Prevalence, structure and expression of urease genes in Shiga toxin-producing Escherichia coli from humans and the environment

Differential expression of urease genes and ureolytic activity of uropathogenic Escherichia coli and Pseudomonas aeruginosa isolates in different nutritional conditions

Uropathogens have adaptation strategies to survive in the host urinary tract by efficiently utilizing and tolerating the urinary metabolites. Many uropathogens harbour the enzyme urease for the breakdown of urea and the enzymatic breakdown of urea increases the pH and facilitate the struvite crystallization. In this study, the differential urease activity of uropathogenic Escherichia coli and Pseudomonas aeruginosa strains was investigated under different nutritional conditions. The experiments included measurement of growth, pH, urease activity, NH4-N generation and urease gene (ureC) expression among the bacterial strains under different conditions. Further, the implications of urea breakdown on the struvite crystallization in vitro and biofilm formation were also assessed. The study included urease positive isolates and for comparison urease negative isolates were included. Compared to the urease negative strains the urease positive strains formed higher biofilms and motility. The urease positive P. aeruginosa showed significantly higher (p < 0.01) pH and urease activity (A557-A630) compared to E. coli under experimental conditions. Further, supplementation of glucose to the growth media significantly increased the urease activity in P. aeruginosa and in contrast, it was significantly lower in E. coli. The expression profile of urease gene (ureC) was significantly higher (p < 0.001) in P. aeruginosa compared to E. coli and was consistent with the biochemical results of the urease activity under the nutritional conditions. The differential urease activity under two nutritional conditions influenced the biogenic struvite crystallization. It correlated with the urease activity showing higher crystallization rate in P. aeruginosa compared to E. coli. The results highlight the differential urease activity in two common uropathogens under different nutritional conditions that may have significant role on the regulation of virulence, pathogenicity and in the kidney stone disease.

Pilot Study of Probiotic Supplementation on Uremic Toxicity and Inflammatory Cytokines in Chronic Kidney Patients

Background:

Bacterial metabolism contributes to the generation of uremic toxins in patients with chronic kidney disease (CKD). It has been investigated the use of probiotics in the reduction of uremic toxins intestinal production.

Objective:

The aim of this pilot study was to evaluate the effect of probiotic supplementation on reducing the production of uremic toxins and the inflammatory profile of CKD patients.

Methods:

We performed a randomized, blind, placebo-controlled, crossover study on patients with CKD stages 3 and 4. The intervention was a probiotic formulation composed of Lactobacillus acidophilus strains given orally three times a day for 3 months. Changes in uremic toxins (p-Cresylsulfate and Indoxyl Sulfate) and serum inflammatory cytokines were the primary endpoints.

Results:

Of the 44 patients randomized, 25 completed the study (mean age 51 ± 9.34, 64% female, mean eGFR 36 ± 14.26 mL/min/1.73m², mean BMI 28.5 ± 5.75 kg/m²). At 3 months, there were no significant changes in any of the studied biomarkers including p-cresylsulfate (p = 0.57), Indoxyl sulfate (p = 0.08) and interleukin-6 (p = 0.55).

Conclusion:

Lactobacillus acidophilus strains given as probiotic were not able to reduce serum levels of uremic toxins and biomarkers of inflammation in CKD patients in stage 3 and 4.

Molecular profiling and antimicrobial resistance of Shiga toxin-producing Escherichia coli O26, O45, O103, O121, O145 and O157 isolates from cattle on cow-calf operations in South Africa

In this study, 140 cattle STEC isolates belonging to serogroups O157, O26, O145, O121, O103 and O45 were characterized for 38 virulence-associated genes, antimicrobial resistance profiles and genotyped by PFGE. The majority of isolates carried both stx1 and stx2 concurrently, stx2c, and stx2d; plasmid-encoded genes ehxA, espP, subA and saa but lacked katP and etpD and eaeA. Possession of eaeA was significantly associated with the presence of nle genes, katP, etpD, ureC and terC. However, saa and subA, stx1c and stx1d were only detected in eaeA negative isolates. A complete OI-122 and most non-LEE effector genes were detected in only two eaeA positive serotypes, including STEC O157:H7 and O103:H2. The eaeA gene was detected in STEC serotypes that are commonly implicated in severe humans disease and outbreaks including STEC O157:H7, STEC O145:H28 and O103:H2. PFGE revealed that the isolates were highly diverse with very low rates of antimicrobial resistance. In conclusion, only a small number of cattle STEC serotypes that possessed eaeA, had the highest number of virulence-associated genes, indicative of their high virulence. Further characterization of STEC O157:H7, STEC O145:H28 and O103:H2 using whole genome sequencing will be needed to fully understand their virulence potential for humans.

Effects of probiotic supplements on the progression of chronic kidney disease: A meta-analysis

BACKGROUND

Chronic kidney disease (CKD) is a worldwide public health problem. Although accumulated data suggested that probiotic supplements played roles in CKD, the results remained controversial. Here, we performed a meta-analysis to assess the effects of probiotic supplements on the CKD progression.

METHODS

A systematic search was conducted through the PubMed, Embase and Cochrane databases until September 2018. Randomized controlled trials with control receiving placebo, evaluating the effects of probiotic supplements on CKD were included.

RESULTS

A total of 10 randomized controlled trials in 8 countries were selected. In the meta-analysis, urea level was significantly reduced in probiotics-administrated non-dialysis patients (mean differences (MD) = -30.01; 95% confidence interval (CI) = [-56.78, -3.25]; P = 0.03) while no significant change was found in the dialysis patients receiving probiotics (MD = 0.1; 95% CI = [-9.28, 9.48]; P = 0.98). Probiotic supplements also exhibited no effect on uric acid (MD = -0.43; 95% CI = [-1.19, 0.33]; P = 0.27), C-reactive protein (MD = -0.48; 95% CI = [-1.29, 0.33]; P = 0.24), creatinine (MD = -0.18; 95% CI = [-0.82, 0.47]; P = 0.59), and estimated glomerular filtration rate (MD = 2.10; 95% CI = [-1.31, 5.52]; P = 0.23) of CKD patients.

CONCLUSION

Our results highlighted that probiotic supplements exerted a statistically significant effect on urea levels in non-dialysis CKD population, while no evidence suggested that probiotics possessed meaningful impacts on the reduction of uric acid, C-reactive protein, creatinine and estimated glomerular filtration rate preservation of CKD population.

Probiotic Supplementation in Chronic Kidney Disease: A Double-blind, Randomized, Placebo-controlled Trial

OBJECTIVE

The objective of the study was to evaluate the effects of probiotic supplementation on the gut microbiota profile and inflammatory markers in chronic kidney disease patients undergoing maintenance hemodialysis (HD).

DESIGN AND METHODS

This was a randomized, double-blind, placebo-controlled study. Forty-six HD patients were assigned to receive 1 of 2 treatments: probiotic (n = 23; Streptococcus thermophilus, Lactobacillus acidophilus e Bifidobacterialongum, 90 billion colony-forming units per day) or placebo (n = 23) daily for 3 months. Blood and feces were collected at baseline and after intervention. The inflammatory markers (C-reactive protein and interleukin-6) were analyzed by immunoenzymatic assay (enzyme-linked immunosorbent assay). Uremic toxins plasma levels (indoxyl sulfate, p-cresyl sulfate, and indole-3-acetic acid) were obtained by Reversed-Phase High-Performance Liquid Chromatography. Routine laboratory parameters were measured by standard techniques. Fecal pH was measured by the colorimetric method, and the gut microbiota profile was assessed by Denaturing Gradient Gel Electrophoresis analysis.

RESULTS

Sixteen patients remained in the probiotic group (11 men, 53.6 ± 11.0 year old, 25.3 ± 4.6 kg/m²) and 17 in the placebo group (10 men, 50.3 ± 8.5 year old, 25.2 ± 5.7 kg/m²). After probiotic supplementation there was a significant increase in serum urea (from 149.6 ± 34.2 mg/dL to 172.6 ± 45.0 mg/dL, P = .02), potassium (from 4.4 ± 0.4 mmol/L to 4.8 ± 0.4 mmol/L, P = .02), and indoxyl sulfate (from 31.2 ± 15.9 to 36.5 ± 15.0 mg/dL, P = .02). The fecal pH was reduced from 7.2 ± 0.8 to 6.5 ± 0.5 (P = .01). These parameters did not change significantly in placebo group. Changes in the percentage delta (Δ) between groups were exhibited with no statistical differences observed. The inflammatory markers and gut profile were not altered by supplementation.

CONCLUSIONS

Aprobiotic supplementation failed to reduce uremic toxins and inflammatory markers. Therefore, probiotic therapy should be chosen with caution in HD patients. Further studies addressing probiotic therapy in chronic kidney disease patients are needed.

Characterization of Shiga Toxin Subtypes and Virulence Genes in Porcine Shiga Toxin-Producing Escherichia coli

Similar to ruminants, swine have been shown to be a reservoir for Shiga toxin-producing Escherichia coli (STEC), and pork products have been linked with outbreaks associated with STEC O157 and O111:H-. STEC strains, isolated in a previous study from fecal samples of late-finisher pigs, belonged to a total of 56 serotypes, including O15:H27, O91:H14, and other serogroups previously associated with human illness. The isolates were tested by polymerase chain reaction (PCR) and a high-throughput real-time PCR system to determine the Shiga toxin (Stx) subtype and virulence-associated and putative virulence-associated genes they carried. Select STEC strains were further analyzed using a Minimal Signature E. coli Array Strip. As expected, stx_2e (81%) was the most common Stx variant, followed by stx_1a (14%), stx_2d (3%), and stx_1c (1%). The STEC serogroups that carried stx_2d were O15:H27, O159:H16 and O159:H-. Similar to stx_2a and stx_2c, the stx_2d variant is associated with development of hemorrhagic colitis and hemolytic uremic syndrome, and reports on the presence of this variant in STEC strains isolated from swine are lacking. Moreover, the genes encoding heat stable toxin (estIa) and enteroaggregative E. coli heat stable enterotoxin-1 (astA) were commonly found in 50 and 44% of isolates, respectively. The hemolysin genes, hlyA and ehxA, were both detected in 7% of the swine STEC strains. Although the eae gene was not found, other genes involved in host cell adhesion, including lpfA_O113 and paa were detected in more than 50% of swine STEC strains, and a number of strains also carried iha, lpfA_O26, lpfA_O157, fedA, orfA, and orfB. The present work provides new insights on the distribution of virulence factors among swine STEC strains and shows that swine may carry Stx1a-, Stx2e-, or Stx2d-producing E. coli with virulence gene profiles associated with human infections.

Bacterial urease and its role in long-lasting human diseases

Urease is a virulence factor found in various pathogenic bacteria. It is essential in colonization of a host organism and in maintenance of bacterial cells in tissues. Due to its enzymatic activity, urease has a toxic effect on human cells. The presence of ureolytic activity is an important marker of a number of bacterial infections. Urease is also an immunogenic protein and is recognized by antibodies present in human sera. The presence of such antibodies is connected with progress of several long-lasting diseases, like rheumatoid arthritis, atherosclerosis or urinary tract infections. In bacterial ureases, motives with a sequence and/or structure similar to human proteins may occur. This phenomenon, known as molecular mimicry, leads to the appearance of autoantibodies, which take part in host molecules destruction. Detection of antibodies-binding motives (epitopes) in bacterial proteins is a complex process. However, organic chemistry tools, such as synthetic peptide libraries, are helpful in both, epitope mapping as well as in serologic investigations.

In this review, we present a synthetic report on a molecular organization of bacterial ureases - genetic as well as structural. We characterize methods used in detecting urease and ureolytic activity, including techniques applied in disease diagnostic processes and in chemical synthesis of urease epitopes. The review also provides a summary of knowledge about a toxic effect of bacterial ureases on human body and about occurrence of anti-urease antibodies in long-lasting diseases.

Contribution of urease to colonization by Shiga toxin-producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) is a food-borne pathogen with a low infectious dose that colonizes the colon in humans and can cause severe clinical manifestations such as hemolytic-uremic syndrome. The urease enzyme, encoded in the STEC chromosome, has been demonstrated to act as a virulence factor in other bacterial pathogens. The NH(3) produced as urease hydrolyzes urea can aid in buffering bacteria in acidic environments as well as provide an easily assimilated source of nitrogen that bacteria can use to gain a metabolic advantage over intact microflora. Here, we explore the role of urease in STEC pathogenicity. The STEC urease enzyme exhibited maximum activity near neutral pH and during the stationary-growth phase. Experiments altering growth conditions performed with three phylogenetically distinct urease-positive strains demonstrated that the STEC ure gene cluster is inducible by neither urea nor pH but does respond to nitrogen availability. Quantitative reverse transcription-PCR (qRT-PCR) data indicate that nitrogen inhibits the transcriptional response. The deletion of the ure gene locus was constructed in STEC strain 88-0643, and the ure mutant was used with the wild-type strain in competition experiments in mouse models to examine the contribution of urease. The wild-type strain was twice as likely to survive passage through the acidic stomach and demonstrated an enhanced ability to colonize the intestinal tract compared to the ure mutant strain. These in vivo experiments reveal that, although the benefit STEC gains from urease expression is modest and not absolutely required for colonization, urease can contribute to the pathogenicity of STEC.

Molecular risk assessment and epidemiological typing of Shiga toxin-producing Escherichia coli by using a novel PCR binary typing system

Shiga toxin-producing Escherichia coli (STEC) is a zoonotic pathogen that causes diarrheal disease in humans and is of public health concern because of its ability to cause outbreaks and severe disease such as hemorrhagic colitis or hemolytic-uremic syndrome. More than 400 serotypes of STEC have been implicated in outbreaks and sporadic human disease. The aim of this study was to develop a PCR binary typing (P-BIT) system that could be used to aid in risk assessment and epidemiological studies of STEC by using gene targets that would represent a broad range of STEC virulence genes. We investigated the distribution of 41 gene targets in 75 O157 and non-O157 STEC isolates and found that P-BIT provided 100% typeability for isolates, gave a diversity index of 97.33% (compared with 99.28% for XbaI pulsed-field gel electrophoresis [PFGE] typing), and produced 100% discrimination for non-O157 STEC isolates. We identified 24 gene targets that conferred the same level of discrimination and produced the same cluster dendrogram as the 41 gene targets initially examined. P-BIT clustering identified O157 from non-O157 isolates and identified seropathotypes associated with outbreaks and severe disease. Numerical analysis of the P-BIT data identified several genes associated with human or nonhuman sources as well as high-risk seropathotypes. We conclude that P-BIT is a useful approach for subtyping, offering the advantage of speed, low cost, and potential for strain risk assessment that can be used in tandem with current molecular typing schema for STEC.

Functional and phylogenetic analysis of ureD in Shiga toxin-producing Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) is a food-borne pathogen that can cause severe health complications and utilizes a much lower infectious dose than other E. coli pathotypes. Despite having an intact ure locus, ureDABCEFG, the majority of EHEC strains are phenotypically urease negative under tested conditions. Urease activity potentially assists with survival fitness by enhancing acid tolerance during passage through the stomach or by aiding with colonization in either human or animal reservoirs. Previously, in the EHEC O157:H7 Sakai strain, a point mutation in ureD, encoding a urease chaperone protein, was identified, resulting in a substitution of an amber stop codon for glutamine. This single nucleotide polymorphism (SNP) is observed in the majority of EHEC O157:H7 isolates and correlates with a negative urease phenotype in vitro. We demonstrate that the lack of urease activity in vitro is not solely due to the amber codon in ureD. Our analysis has identified two additional SNPs in ureD affecting amino acid positions 38 and 205, in both cases determining whether the encoded amino acid is leucine or proline. Phylogenetic analysis based on Ure protein sequences from a variety of urease-encoding bacteria demonstrates that the proline at position 38 is highly conserved among Gram-negative bacteria. Experiments reveal that the L38P substitution enhances urease enzyme activity; however, the L205P substitution does not. Multilocus sequence typing analysis for a variety of Shiga toxin-producing E. coli isolates combined with the ureD sequence reveals that except for a subset of the O157:H7 strains, neither the in vitro urease-positive phenotype nor the ureD sequence is phylogenetically restricted.

Contributions of O island 48 to adherence of enterohemorrhagic Escherichia coli O157:H7 to epithelial cells in vitro and in ligated pig ileal loops

O island 48 (OI-48) of Escherichia coli consists of three functional gene clusters that encode urease, tellurite resistance (Te(r)), and putative adhesins Iha and AIDA-1. The functions of these clusters in enterohemorrhagic E. coli (EHEC) O157:H7 infection are unknown. Deletion mutants for these three regions were constructed and evaluated for their ability to adhere to epithelial cells in vitro and in ligated pig ileal loops. Deletion of the Te(r) gene cluster reduced the ability of the organism to adhere to and form large clusters on IPEC-J2 and HEp-2 cells. Complementation of the mutation by introducing the wild-type ter genes restored adherence and large-cluster formation. Tests in ligated pig ileal loops showed a decrease in colonization by the Te(r)-negative mutant, but the difference was not significant compared to colonization by the wild type (26.4% +/- 21.2% versus 40.1% +/- 19.1%; P = 0.168). The OI-48 aidA gene deletion had no effect on adherence in vitro or in vivo. Deletion of the iha and ureC genes had no effect on adherence in vitro but significantly reduced the colonization of EHEC O157:H7 in the ligated pig intestine. These data suggest that Te(r), Iha, and urease may contribute to EHEC O157:H7 pathogenesis by promoting adherence of the pathogen to the host intestinal epithelium.

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.

Production of verotoxin and distribution of O islands 122 and 43/48 among verotoxin-producing Escherichia coli O103:H2 isolates from cattle and humans

This study investigated variations in the occurrence of markers of O islands 122 and 43/48 and in verotoxin 1 production in 91 verotoxin-producing Escherichia coli (VTEC) O103:H2 strains of bovine and human origins. None of the genes that were investigated appear to be virulence indicators for human O103:H2 VTEC.

Prevention and treatment of enterohemorrhagic Escherichia coli infections in humans

Infections with enterohemorrhagic Escherichia coli (EHEC) result in various clinical symptoms and outcomes ranging from watery or bloody diarrhea to the life-threatening hemolytic-uremic syndrome (HUS). Shiga toxins (Stxs) are supposed to play a major role in the pathogenesis of EHEC infections; however, the role of other putative virulence factors is not fully elucidated. So far, there is only supportive therapy available for the treatment of both EHEC-associated diarrhea and HUS. Antibiotic therapy for the treatment of EHEC-associated diarrhea is discussed. In recent years other therapeutic strategies have been developed, including Gb3 receptor analogues, that bind Stx in the gut or in the circulation, passive immunization with Stx-neutralizing monoclonal antibodies, or active immunization with Stx1 And Stx2 toxoids as a preventive procedure. These approaches have been demonstrated to be effective in animal models but clinical trials are lacking.

A homolog of the O157 urease-encoding O island 48 is present in porcine O149:H10 enterotoxigenic Escherichia coli

The relationship of the urease operon in the highly virulent O149 porcine enterotoxigenic Escherichia coli (ETEC) strain Ro8 to a genomic island (GI) homologous to O island (OI) 48 of O157 enterohemorrhagic E. coli (EHEC) strain EDL933 was investigated. Eighty-four of 84 O149:H10 strains were urease positive whereas 44 of 44 O149:H43 porcine ETEC strains were urease-negative. Seventeen of 17 O149:H10 strains that were tested possessed the OI-48 homolog whereas 24 of 24 O149:H43 strains lacked this OI. Transposon insertions in lipB or guaA genes in strain Ro8 eliminated urease activity while insertions in the caiF gene increased urease activity. When the O149 ure operon was cloned on a high copy number plasmid, urease expression was increased approximately 11-fold in Ro8 and 83-fold in O157 strain EDL933 compared with that in the wild type Ro8. The O149 urease activity was expressed despite the presence of the same premature stop codon in ureD that is present in ure+ O157:H7 strains that are urease-negative. The ure operon in Ro8 consists of 4 893 nucleotides with 99% identity with the ure operons in EHEC O157:H7 strains EDL933 and Sakai, and is part of a GI similar to GI-48 of strain EDL933. This OI, designated OI-48149 , is inserted in the serX tRNA gene in strain Ro8 and contains genes for urease, tellurite resistance, iha and an AIDA-I-like adhesin. The presence of a homolog of the O157:H7 OI-48 in highly virulent O149 porcine ETEC suggests that this OI may contribute to establishment of the bacteria in the intestine.

Anaerobic conditions promote expression of Sfp fimbriae and adherence of sorbitol-fermenting enterohemorrhagic Escherichia coli O157:NM to human intestinal epithelial cells

The sfp gene cluster, unique to sorbitol-fermenting (SF) enterohemorrhagic Escherichia coli (EHEC) O157:NM strains, encodes fimbriae that mediate mannose-resistant hemagglutination in laboratory E. coli strains but are not expressed in wild-type SF EHEC O157:NM strains under standard laboratory conditions. We investigated whether Sfp fimbriae are expressed under conditions that mimic the intestinal environment and whether they contribute to the adherence of SF EHEC O157:NM strains to human intestinal epithelial cells. The transcription of sfpA (encoding the major fimbrial subunit) was upregulated in all strains investigated, and all expressed SfpA and possessed fimbriae that reacted with an anti-SfpA antibody when the strains were grown on solid media under anaerobic conditions. Sfp expression was absent under aerobic conditions and in liquid media. Sfp upregulation under anaerobic conditions was significantly higher on blood agar and a medium simulating the colonic environment than on a medium simulating the ileal environment (P < 0.05). The induction of Sfp fimbriae in SF E. coli O157:NM strains correlates with increased adherence to Caco-2 and HCT-8 cells. Our data indicate that the expression of Sfp fimbriae in SF E. coli O157:NM strains is induced under conditions resembling those of the natural site of infection and that Sfp fimbriae may contribute to the adherence of the organisms to human intestinal epithelium.

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.

A rare presentation of ischemic pseudomembranous colitis due to Escherichia coli O157:H7

Escherichia coli Ol57:H7 infection ranges from mild diarrheal illness to severe hemorrhagic colitis but may rarely be complicated by pseudomembranous colitis and/or necrosis. Herein, we report a sporadic case of ischemic E. coli Ol57:H7 pseudomembranous colitis in an adult that occurred during a national outbreak of E. coli Ol57:H7 in the United States.