive recombinations. The genotypic subtypes and distribution of clinical symptoms suggested that the stx-negative O157 strains with fliCH7 were originally EHEC strains that lost stx The remaining isolates form a distinct and diverse group of atypical EPEC isolates that do not possess the full spectrum of virulence genes, underlining the importance of identifying the H antigen for clinical risk assessment.

Detection of Shiga Toxin-Producing Escherichia coli from Nonhuman Sources and Strain Typing

Shiga toxin-producing Escherichia coli (STEC) strains are commonly found in the intestine of ruminant species of wild and domestic animals. Excretion of STEC with animal feces results in a broad contamination of food and the environment. Humans get infected with STEC through ingestion of contaminated food, by contact with the environment, and from STEC-excreting animals and humans. STEC strains can behave as human pathogens, and some of them, called enterohemorrhagic E. coli (EHEC), may cause hemorrhagic colitis (HC) and hemolytic-uremic syndrome (HUS). Because of the diversity of STEC types, detection strategies for STEC and EHEC are based on the identification of Shiga toxins or the underlying genes. Cultural enrichment of STEC from test samples is needed for identification, and different protocols were developed for this purpose. Multiplex real-time PCR protocols (ISO/CEN TS13136 and USDA/FSIS MLG5B.01) have been developed to specifically identify EHEC by targeting the LEE (locus of enterocyte effacement)-encoded eae gene and genes for EHEC-associated O groups. The employment of more genetic markers (nle and CRISPR) is a future challenge for better identification of EHEC from any kinds of samples. The isolation of STEC or EHEC from a sample is required for confirmation, and different cultivation protocols and media for this purpose have been developed. Most STEC strains present in food, animals, and the environment are eae negative, but some of these strains can cause HC and HUS in humans as well. Phenotypic assays and molecular tools for typing EHEC and STEC strains are used to detect and characterize human pathogenic strains among members of the STEC group.

An Environmental Shiga Toxin-Producing Escherichia coli O145 Clonal Population Exhibits High-Level Phenotypic Variation That Includes Virulence Traits

Shiga toxin-producing Escherichia coli (STEC) serotype O145 is one of the major non-O157 serotypes associated with severe human disease. Here we examined the genetic diversity, population structure, virulence potential, and antimicrobial resistance profiles of environmental O145 strains recovered from a major produce production region in California. Multilocus sequence typing analyses revealed that sequence type 78 (ST-78), a common ST in clinical strains, was the predominant genotype among the environmental strains. Similarly, all California environmental strains belonged to H28, a common H serotype in clinical strains. Although most environmental strains carried an intact fliC gene, only one strain retained swimming motility. Diverse stx subtypes were identified, including stx1a, stx2a, stx2c, and stx2e. Although no correlation was detected between the stx genotype and Stx1 production, high Stx2 production was detected mainly in strains carrying stx2a only and was correlated positively with the cytotoxicity of Shiga toxin. All environmental strains were capable of producing enterohemolysin, whereas only 10 strains were positive for anaerobic hemolytic activity. Multidrug resistance appeared to be common, as nearly half of the tested O145 strains displayed resistance to at least two different classes of antibiotics. The core virulence determinants of enterohemorrhagic E. coli were conserved in the environmental STEC O145 strains; however, there was large variation in the expression of virulence traits among the strains that were highly related genotypically, implying a trend of clonal divergence. Several cattle isolates exhibited key virulence traits comparable to those of the STEC O145 outbreak strains, emphasizing the emergence of hypervirulent strains in agricultural environments.

Sequence Variations in the Flagellar Antigen Genes fliCH25 and fliCH28 of Escherichia coli and Their Use in Identification and Characterization of Enterohemorrhagic E. coli (EHEC) O145:H25 and O145:H28

Enterohemorrhagic E. coli (EHEC) serogroup O145 is regarded as one of the major EHEC serogroups involved in severe infections in humans. EHEC O145 encompasses motile and non-motile strains of serotypes O145:H25 and O145:H28. Sequencing the fliC-genes associated with the flagellar antigens H25 and H28 revealed the genetic diversity of the fliCH25 and fliCH28 gene sequences in E. coli. Based on allele discrimination of these fliC-genes real-time PCR tests were designed for identification of EHEC O145:H25 and O145:H28. The fliCH25 genes present in O145:H25 were found to be very similar to those present in E. coli serogroups O2, O100, O165, O172 and O177 pointing to their common evolution but were different from fliCH25 genes of a multiple number of other E. coli serotypes. In a similar way, EHEC O145:H28 harbor a characteristic fliCH28 allele which, apart from EHEC O145:H28, was only found in enteropathogenic (EPEC) O28:H28 strains that shared some common traits with EHEC O145:H28. The real time PCR-assays targeting these fliCH25[O145] and fliCH28[O145] alleles allow better characterization of EHEC O145:H25 and EHEC O145:H28. Evaluation of these PCR assays in spiked ready-to eat salad samples resulted in specific detection of both types of EHEC O145 strains even when low spiking levels of 1-10 cfu/g were used. Furthermore these PCR assays allowed identification of non-motile E. coli strains which are serologically not typable for their H-antigens. The combined use of O-antigen genotyping (O145wzy) and detection of the respective fliCH25[O145] and fliCH28[O145] allele types contributes to improve identification and molecular serotyping of E. coli O145 isolates.

Genetic Diversity of the fliC Genes Encoding the Flagellar Antigen H19 of Escherichia coli and Application to the Specific Identification of Enterohemorrhagic E. coli O121:H19

Enterohemorrhagic Escherichia coli (EHEC) O121:H19 belong to a specific clonal type distinct from other classical EHEC and major enteropathogenic E. coli groups and is regarded as one of the major EHEC serogroups involved in severe infections in humans. Sequencing of the fliC genes associated with the flagellar antigen H19 (fliCH19) revealed the genetic diversity of the fliCH19 gene sequences in E. coli. A cluster analysis of 12 fliCH19 sequences, 4 from O121 and 8 from non-O121 E. coli strains, revealed five different genotypes. All O121:H19 strains fell into one cluster, whereas a second cluster was formed by five non-O121:H19 strains. Cluster 1 and cluster 2 strains differ by 27 single nucleotide exchanges in their fliCH19 genes (98.5% homology). Based on allele discrimination of the fliCH19 genes, a real-time PCR test was designed for specific identification of EHEC O121:H19. The O121 fliCH19 PCR tested negative in 73 E. coli H19 strains that belonged to serogroups other than O121, including 28 different O groups, O-nontypeable H19, and O-rough:H19 strains. The O121 fliCH19 PCR reacted with all 16 tested O121:H19 strains and 1 O-rough:H19 strain which was positive for the O121 wzx gene. A cross-reaction was observed only with E. coli H32 strains which share sequence similarities in the target region of the O121 fliCH19 PCR. The combined use of O-antigen genotyping (O121 wzx) and the detection of O121 fliCH19 allele type contributes to improving the identification and molecular serotyping of EHEC O121:H19 motile and nonmotile strains and variants of these strains lacking stx genes.

Use of the ecf1 gene to detect Shiga toxin-producing Escherichia coli in beef samples

Escherichia coli O157:H7 and six serovars (O26, O103, O121, O111, O145, and O45) are frequently implicated in severe clinical illness worldwide. Standard testing methods using stx, eae, and O serogroup-specific gene sequences for detecting the top six non-O157 STEC bear the disadvantage that these genes may reside, independently, in different nonpathogenic organisms, leading to false-positive results. The ecf operon has previously been identified in the large enterohemolysin-encoding plasmid of eae-positive Shiga toxin-producing E. coli (STEC). Here, we explored the utility of the ecf operon as a single marker to detect eae-positive STEC from pure broth and primary meat enrichments. Analysis of 501 E. coli isolates demonstrated a strong correlation (99.6%) between the presence of the ecf1 gene and the combined presence of stx, eae, and ehxA genes. Two large studies were carried out to determine the utility of an ecf1 detection assay to detect non-O157 STEC strains in enriched meat samples in comparison to the results using the U. S. Department of Agriculture Food Safety and Inspection Service (FSIS) method that detects stx and eae genes. In ground beef samples (n = 1,065), the top six non-O157 STEC were detected in 4.0% of samples by an ecf1 detection assay and in 5.0% of samples by the stx- and eae-based method. In contrast, in beef samples composed largely of trim (n = 1,097), the top six non-O157 STEC were detected at 1.1% by both methods. Estimation of false-positive rates among the top six non-O157 STEC revealed a lower rate using the ecf1 detection method (0.5%) than using the eae and stx screening method (1.1%). Additionally, the ecf1 detection assay detected STEC strains associated with severe illness that are not included in the FSIS regulatory definition of adulterant STEC.

Carbohydrates as new probes for the identification of closely related Escherichia coli strains using surface plasmon resonance imaging

Prevention of foodborne diseases depends highly on our ability to control rapidly and accurately a possible contamination of food. So far, standard procedures for bacterial detection require time-consuming bacterial cultures on plates before the pathogens can be detected and identified. We present here an innovative biochip, based on direct differential carbohydrate recognitions of five closely related Escherichia coli strains, including the enterohemorragic E. coli O157:H7. Our device relies on efficient grafting of simple carbohydrates on a gold surface and on the monitoring of their interactions with bacteria during their culture using surface plasmon resonance imaging. We show that each of the bacteria interacts in a different way with the carbohydrate chip. This allows the detection and discrimination of the tested bacterial strains in less than 10 h from an initial bacterial concentration of 10(2) CFU·mL(-1). This is an improvement over previously described systems in terms of cost, easiness to use, and stability. Easily conceived and easily regenerated, this tool is promising for the future of food safety.

Multiplex real-time PCR and culture methods for detection of Shiga toxin-producing Escherichia coli and Salmonella Thompson in strawberries, a lettuce mix and basil

An appropriate approach of high throughput multi-screening was verified for Shiga toxin-producing Escherichia coli (STEC) and Salmonella spp. in strawberries, lettuce and basil. Sample replicates were inoculated with STEC O157 or O26 and Salmonella Thompson (ca. 10-70, 100-700 and 1000-7000 cfu/25 g) and analysed after 1 and 5 days of storage (strawberries and lettuce at 7 °C and basil at 10 °C). After 18-24 h of enrichment at 37 °C in buffered peptone water, detection was performed using the GeneDisc multiplex PCR (stx1, stx2, eae and iroB genes) and selective culture media for isolation of STEC (with immunomagnetic separation (IMS)) and Salmonella spp. in parallel. After 1 day, the pathogenic strains were recovered from all samples for all inoculum levels, whereas reduced detection rates of STEC O157 and S. Thompson were observed after 5 days of storage in case of strawberries, in particular for the lowest inoculums level, suggesting superior survival potential for STEC O26. Overall, this study indicates the ability of PCR based screening methods for reproducible multi-detection of low numbers (10-70 cfu/25 g) of STEC and Salmonella in this type of foods. However, for the basil samples, PCR needed twofold dilution of the DNA extract to overcome inhibition. It was noted that on several occasions growth of competitive microbiota obstructed finding presumptive colonies on the selective agar media, whereas the use of an additional agar medium such as CHROMagar STEC (without IMS) improved recovery rate of STEC.

Shiga Toxin/Verocytotoxin-Producing Escherichia coli Infections: Practical Clinical Perspectives

Escherichia coli strains that produce Shiga toxins/verotoxins are rare, but important, causes of human disease. They are responsible for a spectrum of illnesses that range from the asymptomatic to the life-threatening hemolytic-uremic syndrome; diseases caused by E. coli belonging to serotype O157:H7 are exceptionally severe. Each illness has a fairly predictable trajectory, and good clinical practice at one phase can be inappropriate at other phases. Early recognition, rapid and definitive microbiology, and strategic selection of tests increase the likelihood of good outcomes. The best management of these infections consists of avoiding antibiotics, antimotility agents, and narcotics and implementing aggressive intravenous volume expansion, especially in the early phases of illness.

Treatment of Shiga toxin-producing Escherichia coli infections

The management of Shiga toxin-producing Escherichia coli (STEC) infections is reviewed. Certain management practices optimize the likelihood of good outcomes, such as avoidance of antibiotics during the pre-hemolytic uremic syndrome phase, admission to hospital, and vigorous intravenous volume expansion using isotonic fluids. The successful management of STEC infections is based on recognition that a patient might have an STEC infection, and appropriate use of the microbiology laboratory. The timeliness of STEC identification cannot be overemphasized, because it avoids therapies prompted by inappropriate additional testing and directs the clinician to focus on effective management strategies. The opportunities during STEC infections to avert the worst outcomes are brief, and this article emphasizes practical matters relevant to making a diagnosis, anticipating the trajectory of illness, and optimizing care.

Multistate outbreak of Escherichia coli O145 infections associated with romaine lettuce consumption, 2010

Non-O157 Shiga toxin-producing Escherichia coli (STEC) can cause severe illness, including hemolytic uremic syndrome (HUS). STEC O145 is the sixth most commonly reported non-O157 STEC in the United States, although outbreaks have been infrequent. In April and May 2010, we investigated a multistate outbreak of STEC O145 infection. Confirmed cases were STEC O145 infections with isolate pulsed-field gel electrophoresis patterns indistinguishable from those of the outbreak strain. Probable cases were STEC O145 infections or HUS in persons who were epidemiologically linked. Case-control studies were conducted in Michigan and Ohio; food exposures were analyzed at the restaurant, menu, and ingredient level. Environmental inspections were conducted in implicated food establishments, and food samples were collected and tested. To characterize clinical findings associated with infections, we conducted a chart review for case patients who sought medical care. We identified 27 confirmed and 4 probable cases from five states. Of these, 14 (45%) were hospitalized, 3 (10%) developed HUS, and none died. Among two case-control studies conducted, illness was significantly associated with consumption of shredded romaine lettuce in Michigan (odds ratio [OR] = undefined; 95% confidence interval [CI] = 1.6 to undefined) and Ohio (OR = 10.9; 95% CI = 3.1 to 40.5). Samples from an unopened bag of shredded romaine lettuce yielded the predominant outbreak strain. Of 15 case patients included in the chart review, 14 (93%) had diarrhea and abdominal cramps and 11 (73%) developed bloody diarrhea. This report documents the first foodborne outbreak of STEC O145 infections in the United States. Current surveillance efforts focus primarily on E. coli O157 infections; however, non-O157 STEC can cause similar disease and outbreaks, and efforts should be made to identify both O157 and non-O157 STEC infections. Providers should test all patients with bloody diarrhea for both non-O157 and O157 STEC.

Genetic characteristics of Shiga toxin-producing E. coli O157, O26, O103, O111 and O145 isolates from humans, food, and cattle in Belgium

In this study, we characterized 272 Shiga toxin-producing Escherichia coli (STEC) isolates from humans, food, and cattle in Belgium [O157 (n = 205), O26 (n = 31), O103 (n = 15), O111 (n = 10), O145 (n = 11)] for their virulence profile, whole genome variations and relationships on different genetic levels. Isolates of O157 displayed a wide variation of stx genotypes, heterogeneously distributed among pulsogroups (80% similarity), but with a concordance at the pulsosubgroup level (90% similarity). Of all serogroups evaluated, the presence of eae was conserved, whereas genes encoded on the large plasmid (ehx, espP, katP) occurred in variable combinations in O26, O103, and O145. The odds of having haemolytic uraemic syndrome was less for all genotypes stx2a, stx2c, stx1/stx2c, and stx1 compared to genotype stx2a/stx2c; and for patients aged >5 years compared to patients aged ≤ 5 years. Based on the genetic typing and by using epidemiological data, we could confirm outbreak isolates and suggest epidemiological relationships between some sporadic cases. Undistinguishable pulsotypes or clones with minor genotypic variations were found in humans, food, and cattle in different years, which demonstrated the important role of cattle as a reservoir of STEC O157, and the circulation and persistence of pathogenic clones.

Identification of intermediate in evolutionary model of enterohemorrhagic Escherichia coli O157

Single-nucleotide polymorphism typing found missing link between human strains in strain from deer.

Highly pathogenic enterohemorrhagic Escherichia coli (EHEC) O157 cause a spectrum of clinical signs that include diarrhea, bloody diarrhea, and hemolytic uremic syndrome. The current evolutionary model of EHEC O157:H7/H^– consists of a stepwise evolution scenario proceeding from O55:H7 to a node (hypothetical intermediate) that then branches into sorbitol-fermenting (SF) O157:H^– and non-SF (NSF) O157:H7. To identify this hypothetical intermediate, we performed single nucleotide polymorphism analysis by sequencing of 92 randomly distributed backbone genomic regions of 40 O157:H7/H^– isolates. Overall, 111 single nucleotide polymorphisms were identified in 75/92 partial open reading frames after sequencing 51,041 nt/strain. The EHEC O157:H7 strain LSU-61 from deer occupied an intermediate position between O55:H7 and both O157 branches (SF and NSF O157), complementing the stepwise evolutionary model of EHEC O157:H7/H^–. The animal origin of this intermediate emphasizes the value of nonhuman reservoirs in the clarification of the evolution of human pathogens.

Methods for genotyping verotoxin-producing Escherichia coli

Verotoxin-producing Escherichia coli (VTEC) is annually incriminated in more than 100,000 cases of enteric foodborne human disease and in losses amounting to $US 2.5 billion every year. A number of genotyping methods have been developed to track VTEC infections and determine diversity and evolutionary relationships among these microorganisms. These methods have facilitated monitoring and surveillance of foodborne VTEC outbreaks and early identification of outbreaks or clusters of outbreaks. Pulsed-field gel electrophoresis (PFGE) has been used extensively to track and differentiate VTEC because of its high discriminatory power, reproducibility and ease of standardization. Multiple-locus variable-number tandem-repeats analysis (MLVA) and microarrays are the latest genotyping methods that have been applied to discriminate VTEC. MLVA, a simpler and less expensive method, is proving to have a discriminatory power comparable to that of PFGE. Microarrays are successfully being applied to differentiate VTEC and make inferences on genome diversification. Novel methods that are being evaluated for subtyping VTEC include the detection of single nucleotide polymorphisms and optical mapping. This review discusses the principles, applications, advantages and disadvantages of genotyping methods that have been used to differentiate VTEC strains. These methods have been mainly used to differentiate strains of O157:H7 VTEC and to a lesser extent non-O157 VTEC.

Characterization of the relationship between integrase, excisionase and antirepressor activities associated with a superinfecting Shiga toxin encoding bacteriophage

Shigatoxigenic Escherichia coli emerged as new food borne pathogens in the early 1980s, primarily driven by the dispersal of Shiga toxin-encoding lambdoid bacteriophages. At least some of these Stx phages display superinfection phenotypes, which differ significantly from lambda phage itself, driving through in situ recombination further phage evolution, increasing host range and potentially increasing the host's pathogenic profile. Here, increasing levels of Stx phage Φ24(B) integrase expression in multiple lysogen cultures are demonstrated along with apparently negligible repression of integrase expression by the cognate CI repressor. The Φ24(B) int transcription start site and promoter region were identified and found to differ from in silico predictions. The unidirectional activity of this integrase was determined in an in situ, inducible tri-partite reaction. This indicated that Φ24(B) must encode a novel directionality factor that is controlling excision events during prophage induction. This excisionase was subsequently identified and characterized through complementation experiments. In addition, the previous proposal that a putative antirepressor was responsible for the lack of immunity to superinfection through inactivation of CI has been revisited and a new hypothesis involving the role of this protein in promoting efficient induction of the Φ24(B) prophage is proposed.

Enterohaemorrhagic Escherichia coli haemolysin is cleaved and inactivated by serine protease EspPα

The haemolysin from enterohaemorrhagic Escherichia coli (EHEC-Hly) and the serine protease EspPα are putative virulence factors of EHEC. We investigated the interplay between these secreted factors and demonstrate that EspPα cleaves the 107 kDa large EHEC-Hly. Degradation was observed when purified EspPα was added to a growing culture of an EHEC-Hly-expressing strain, with isolated proteins and with coexpressing strains, and was independent of the EHEC serotype. EHEC-Hly breakdown occurred as a multistage process with the formation of characteristic fragments with relative molecular masses of ∼82 kDa and/or ∼84 kDa and ∼34 kDa. The initial cleavage occurred in the N-terminal hydrophobic domain of EHEC-Hly between Leu²³⁵ and Ser²³⁶ and abolished its haemolytic activity. In a cellular infection system, the cytolytic potential of EHEC-Hly-secreting recombinant strains was abolished when EspPα was coexpressed. EHEC in contact with human intestinal epithelial cells simultaneously upregulated their EHEC-Hly and EspP indicating that both molecules might interact under physiological conditions. We propose the concept of bacterial effector molecule interference (BEMI), reflecting the concerted interplay of virulence factors. Interference between effector molecules might be an additional way to regulate virulence functions and increases the complexity of monomolecular phenotypes.

Multiplex PCR assay for the detection of five putative virulence genes encoded in verotoxigenic Escherichia coli plasmids

The aim was to perform a pentavalent PCR assay for the detection of putative virulence genes encoded in VTEC plasmids, katP, espP, subA, stcE, and ehxA. The five-specific primer pairs used in the assay do not interfere with each other and generate amplification products of 914, 774, 556, 399, and 262 bp. It was selected at random 39 strains belonged to 20 serotypes in order to evaluate the multiplex in a wide variety of strains. The results of this study indicate that it is possible to perform simultaneous amplification and search for recognized plasmid-encoded virulence markers from different E. coli serotypes and apply this technique to the genetic characterization of E. coli strains isolated from reservoirs, foods or patients. This complementary technique is a useful tool to detect interstrain differences for epidemiological studies and to provide information that could be related to the risk of human infection.

Chromosomal instability in enterohaemorrhagic Escherichia coli O157:H7: impact on adherence, tellurite resistance and colony phenotype

Tellurite (Tel) resistant enterohaemorrhagic Escherichia coli (EHEC) O157:H7 is a global pathogen. In strain EDL933 Tel resistance (Tel^R) is encoded by duplicate ter cluster in O islands (OI) 43 and 48, which also harbour iha, encoding the adhesin and siderophore receptor Iha. We identified five EHEC O157:H7 strains that differentiate into large (L) colonies and small (S) colonies with high and low Tel minimal inhibitory concentrations (MICs) respectively. S colonies (Tel-MICs ≤ 4 µg ml⁻¹) sustained large internal deletions within the Tel^R OIs via homologous recombination between IS elements and lost ter and iha. Moreover, complete excision of the islands occurred by site-specific recombination between flanking direct repeats. Complete excision of OI 43 and OI 48 occurred in 1.81 × 10⁻³ and 1.97 × 10⁻⁴ cells in culture, respectively; internal deletion of OI 48 was more frequent (9.7 × 10⁻¹ cells). Under iron limitation that promotes iha transcription, iha-negative derivatives adhered less well to human intestinal epithelial cells and grew slower than did their iha-positive counterparts. Experiments utilizing iha deletion and complementation mutants identified Iha as the major factor responsible for these phenotypic differences. Spontaneous deletions affecting Tel^R OIs contribute to EHEC O157 genome plasticity and might impair virulence and/or fitness.

Biochemical properties, enterohaemolysin production and plasmid carriage of Shiga toxin-producing Escherichia coli strains

Thirty-eight strains of Shiga toxin-producing Escherichia coli (STEC) were characterised in terms of biochemical properties, enterohaemolysin production and plasmid carriage. A wide variation in the biochemical properties was observed among the STEC, with 14 distinct biotypes identified. Biotype 1 was the most common, found in 29% of the strains. Enterohaemolysin production was detected in 29% of the strains. Most of the bacterial strains (95%) carried one or more plasmids and considerable heterogeneity in size and combinations was observed. Seven distinct plasmid profiles were identified. The most common profile, characterised by the presence of a single plasmid of ~90 kb, was found in 50% of these strains. These data indicate extensive diversity among STEC strains. No correlation was found among biotype, serotype, enterohaemolysin production and plasmid profile.

Phylogenetic analysis of enterohemorrhagic Escherichia coli O157, Germany, 1987-2008

Clones of this organism persisted during the study period.

Multilocus variable number tandem repeat analysis (MLVA) is a subtyping technique for characterizing human pathogenic bacteria such as enterohemorrhagic Escherichia coli (EHEC) O157. We determined the phylogeny of 202 epidemiologically unrelated EHEC O157:H7/H^– clinical isolates through 8 MLVA loci obtained in Germany during 1987–2008. Biodiversity in the loci ranged from 0.66 to 0.90. Four of 8 loci showed null alleles and a frequency <44.1%. These loci were distributed among 48.5% of all strains. Overall, 141 MLVA profiles were identified. Phylogenetic analysis assigned 67.3% of the strains to 19 MLVA clusters. Specific MLVA profiles with an evolutionary persistence were identified, particularly within sorbitol-fermenting EHEC O157:H^–.These pathogens belonged to the same MLVA cluster. Our findings indicate successful persistence of this clone.

Alteration of flagellar phenotype of Escherichia coli strain P12b, the standard type strain for flagellar antigen H17, possessing a new non-fliC flagellin gene flnA, and possible loss of original flagellar phenotype and genotype in the course of subculturing through semisolid media

A practically important phenomenon, resulting in the loss of the original flagellar phenotype (genotype) of bacteria, is described in the Escherichia coli H17 type strain P12b possessing two distinct genes for H17 and H4 flagellins, respectively. By PCR, sequencing, and phylogenetic investigation, the H17 gene (originally expressed) was considered a new non-fliC flagellin gene and assigned flnA, while the H4 gene (originally cryptic) was reaffirmed as fliC. H17 and H4 flagella differed morphologically. The phenomenon consisted in the replacement of H17 cells by H4 cells during subculturing through certain semisolid media and resulted from the excision of flnA (H17) entirely or in part. The substitution rate depended on the density and nutrient composition of media and reached 100% even after a single passage through 0.3% LB agar. Such phenomenon can lead to an unexpected loss of original H17 phenotype. Our review of the literature showed that the loss of the original flagellar genotype (phenotype) of P12b has occurred in some laboratories while the authors continued to consider their cultures H17. We showed how to distinguish these alternative flagellin genotypes using popular fliC primers. Attention was also paid to possible discrepancies between serological and molecular results in flagellar typing of E. coli.

Phenotypic and genotypic traits of Shiga toxin-negative E. coli O157:H7/H(-) bovine and porcine strains

Enterohemorrhagic E. coli (EHEC) O157:H7/H(-) (nonmotile) exist as Shiga toxin gene (stx)-positive and stx-negative variants in patients and the environment. We analyzed molecular characteristics, phenotypes, and the phylogenetic background of three stx-negative E. coli O157:H7/H(-) strains isolated from cattle and a pig and compared them with those of human EHEC and stx-negative E. coli O157:H7/H(-). All three animal strains contained fliCH7 and two contained eae. One eae-positive strain (O157:H(-)) was sorbitol-fermenting (SF) and the other (O157:H7) was non-sorbitol-fermenting (nSF). These two strains shared a spectrum of non-stx putative virulence and fitness genes with human nSF and SF EHEC and stx-negative E. coli O157:H7/H(-) and belonged, similar to the vast majority of human isolates, to sequence type (ST) 11 in multilocus sequence typing. In contrast, the eae-negative O157:H7 animal isolate, which was SF, differed in spectrum of virulence genes and also differed phylogenetically (ST717) from the two eae-positive strains and the human EHEC and stx-negative E. coli O157:H7/H(-). In contrast to efforts with human stx-negative E. coli O157:H(-), attempts to transduce the two stx-negative/eae-positive animal O157:H7/H(-) strains with stx(2)-encoding phages from human SF and nSF EHEC O157:H7/H(-) failed, despite the animal strains having intact loci where such phages integrate in human EHEC O157 (wrbA and yecE). The role of animal stx-negative/eae-positive and stx-negative/eae-negative E. coli O157:H7/H(-) in their natural source and in human infections needs further investigation.

Sorbitol-fermenting Shiga toxin-producing Escherichia coli O157 in Austria

Infections with enterohemorrhagic Escherichia coli (EHEC) are the major cause of hemolytic uremic syndrome (HUS), the most common cause of acute renal failure in childhood. Shiga toxins are considered to be the most important virulence factor of EHEC strains. Non-sorbitol-fermenting EHEC O157:H7 is still the most prevalent serotype isolated worldwide; however, sorbitol-fermenting (SF) EHEC O157:H- (H- indicates nonmotility) strains are increasingly reported. Thirteen SF EHEC O157:H- strains (11 of human origin, two from animals) were detected in Austria between 2002 and 2008. Among the 11 human cases, seven suffered from HUS, two from diarrhea and the remaining two were asymptomatic. Seven of the cases were identified in patients living in or visiting (in one case) the province Salzburg, four were in patients from the province Vorarlberg. Three outbreaks with no more than three persons involved were detected, the other four cases occurred sporadically. The pulsed-field gel-electrophoresis banding patterns of the 13 SF EHEC O157:H- isolates were grouped into three distinct clusters (groups 1, 2 and 3). Strains of the three outbreaks were identical (except for one outbreak strain with one band difference) within each outbreak. In comparison, the Bavarian epidemic strain showed a pattern different from all SF O157:H- strains isolated in Austria. For effective detection of SF EHEC O157:H-, screening for Shiga toxins by ELISA and/or Shiga toxin genes by PCR is absolutely necessary; screening on the basis of phenotypic characteristics such as sorbitol-non-fermentation is not sufficient. Typing methods relying solely on investigation of O157 will detect these strains but should nevertheless also be avoided, so that the prevalent non-O157 strains causing HUS are not missed.

Intrahost genome alterations in enterohemorrhagic Escherichia coli

Bacterial chromosomes are not fixed molecules; they evolve over the course of infections in human beings. During infection, a variety of strong selective pressures are exerted on the pathogen. The resulting genetic changes that occur in intestinal pathogens might influence clinical outcome and have an impact on diagnosis and epidemiology. Enterohemorrhagic Escherichia coli (EHEC) is a good example of this process. These zoonotic pathogens cause diarrhea, bloody diarrhea, and hemolytic uremic syndrome in human beings, whereas in their natural habitat they mostly are asymptomatic colonizers. Thus, EHEC must be able to quickly adapt from one milieu to another. The greatest challenge it might face is to infect human beings--profound chromosomal changes occur during the brief period that EHEC passes through the human gastrointestinal tract, leading to gains and losses of virulence determinants. The intensive study of human enteric factors that induce or modulate pathogen chromosome instability could provide important information about host-microbial interactions.

Shiga toxin, cytolethal distending toxin, and hemolysin repertoires in clinical Escherichia coli O91 isolates

Shiga toxin (Stx)-producing Escherichia coli (STEC) strains of serogroup O91 are the most common human pathogenic eae-negative STEC strains. To facilitate diagnosis and subtyping of these pathogens, we genotypically and phenotypically characterized 100 clinical STEC O91 isolates. Motile strains expressed flagellar antigens H8 (1 strain), H10 (2 strains), H14 (52 strains), and H21 (20 strains) or were H nontypeable (Hnt) (10 strains); 15 strains were nonmotile. All nonmotile and Hnt strains possessed the fliC gene encoding the flagellin subunit of the H14 antigen (fliC(H14)). Most STEC O91 strains possessed enterohemorrhagic E. coli hlyA and expressed an enterohemolytic phenotype. Among seven stx alleles identified, stx(2dact), encoding mucus- and elastase-activatable Stx2d, was present solely in STEC O91:H21, whereas most strains of the other serotypes possessed stx(1). Moreover, only STEC O91:H21 possessed the cdt-V cluster, encoding cytolethal distending toxin V; the toxin was regularly expressed and was lethal to human microvascular endothelial cells. Infection with STEC O91:H21 was associated with hemolytic-uremic syndrome (P = 0.0015), whereas strains of the other serotypes originated mostly in patients with nonbloody diarrhea. We conclude that STEC O91 clinical isolates belong to at least four lineages that differ by H antigens/fliC types, stx genotypes, and non-stx putative virulence factors, with accumulation of virulence determinants in the O91:H21 lineage. Isolation of STEC O91 from patients' stools on enterohemolysin agar and the rapid initial subtyping of these isolates using fliC genotyping facilitate the identification of these emerging pathogens in clinical and epidemiological studies and enable prediction of the risk of a severe clinical outcome.

Detection and characterization of the fimbrial sfp cluster in enterohemorrhagic Escherichia coli O165:H25/NM isolates from humans and cattle

The sfp cluster, encoding Sfp fimbriae and located in the large plasmid of sorbitol-fermenting (SF) enterohemorrhagic Escherichia coli (EHEC) O157 (pSFO157), has been considered a unique characteristic of this organism. We discovered and then characterized the sfp cluster in EHEC O165:H25/NM (nonmotile) isolates of human and bovine origin. All seven strains investigated harbored a complete sfp cluster (carrying sfpA, sfpH, sfpC, sfpD, sfpJ, sfpF, and sfpG) of 6,838 bp with >99% nucleotide sequence homology to the sfp cluster of SF EHEC O157:NM. The sfp cluster in EHEC O165:H25/NM strains was located in an approximately 80-kb (six strains) or approximately 120-kb (one strain) plasmid which differed in structure, virulence genes, and sfp flanks from pSFO157. All O165:H25/NM strains belonged to the same multilocus sequence type (ST119) and were only distantly phylogenetically related to SF EHEC O157:NM (ST11). The highly conserved sfp cluster in different clonal backgrounds suggests that this segment was acquired independently by EHEC O165:H25 and SF EHEC O157:NM. Its presence in an additional EHEC serotype extends the diagnostic utility of PCR targeting sfpA as an easy and efficient approach to seek EHEC in patients' stools. The reasons for the convergence of pathogenic EHEC strains on a suite of virulence loci remain unknown.

Analysis of collection of hemolytic uremic syndrome-associated enterohemorrhagic Escherichia coli

Multilocus sequence typing of 169 non-O157 enterohemorrhagic Escherichia coli (EHEC) isolated from patients with hemolytic uremic syndrome (HUS) demonstrated 29 different sequence types (STs); 78.1% of these strains clustered in 5 STs. From all STs and serotypes identified, we established a reference panel of EHEC associated with HUS (HUSEC collection).

Treatment and outcome of Shiga-toxin-associated hemolytic uremic syndrome (HUS)

Hemolytic uremic syndrome (HUS) is the most common cause of acute renal failure in childhood and the reason for chronic renal replacement therapy. It leads to significant morbidity and mortality during the acute phase. In addition to acute morbidity and mortality, long-term renal and extrarenal complications can occur in a substantial number of children years after the acute episode of HUS. The most common infectious agents causing HUS are enterohemorrhagic Escherichia coli (EHEC)-producing Shiga toxin (and belonging to the serotype O157:H7) and several non-O157:H7 serotypes. D(+) HUS is an acute disease characterized by prodromal diarrhea followed by acute renal failure. The classic clinical features of HUS include the triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. HUS mortality is reported to be between 3% and 5%, and death due to HUS is nearly always associated with severe extrarenal disease, including severe central nervous system (CNS) involvement. Approximately two thirds of children with HUS require dialysis therapy, and about one third have milder renal involvement without the need for dialysis therapy. General management of acute renal failure includes appropriate fluid and electrolyte management, antihypertensive therapy if necessary, and initiation of renal replacement therapy when appropriate. The prognosis of HUS depends on several contributing factors. In general "classic" HUS, induced by EHEC, has an overall better outcome. Totally different is the prognosis in patients with atypical and particularly recurrent HUS. However, patients with severe disease should be screened for genetic disorders of the complement system or other underlying diseases.

Phenotypic and genotypic characterization of verotoxin-producing Escherichia coli O103:H2 isolates from cattle and humans

Characterization of important non-O157 verotoxin-producing Escherichia coli (VTEC) has lagged considerably behind that of O157:H7 strains. This study characterized 91 VTEC O103:H2 strains from bovine and human sources and of North American and European origins by virulence or putative virulence genes, pulsed-field gel electrophoresis (PFGE) patterns, plasmid profiles, antimicrobial resistance, and colicin production. All strains were positive for vt1 and eae-epsilon; 97% were positive for ehxA; and all were negative for hlyA. Two strains carried vt2. There were 66 PFGE patterns grouped in six clusters, and there were 25 different plasmid profiles. Plasmid-encoded katP and etp genes were significantly more frequent in European than in North American human strains. The distribution of selected phenotypes was as follows: enterohemorrhagic E. coli (EHEC) hemolysin, 95%; colicin production, 38%; antimicrobial resistance, 58%. All the strains were negative for the alpha-hemolytic phenotype. In conclusion, the VTEC O103:H2 strains were diverse, as shown by PFGE, plasmid profiles, virulence markers, and antimicrobial resistance patterns, and all strains showed an EHEC hemolytic phenotype instead of the alpha-hemolytic phenotype that has been shown previously.

New immuno-PCR assay for detection of low concentrations of shiga toxin 2 and its variants

Shiga toxin (Stx)-producing Escherichia coli (STEC) strains secrete toxins that are major virulence factors and diagnostic targets, but some STEC strains secrete Stx in amounts that cannot be detected using conventional cell cytotoxicity or immunological assays. Therefore, there is an urgent need for more-sensitive Stx detection methods. We describe the development of an assay that can detect low concentrations of Stx2 and its variants. An immuno-PCR Stx2 assay was developed based on an enzyme immunoassay (EIA) combining antibody capture and DNA amplification to increase the signal. The immuno-PCR assay detected 10 pg/ml of purified Stx2, compared to 1 ng/ml Stx2 detected by commercial EIA. Consequently, immuno-PCR detected Stx2 and its variants in STEC strains that produce the toxins at levels that are nondetectable by using the EIA, as well as the Stx2 in EIA-negative enriched stool cultures from patients. Our data demonstrate that the immuno-PCR developed here is a highly sensitive and specific method for the detection of trace amounts of Stx2 and Stx2 variants. It is therefore suitable for use by clinical microbiological laboratories to improve the toxin detection in clinical samples.

Recycling of Shiga toxin 2 genes in sorbitol-fermenting enterohemorrhagic Escherichia coli O157:NM

Using colony blot hybridization with stx(2) and eae probes and agglutination in anti-O157 lipopolysaccharide serum, we isolated stx(2)-positive and eae-positive sorbitol-fermenting (SF) enterohemorrhagic Escherichia coli (EHEC) O157:NM (nonmotile) strains from initial stool specimens and stx-negative and eae-positive SF E. coli O157:NM strains from follow-up specimens (collected 3 to 8 days later) from three children. The stx-negative isolates from each patient shared with the corresponding stx(2)-positive isolates fliC(H7), non-stx virulence traits, and multilocus sequence types, which indicates that they arose from the stx(2)-positive strains by loss of stx(2) during infection. Analysis of the integrity of the yecE gene, a possible stx phage integration site in EHEC O157, in the consecutive stx(2)-positive and stx-negative isolates demonstrated that yecE was occupied in stx(2)-positive but intact in stx-negative strains. It was possible to infect and lysogenize the stx-negative E. coli O157 strains in vitro using an stx(2)-harboring bacteriophage from one of the SF EHEC O157:NM isolates. The acquisition of the stx(2)-containing phage resulted in the occupation of yecE and production of biologically active Shiga toxin 2. We conclude that the yecE gene in SF E. coli O157:NM is a hot spot for excision and integration of Shiga toxin 2-encoding bacteriophages. SF EHEC O157:NM strains and their stx-negative derivatives thus represent a highly dynamic system that can convert in both directions by the loss and gain of stx(2)-harboring phages. The ability to recycle stx(2), a critical virulence trait, makes SF E. coli O157:NM strains ephemeral EHEC that can exist as stx-negative variants during certain phases of their life cycle.

The Shiga toxin genotype rather than the amount of Shiga toxin or the cytotoxicity of Shiga toxin in vitro correlates with the appearance of the hemolytic uremic syndrome

Shiga toxins (Stx) are believed to play a key role in the pathogenesis of diseases caused by Stx-producing Escherichia coli (STEC), including the potentially life-threatening hemolytic uremic syndrome (HUS). In this study, 201 STEC strains collected from patients and environmental sources were investigated with regard to the stx genotypes and pathogenicity. The stx(2) and stx(2c) alleles were associated with high virulence and the ability to cause HUS, whereas stx(2d), stx(2e,)stx(1), and stx(1c) occurred in milder or asymptomatic infections. Quantification of Stx using an enzyme immunoassay and the Vero cell cytotoxicity assay showed no significant differences between the strains associated with HUS and those causing milder diseases. We hypothesize that the stx genotype and perhaps other yet unknown virulence factors rather than the amount of Stx or the in vitro cytotoxicity correlate with the development of HUS.