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

Prevalence and In Vivo Assessment of Virulence in Shiga Toxin-Producing Escherichia coli Clinical Isolates from Greater Cairo Area

Background: Shiga toxin-producing Escherichia coli (STEC) has been identified as an important etiologic agent of human disease in Egypt. Aims: To investigate the occurrence and describe the characterization as well as prevalence of STEC in Greater Cairo hospitals as well as molecular characterization of virulence and resistance genes. Methods: Four hundred seventy E. coli clinical isolates were collected from eight hospitals and analyzed by genotypic and phenotypic methods for STEC, followed by histopathological examination and scoring of different organs lesions. Results: The highest proportion of isolates was from urine (151 isolates), whereas the lowest was from splenic drain (3 isolates). In tandem, when serogrouping was performed, 15 serogroups were obtained where the most prevalent was O157 and the least prevalent was O151. All isolates were positive when screened for identity gene gad A, while only typable strains were screened for seven virulence genes stx1 (gene encoding Shiga toxin 1), stx2 (gene encoding Shiga toxin 2), tsh (gene encoding thermostable hemagglutinin), eaeA (gene encoding intimin), invE (gene encoding invasion protein), aggR (gene encoding aggregative adherence transcriptional regulator), and astA (aspartate transaminase) where the prevalence was 48%, 30%, 50%, 57%, 7.5%, 12%, and 58%, respectively. Of 254 typable isolates, 152 were STEC carrying stx1 or stx2 genes or both. Conclusions: Relying on in vivo comparison between different E. coli pathotypes via histopathological examination of different organs, E. coli pathotypes could be divided into mild virulent, moderate virulent, and high virulent strains. Statistical analysis revealed significant correlation between different serogroups and presence of virulence genes.

Shiga Toxin-Producing Escherichia coli in the Long-Term Survival Phase Exhibit Higher Chlorine Tolerance and Less Sublethal Injury Following Chlorine Treatment of Romaine Lettuce

The extent of chlorine inactivation and sublethal injury of stationary-phase (STAT) and long-term survival-phase (LTS) cells of Shiga toxin-producing Escherichia coli (STEC) in vitro and in a lettuce postharvest wash model was investigated. Four STEC strains were cultured in tryptic soy broth supplemented with 0.6% (w/v) yeast extract (TSBYE; 35°C) for 24 h and 21 d to obtain STAT and LTS cells, respectively. Minimum bactericidal concentration (MBC) and dose-response assays were performed to determine chlorine's antibacterial efficacy against STAT and LTS cells. Chlorine solutions (pH 6.5) and romaine lettuce were each inoculated with STAT and LTS cells to obtain initial populations of ∼7.8 log colony-forming units (CFU)/mL. Survivors in chlorine solutions were determined after 30 s. Inoculated lettuce samples were held at 22°C ± 1°C for 2 h or 20 h and then exposed to chlorine (10-40 ppm) for 60 s. Survivors were enumerated on nonselective and selective agar media following incubation (35°C, 48 h). The MBC for STAT and LTS cells was 0.04 and 0.08 ppm, respectively. Following exposure (30 s) to chlorine at 2.5, 5.0, and 10 ppm, STAT cells were reduced to <1.0 log CFU/mL, whereas LTS survivors were at 5.10 (2.5 ppm), 3.71 (5.0 ppm), and 2.55 (10 ppm) log CFU/mL. At 20 and 40 ppm chlorine, greater log CFU reductions of STAT cells (1.64 and 1.85) were observed compared with LTS cells (0.94 and 0.83) after 2 h of cell contact with lettuce (p < 0.05), but not after 20 h. Sublethal injury in STEC after chlorine (40 ppm) treatment was lower in LTS compared with STAT survivors (p < 0.05). Compared with STAT cells, LTS cells of STEC seem to have higher chlorine tolerance as planktonic cells and as attached cells depending on cell contact time on lettuce. In addition, a higher percentage of LTS cells, compared with STAT cells, survive in a noninjured state after chlorine (40 ppm) treatment of lettuce.

Virulence Genes, Shiga Toxin Subtypes, Serogroups, and Clonal Relationship of Shiga Toxin-Producing Escherichia Coli Strains Isolated from Livestock and Companion Animals

Shiga toxin-producing Escherichia coli (STEC) is a zoonotic pathogen that causes severe illness in humans and is an important cause of foodborne disease. In Chile, there is limited information on the virulence characteristics of this pathogen in livestock, and none in companion animals. The aim of this study was to characterize STEC strains isolated from cattle, swine, dogs, and cats, in Chile, in terms of the presence of Shiga toxin types and subtypes, virulence genes, serogroups, and clonality. One-thousand two-hundred samples were collected, isolating 54 strains (4.5%), where stx1a (68.5%) and ehxA (74.1%) were the most frequently detected virulence genes. Only one strain belonging to the most clinically relevant serogroups was identified. Pulsed field gel electrophoresis analysis showed high clonal diversity among strains isolated from cattle, while those from swine showed the same pattern. This study provides further evidence regarding cattle and swine in Chile as a potential source of a wide variety of STEC strains that could potentially cause severe illness in humans, and that companion animals do not seem to represent a relevant reservoir. It also argues that preventive and control strategies should not be focused on detecting serogroups, but instead, on detecting their determinants of virulence.

Virulence gene profiles and phylogeny of Shiga toxin-positive Escherichia coli strains isolated from FDA regulated foods during 2010-2017

Illnesses caused by Shiga toxin-producing Escherichia coli (STECs) can be life threatening, such as hemolytic uremic syndrome (HUS). The STECs most frequently identified by USDA's Microbiological Data Program (MDP) carried toxin gene subtypes stx1a and/or stx2a. Here we described the genome sequences of 331 STECs isolated from foods regulated by the FDA 2010-2017, and determined their genomic identity, serotype, sequence type, virulence potential, and prevalence of antimicrobial resistance. Isolates were selected from the MDP archive, routine food testing by FDA field labs (ORA), and food testing by a contract company. Only 276 (83%) strains were confirmed as STECs by in silico analysis. Foods from which STECs were recovered included cilantro (6%), spinach (25%), lettuce (11%), and flour (9%). Phylogenetic analysis using core genome MLST revealed these STEC genomes were highly variable, with some clustering associated with ST types and serotypes. We detected 95 different sequence types (ST); several ST were previously associated with HUS: ST21 and ST29 (O26:H11), ST11 (O157:H7), ST33 (O91:H14), ST17 (O103:H2), and ST16 (O111:H-). in silico virulome analyses showed ~ 51% of these strains were potentially pathogenic [besides stx gene they also carried eae (25%) or 26% saa (26%)]. Virulence gene prevalence was also determined: stx1 only (19%); stx2 only (66%); and stx1/sxt2 (15%). Our data form a new WGS dataset that can be used to support food safety investigations and monitor the recurrence/emergence of E. coli in foods.

Multiplex Nucleic Acid Amplification Testing to Diagnose Gut Infections: Challenges, Opportunities, and Result Interpretation

Multiplex nucleic acid testing is increasingly used to diagnose childhood gastroenteritis. The advantages of this disruptive technology include rapidity, sensitivity, and ability to detect pathogenic viruses, bacteria, and parasites simultaneously. The drawbacks are its capacity to identify organisms of uncertain clinical significance in North American children, cost, and inability to provide viable bacteria for strain typing by public health authorities. However, this technology will certainly improve our knowledge of the causes of human gut infections. As data emerge, physicians should interpret results cautiously, and, most important, consider the context of the presentation before making clinical decisions based on the readouts.

Detection, Characterization, and Typing of Shiga Toxin-Producing Escherichia coli

Shiga toxin-producing Escherichia coli (STEC) are responsible for gastrointestinal diseases reported in numerous outbreaks around the world. Given the public health importance of STEC, effective detection, characterization and typing is critical to any medical laboratory system. While non-O157 serotypes account for the majority of STEC infections, frontline microbiology laboratories may only screen for STEC using O157-specific agar-based methods. As a result, non-O157 STEC infections are significantly under-reported. This review discusses recent advances on the detection, characterization and typing of STEC with emphasis on work performed at the Alberta Provincial Laboratory for Public Health (ProvLab). Candidates for the detection of all STEC serotypes include chromogenic agars, enzyme immunoassays (EIA) and quantitative real time polymerase chain reaction (qPCR). Culture methods allow further characterization of isolates, whereas qPCR provides the greatest sensitivity and specificity, followed by EIA. The virulence gene profiles using PCR arrays and stx gene subtypes can subsequently be determined. Different non-O157 serotypes exhibit markedly different virulence gene profiles and a greater prevalence of stx1 than stx2 subtypes compared to O157:H7 isolates. Finally, recent innovations in whole genome sequencing (WGS) have allowed it to emerge as a candidate for the characterization and typing of STEC in diagnostic surveillance isolates. Methods of whole genome analysis such as single nucleotide polymorphisms and k-mer analysis are concordant with epidemiological data and standard typing methods, such as pulsed-field gel electrophoresis and multiple-locus variable number tandem repeat analysis while offering additional strain differentiation. Together these findings highlight improved strategies for STEC detection using currently available systems and the development of novel approaches for future surveillance.

Isolation and characterization of Shiga toxigenic Escherichia coli of animal and bird origin by multiplex polymerase chain reaction

AIM

The purpose of this study was to determine the virulence genes and serotype of Shiga toxin producing Escherichia coli (STEC) strains isolated from animals and birds.

MATERIALS AND METHODS

A total of 226 different samples viz., fecal, intestinal content, rectal swab and heart blood were collected from different clinically affected/healthy animals and birds and were streaked on McConkeys' lactose agar and eosin methylene blue agar for isolation of E. coli, confirmed by staining characteristics and biochemical tests. By polymerase chain reaction (PCR) all the E. coli isolates were screened for certain virulence genes, viz., Shiga toxin 1 (stx1), stx2 and eae and enterohemolytic (Ehly) phenotype was observed in washed sheep blood agar plate. All the isolated E. coli strains were forwarded to the National Salmonella and Escherichia Centre, Central Research Institute, Kasauli (Himachal Pradesh) for serotyping.

RESULTS

Out of 226 samples 138 yielded E. coli. All the isolates were screened for molecular detection of different virulent genes, viz. stx1, stx2 and eae, based on which 36 (26.08%) were identified as STEC. Among those STEC isolates, 15 (41.67%), 14 (38.89%), 1 (2.78%) exhibited eae, stx2, stx1 alone, respectively, whereas 4 (11.11%) and 2 (5.56%) carried both stx1 and stx2, stx2 and eae, respectively. Among the STEC isolates 22 were belonged to 15 different sero-groups, viz., O2, O20, O22, O25, O43, O60, O69, O90, O91, O95, O106, O118, O130, O162 and O170 and others were untypable. Ehly phenotype was observed in 10 (27.78%) the STEC isolates.

CONCLUSION

The present study concluded that STEC could be isolated from both clinically affected as well as healthy animals and birds. Regular monitoring of more samples from animal and bird origin is important to identify natural reservoir of STEC to prevent zoonotic infection.

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.

Persistence of Escherichia coli O157 and non-O157 strains in agricultural soils

Shiga toxin producing Escherichia coli O157 and non-O157 serogroups are known to cause serious diseases in human. However, research on the persistence of E. coli non-O157 serogroups in preharvest environment is limited. In the current study, we compared the survival behavior of E. coli O157 to that of non-O157 E. coli strains in agricultural soils collected from three major fresh produce growing areas of California (CA) and Arizona (AZ). Results showed that the nonpathogenic E. coli O157:H7 4554 survived longer than the pathogenic E. coli O157:H7 EDL933 in Imperial Valley CA and Yuma AZ, but not in soils from the Salinas area. However, E. coli O157:NM was found to persist significantly longer than E. coli O157:H7 EDL933 in all soil tested from the three regions. Furthermore, two non-O157 (E. coli O26:H21 and E. coli O103:H2) survived significantly longer than E. coli O157:H7 EDL933 in all soils tested. Pearson correlation analysis showed that survival of the E. coli strains was affected by different environmental factors. Our data suggest that survival of E. coli O157 and non-O157 may be strain and soil specific, and therefore, care must be taken in data interpretation with respect to survival of this pathogen in different soils.

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.

Shiga toxin-producing Escherichia coli: a single-center, 11-year pediatric experience

The aim of this study was to identify the best practices for the detection of Shiga toxin-producing Escherichia coli (STEC) in children with diarrheal illness treated at a tertiary care center, i.e., sorbitol-MacConkey (SMAC) agar culture, enzyme immunoassay (EIA) for Shiga toxin, or the simultaneous use of both methods. STEC was detected in 100 of 14,997 stool specimens submitted for enteric culture (0.7%), with 65 cases of E. coli O157. Among E. coli O157 isolates, 57 (88%) were identified by both SMAC agar culture and EIA, 6 (9%) by SMAC agar culture alone, and 2 (3%) by EIA alone. Of the 62 individuals with diarrheal hemolytic uremic syndrome (HUS) seen at our institution during the study period, 16 (26%) had STEC isolated from cultures at our institution and 15 (24%) had STEC isolated at other institutions. No STEC was recovered in 31 cases (50%). Of the HUS cases in which STEC was isolated, 28 (90%) were attributable to E. coli O157 and 3 (10%) were attributable to non-O157 STEC. Consistent with previous studies, we have determined that a subset of E. coli O157 infections will not be detected if an agar-based method is excluded from the enteric culture workup; this has both clinical and public health implications. The best practice would be concomitant use of an agar-based method and a Shiga toxin EIA, but a Shiga toxin EIA should not be considered to be an adequate stand-alone test for detection of E. coli O157 in clinical samples.

Interactive effects of temperature, pH, and water activity on the growth kinetics of Shiga toxin-producing Escherichia coli O104:H4 3

The risk of non-O157 Shiga toxin-producing Escherichia coli strains has become a growing public health concern. Several studies characterized the behavior of E. coli O157:H7; however, no reports on the influence of multiple factors on E. coli O104:H4 are available. This study examined the effects and interactions of temperature (7 to 46°C), pH (4.5 to 8.5), and water activity (aw ; 0.95 to 0.99) on the growth kinetics of E. coli O104:H4 and developed predictive models to estimate its growth potential in foods. Growth kinetics studies for each of the 23 variable combinations from a central composite design were performed. Growth data were used to obtain the lag phase duration (LPD), exponential growth rate, generation time, and maximum population density (MPD). These growth parameters as a function of temperature, pH, and aw as controlling factors were analyzed to generate second-order response surface models. The results indicate that the observed MPD was dependent on the pH, aw, and temperature of the growth medium. Increasing temperature resulted in a concomitant decrease in LPD. Regression analysis suggests that temperature, pH, and aw significantly affect the LPD, exponential growth rate, generation time, and MPD of E. coli O104:H4. A comparison between the observed values and those of E. coli O157:H7 predictions obtained by using the U. S. Department of Agriculture Pathogen Modeling Program indicated that E. coli O104:H4 grows faster than E. coli O157:H7. The developed models were validated with alfalfa and broccoli sprouts. These models will provide risk assessors and food safety managers a rapid means of estimating the likelihood that the pathogen, if present, would grow in response to the interaction of the three variables assessed.

Regional variation in the prevalence of E. coli O157 in cattle: a meta-analysis and meta-regression

BACKGROUND

Escherichia coli O157 (EcO157) infection has been recognized as an important global public health concern. But information on the prevalence of EcO157 in cattle at the global and at the wider geographical levels is limited, if not absent. This is the first meta-analysis to investigate the point prevalence of EcO157 in cattle at the global level and to explore the factors contributing to variation in prevalence estimates.

METHODS

Seven electronic databases- CAB Abstracts, PubMed, Biosis Citation Index, Medline, Web of Knowledge, Scirus and Scopus were searched for relevant publications from 1980 to 2012. A random effect meta-analysis model was used to produce the pooled estimates. The potential sources of between study heterogeneity were identified using meta-regression.

PRINCIPAL FINDINGS

A total of 140 studies consisting 220,427 cattle were included in the meta-analysis. The prevalence estimate of EcO157 in cattle at the global level was 5.68% (95% CI, 5.16-6.20). The random effects pooled prevalence estimates in Africa, Northern America, Oceania, Europe, Asia and Latin America-Caribbean were 31.20% (95% CI, 12.35-50.04), 7.35% (95% CI, 6.44-8.26), 6.85% (95% CI, 2.41-11.29), 5.15% (95% CI, 4.21-6.09), 4.69% (95% CI, 3.05-6.33) and 1.65% (95% CI, 0.77-2.53), respectively. Between studies heterogeneity was evidenced in most regions. World region (p<0.001), type of cattle (p<0.001) and to some extent, specimens (p = 0.074) as well as method of pre-enrichment (p = 0.110), were identified as factors for variation in the prevalence estimates of EcO157 in cattle.

CONCLUSION

The prevalence of the organism seems to be higher in the African and Northern American regions. The important factors that might have influence in the estimates of EcO157 are type of cattle and kind of screening specimen. Their roles need to be determined and they should be properly handled in any survey to estimate the true prevalence of EcO157.

Shiga toxin-producing Escherichia coli O157 is more likely to lead to hospitalization and death than non-O157 serogroups--except O104

The clinical spectrum following infection with Shiga toxin-producing Escherichia coli (STEC) is wide ranging and includes hemorrhagic colitis and life-threatening hemolytic uremic syndrome (HUS). Severity of STEC illness depends on patients' age and strongly on the infecting strains' virulence. Serogroup O157 is often assumed to be more virulent than others. Age-adjusted population-based data supporting this view are lacking thus far.

We conducted a large retrospective cohort study among patients of community-acquired gastroenteritis or HUS diagnosed with STEC infection, reported in Germany January 2004 through December 2011. Age-adjusted risks for reported hospitalization and death, as proxies for disease severity, were estimated for STEC serogroups separately, and compared with STEC O157 (reference group) using Poisson regression models with robust error estimation.

A total of 8,400 case-patients were included in the analysis; for 2,454 (29%) and 30 (0.4%) hospitalization and death was reported, respectively. Highest risks for hospitalization, adjusted for age and region of residence, were estimated for STEC O104 (68%; risk ratio [RR], 1.33; 95% confidence interval [CI], 1.19–1.45), followed by STEC O157 (46%). Hospitalization risks for the most prevalent non-O157 serogroups (O26, O103, O91, O145, O128, O111) were consistently and markedly lower than for O157, with the highest RR for O145 (0.54; 95% CI, 0.41–0.70) and the lowest for O103 (0.27; 95% CI, 0.20–0.35). Mortality risk of O104 was similar to O157 (1.2% each), but the group of all other non-O157 STEC had only 1/10 the risk (RR, 0.09; 95% CI, 0.02–0.32) compared to O157.

The study provides population-based and age-adjusted evidence for the exceptional high virulence of STEC O157 in relation to non-O157 STEC other than O104. Timely diagnosis and surveillance of STEC infections should prioritize HUS-associated E. coli, of which STEC O157 is the most important serogroup.

A polyclonal antibody based immunoassay detects seven subtypes of Shiga toxin 2 produced by Escherichia coli in human and environmental samples

BACKGROUND

Shiga toxin-producing Escherichia coli (STEC) are frequent causes of severe human diseases ranging from diarrhea to hemolytic uremic syndrome. The existing strategy for detection of STEC relies on the unique sorbitol-negative fermentation property of the O157 strains, the most commonly identified serotype has been E. coli O157. It is becoming increasingly evident, however, that numerous non-O157 STEC serotypes also cause outbreaks and severe illnesses. It is necessary to have new methods that are capable of detecting all STEC strains.

METHODS AND FINDINGS

Here we describe the development of a sandwich ELISA assay for detecting both O157 and non-O157 STECs by incorporating a novel polyclonal antibody (pAb) against Stx2. The newly established immunoassay was capable of detecting Stx2a spiked in environmental samples with a limit of detection between 10 and 100 pg/mL in soil and between 100 and 500 pg/mL in feces. When applied to 36 bacterial strains isolated from human and environmental samples, this assay detected Stx2 in all strains that were confirmed to be stx2-positive by real-time PCR, demonstrating a 100% sensitivity and specificity.

CONCLUSIONS

The sandwich ELISA developed in this study will enable any competent laboratory to identify and characterize Stx2-producing O157 and non-O157 strains in human and environmental samples, resulting in rapid diagnosis and patient care. The results of epitope mapping from this study will be useful for further development of a peptide-based antibody and vaccine.

Characteristics of clinical Shiga toxin-producing Escherichia coli isolated from British Columbia

Shiga toxin-producing Escherichia coli (STEC) are significant public health threats. Although STEC O157 are recognized foodborne pathogens, non-O157 STEC are also important causes of human disease. We characterized 10 O157:H7 and 15 non-O157 clinical STEC derived from British Columbia (BC). Eae, hlyA, and stx were more frequently observed in STEC O157, and 80 and 100% of isolates possessed stx₁ and stx₂, respectively. In contrast, stx₁ and stx₂ occurred in 80 and 40% of non-O157 STEC, respectively. Comparative genomic fingerprinting (CGF) revealed three distinct clusters (C). STEC O157 was identified as lineage I (LI; LSPA-6 111111) and clustered as a single group (C1). The cdi gene previously observed only in LII was seen in two LI O157 isolates. CGF C2 strains consisted of diverse non-O157 STEC while C3 included only O103:H25, O118, and O165 serogroup isolates. With the exception of O121 and O165 isolates which were similar in virulence gene complement to STEC O157, C1 O157 STEC produced more Stx2 than non-O157 STEC. Antimicrobial resistance (AMR) screening revealed resistance or reduced sensitivity in all strains, with higher levels occurring in non-O157 STEC. One STEC O157 isolate possessed a mobile bla_CMY-2 gene transferrable across genre via conjugation.

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.

Discrimination of enterohemorrhagic Escherichia coli (EHEC) from non-EHEC strains based on detection of various combinations of type III effector genes

Enterohemorrhagic Escherichia coli (EHEC) strains comprise a subgroup of Shiga-toxin (Stx)-producing E. coli (STEC) and are characterized by a few serotypes. Among these, seven priority STEC serotypes (O26:H11, O45:H2, O103:H2, O111:H8, O121:H19, O145:H28, and O157:H7) are most frequently implicated in severe clinical illness worldwide. Currently, standard methods using stx, eae, and O-serogroup-specific gene sequences for detecting the top 7 EHEC serotypes bear the disadvantage that these genes can be found in non-EHEC strains as well. Here, we explored the suitability of ureD, espV, espK, espN, Z2098, and espM1 genes and combinations thereof as candidates for a more targeted EHEC screening assay. For a very large panel of E. coli strains (n = 1,100), which comprised EHEC (n = 340), enteropathogenic E. coli (EPEC) (n = 392), STEC (n = 193), and apathogenic strains (n = 175), we showed that these genetic markers were more prevalent in EHEC (67.1% to 92.4%) than in EPEC (13.3% to 45.2%), STEC (0.5% to 3.6%), and apathogenic E. coli strains (0 to 2.9%). It is noteworthy that 38.5% of the EPEC strains that tested positive for at least one of these genetic markers belonged to the top 7 EHEC serotypes, suggesting that such isolates might be Stx-negative derivatives of EHEC. The associations of espK with either espV, ureD, or Z2098 were the best combinations for more specific and sensitive detection of the top 7 EHEC strains, allowing detection of 99.3% to 100% of these strains. In addition, detection of 93.7% of the EHEC strains belonging to other serotypes than the top 7 offers a possibility for identifying new emerging EHEC strains.

Molecular epidemiology ofEscherichia colidiarrhoea in children in Tehran

From July to December 2003, four categories of diarrhoeagenic Escherichia coli were investigated in Tehranian children with acute diarrhoea. Stool specimens of children under 5 years of age with diarrhoea (n=200) and matched controls (n=200) without diarrhoea were studied for the presence of entero-aggregative (EAEC), enteropathogenic (EPEC), enterotoxigenic (ETEC) and Shiga toxin-producing (STEC) E. coli by PCR identification of six different genes of diarrhoeagenic E. coli. STEC isolates were typed by O157 and H7 antisera. EAEC was the most prevalent category and was found in 24% of patients with diarrhoea and 8% of controls (p<0.0001). ETEC was isolated in 15.5% of patients with diarrhoea but not in any controls ( p<0.0001), STEC in 15% of patients and 2% of controls (p<0.0001) and EPEC in 6% of patients and 5% of controls. Of 30 STEC isolates from patients with diarrhoea, seven were O157:H7 and 23 were non-O157:H7.

Evaluation of MALDI-TOF mass spectroscopy methods for determination of Escherichia coli pathotypes

It is rapidly becoming apparent that many E. coli pathotypes cause a considerable burden of human disease. Surveillance of these organisms is difficult because there are few or no simple, rapid methods for detecting and differentiating the different pathotypes. MALDI-TOF mass spectroscopy has recently been rapidly and enthusiastically adopted by many clinical laboratories as a diagnostic method because of its high throughput, relatively low cost, and adaptability to the laboratory workflow. To determine whether the method could be adapted for E. coli pathotype differentiation the Bruker Biotyper methodology and a second methodology adapted from the scientific literature were tested on isolates representing eight distinct pathotypes and two other groups of E. coli. A total of 136 isolates was used for this study. Results confirmed that the Bruker Biotyper methodology that included extraction of proteins from bacterial cells was capable of identifying E. coli isolates from all pathotypes to the species level and, furthermore, that the Bruker extraction and MALDI-TOF MS with the evaluation criteria developed in this work was effective for differentiating most pathotypes.

Towards a molecular definition of enterohemorrhagic Escherichia coli (EHEC): detection of genes located on O island 57 as markers to distinguish EHEC from closely related enteropathogenic E. coli strains

Among strains of Shiga-toxin (Stx) producing Escherichia coli (STEC), seven serogroups (O26, O45, O103, O111, O121, O145, and O157) are associated with severe clinical illness in humans. These strains are also called enterohemorrhagic E. coli (EHEC), and the development of methods for their reliable detection from food has been challenging thus far. PCR detection of major EHEC virulence genes stx1, stx2, eae, and O-serogroup-specific genes is useful but does not identify EHEC strains specifically. Searching for the presence of additional genes issued from E. coli O157:H7 genomic islands OI-122 and OI-71 increases the specificity but does not clearly discriminate EHEC from enteropathogenic E. coli (EPEC) strains. Here, we identified two putative genes, called Z2098 and Z2099, from the genomic island OI-57 that were closely associated with EHEC and their stx-negative derivative strains (87% for Z2098 and 91% for Z2099). Z2098 and Z2099 were rarely found in EPEC (10% for Z2098 and 12% for Z2099), STEC (2 and 15%), and apathogenic E. coli (1% each) strains. Our findings indicate that Z2098 and Z2099 are useful genetic markers for a more targeted diagnosis of typical EHEC and new emerging EHEC strains.

Evaluation of a new chromogenic agar medium for detection of Shiga toxin-producing Escherichia coli (STEC) and relative prevalences of O157 and non-O157 STEC in Manitoba, Canada

This study assesses the detection performance of CHROMagar STEC medium relative to a reference cytotoxin assay and describes the current relative prevalence of O157 and non-O157 Shiga toxin-producing Escherichia coli (STEC) serotypes within the province of Manitoba, Canada. Over a 10-month period, 205 nonfrozen routine stool submissions to Cadham Provincial Laboratory (CPL) were used to assess the performance of CHROMagar STEC. Of the 205 stools, 14 were identified as true positives by a cytotoxin assay, with resultant CHROMagar STEC sensitivity, specificity, and positive predictive and negative predictive values of 85.7%, 95.8%, 60.0%, and 98.9%, respectively. Using a separate panel of 111 STEC strains, CHROMagar STEC was shown to support the growth of 96 (86.5%) isolates. To assess relative prevalence, attempts were made to isolate by any means all STEC strains identified at CPL over a 17-month period. Of 49 isolates (representing 86.0% of all STEC infections detected), only 28.6% were O157 STEC strains. Of the 35 non-O157 STEC strains, 29 were subjected to further molecular analysis. In contrast to earlier results from our area, carriage of stx(2) appears to have increased. Overall, although CHROMagar STEC is not recommended as a primary screen, our results indicate that it is an effective supplemental medium for the isolation of probable STEC strains. Increased isolation of these serotypes is warranted to better understand their prevalence, clinical characteristics, and epidemiology and aid in the development or enhancement of food safety control programs targeting all STEC serotypes.

Diarrhea etiology in a pediatric emergency department: a case control study

BACKGROUND

The etiology of childhood diarrhea is frequently unknown.

METHODS

We sought Aeromonas, Campylobacter, Escherichia coli O157:H7, Pleisiomonas shigelloides, Salmonella, Shigella, Vibrio, and Yersinia (by culture), adenoviruses, astroviruses, noroviruses, rotavirus, and Shiga toxin-producing E. coli (STEC; by enzyme immunoassay), Clostridium difficile (by cytotoxicity), parasites (by microscopy), and enteroaggregative E. coli (EAEC; by polymerase chain reaction [PCR] analysis) in the stools of 254 children with diarrhea presenting to a pediatric emergency facility. Age- and geographic-matched community controls without diarrhea (n = 452) were similarly studied, except bacterial cultures of the stool were limited only to cases.

RESULTS

Twenty-nine (11.4%) case stools contained 13 Salmonella, 10 STEC (6 O157:H7 and 4 non-O157:H7 serotypes), 5 Campylobacter, and 2 Shigella. PCR-defined EAEC were present more often in case (3.2%) specimens than in control (0.9%) specimens (adjusted odds ratio [OR], 3.9; 95% confidence interval [CI], 1.1-13.7), and their adherence phenotypes were variable. Rotavirus, astrovirus, and adenovirus were more common among cases than controls, but both groups contained noroviruses and C. difficile at similar rates. PCR evidence of hypervirulent C. difficile was found in case and control stools; parasites were much more common in control specimens.

CONCLUSIONS

EAEC are associated with childhood diarrhea in Seattle, but the optimal way to identify these agents warrants determination. Children without diarrhea harbor diarrheagenic pathogens, including hypervirulent C. difficile. Our data support the importance of taking into account host susceptibility, microbial density, and organism virulence traits in future case-control studies, not merely categorizing candidate pathogens as being present or absent.

High temperature in combination with UV irradiation enhances horizontal transfer of stx2 gene from E. coli O157:H7 to non-pathogenic E. coli

Background

Shiga toxin (stx) genes have been transferred to numerous bacteria, one of which is E. coli O157:H7. It is a common belief that stx gene is transferred by bacteriophages, because stx genes are located on lambdoid prophages in the E. coli O157:H7 genome. Both E. coli O157:H7 and non-pathogenic E. coli are highly enriched in cattle feedlots. We hypothesized that strong UV radiation in combination with high temperature accelerates stx gene transfer into non-pathogenic E. coli in feedlots.

Methodology/Principal Findings

E. coli O157:H7 EDL933 strain were subjected to different UV irradiation (0 or 0.5 kJ/m²) combination with different temperature (22, 28, 30, 32, and 37°C) treatments, and the activation of lambdoid prophages was analyzed by plaque forming unit while induction of Stx2 prophages was quantified by quantitative real-time PCR. Data showed that lambdoid prophages in E. coli O157:H7, including phages carrying stx2, were activated under UV radiation, a process enhanced by elevated temperature. Consistently, western blotting analysis indicated that the production of Shiga toxin 2 was also dramatically increased by UV irradiation and high temperature. In situ colony hybridization screening indicated that these activated Stx2 prophages were capable of converting laboratory strain of E. coli K12 into new Shiga toxigenic E. coli, which were further confirmed by PCR and ELISA analysis.

Conclusions/Significance

These data implicate that high environmental temperature in combination with UV irradiation accelerates the spread of stx genes through enhancing Stx prophage induction and Stx phage mediated gene transfer. Cattle feedlot sludge are teemed with E. coli O157:H7 and non-pathogenic E. coli, and is frequently exposed to UV radiation via sunlight, which may contribute to the rapid spread of stx gene to non-pathogenic E. coli and diversity of shiga toxin producing E. coli.

Epidemiology of Shiga toxin producing Escherichia coli in Australia, 2000-2010

BACKGROUND

Shiga toxin-producing Escherichia coli (STEC) are an important cause of gastroenteritis in Australia and worldwide and can also result in serious sequelae such as haemolytic uraemic syndrome (HUS). In this paper we describe the epidemiology of STEC in Australia using the latest available data.

METHODS

National and state notifications data, as well as data on serotypes, hospitalizations, mortality and outbreaks were examined.

RESULTS

For the 11 year period 2000 to 2010, the overall annual Australian rate of all notified STEC illness was 0.4 cases per 100,000 per year. In total, there were 822 STEC infections notified in Australia over this period, with a low of 1 notification in the Australian Capital Territory (corresponding to a rate of 0.03 cases per 100,000/year) and a high of 413 notifications in South Australia (corresponding to a rate of 2.4 cases per 100,000/year), the state with the most comprehensive surveillance for STEC infection in the country. Nationally, 71.2% (504/708) of STEC infections underwent serotype testing between 2001 and 2009, and of these, 58.0% (225/388) were found to be O157 strains, with O111 (13.7%) and O26 (11.1%) strains also commonly associated with STEC infections. The notification rate for STEC O157 infections Australia wide between 2001-2009 was 0.12 cases per 100,000 per year. Over the same 9 year period there were 11 outbreaks caused by STEC, with these outbreaks generally being small in size and caused by a variety of serogroups. The overall annual rate of notified HUS in Australia between 2000 and 2010 was 0.07 cases per 100,000 per year. Both STEC infections and HUS cases showed a similar seasonal distribution, with a larger proportion of reported cases occurring in the summer months of December to February.

CONCLUSIONS

STEC infections in Australia have remained fairly steady over the past 11 years. Overall, the incidence and burden of disease due to STEC and HUS in Australia appears comparable or lower than similar developed countries.

Epidemiology of a large restaurant-associated outbreak of Shiga toxin-producingEscherichia coliO111:NM

In August 2008, a large outbreak of Shiga toxin-producingEscherichia coli(STEC) O111:NM infections associated with a buffet-style restaurant in rural Oklahoma was identified. A case-control study of restaurant patrons and a retrospective cohort study of catered event attendees were conducted coupled with an environmental investigation to determine the outbreak's source and mode of transmission. Of 1823 persons interviewed, 341 (18·7%) met the outbreak case definition; 70 (20·5%) were hospitalized, 25 (7·3%) developed haemolytic uraemic syndrome, and one died. Multiple food items were significantly associated with illness by both bivariate and multivariate analyses, but none stood out as a predominant transmission vehicle. All water, food, and restaurant surface swabs, and stool cultures from nine ill employees were negative for the presence of Shiga toxin andE. coliO111:NM although epidemiological evidence suggested the outbreak resulted from cross-contamination of restaurant food from food preparation equipment or surfaces, or from an unidentified infected food handler.

Ten-year trends and risk factors for non-O157 Shiga toxin-producing Escherichia coli found through Shiga toxin testing, Connecticut, 2000-2009

BACKGROUND

The epidemiology over time of non-O157 Shiga toxin-producing Escherichia coli (STEC) is unknown. Since 1999, increasing numbers of laboratories in Connecticut have been testing for ST rather than culturing for O157, enabling identification of non-O157 STEC.

METHODS

Beginning in 2000, Connecticut laboratories were required to submit ST-positive broths to the State Laboratory for isolation and typing of STEC. The ratio of non-O157:O157 from laboratories conducting ST testing was used to determine state-level estimates for non-O157 STEC. Patients with STEC were interviewed for exposure factors in the 7 days preceding illness. Incidence trends, clinical features, and epidemiology of non-O157 and O157 STEC infections were compared.

RESULTS

From 1 January 2000 through 31 December 2009, ST testing detected 392 (59%) of 663 reported STEC infections; 229 (58%) of the isolates were non-O157. The estimated incidence of STEC infection decreased by 34%. O157 and the top 4 non-O157 serogroups, O111, O103, O26, and O45, were a stable percentage of all STEC isolates over the 10-year period. Bloody diarrhea, hospitalization, and hemolytic uremic syndrome were more common in patients with O157 STEC than in patients with non-O157 STEC infection. Exposure risks of patients with non-O157 STEC infection differed from those of patients with O157 STEC infection primarily in international travel (15.3% vs 2.5%; P < .01). Non-O157 types differed from each other with respect to several epidemiologic and exposure features.

CONCLUSIONS

Both O157 and non-O157 STEC infection incidence decreased from 2000 through 2009. Although infection due to O157 is the most common and clinically severe STEC infection, it accounts for a minority of all clinically significant STEC infections. STEC appear to be a diverse group of organisms that have some differences as well as many epidemiologic and exposure features in common.

Enhanced surveillance of non-O157 verotoxin-producing Escherichia coli in human stool samples from Manitoba

BACKGROUND

Relatively few enhanced surveillance studies have been undertaken to investigate the extent to which verotoxin-producing non-O157 serotypes of Escherichia coli occur in stool samples received for the detection of verotoxin-producing organisms.

OBJECTIVES

To describe the prevalence, molecular and epidemiological characteristics, and geographical patterns associated with non-O157 verotoxin-producing E coli (VTEC) in Manitoba.

RESULTS

Thirty-two VTEC isolates consisting of 10 serogroups and 13 different serotypes were isolated over a 22-month period. Twenty-three isolates (71.8%) possessed verotoxin-encoding gene stx1 only, five isolates (15.6%) possessed stx2 only, two isolates (6.3%) possessed both stx1 and stx2, and two isolates (6.3%) possessed stx2c. Only three instances of indistinguishable pulsed-field gel electrophoresis patterns were identified. The age of the individuals from whom non-O157 VTEC were isolated ranged from eight months to 87 years. Mean and median ages were 30 and 22 years of age, respectively. Some areas of the province appeared to experience a higher than expected number of non-O157 E coli in comparison with the number of stools that were received from these areas.

CONCLUSIONS

The present study demonstrated a large number of infections associated with non-O157 VTEC in Manitoba. Most non-O157 cases appear to result from sporadic infections, and these occur typically in rural areas. Continued enhanced surveillance is necessary to understand the temporal patterns of non-O157 VTEC and the underlying epidemiological factors driving these patterns.

Prevalence, distribution and evolutionary significance of the IS629 insertion element in the stepwise emergence of Escherichia coli O157:H7

Background

Insertion elements (IS) are known to play an important role in the evolution and genomic diversification of Escherichia coli O157:H7 lineages. In particular, IS629 has been found in multiple copies in the E. coli O157:H7 genome and is one of the most prevalent IS in this serotype. It was recently shown that the lack of O157 antigen expression in two O rough E. coli O157:H7 strains was due to IS629 insertions at 2 different locations in the gne gene that is essential for the O antigen biosynthesis.

Results

The comparison of 4 E. coli O157:H7 genome and plasmid sequences showed numerous IS629 insertion sites, although not uniformly distributed among strains. Comparison of IS629s found in O157:H7 and O55:H7 showed the presence of at least three different IS629 sub-types. O157:H7 strains carry IS629 elements sub-type I and III whereby the ancestral O55:H7 carries sub-type II. Analysis of strains selected from various clonal groups defined on the E. coli O157:H7 stepwise evolution model showed that IS629 was not observed in sorbitol fermenting O157 (SFO157) clones that are on a divergent pathway in the emergence of O157:H7. This suggests that the absence of IS629 in SFO157 strains probably occurred during the divergence of this lineage, albeit it remains uncertain if it contributed, in part, to their divergence from other closely related strains.

Conclusions

The highly variable genomic locations of IS629 in O157:H7 strains of the A6 clonal complex indicates that this insertion element probably played an important role in genome plasticity and in the divergence of O157:H7 lineages.

Development of a sensitive detection method for stressed E. coli O157:H7 in source and finished drinking water by culture-qPCR

A sensitive and specific method that also demonstrates viability is of interest for detection of E. coli O157:H7 in drinking water. A combination of culture and qPCR was investigated. Two triplex qPCRs, one from a commercial source and another designed for this study were optimized from 5 different assays to be run on a single qPCR plate. The qPCR assays were specific for 33 E. coli O157:H7 strains tested and detected 500 cells spiked in a background of 10(8) nontarget bacterial cells. The qPCR detection was combined with an enrichment process using Presence Absence (P/A) broth to detect chlorine and starvation stressed cells. qPCR analysis performed post-enrichment allowed the detection of 3-4 cells/L as indicated by a sharp increase in fluorescence (lowering of Ct values) from pre-enrichment levels, demonstrating a 5-6 log increase in the number of cells. When six vulnerable untreated surface water samples were examined, only one was positive for viable E. coli O157:H7 cells. These results suggest that the culture-PCR procedure can be used for rapid detection of E. coli O157:H7 in drinking water.

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

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

Shiga toxin-producing Escherichia coli in children: diagnosis and clinical manifestations of O157:H7 and non-O157:H7 infection

Shiga toxin-producing Escherichia coli (STEC), a cause of food-borne colitis and hemolytic-uremic syndrome in children, can be serotype O157:H7 (O157) or other serotypes (non-O157). E. coli O157 can be detected by culture with sorbitol-MacConkey agar (SMAC), but non-O157 STEC cannot be detected with this medium. Both O157 and non-O157 STEC can be detected by immunoassay for Shiga toxins 1 and 2. The objectives of this study were first to compare the diagnostic utility of SMAC to that of the Premier EHEC enzyme immunoassay (Meridian Diagnostics) for detection of STEC in children and second to compare the clinical and laboratory characteristics of children with serotype O157:H7 STEC and non-O157:H7 STEC infections. Stool samples submitted for testing for STEC between April 2004 and September 2009 were tested by both SMAC culture and the Premier EHEC assay at Children's Hospital Boston. Samples positive by either test were sent for confirmatory testing and serotyping at the Hinton State Laboratory Institute (HSLI). Chart review was performed on children with confirmed STEC infection. Of 5,110 children tested for STEC, 50 (0.9%) had STEC infection confirmed by culture; 33 were O157:H7 and 17 were non-O157:H7. The Premier EHEC assay and SMAC culture detected 96.0% and 58.0% of culture-confirmed STEC isolates (any serotype), respectively, and 93.9% and 87.9% of STEC O157:H7 isolates, respectively. There were no significant differences in disease severity or laboratory manifestations of STEC infection between children with O157:H7 and those with non-O157 STEC. The Premier EHEC assay was significantly more sensitive than SMAC culture for diagnosis of STEC, and O157:H7 and non-O157:H7 STEC caused infections of similar severity in children.

Shiga-toxigenic Escherichia coli detection in stool samples screened for viral gastroenteritis in Alberta, Canada

Shiga-toxigenic Escherichia coli (STEC) is an important cause of diarrheal disease. The most notorious STEC serotype is O157:H7, which is associated with hemorrhagic colitis and hemolytic-uremic syndrome (HUS). As a result, this serotype is routinely screened for in clinical microbiology laboratories. With the bias toward the identification of the O157 serogroup in routine diagnostic processes, non-O157 STEC has been largely underrepresented in the epidemiology of STEC infections. This diagnostic bias is further complicated by the fact that many non-O157 STEC infections cause nonspecific gastroenteritis symptoms reminiscent of enteric viral infections. In this study, real-time PCR was used to amplify Shiga toxin genetic determinants (stx(1) and stx(2)) from enriched stool samples that were initially submitted for the testing of enteric viruses in patients with suspected viral gastroenteritis between May and September of 2006, 2007, and 2008 (n = 2,702). Samples were submitted from the province of Alberta, Yukon, the Northwest Territories, and Nunavut, Canada. A total of 38 samples (1.4%) tested positive for Shiga toxin genes, and 15 isolates were cultured for further characterization. Several of the serotypes identified (O157:H7, O26:HNM, O26:H11, O103:H25, O121:H19, and O145:HNM) have been previously associated with outbreaks and HUS. This study outlines the importance of combining molecular methods with classical culture techniques to enhance the detection of emerging non-O157 as well as O157 serotypes in diarrheal stool samples. Furthermore, atypical diarrhea disease caused by non-O157 STEC can be routinely missed due to screening only for viral agents.

Non-O157 verotoxigenic Escherichia coli and beef: a Canadian perspective

Verotoxigenic Escherichia coli (VTEC) are important foodborne pathogens in Canada. VTEC of the O157:H7 serogroup have been the focus of regulatory action and surveillance in both Canada and the USA, due to their role in a number of high profile outbreaks. However, there is increasing evidence that other VTEC serogroups cause a substantial proportion of human illness. This issue is of particular importance to the cattle industry due to the role of beef as a vehicle for VTEC transmission. In this review, the evidence for non-O157 VTEC as cause of human illness in Canada and the potential for Canadian beef and cattle to serve as a source of VTEC are presented. In addition, the available strategies for the control of VTEC in cattle and beef are discussed.

Comparison of Shiga toxin-producing Escherichia coli detection methods using clinical stool samples

Molecular diagnostic tools capable of identifying Shiga toxin-specific genetic determinants in stool specimens permit an unbiased approach to detect Shiga toxin-producing Escherichia coli (STEC) in clinical samples and can indicate when culture-based isolation methods are required. It is increasingly recognized that clinically relevant STEC are not limited to the singular O157 serotypes, and therefore diagnostic assays targeting toxin-encoding determinants must be able to account for any genetic variation that exists between serotypes. In this study conventional PCR and four real-time PCR assays (HybProbe, TaqMan, SYBR Green, and LUX) targeting the stx1 and stx2 Shiga toxin coding sequences were used to identify STEC in enriched stool samples (n = 36) and a panel of O157 and non-O157 strains (n = 64). PCR assays targeting stx1 and stx2 had variable specificity and sensitivity values with enriched stool samples. Molecular assays using DNA from pure cultures revealed that some primers were not sensitive to all stx2 variants. This evaluation concluded that the TaqMan-based probes were most appropriate in high throughput clinical diagnostic laboratories in consideration of cost, turn around time, and assay performance.

Shiga toxin-producing Escherichia coli, New Mexico, USA, 2004-2007

Sporadic infection with Shiga toxin–producing Escherichia coli (STEC) in New Mexico increased from 0.9 cases per 100,000 population (95% confidence interval [CI] 0.5–1.36) in 2004 to 1.7 (95% CI 1.14–2.26) in 2007. Non-O157 STEC was more common in nonwhite residents, children <5 years of age, and urban residents.

Shiga toxin-producing Escherichia coli, New Mexico, USA, 2004-2007

Sporadic infection with Shiga toxin-producing Escherichia coli (STEC) in New Mexico increased from 0.9 cases per 100,000 population (95% confidence interval [CI] 0.5-1.36) in 2004 to 1.7 (95% CI 1.14-2.26) in 2007. Non-O157 STEC was more common in nonwhite residents, children <5 years of age, and urban residents.

Evaluation of host-specific Bacteroidales 16S rRNA gene markers as a complementary tool for detecting fecal pollution in a prairie watershed

Our ability to identify and eliminate fecal contamination of water, now and in the future, is essential to reduce incidences of waterborne disease. Bacterial source tracking is a recently developed approach for identifying sources of fecal pollution. PCR primers designed by Bernhard and Field [Bernhard, A.E., Field, K.G., 2000a. A PCR assay to discriminate human and ruminant feces on the basis of host differences in Bacteroides-Prevotella genes encoding 16S rRNA. Appl. Environ. Microbiol. 66(10), 4571-4574] and Dick et al. [Dick, L.K., Bernhard, A.E., Brodeur, T.J., Santo Domingo, J.W., Simpson, J.M., Walters, S.P., Field, K.G., 2005. Host distributions of uncultivated fecal Bacteroidales bacteria reveal genetic markers for fecal source identification. Appl. Environ. Microbiol. 71(6), 3184-3191] for the detection of human (HF183), pig (PF163) and ruminant (CF128) specific Bacteroidales 16s rRNA genetic markers were tested for their suitability in detecting fecal pollution in Saskatchewan, Canada. The sensitivity and specificity of these primers were assessed by testing eight raw human sewage samples and 265 feces from 12 different species in Saskatchewan. The specificity of each primer set was > or =94%. The accuracy of HF183 and PF163 to distinguish between the different species was 100%, whereas CF128 cross-reacted with 22% of the pig feces. Occurrence of the host-specific Bacteroidales markers and the conventional indicator Escherichia coli in relation to several enteropathogens was investigated in 70 water samples collected from different sites along the Qu'Appelle River (Saskatchewan, Canada). Human and ruminant fecal markers were identified in 41 and 14% of the water samples, respectively, whereas the pig marker was never detected in the river water. The largest concentrations in E. coli counts were concomitant to the simultaneous detection of HF183 and CF128. Thermotolerant Campylobacter spp., Salmonella spp. and Shiga toxin genes (stx1 and stx2)-positive E. coli (STEC) were detected in 6, 7 and 63% of the water samples, respectively. However, none of the stx positive water samples were positive for the E. coli O157:H7 gene marker (uidA). Odds ratios analysis suggests that CF128 may be predictive for the presence of Salmonella spp. in the river investigated. None of the fecal indicators were able to confidently predict the presence of thermotolerant Campylobacter spp. and STEC.

Hemolytic uremic syndrome (HUS)--incidence and etiologies at a regional Children's Hospital in 2001-2006

Hemolytic uremic syndrome (HUS) is a serious health concern in children. HUS has primarily been linked to Escherichia coli O157:H7 infections, but non-O157 strains are gaining attention. Hemolytic anemia, thrombocytopenia, and acute renal failure are the characteristics of the syndrome. This study investigated the incidence of HUS at a regional Children's Hospital between 2001 and 2006 by retrospective review. Cases of HUS were investigated for outcomes based on stool culture and an association of acute pancreatitis. A total of 44 cases were identified, of which 57% were female and 43% were male, with an age distribution of 13 months to 17 years and a median age of 3.44 years. Data revealed 13 cases in 2006 compared to two cases in 2001, with 84% of all illnesses occurring in the summer and fall seasons. The median duration of thrombocytopenia was eight days and 50% of all cases required dialysis. E. coli O157:H7 was the predominant pathogen; however, 53% of the cases had unknown etiology. This data may suggest a growing number of cases from 2001 to 2006 and a role for agents other than E. coli O157:H7. E. coli O157:H7 caused longer intensive care unit (ICU) stay. No association between HUS and acute pancreatitis was found.

Genomic diversity of pathogenic Escherichia coli of the EHEC 2 clonal complex

BACKGROUND

Evolutionary analyses of enterohemorrhagic Escherichia coli (EHEC) have identified two distantly related clonal groups: EHEC 1, including serotype O157:H7 and its inferred ancestor O55:H7; and EHEC 2, comprised of several serogroups (O26, O111, O118, etc.). These two clonal groups differ in their virulence and global distribution. Although several fully annotated genomic sequences exist for strains of serotype O157:H7, much less is known about the genomic composition of EHEC 2. In this study, we analyzed a set of 24 clinical EHEC 2 strains representing serotypes O26:H11, O111:H8/H11, O118:H16, O153:H11 and O15:H11 from humans and animals by comparative genomic hybridization (CGH) on an oligoarray based on the O157:H7 Sakai genome.

RESULTS

Backbone genes, defined as genes shared by Sakai and K-12, were highly conserved in EHEC 2. The proportion of Sakai phage genes in EHEC 2 was substantially greater than that of Sakai-specific bacterial (non-phage) genes. This proportion was inverted in O55:H7, reiterating that a subset of Sakai bacterial genes is specific to EHEC 1. Split decomposition analysis of gene content revealed that O111:H8 was more genetically uniform and distinct from other EHEC 2 strains, with respect to the Sakai O157:H7 gene distribution. Serotype O26:H11 was the most heterogeneous EHEC 2 subpopulation, comprised of strains with the highest as well as the lowest levels of Sakai gene content conservation. Of the 979 parsimoniously informative genes, 15% were found to be compatible and their distribution in EHEC 2 clustered O111:H8 and O118:H16 strains by serotype. CGH data suggested divergence of the LEE island from the LEE1 to the LEE4 operon, and also between animal and human isolates irrespective of serotype. No correlation was found between gene contents and geographic locations of EHEC 2 strains.

CONCLUSION

The gene content variation of phage-related genes in EHEC 2 strains supports the hypothesis that extensive modular shuffling of mobile DNA elements has occurred among EHEC strains. These results suggest that EHEC 2 is a multiform pathogenic clonal complex, characterized by substantial intra-serotype genetic variation. The heterogeneous distribution of mobile elements has impacted the diversification of O26:H11 more than other EHEC 2 serotypes.

Isolation and detection of Shiga toxin-producing Escherichia coli in clinical stool samples using conventional and molecular methods

The isolation of Shiga toxin-producing Escherichia coli (STEC) other than serogroup O157 from clinical stool samples is problematic due to the lack of differential phenotypic characteristics from non-pathogenic E. coli. The development of molecular reagents capable of identifying both toxin and serogroup-specific genetic determinants holds promise for a more comprehensive characterization of stool samples and isolation of STEC strains. In this study, 876 stool samples from paediatric patients with gastroenteritis were screened for STEC using a cytotoxicity assay, commercial immunoassay and a conventional PCR targeting Shiga-toxin determinants. In addition, routine culture methods for isolating O157 STEC were also performed. The screening assays identified 45 stools presumptively containing STEC, and using non-differential culture techniques a total of 20 O157 and 22 non-O157 strains were isolated. These included STEC serotypes O157 : H7, O26 : H11, O121 : H19, O26 : NM, O103 : H2, O111 : NM, O115 : H18, O121 : NM, O145 : NM, O177 : NM and O5 : NM. Notably, multiple STEC serotypes were isolated from two clinical stool samples (yielding O157 : H7 and O26 : H11, or O157 : H7 and O103 : H2 isolates). These data were compared to molecular serogroup profiles determined directly from the stool enrichment cultures using a LUX real-time PCR assay targeting the O157 fimbrial gene lpfA, a microsphere suspension array targeting allelic variants of espZ and a gnd-based molecular O-antigen serogrouping method. The genetic profile of individual stool cultures indicated that the espZ microsphere array and lpfA real-time PCR assay could accurately predict the presence and provide preliminary typing for the STEC strains present in clinical samples. The gnd-based molecular serogrouping method provided additional corroborative evidence of serogroup identities. This toolbox of molecular methods provided robust detection capabilities for STEC in clinical stool samples, including co-infection of multiple serogroups.

Shiga toxin-associated hemolytic uremic syndrome and thrombotic thrombocytopenic purpura: distinct mechanisms of pathogenesis

The hemolytic uremic syndrome (HUS) of childhood is, in its most common form, a non-immune microangiopathic hemolytic anemia. HUS typically follows an enteric infection with a Shiga toxin-producing Escherichia coli, usually belonging to serotype O157:H7. The antecedent infection is almost always manifested as non-bloody diarrhea. In about 80% of cases, the diarrhea becomes bloody between one and five days after the onset of diarrhea. The courses of acute gastrointestinal infections, and of HUS, in adults and children are similar. There are no convincing data that this easily recognizable form of microangiopathy is related to any inborn or acquired deficiency of ADAMTS13, and plasma therapies are not justified on either theoretical or empirical grounds. Similarly, there are no realistic animal data to support use of plasma exchange or infusion in children or adults with, or at risk for, HUS secondary to gastrointestinal infection with E. coli O157:H7. Best clinical practices involve rapid and accurate clinical and microbiological identification of infected patients, volume expansion, and support of the intestinal and extraintestinal complications that can ensue during acute enteric infection and associated HUS. Clinical clues include a sequence of events where the stool becomes bloody after a several-day interval of bloody diarrhea, considerable abdominal pain, five or more stools in the 24 h before presentation, pain on defection, and absence of fever at the time of presentation. Diagnosis should rely primarily on sorbitol MacConkey agar culture. Shiga toxin testing should not be used as the only screen to identify infected patients.