Serodiagnosis of infection with verocytotoxin-producing Escherichia coli

Human sera (167) were screened for antibodies to lipopolysaccharide (LPS) prepared from strains of Verocytotoxin-producing Escherichia coli (VTEC) belonging to a range of serogroups, secreted proteins expressed by attaching and effacing VTEC, enterohaemolysin and H = 7 flagellar proteins. Twelve sera (about 7%) contained antibodies to the LPS of E. coli 05 (one), 026 (two), 0115 (two), 0145 (one), 0163 (one) and 0165 (five). Sera containing antibodies to the LPS of E. coli O26 and O145 also contained antibodies to secreted proteins of 100 and 40 kDa. An additional 34 sera, known to contain antibodies to the lipopolysaccharide of E. coli O157, were examined for antibodies to enterohaemolysin, H = 7 flagellar antigens and bacterial cell surface-associated proteins of 5, 6 and 22 kDa. Three sera contained antibodies to enterohaemolysin and one serum contained antibodies to flagellar proteins. Antibodies to membrane-associated proteins were not detected. It was concluded that enterohaemolysin, H = 7 flagellar proteins and the cell surface-associated proteins were unsuitable for use in immunoassays for providing evidence of infection with VTEC.

Parenteral immunization with a glycoconjugate vaccine containing the O157 antigen of Escherichia coli O157:H7 elicits a systemic humoral immune response in mice, but fails to prevent colonization by the pathogen

The results of the present study show that whereas both BALB/c and C57BL/6 mice parenterally inoculated with a horse serum albumin-Escherichia coli O157 antigen conjugate vaccine develop systemic, specific antibodies to the carrier protein, only the former mice routinely develop antibodies to the carbohydrate O157 moiety. However, little convincing evidence was found to show that these antibodies transuded into the intestinal tract either naturally or in response to an oral inoculum of the pathogen. Moreover, this vaccination procedure failed to protect mice against intestinal colonization following oral challenge with the pathogen. Thus, the results of this study suggest that parenteral vaccination might be an unsuitable strategy for combatting E. coli O157:H7 organisms located in the gut.

Adsorption of endogenous polyphenols relieves the inhibition by fruit juices and fresh produce of immuno-PCR detection of Escherichia coli O157:H7

The immuno-polymerase chain reaction (PCR) approaches facilitate rapid (8 h) detection of Escherichia coli O157:H7 in contaminated dairy products and ground beef samples with detection sensitivities approaching 1 colony forming unit (cfu) g-1 ml-1. However, no PCR products were obtained when the method was applied to identify E. coli O157:H7 in tainted apple juice. Enzyme-linked immuno-assay (ELISA) results suggested non-specific binding of endogenous polyphenols (ubiquitous in plant products) to antibodies present on the surface of the immunobeads, making the latter unavailable for capturing the target bacteria Treatment of the test sample, prior to IMS, with a synthetic fining agent, polyvinylpyrrolidone, restored the full function and sensitivity of the immuno-PCR. The study demonstrates the suitability of the improved method as a generic strategy for rapid screening of fruit juices and plant produce for E. coli O157:H7.

Detection of Escherichia coli O157:H7 from Musca domestica (Diptera: Muscidae) at a cattle farm in Japan

Enterohemorrhagic Escherichia coli (EHEC) O157:H7 was isolated for the first time from Musca domestica L. A total of 310 fly samples was collected from 4 different farms in Obihiro-City, Hokkaido, in the summer and autumn of 1997;5 samples carried E. coli serotype O157:H7. Using ELISA and Vero cell cytotoxicity assay, 3 isolates from 1 cattle farm produced both active Shiga-toxin type 1 (Stx1) and 2 (Stx2). These isolates also carried hemolysin and eaeA genes and harbored the 90-kb virulence plasmid of EHEC O157:H7. Based on plasmid profiles, antibiotic patterns, polymerase chain reaction (PCR)-based DNA finger printing analysis using random amplified polymorphic DNA, pulsed field gel electrophoresis analysis, and DNA sequences of stx1 and stx2, all 3 isolates from fly samples were identical. These results indicate that the house fly is capable of carrying the toxigenic EHEC O157:H7 involved in human disease.

Analysis of enterohemorrhagic Escherichia coli serotype O157:H7 by flow cytometry using monoclonal antibodies

To develop a rapid and specific method to detect and/or identify enterohemorrhagic Escherichia coli O157:H7, two mouse monoclonal antibodies (MAbs) were prepared. Specificities of these two MAbs (1D9 and 3E8) were determined by flow cytometry method (FCM). MAbs 3E8 and 1D9 were found to react with E. coli O157:H7, Citrobacter freundii and Salmonella group N (O:30), but not with Escherichia hermannii. With a mixture containing strains of E. coli O157:H7 and E. coli O6:H1, two different peaks appeared in FCM with MAbs, whereas a single peak appeared with polyclonal rabbit antiserum. From these findings, FCM with MAb is suggested to be a rapid, specific, and useful method to detect and identify strain(s) of E. coli O157:H7 in food ingredients.

Translocated intimin receptors (Tir) of Shiga-toxigenic Escherichia coli isolates belonging to serogroups O26, O111, and O157 react with sera from patients with hemolytic-uremic syndrome and exhibit marked sequence heterogeneity

The capacity to form attaching and effacing (A/E) lesions on the surfaces of enterocytes is an important virulence trait of several enteric pathogens, including enteropathogenic Escherichia coli (EPEC) and Shiga-toxigenic E. coli (STEC). Formation of such lesions depends upon an interaction between a bacterial outer membrane protein (intimin) and a bacterially encoded receptor protein (Tir) which is exported from the bacterium and translocated into the host cell membrane. Intimin, Tir, and several other proteins necessary for generation of A/E lesions are encoded on a chromosomal pathogenicity island termed the locus for enterocyte effacement (LEE). Reports of sequence heterogeneity and antigenic variation in the region of intimin believed to be responsible for receptor binding raise the possibility that the receptor itself is also heterogeneous. We have examined this by cloning and sequencing tir genes from three different STEC strains belonging to serogroups O26, O111, and O157. The deduced amino acid sequences for the Tir homologues from these strains varied markedly, exhibiting only 65.4, 80.2, and 56.7% identity, respectively, to that recently reported for EPEC Tir. STEC Tir is also highly immunogenic in humans. Western blots of E. coli DH5alpha expressing the various STEC tir genes cloned in pBluescript [but not E. coli DH5alpha(pBluescript)] reacted strongly with convalescent sera from patients with hemolytic-uremic syndrome (HUS) caused by known LEE-positive STEC. Moreover, no reaction was seen when the various clone lysates were probed with serum from a patient with HUS caused by a LEE-negative STEC or with serum from a healthy individual. Covariation of exposed epitopes on both intimin and Tir may be a means whereby STEC avoid host immune responses without compromising adhesin-receptor interaction.

Sequencing of Escherichia coli O111 O-antigen gene cluster and identification of O111-specific genes

Shiga toxin (Stx)-producing Escherichia coli strains of serogroup O111 are the most frequently isolated non-O157 strains causing outbreaks of gastroenteritis with hemolytic-uremic syndrome. The O111 O-antigen gene cluster had been cloned and about half of it has been sequenced; we have now sequenced the remainder of the gene cluster, which is 12.5 kb in length and which comprises 11 genes. On the basis of sequence similarity, we have identified all the O-antigen genes expected, including five sugar biosynthetic pathway genes, three transferase genes, the O-unit flippase gene, and the O-antigen polymerase gene. By PCR testing with E. coli strains representing all 166 O-antigen forms, some randomly selected gram-negative bacteria, and Salmonella enterica serovar Adelaide, we showed that four O-antigen genes are highly specific to O111. This work provides the basis for a sensitive test for the rapid detection of E. coli O111. This is important both for decisions related to patient care, because early treatment may reduce the risk of life-threatening complications, and for the detection of sources of contamination.

[Evaluation of immunochromatography-based rapid detection kit for fecal Escherichia coli O157]

"Quix" is an immunochromatography-based direct detection kit for the E. coli O157 LPS antigen in the patient's stool. The present study was conducted to evaluate the efficacy of the kit for rapid diagnosis of enterohemorrhagic Escherichia coli (EHEC) O157 infection. Sensitivity of the kit was determined using a pure culture of a clinical isolate of E. coli O157. Analytical sensitivity was found to be 5 x 10(5) CFU/ml. When compared with the culture method using fecal samples of 64 patients and with bloody diarrhea, sensitivity and specificity were 95.0% (19/20) and 86.4% (38/44), respectively, and overall agreement to culture method was 89.1% (57/64). One patient was found positive by culture method while negative in the present method, where the sample contained a low number of the cells less than the detection limit. Four of the six patients with a negative result by culture method and positive in the present method, were confirmed E. coli O157 infection by positive IgM antibody response against the E. coli O157 LPS. The discrepancy between the two methods seemed to be attributable to antibiotic administration. In one patient, Salmonella urbana (O30(1)30(2)) was detected. The O30(1) antigen of this bacterium is well known to be identical to the E. coli O157 antigen. When the present method was compared with an ELISA-based E. coli O157 LPS antigen detection kit, sensitivity and specificity were 100% (11/11) and 82.1% (23/28), and overall agreement to ELISA method was 87.2% (34/39). From these findings, Quix is useful as a rapid diagnostic kit in the primary clinics, outpatient or bedside use. E. coli O157 LPS antigen in patient's fecal samples can be detected in about five minutes with this simple procedure. Early diagnosis using such a simple kit will largely contribute for the early treatment and prevention of severe complications of the E. coli O157 infection.

Susceptibility of three strains of conventional adult mice to intestinal colonization by an isolate of Escherichia coli O157:H7

Three mouse strains were assessed for their susceptibility to intestinal colonization by a strain of the enteric bacterial pathogen Escherichia coli O157:H7. Following intragastric inoculation of E. coli O157:H7, the intestines of young adult female CD1, BALB/c, and C57BL/6 mice became colonized, as evidenced by faecal shedding of the pathogen for periods of up to 5 weeks. None of the three mouse strains examined developed overt disease in response to colonization by the organism. Following clearance of the primary inoculum, BALB/c mice, but not CD1 or C57BL/6 mice, appeared to acquire enhanced resistance to recolonization by E. coli O157:H7, as evidenced by a decreased faecal shedding period. This enhanced resistance correlated with the presence and persistence of immunoglobulin A, but not immunoglobulin G, in the serum and faeces directed against the O157 antigen. The implications of these findings to vaccine development against E. coli O157:H7 are discussed.

Identification of a rough strain of Escherichia coli O157:H7 that produces no detectable O157 antigen

MA6, an O157:H7-like strain, did not react with most anti-O157 kits examined; however, it had the rfbE gene that is essential for O157 expression and carried O157:H7 virulence factors. Lipopolysaccharide analysis showed that MA6 is a rough strain that does not produce the O157 antigen, but genetically, it belongs in the O157:H7 clonal group.

Escherichia coli O157 serology: false-positive ELISA results caused by human antibodies binding to bovine serum albumin

An analysis of farm workers and rural dwellers for serum antibodies to the lipopolysaccharide (LPS) of Escherichia coli O157 detected sera with antibodies binding to bovine serum albumin (BSA) by ELISA. These antibodies were not specific for BSA when examined by immunoblotting, and the ELISA values were reduced to a background level when plates were blocked with normal rabbit serum.

Development of a magnetic microplate chemifluorimmunoassay for rapid detection of bacteria and toxin in blood

A magnetic microplate chemifluorimmunoassay (MMCIA) is described using an immunomagnetic separation and a fluorescent microplate technique for rapid detection of low-level Escherichia coli O157:H7, Bacillus subtilis var. niger spores, and Staphylococcal enterotoxin type B from whole blood. In general, the MMCIA has at least several-fold more sensitivity than the conventional enzyme-linked immunosorbent assay. In addition, the assay sensitivities using direct fluorochrome label as the reporter, or alkaline phosphatase (AP) with various assay substrates, such as pNPP and AttoPhos, were assessed.

Profiles of circulating inflammatory- and anti-inflammatory cytokines in patients with hemolytic uremic syndrome due to E. coli O157 infection

The systemic inflammatory response to Escherichia coli O157 infection was studied from the profiles of circulating inflammatory and anti-inflammatory cytokines. Twelve patients transferred sequentially to our hospital for the intensive care with acute illness due to Escherichia coli O157 infection and the possible form of haemolytic uraemic syndrome were included in this study. Increased circulating concentrations of tumour necrosis factor, interleukin 6, interleukin 8, granulocyte colony-stimulating factor, and interleukin 10 were found in patients with various stages of this infection and haemolytic uraemic syndrome. Especially, the degree of the increase of circulating interleukin 10 in those who had a typical signs of haemolytic uraemic syndrome was higher than those of other inflammatory cytokines. Two groups of E. coli infection could be classified into one with a typical haemolytic uraemic syndrome and the other with atypically bacteremic state over haemolytic uraemic syndrome according to these cytokine levels.

Development of a colony lift immunoassay to facilitate rapid detection and quantification of Escherichia coli O157:H7 from agar plates and filter monitor membranes

E. coli O157:H7 is a food-borne adulterant that can cause hemorrhagic ulcerative colitis and hemolytic uremic syndrome. Faced with an increasing risk of foods contaminated with E. coli O157:H7, food safety officials are seeking improved methods to detect and isolate E. coli O157:H7 in hazard analysis and critical control point systems in meat- and poultry-processing plants. A colony lift immunoassay was developed to facilitate the positive identification and quantification of E. coli O157:H7 by incorporating a simple colony lift enzyme-linked immunosorbent assay with filter monitors and traditional culture methods. Polyvinylidene difluoride (PVDF) membranes (Millipore, Bedford, Mass.) were prewet with methanol and were used to make replicates of every bacterial colony on agar plates or filter monitor membranes that were then reincubated for 15 to 18 h at 36 +/- 1 degree C, during which the colonies not only remained viable but were reestablished. The membranes were dried, blocked with blocking buffer (Kirkegaard and Perry Laboratories [KPL], Gaithersburg, Md.), and exposed for 7 min to an affinity-purified horseradish peroxidase-labeled goat anti-E. coli O157 antibody (KPL). The membranes were washed, exposed to a 3,3',5,5'-tetramethylbenzidine membrane substrate (TMB; KPL) or aminoethyl carbazole (AEC; Sigma Chemical Co., St. Louis, Mo.), rinsed in deionized water, and air dried. Colonies of E. coli O157:H7 were identified by either a blue (via TMB) or a red (via AEC) color reaction. The colored spots on the PVDF lift membrane were then matched to their respective parent colonies on the agar plates or filter monitor membranes. The colony lift immunoassay was tested with a wide range of genera in the family Enterobacteriaceae as well as different serotypes within the E. coli genus. The colony lift immunoassay provided a simple, rapid, and accurate method for confirming the presence of E. coli O157:H7 colonies isolated on filter monitors or spread plates by traditional culture methods. An advantage of using the colony lift immunoassay is the ability to test every colony serologically on an agar plate or filter monitor membrane simultaneously for the presence of the E. coli O157 antigen. This colony lift immunoassay has recently been successfully incorporated into a rapid-detection, isolation, and quantification system for E. coli O157:H7, developed in our laboratories for retail meat sampling.

[Identification of Escherichia coli O157 antigen by polymerase chain reaction]

An assay was developed for the specific detection of Escherichia coli O157 using PCR, because O serological cross-reactivities have been reported between E. coli O157 and some E. coli, other bacterial species. PCR amplification of E. coli O157 rfbE (Ec O157:H7) gene that is necessary for the expression of the O157 antigen, was performed for the identification of E. coli O157. All Shiga toxin-producing Escherichia coli (STEC) O157:H7 and O157:H, non-STEC O157 strains were positive, and other non-O157 E. coli strains were negative by PCR. All tested strains of other bacterial species, like Salmonella O30 and Citrobacter freundii which gave positive results with O157 detection kits, were negative by PCR. It is recommended that PCR amplification of O157 rfbE gene is one of the most specific method for E. coli O157 identification.

The immunohistological diagnosis of E. coli O157:H7 colitis: possible association with colonic ischemia

OBJECTIVE

E. coli O157:H7 may cause hemorrhagic colitis resembling ischemic colitis. Diagnosis is usually made by finding sorbitol-negative colonies on MacConkey agar that react with O157 and H7 antisera. Most ischemic colitis is idiopathic, but some may be caused by E. coli O157:H7, inasmuch as this organism can produce fibrin thrombi in colon vasculature. The objectives of this study were to determine whether E. coli O157:H7 infection can be diagnosed retrospectively from paraffin blocks of colon sections and whether an association exists between E. coli O157:H7 infection and colonic ischemia.

METHODS

Paraffin-embedded sections of normal colon (n = 2) and various colitides [ischemic (n = 11), E. coli O157:H7 (n = 2), IBD (n = 8) and pseudomembranous (n = 3)] were used. Sections were deparaffinized, rehydrated, incubated with 3% peroxide in methanol, rinsed, and incubated with peroxidase-labeled antibody isolated from goats immunized with whole E. coli O157:H7. Sections were stained with peroxidase chromagen reagent and counterstained with hematoxylin. Coarse, granular, orange-brown staining was considered positive. To determine the localization of the chromagen deposits, three cases that stained positive, including one of the culture-proved E. coli O157:H7 colitis and two of colonic ischemia, were processed for electron microscopy.

RESULTS

Both cases (100%) of E. coli O157:H7 colitis and three of 11 (27.3%) cases of ischemic colitis stained positive by light microscopy. In one culture-proved case, electron microscopy demonstrated staining of bacillary structures; in two cases of colonic ischemia, extensive deposits of chromagen material were present that were associated neither with inflammatory cells nor with bacterial forms.

CONCLUSIONS

Immunoperoxidase staining of archival sections may be used to diagnose E. coli O157:H7 infection. An etiological role for this organism is possible in some cases of colonic ischemia.

The use of serodiagnosis in the retrospective investigation of a nursery outbreak associated with Escherichia coli O157:H7

AIMS

To use serology to investigate an outbreak of verocytotoxin (VT) producing Escherichia coli O157 in a hospital nursery, following the detection of faecal E coli O157 (phage type 49) producing VT type 2.

METHODS

ELISA and immunoblotting techniques, based on lipopolysaccharide (LPS) purified from E coli O157; diagnostic bacteriology; serotyping and phage typing; DNA probes for VT.

RESULTS

29 of 126 sera contained antibodies to the LPS of E coli O157: 10 were from children, three were from staff, and 11 were from hospital kitchen staff. Five parents of children attending the nursery were antibody positive. Sixty four sera from other hospital staff and controls did not contain antibodies to the LPS of E coli O157.

CONCLUSIONS

Serology detected evidence of infection with E coli O157 in 23% of sera examined. By bacteriology alone, only a single case of infection with E coli O157 would have been detected. Serology is valuable in providing evidence of infection with E coli O157.

Prostaglandin and fatty acid modulation of Escherichia coli O157 phagocytosis by human monocytic cells

Phagocytosis by human monocytes is an important primary survival mechanism particularly during bacterial infection. However, the processes that control the events and mediators involved in the activation of monocytes and their impact on the phagocytosis of bacteria are poorly understood. The effect of bacterial endotoxin, interleukin-1 beta (IL-1 beta), fatty acids and prostaglandin E2 (PGE2) on the phagocytosis of fluoroscein isothiocyanate (FITC)-labelled Escherichia coli (O157) by human blood monocytes and U937 cells was studied by flow cytometry. Endotoxin increased the phagocytosis of labelled bacteria by both monocytes and U937 cells. IL-1 beta and the polyunsaturated fatty acids; dihomo-gamma-linolenic and arachidonic acids also increased the phagocytic activity of both monocytes and U937 cells. In contrast, PGE2 suppressed phagocytosis in a concentration-dependent manner. The cyclo-oxygenase inhibitor, ketoprofen, further enhanced the increased phagocytic activity in the presence of endotoxin and interleukin-1 (IL-1) indicating suppression by endogenous prostaglandins. This was confirmed by the data which showed that lipopolysaccharide (LPS) and IL-1 increased PGE2 release and ketoprofen inhibited release. Endotoxin and fatty acids increased IL-1 beta release also, whereas PGE2 inhibited release. The data suggest that phagocytic activity may be linked to changes in IL-1 levels. The data presented in this study also suggest that monocyte phagocytosis in the course of bacterial infection would be altered during pathophysiological events which result in elevation of extracellular fatty acids.

Sensitivities and specificities of premier E. coli O157 and premier EHEC enzyme immunoassays for diagnosis of infection with verotxin (Shiga-like toxin)-producing Escherichia coli. The SYNSORB Pk Study investigators

This study describes the performance of two rapid enzyme immunoassays, Premier E. coli O157 and Premier EHEC (Meridian Diagnostics Inc., Cincinnati, Ohio) for the detection in stools of Escherichia coli O157 and verotoxins (Shiga-like toxins), respectively. Both tests were performed on stools from 876 children presenting to eight emergency departments with diarrhea. Standard culture, including E. coli O157:H7 isolation, was performed, and paired sera were taken for anti-O157-lipopolysaccharide antibody determination. Stools from patients enrolled in the study, and those yielding discordant results, were sent to a reference laboratory for repeat testing and further investigation, including cytotoxicity and non-O157 verotoxin-producing E. coli culture. Results were classified as field results (obtained in the eight site laboratories) and resolved results (obtained after repeat testing in the central laboratory). The "gold standard" for sensitivity of both tests and for specificity of Premier E. coli O157 was isolation of E. coli O157:H7 or a fourfold anti-O157 antibody rise. Specimens positive by the Premier EHEC test and negative for E. coli O157 culture were examined for non-O157 verotoxin-producing E. coli. The field sensitivity of Premier E. coli O157 was 86%, that of Premier EHEC was 89%, and the specificity of Premier E. coli O157 was 98%. Ten of 13 discordant Premier E. coli O157 results were reassigned as true results after repeat testing. Ten non-O157 verotoxin-producing E. coli isolates were recovered from Premier EHEC-positive, E. coli O157 culture-negative stools. Only one specimen gave an unequivocally false-positive Premier EHEC result. Both tests are highly sensitive and are specific if correctly performed. The Premier EHEC test will be particularly valuable as a practical routine test for the detection of non-O157 verotoxin-producing E. coli.

Immunomagnetic separation with mediated flow injection analysis amperometric detection of viable Escherichia coli O157

The coupling of an immunological separation (using immunomagnetic beads) with amperometric flow injection analysis detection of viable bacteria is presented. Using a solution containing Escherichia coli O157, the electrochemical response with two different mediators [potassium hexacyanoferrate(III) and 2,6-dichlorophenolindophenol] was evaluated in the FIA system. Antibody-derivatized Dynabeads were used to selectively separate E. coli O157 from a matrix. The kinetics and the capacity parameters regarding the attachment of bacteria to the immunobeads were studied. The immunomagnetic separation was then used in conjunction with electrochemical detection to measure the concentration of viable bacteria. A calibration curve of colony-forming units (cfu) against electrochemical response was obtained. The detection limit for this rapid microbiological method was 10(5) cfu mL-1, and the complete assay was performed in 2 h. Some advantages over ELISA methods are the direct detection of viable cells (and not total bacterial load) and the need for only one antibody (not enzyme-labeled), thus making the assay faster (only one washing step is necessary) and less expensive.

Isolation of a nonpathogenic strain of Citrobacter sedlakii which expresses Escherichia coli O157 antigen

A nonpathogenic strain of Citrobacter sedlakii which expresses the Escherichia coli O157 antigen is described. The discovery of this strain emphasizes the necessity of additional biochemical and/or toxigenicity testing when isolates react with E. coli O157 latex reagents.