Impact of free verotoxin testing on epidemiology of diarrhea caused by verotoxin-producing Escherichia coli

Enzyme-Linked Phage Receptor Binding Protein Assays (ELPRA) Enable Identification of Bacillus anthracis Colonies

Bacteriophage receptor binding proteins (RBPs) are employed by viruses to recognize specific surface structures on bacterial host cells. Recombinant RBPs have been utilized for detection of several pathogens, typically as fusions with reporter enzymes or fluorescent proteins. Identification of Bacillus anthracis, the etiological agent of anthrax, can be difficult because of the bacterium's close relationship with other species of the Bacillus cereussensu lato group. Here, we facilitated the identification of B. anthracis using two implementations of enzyme-linked phage receptor binding protein assays (ELPRA). We developed a single-tube centrifugation assay simplifying the rapid analysis of suspect colonies. A second assay enables identification of suspect colonies from mixed overgrown solid (agar) media derived from the complex matrix soil. Thus, these tests identified vegetative cells of B. anthracis with little processing time and may support or confirm pathogen detection by molecular methods such as polymerase chain reaction.

Shiga toxin producing Escherichia coli-associated diarrhea and hemolytic uremic syndrome in young children in Romania

Background

Diarrheagenic Escherichia coli (E. coli) is an important cause of diarrheal diseases in both developing countries and industrialized countries. An outbreak of hemolytic uremic syndrome (HUS) in young children from southern Romania was reported in early 2016 and was attributed to Shiga toxin producing E. coli (STEC) O26 infection. The aim of this study was to determine the prevalence, demographic and clinical characteristics of STEC infections in children hospitalized with diarrhea in Brașov in the central region of Romania. We also described the occurrence of HUS among hospitalized children, close in time to the 2016 HUS outbreak in southern Romania.

Methods

A prospective study was conducted between March and December 2016 among 722 children aged 1–30 months hospitalized with acute diarrhea. Stool samples obtained from patients with diarrhea were tested for the presence of Shiga toxin type 1 (STX1) and type 2 (STX2) by an immunochromatographic assay, and other enteropathogens. Demographic and clinical information on cases of HUS diagnosed in the same hospital was obtained from medical records.

Results

Overall 46/722 (6.4%) children (mean age 10.3 months, 32.6% females) hospitalized with diarrhea tested positive for STX1 or STX2; of these 79% were positive for both STX1 and STX2, 16% for STX2 only, and 5% for STX1 only. Bloody diarrhea, vomiting and fever were documented in 32.6%, 52.1% and 50.0%, respectively of patients with STEC infection. Eleven confirmed HUS cases (mean age 20 months, five females) were identified between 2014 and 2016 with prodromal diarrhea reported in 10 of them. Three of the 11 HUS patients required hemodialysis.

Conclusions

STEC prevalence among young children with diarrhea in Romania was high and the risk of HUS is emerging. The establishment of a systematic laboratory-based surveillance program including identification of the circulating STEC strains coupled with epidemiological investigation of HUS patients is warranted to determine the source and mode of transmission of STEC and prevent of STEC-associated diarrhea and HUS.

Occurrence of potentially human-pathogenic Escherichia coli O103 in Norwegian sheep

The investigation of an outbreak of hemorrhagic-uremic syndrome in Norway in 2006 indicated that the outbreak strain Escherichia coli O103:H25 could originate from sheep. A national survey of the Norwegian sheep population was performed, with the aim of identifying and describing a possible reservoir of potentially human-pathogenic E. coli O103, in particular of the H types 2 and 25. The investigation of fecal samples from 585 sheep flocks resulted in 1,222 E. coli O103 isolates that were analyzed for the presence of eae and stx genes, while a subset of 369 isolates was further examined for flagellar antigens (H typing), stx subtypes, bfpA, astA, and molecular typing by pulsed-field gel electrophoresis (PFGE). The total ovine E. coli O103 serogroup was genetically diverse by numbers of H types, virulotypes, and PFGE banding patterns identified, although a tendency of clustering toward serotypes was seen. The flocks positive for potentially human-pathogenic E. coli O103 were geographically widely distributed, and no association could be found with county or geographical region. The survey showed that eae-negative, stx-negative E. coli O103, probably nonpathogenic to humans, is very common in sheep, with 27.5% of flocks positive. Moreover, the study documented a low prevalence (0.7%) of potentially human-pathogenic Shiga toxin-producing E. coli O103:H2, while STEC O103:H25 was not detected. However, 3.1% and 5.8% of the flocks were positive for enteropathogenic E. coli O103 belonging to H types 2 and 25, respectively. These isolates are of concern as potential human pathogens by themselves but more importantly as possible precursors for human-pathogenic STEC.

Molecular characterization reveals three distinct clonal groups among clinical shiga toxin-producing Escherichia coli strains of serogroup O103

Shiga toxin-producing Escherichia coli (STEC) is one of the most important groups of food-borne pathogens, and STEC strains belonging to the serotype O103:H2 can cause diarrhea, hemorrhagic colitis, and hemolytic-uremic syndrome in humans. STEC O103:non-H2 strains are also sometimes isolated from human patients, but their genetic characteristics and role in significant human enteric disease are not yet understood. Here, we investigated 17 STEC O103:non-H2 strains, including O103:H11, O103:H25, O103:HUT (UT [untypeable]), and O103:H- (nonmotile) isolated in Japan, and their characteristics were compared to those of STEC O103:H2 and other serotype STEC strains. Sequence analyses of fliC and eae genes revealed that strains possessed any of the following combinations: fliC-H2/eae-epsilon, fliC-H11/eae-beta1, and fliC-H25/eae-theta, where fliC-H2, -H11, and -H25 indicate fliC genes encoding H2, H11, and H25 flagella antigens, respectively, and eae-epsilon, -beta1, and -theta indicate eae genes encoding epsilon, beta1, and theta subclass intimins, respectively. Phylogenetic analysis based on the sequences of seven housekeeping genes demonstrated that the O103:H11/[fliC-H11] and O103:H25/[fliC-H25] strains formed two distinct groups, different from that of the O103:H2/[fliC-H2] strains. Interestingly, a group consisting of O103:H11 strains was closely related to STEC O26:H11, which is recognized as a most important non-O157 serotype, suggesting that the STEC O103:H11 and STEC O26:H11 clones evolved from a common ancestor. The multiplex PCR system for the rapid typing of STEC O103 strains described in the present study may aid clinical and epidemiological studies of the STEC O103:H2, O103:H11, and O103:H25 groups. In addition, our data provide further insights into the high variability of STEC stains with emerging new serotypes.

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.

Conserved Stx2 phages from Escherichia coli O103:H25 isolated from patients suffering from hemolytic uremic syndrome

BACKGROUND

One of the main virulence factors produced by Shiga toxin-producing Escherichia coli is the Shiga toxin (Stx), which is encoded on lambdoid phages (Stx phage). In Norway, an outbreak of hemorrhagic colitis and hemolytic uremic syndrome (HUS) caused by E. coli O103:H25 was reported during the winter of 2006, but stx(2)-positive isolates were only retrieved from two human samples.

METHODS

Isolates of E. coli O103:H25 from patients with HUS in Norway, including sporadic cases and the outbreak cases, were investigated for the presence of phages encoding stx(2). The induced Stx phages were characterized morphologically and genetically, and the host susceptibility for these phages of various E. coli O103 isolates, including O103:H25 stx(2) negative isolates from the outbreak, was tested by a plaque assay.

RESULTS

The Stx2 phages in this study are very closely related in terms of morphology, sequence identity, and host infectivity. There may be a conserved phage within the E. coli O103:H25 population.

CONCLUSIONS

It is proposed that the Stx2 phage, present in the environment either as free phage particles or within a limited pool of Stx-producing E. coli O103 strains, have infected or integrated in the stx(2)-negative E. coli O103:H25 isolates from the Norwegian outbreak.

Presence of non-O157 Shiga toxin-producing Escherichia coli in feces from feedlot cattle in Alberta and absence on corresponding beef carcasses

The study objectives were to determine the prevalence and serotypes of non-O157 Shiga toxin-producing Escherichia coli (STEC) in pens of feedlot cattle and on corresponding beef carcasses. We collected 25 fecal samples from 84 pens in 21 Alberta feedlots and 40 carcass swabs from each preslaughter pen for analysis by culture and polymerase chain reaction (PCR). Non-O157 STEC were recovered from feces from 12 (14%) of the 84 pens and 12 (57%) of the 21 feedlots by examination of 1 E. coli isolate positive for 4-methylumbelliferyl-beta-beta-glucuronide per sample. Twelve non-O157 serotypes were detected, but 7 of the 15 STEC isolates lacked the accessory virulence genes eae and hlyA. Although 115 (7%) of the carcass broths were PCR-positive, no STEC isolates were recovered from the 1650 carcasses sampled. Our data indicate that multiple non-O157 STEC serotypes may be present in cattle feces, yet are unlikely to be recovered from the corresponding beef carcasses when 20 colonies per sample from PCR-positive broth cultures are analyzed.

The emerging clinical importance of non-O157 Shiga toxin-producing Escherichia coli

In 1982, hemorrhagic colitis and hemolytic-uremic syndrome were linked to infection with Escherichia coli O157:H7, a serotype now classified as Shiga toxin-producing E. coli (STEC). Thereafter, hemorrhagic colitis and hemolytic-uremic syndrome associated with non-O157 STEC serogroups were reported, with the frequency of non-O157 STEC illness rivaling that of O157:H7 in certain geographic regions. In the United States, non-O157 E. coli may account for up to 20%-50% of all STEC infections. A high index of suspicion, paired with options to test for non-O157 STEC infection, are necessary for early recognition and appropriate treatment of these infections. Supportive care without the use of antibiotics is currently considered to be optimal treatment for all STEC infections. This commentary provides a perspective on the non-O157 STEC as human pathogens, how and when the clinician should approach the diagnosis of these organisms, and the challenges ahead.

Community-wide outbreaks of clonally related CTX-M-14 beta-lactamase-producing Escherichia coli strains in the Calgary health region

Enterobacteriaceae producing extended-spectrum beta-lactamases (ESBLs) typically cause nosocomial infections. Previous surveillance in the Calgary Health Region showed that Escherichia coli strains producing ESBLs were common among community patients. During the period (2000 to 2002): 23 of 157 (15%) of the strains were positive for blaCTX-M genes from the CTX-M-I group (CTX-M-1-like) and 87 of 157 (55%) of the strains were positive for blaCTX-M genes from the CTX-M-III group (CTX-M-14-like). The objective of this study was to investigate the molecular epidemiology of these strains. The beta-lactamases were characterized, and the genetic relatedness of the isolates was analyzed by digesting genomic DNA with the restriction endonuclease XbaI and by performing pulse-field gel electrophoresis (PFGE). PFGE revealed two closely related restriction patterns (clusters CTXM14A and CTXM14AR) among 67 (77%) CTX-M-14 producers. These strains from CTXM14A had nearly identical susceptibility patterns and were isolated most often from urine samples obtained at community sites during 2000 and 2001. Strains from the CTX-M-1-like and CTX-M-negative groups were unrelated to clusters CTXM14, CTXM14AR, and CTXM14NR. We conclude that clonally related strains of E. coli producing CTX-M-14 beta-lactamases were responsible for a predominantly community-wide outbreak. Further studies are warranted to investigate whether community-onset diseases caused by ESBL-producing E. coli are related to a point source or transmission within the community.

Evaluation of performance and potential clinical impact of ProSpecT Shiga toxin Escherichia coli microplate assay for detection of Shiga Toxin-producing E. coli in stool samples

Shiga toxin-producing Escherichia coli bacteria (STEC) are emerging pathogens capable of producing sporadic and epidemic diarrhea, hemorrhagic colitis, and potentially life-threatening hemolytic-uremic syndrome. Although the presence of E. coli O157 can be readily detected in stool by sorbitol-MacConkey agar culture (SMAC), STEC non-O157 serotypes cannot. In contrast to culture, testing for the presence of Shiga toxins 1 and 2 in stool detects both O157 and non-O157 STEC serotypes capable of causing disease. Over two consecutive summers, we evaluated the performance of the ProSpecT Shiga toxin E. coli Microplate assay (Alexon-Trend, Ramsey, Minn.), an enzyme immunoassay for the detection of Shiga toxins 1 and 2, on all stools submitted for culture of enteric pathogens, and the potential clinical impact of Shiga toxin detection. Twenty-nine stool specimens were STEC positive by ProSpecT assay. Twenty-seven of 29 STEC-positive isolates were confirmed by SMAC and serotyping or by a second enzyme immunoassay and PCR (positive predictive value, 93%). Thirteen of 27 confirmed Shiga toxin-producing strains were serotype O157. The remaining 14 strains represented 8 other serotypes. The ProSpecT assay was 100% sensitive and specific for detection of E. coli O157 in stool (7 of 7) compared to SMAC. In addition, the ProSpecT assay detected twice as many STEC as SMAC. Fifty-two percent of confirmed STEC-positive stools were nonbloody. Thus, in our population, screening strategies that test only visibly bloody stools for STEC would miss a majority of cases. Eleven (41%) STEC-positive patients were hospitalized, and eight (30%) developed severe disease (two developed hemolytic-uremic syndrome, and six developed hemorrhagic colitis). Prior to detection of STEC infection, seven (26%) and eight patients (30%) underwent unnecessary diagnostic procedures or received potentially deleterious empirical treatment, respectively. We propose that establishing a specific diagnosis of STEC may have prevented these potentially harmful interventions. We conclude that the ProSpecT assay is sensitive and specific for the detection of Shiga toxins 1 and 2 in stool and has potentially significant clinical impact for the individual patient and public health. Shiga toxin assays should be considered for routine use in settings where prevalence of STEC disease warrants testing.

Shiga toxin-producing Escherichia coli in the feces of Alberta feedlot cattle

Shiga toxin-producing Escherichia coli (STEC) are a public health concern. Bacterial culture techniques commonly used to detect E. coli O157:H7 will not detect other STEC serotypes. Feces from cattle and other animals are a source of O157:H7 and other pathogenic serotypes of STEC. The objective of this study was to estimate the pen-level prevalence of Shiga toxins and selected STEC serotypes in pre-slaughter feedlot cattle. Composite fecal samples were cultured and a polymerase chain reaction (PCR) was used to detect genes for Shiga toxins (stx1 and stx2) and genes for O157:H7, O111:H8, and O26:H11 serotypes. Evidence of Shiga toxins was found in 23 pens (92%), O157:H7 in 2 (8%), O111:H8 in 5 (20%), and O26:H11 in 20 (80%) of the 25 pens investigated. Although pen-level prevalence estimates for Shiga toxins and non-O157 serotypes seem high relative to O157:H7, further effort is required to determine the human health significance of non-O157 serotypes of STEC in feedlot cattle.

Outbreak of Shiga Toxin–ProducingEscherichia coliO111:H8 Infections among Attendees of a High School Cheerleading Camp

Few US clinical laboratories screen stool specimens for Shiga toxin-producing Escherichia coli (STEC) other than E. coli O157. An outbreak of STEC O111:H8 infections indistinguishable from E. coli O157:H7 at a youth camp highlights the need to improve non-O157 STEC surveillance. Interviews of 521 (80%) of 650 attendees revealed 55 (11%) were ill; 2 developed hemolytic-uremic syndrome. Illness was associated with consuming salad during the camp's first lunch meal (hazard ratio [HR], 4.68; P<.01), consuming ice provided in barrels on the camp's final day (HR, 3.41; P<.01), eating cob corn (HR, 3.22; P<.01), and eating a dinner roll (HR, 2.82; P<.01). Cultures of 2 of 11 stools yielded E. coli O111:H8. Results of serologic testing and additional stool cultures demonstrated no evidence of infection with other bacterial pathogens, including E. coli O157, and supported infection with E. coli O111. Clinical laboratories should routinely screen suspect specimens for non-O157 STEC and should serotype and report Shiga-positive isolates.

Serotypes, virulence genes, and intimin types of Shiga toxin (verotoxin)-producing Escherichia coli isolates from human patients: prevalence in Lugo, Spain, from 1992 through 1999

We have analyzed the prevalence of Shiga toxin-producing Escherichia coli (STEC) in stool specimens of patients with diarrhea or other gastrointestinal alterations from the Xeral-Calde Hospital of Lugo City (Spain). STEC strains were detected in 126 (2.5%) of 5,054 cases investigated, with a progressive increase in the incidence from 0% in 1992 to 4.4% in 1999. STEC O157:H7 was isolated in 24 cases (0.5%), whereas non-O157 STEC strains were isolated from 87 patients (1.7%). STEC strains were (after Salmonella and Campylobacter strains) the third most frequently recovered enteropathogenic bacteria. A total of 126 human STEC isolates were characterized in this study. PCR showed that 43 (34%) isolates carried stx(1) genes, 45 (36%) possessed stx(2) genes and 38 (30%) carried both stx(1) and stx(2). A total of 88 (70%) isolates carried an ehxA enterohemolysin gene, and 70 (56%) isolates possessed an eae intimin gene (27 isolates with type gamma1, 20 with type beta1, 8 with type zeta, 5 with type gamma2, and 3 with type epsilon). STEC isolates belonged to 41 O serogroups and 66 O:H serotypes, including 21 serotypes associated with hemolytic uremic syndrome and 30 new serotypes not previously reported among human STEC strains in other studies. Although the 126 STEC isolates belonged to 81 different seropathotypes (associations between serotypes and virulence genes), only four accounted for 31% of isolates. Seropathotype O157:H7 stx(1) stx(2) eae-gamma1 ehxA was the most common (13 isolates) followed by O157:H7 stx(2) eae-gamma1 ehxA (11 isolates), O26:H11 stx(1) eae-beta1 ehxA (11 isolates), and O111:H- stx(1) stx(2) eae-gamma2 ehxA (4 isolates). Our results suggest that STEC strains are a significant cause of human infections in Spain and confirm that in continental Europe, infections caused by STEC non-O157 strains are more common than those caused by O157:H7 isolates. The high prevalence of STEC strains (both O157:H7 and non-O157 strains) in human patients, and their association with serious complications, strongly supports the utilization of protocols for detection of all serotypes of STEC in Spanish clinical microbiology laboratories.

An epidemiological study on Verotoxin-producing Escherichia coli (VTEC) infection among population of northern region of Iran (Mazandaran and Golestan provinces)

Faecal samples from 3268 randomly selected inhabitants of two provinces in the northern region of Iran were screened to detect Verotoxin-producing Escherichia coli (VTEC) using colony sweep polymyxin-B extraction method. Non-sorbitol fermentation phenotype and slide agglutination with O157 and H7 antisera used to detect this serotype. We found that 0.7% of the population were infected with VTEC, however none of the isolates belonged to O157:H7 serotype. We also found that children < 6 years of age were at highest risk of infection with VTEC (p < 0.05). Moreover, a significant association was found between the VTEC and diarrhoeal cases at the same age group (p < 0.001). Overall distribution of the VTEC isolates in the general population was found to be random, though a kind of clustered distribution could be noticed.

Evaluation of the duopath verotoxin test for detection of shiga toxins in cultures of human stools

The Duopath Verotoxin test (Merck KgaA, Darmstadt, Germany) is a newly developed immunochromatographic test for the confirmation of Shiga toxin (Stx)-producing Escherichia coli (STEC) strains from food products. This test detects both Stx 1 (Stx1)-positive and Stx2-positive samples individually with the same device. By modification of the original protocol, the present study evaluated its performance and feasibility for clinical application with human stool samples, consisting of 41 frozen samples known to contain STEC isolates (O157:H7 and non-O157 serotypes) and 250 fresh specimens. The test specimens were polymyxin B extracts of colony sweeps taken from overnight sorbitol-MacConkey agar cultures of stools containing STEC isolates and other bacteria. All 41 frozen STEC-positive stool samples were positive by the Duopath Verotoxin test, as were 2 fresh stool samples with culture-confirmed STEC O157 infection. Thus, 100% sensitivity and no false-positive results were obtained when the Premier EHEC assay (Meridian Bioscience, Cincinnati, Ohio) was used as the "gold standard." The Duopath Verotoxin test is simple to perform and easy to interpret, providing a turnaround time of 24 h. Despite its original intended use, the Duopath Verotoxin test has a great potential for clinical application.

Verotoxin 1 binding to intestinal crypt epithelial cells results in localization to lysosomes and abrogation of toxicity

Verotoxins (VTs) are important virulence factors of enterohaemorrhagic Escherichia coli (EHEC), a group of bacteria associated with severe disease sequelae in humans. The potent cytotoxic activity of VTs is important in pathogenicity, resulting in the death of cells expressing receptor Gb3 (globotriaosylceramide). EHEC, particularly serotype O157:H7, frequently colonize reservoir hosts (such as cattle) in the absence of disease, however, the basis to avirulence in this host has been unclear. The objective of this study was assessment of interaction between VT and intestinal epithelium, which represents the major interface between the host and enteric organisms. Bovine intestinal epithelial cells expressed Gb3 in vitro in primary cell cultures, localizing specifically to proliferating crypt cells in corroboration with in situ immunohistological observations on intestinal mucosa. Expression of receptor by these cells contrasts with the absence of Gb3 on human intestinal epithelium in vivo. Despite receptor expression, VT exhibited no cytotoxic activity against bovine epithelial cells. Sub-cellular localization of VT indicated that this toxin was excluded from endoplasmic reticulum but localized to lysosomes, corresponding with abrogation of cytotoxicity. VT intracellular trafficking was unaffected by treatment of primary cell cultures with methyl-beta-cyclodextrin, indicating that Gb3 in these cells is not associated with lipid rafts but is randomly distributed in the membrane. The combination of Gb3 isoform, membrane distribution and VT trafficking correlate with observations of other receptor-positive cells that resist verocytotoxicity. These studies demonstrate that intestinal epithelium is an important determinant in VT interaction with major implications for the differential consequences of EHEC infection in reservoir hosts and humans.

Consequences of EHEC colonisation in humans and cattle

While many factors have been associated with human EHEC infection, the full role these play in both human and ruminant hosts are not yet clear despite much investigation. It is hoped that the continued intense international research effort into EHEC will provide further insights into the commensal versus pathogenic lifestyles of E. coli and lead to approaches to reduce EHEC carriage in ruminants as well as prevent or treat human disease.

Shiga toxin-producing Escherichia coli in children with diarrhea: a prospective point-of-care study

OBJECTIVE

To conduct a prospective cohort study to determine the frequency and characteristics of Shiga toxin (Stx)-producing Escherichia coli (STEC) infections in children with diarrhea attending an emergency department and a private clinic in Seattle, Washington.

METHODS

Between November 1998 and October 2001, 1851 stools were processed for STEC by sorbitol-MacConkey (SMAC) agar screening and a commercial Stx enzyme immunoassay (EIA).

RESULTS

STEC belonging to serotypes O157:H7 (n = 28), O103:H2 (n = 4), O118:H16 (n = 2), O26:H11, O111:nonmotile, O111:H8, O121:H19, and O rough:H11 (n = 1 each) were recovered from 39 (2.1%) stools. EIA and SMAC agar detected 89% and 100% of the patients with E coli O157:H7, respectively. E coli O157:H7-infected patients had significantly higher frequencies of bloody stools, fecal leukocytes, and abdominal tenderness and shorter symptom duration. Hemolytic uremic syndrome developed in 5 (18%) and none of the children infected with E coli O157:H7 and non-O157:H7 STEC, respectively (P =.30).

CONCLUSIONS

E coli O157:H7 is the predominant STEC in this population. Children infected with E coli O157:H7 have clinical presentations different from those whose stools contain non-O157:H7 STEC. Culture and Stx detection are needed to optimally detect STEC of all serotypes in stools. SMAC agar screening should not be replaced by EIA.

Phenotypic and genotypic characterization of Escherichia coli verotoxin-producing isolates from humans and pigs

The aim of this study was to characterize verotoxin-producing Escherichia coli (VTEC) isolates obtained from humans and pigs in the same geographic areas and during the same period of time in order to determine whether porcine VTEC isolates could be related to human cases of diarrhea and also to detect the presence of virulence factors in these isolates. From 1,352 human and 620 porcine fecal samples, 11 human and 18 porcine verotoxin-positive isolates were obtained by the VT immunoblot or the individual colony testing technique. In addition, 52 porcine VTEC strains isolated from diseased pigs at the Faculté de médecine vétérinaire during the same period or from fecal samples collected previously isolated at slaughterhouses were characterized in this study. Antimicrobial resistance profiles were different between human and porcine isolates. In general, the serotypes observed in the two groups were different. No porcine isolate was of serotype O157:H7; however, one isolate was O91:NM, a serotype that has been associated with hemorrhagic colitis in humans. Also, one serotype (O8:H19) was found in isolates from both species; however, the O8:H19 isolates of the two groups were of different pathotypes. The pathotypes observed in the human and porcine isolates were different, with the exception of VT2vx-positive isolates; the serotypes of these isolates from the two groups were nevertheless different. Pulsed-field gel electrophoresis analysis indicated no relatedness between the human and porcine isolates. In conclusion, these results suggest that the porcine and human isolates of the present study were not genetically related. Most porcine VTEC isolates did not possess known virulence factors required to infect humans. However, certain non-O157:H7 porcine VTECs may potentially infect humans.

Shiga toxin-producing Escherichia coli in beef heifers grazing an irrigated pasture

Shiga toxin-producing Escherichia coli (STEC) produce toxins that have been associated with several human illnesses. E. coli O157:H7 is the most well-studied STEC and was first associated with consumption of improperly cooked ground beef in 1982. E. coli O157:H7 is not the only foodborne STEC because other STEC serotypes are also associated with human illnesses. The objective of this study was to assess prevalence of STEC in 23 yearling beef (Angus) heifers grazing an irrigated grass pasture in spring (April), summer (July), fall (October), and winter (December) of 1999. A total of 86 fecal samples were rectally collected and were subjected to microbiological testing for the presence of STEC. Nine E. coli isolates from five heifers (one in spring and fall and three in winter) were toxic to Vero cells. Of these isolates, four were E. coli O157:H7, two belonged to the serogroup O6, one O39:NM, one O113:H-, and the final isolate was untypable. The STEC prevalence rate in our herd ranged from 4% (spring) to 15% (winter). Based on detecting both O157:H7 and non-O157:H7 STEC in our heifers, it is clear that screening fecal samples should not be limited to E. coli O157:H7. Identification of STEC-positive cattle prior to slaughter should help in reducing the risk of beef contamination with such foodborne pathogens if pre- and/or postharvest control measures are applied to such animals.

Edema disease as a model for systemic disease induced by Shiga toxin-producing E. coli

Edema disease (ED) is a naturally occurring disease of weaned pigs caused by host adapted strains of E. coli that produce Shiga toxin (STEC). We determined the temporal and quantitative relationships between intestinal colonization by STEC, levels of Shiga toxin (Stx2e) in the gut, in the blood, and clinical manifestations of ED. Bacterial colonization (10(8) CFU/cm ileum) was highest 4 days post inoculation (pi) in animals that did not develop clinical disease and 6 days pi in animals with clinical signs of ED. The mean time for the development of clinical signs of ED was 6 days pi (range 4-10). Average peak titers of Stx2e in the ileum were 1:16,384 in asymptomatic animals and 1:32,768 in clinical animals. Titers of Stx2e in the feces reflected the toxin titers in the ileum but were lower. Intestinal titers of Stx2e and the density of bacterial colonization were predictive of clinical ED for a group of animals but not for individuals. Approximately 50% of the pigs that had Stx2e titers of > or = 1:4096 and a bacterial density of > or = 10(6) CFU/cm in their ileum, had clinical ED. Pigs that had intestinal Stx2e titers < 1:4096 were asymptomatic. Stx2e was detected in the red cell fraction of blood from some of the pigs with clinical ED and in some that were asymptomatic. Stx2e was not detected in the serum of any animals. ED may be a useful model for predicting the temporal and quantitative relationships between bacterial colonization, Stx levels in the gut and blood and systemic disease for STEC in other species.

Pathogenesis and diagnosis of Shiga toxin-producing Escherichia coli infections

Since their initial recognition 20 years ago, Shiga toxin-producing Escherichia coli (STEC) strains have emerged as an important cause of serious human gastrointestinal disease, which may result in life-threatening complications such as hemolytic-uremic syndrome. Food-borne outbreaks of STEC disease appear to be increasing and, when mass-produced and mass-distributed foods are concerned, can involve large numbers of people. Development of therapeutic and preventative strategies to combat STEC disease requires a thorough understanding of the mechanisms by which STEC organisms colonize the human intestinal tract and cause local and systemic pathological changes. While our knowledge remains incomplete, recent studies have improved our understanding of these processes, particularly the complex interaction between Shiga toxins and host cells, which is central to the pathogenesis of STEC disease. In addition, several putative accessory virulence factors have been identified and partly characterized. The capacity to limit the scale and severity of STEC disease is also dependent upon rapid and sensitive diagnostic procedures for analysis of human samples and suspect vehicles. The increased application of advanced molecular technologies in clinical laboratories has significantly improved our capacity to diagnose STEC infection early in the course of disease and to detect low levels of environmental contamination. This, in turn, has created a potential window of opportunity for future therapeutic intervention.

Evaluation of the premier EHEC assay for detection of Shiga toxin-producing Escherichia coli

An enzyme-linked immunosorbent assay for the detection of Shiga toxins (Premier EHEC assay; Meridian Diagnostics, Inc.) was compared to conventional sorbitol-MacConkey culture for the recovery of enterohemorrhagic Escherichia coli. A total of 74 enteric pathogens, including 8 E. coli O157:H7 isolates, were recovered from 974 stool specimens. Two of these specimens were not tested by Premier assaying due to insufficient sample and are not considered in the data analysis. The Premier EHEC assay detected the 6 evaluable specimens which were culture positive for E. coli O157:H7 and identified an additional 10 specimens as containing Shiga toxin. Seven isolates were recovered from these 10 specimens by an immunoblot assay and were confirmed as toxin producers by a cytotoxin assay. Of these seven, four isolates were serotype O157:H7, one was O26:NM, one was O6:H-, and one was O untypeable:H untypeable. Three specimens contained Shiga toxin by both EHEC immunoassaying and cytotoxin testing; however, no cytotoxin-producing E. coli could be recovered. The sorbitol-MacConkey method had a sensitivity and a specificity of 60 and 100%, respectively, while the Premier EHEC assay had a sensitivity and a specificity of 100 and 99.7%, respectively, for E. coli O157:H7 only. The Premier EHEC assay also detected an additional 20% Shiga toxin-producing E. coli (STEC) that were non-O157:H7. Thus, the Premier EHEC assay is a sensitive and specific method for the detection of all STEC isolates. Routine use would improve the detection of E. coli O157:H7 and allow for determination of the true incidence of STEC other than O157:H7. The presence of blood in the stool and/or the ages of the patients were poor predictors of the presence of STEC. Criteria need to be determined which would allow for the cost-effective incorporation of this assay into the routine screen for enteric pathogens in high-risk individuals, especially children.

Isolation of Shiga-like toxin producing Escherichia coli (O157 and non-O157) in a community hospital

During a 25-week period (June to November 1995), stool specimens with an abnormal appearance (semiliquid to liquid, containing gross mucus or blood) were selected for testing with a new EIA method for detection of Shiga-like toxin-producing Escherichia coli (O157:H7 and non-O157 serotypes). The 270 specimens tested originated from different patients. Eleven of the 270 were positive by EIA for Shiga-like toxin (SLT). Escherichia coli O157:H7 was recovered from six of the EIA-positive specimens, and the remaining five positive samples produced non-O157 isolates.

Rapid Immunoassay for detection of Escherichia coli O157 directly from stool specimens

A new and rapid ( < 1 h) enzyme-linked immunosorbent assay (ELISA) was compared with conventional sorbitol-MacConkey agar (SMAC) culture for the detection of Escherichia coli O157 from stool specimens. Among 34 positive specimens, confirmed by colony-sweeping and immunofluorescence stain methods, 6 did not exhibit visible sorbitol-negative colonies on SMAC. These six specimens would have been considered to be negative if SMAC alone had been used. The ELISA detected 31 of the 34 positive samples, including 5 of the above-mentioned 6 false-negative samples, resulting in a sensitivity and specificity of 91.2 and 99.5%, respectively. Cross-reactivity with other enteric pathogens was not noted by ELISA. The SMAC method had a sensitivity and specificity of 82.4 and 100%, respectively. The ELISA-negative specimens do not require culture confirmation, whereas positive results must be considered to be presumptive until confirmed by culture. The test is accurate and is easy to perform, making it a very efficient method for screening stool specimens for E. coli O157.