Enzyme-linked immunosorbent assay for Escherichia coli heat-stable enterotoxin

Early detection of E. coli and total coliform using an automated, colorimetric and fluorometric fiber optics-based device

Lack of access to clean water is a major global issue that affects millions of people worldwide. Drinking contaminated water can be extremely hazardous, so it is imperative that it is tested sufficiently. One method commonly used to determine the quality of water is testing for both E. coli and total coliform. Here, we present a cost-effective and automated device which can concurrently test drinking water samples for both E. coli and total coliform using an EPA-approved reagent. Equipped with a Raspberry Pi microcontroller and camera, we perform automated periodic measurements of both the absorption and fluorescence of the water under test over 24 hours. In each test, 100 mL of the water sample is split into a custom designed 40-well plate, where the transmitted blue light and the fluorescent light (under UV excitation) are collected by 520 individual optical fibers. Images of these fiber outputs are then acquired periodically, and digitally processed to determine the presence of the bacteria in each well of the 40-well plate. We demonstrate that this cost-effective device, weighing 1.66 kg, can automatically detect the presence of both E. coli and total coliform in drinking water within ∼16 hours, down to a level of one colony-forming unit (CFU) per 100 mL. Furthermore, due to its automated analysis, this approach is also more sensitive than a manual count performed by an expert, reducing the time needed to determine whether the water under test is safe to drink or not.

Escherichia coli heat-stable enterotoxin (STa)-biotin conjugates for the titration of STa antisera by an enzyme-linked immunosorbent assay

The development of a new approach to the diagnosis of infectious diarrhoea, caused by Escherichia coli heat-stable enterotoxin (ST), was preceded by a preliminary study. The purpose of the latter was to establish whether three preparations of ST produced by a human isolate of enterotoxigenic E. coli (STa), obtained at different steps of the purification procedure (involving Amberlite XAD2 resin chromatography (P3), a gel filtration chromatography on a Biogel P4 (P2) or a disc-gel electrophoresis (P1)), could be employed to titrate antisera to STa using an ST-biotin enzyme-linked immunosorbent assay (ELISA). The solid-phase STa was obtained by first coupling the toxin to biotinyl-N-hydroxysuccinimide and then binding this conjugate to avidin adsorbed to flat-bottomed polystyrene microtitre plates. Using these reagents, the assay conditions were examined. Checkerboard tests determined optimal biotin-P3, P2 or P1 toxin conjugate concentrations to be used as the immunosorbent for P3, P2 and P1 antiserum titration. The immunosorbent prepared with STa purified only on Amberlite XAD2 resin was unable to differentiate significantly between P3, P2 or P1 antisera. Immunosorbent prepared with P2 or P1 detected widely differing titres between the three antisera and gave more sensitive results. Only small but questionable differences were observed between P2 and P1 toxin preparations.

Recombinant fusion protein for simple detection of Escherichia coli heat-stable enterotoxin by GM1 enzyme-linked immunosorbent assay

A recombinant gene fusion protein composed of an Escherichia coli heat-stable enterotoxin (STa) peptide epitope fused to the amino end of the cholera toxin B subunit was used to detect STa produced by clinical isolates of enterotoxigenic E. coli (STa-ETEC) by a single monoclonal antibody-based inhibition GM1 enzyme-linked immunosorbent assay. In this test, 100% sensitivity and 100% specificity were observed for use of the recombinant protein in either its purified form or as crude Vibrio cholerae culture supernatants in detection of STa-ETEC.

Hyperproduction of heat-stable enterotoxin (STA4) of Escherichia coli and analysis of the unusual electrophoretic behavior of reduced and alkylated forms of STAs

The methanol-soluble heat-stable enterotoxin gene (estA4) of Escherichia coli (STA4) yielded 128-fold more toxin when expressed by a T7 RNA polymerase driven system than when driven by its own promoter. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of in vivo [35S]cysteine radiolabeled products of the cloned gene revealed an apparent molecular mass larger than that expected for a 19 amino acid polypeptide (mol. wt. 2049). Purified [125I]radiolabeled enterotoxin, STA1 (mol. wt. 1979) showed an Mr of 3800 when reduced, 2000 when reduced and carboxylated, and 14,500 when reduced and carboxyamidated. Similar changes after carboxyamidation were obtained with two different chemically synthesized STAs. These unusual electrophoretic mobilities were shown to be common to all STAs studied. Alkylation of the reduced STA species occurred only at the six cysteine residues of the toxin. Upon gel filtration the native, reduced, and reduced and alkylated forms of STAs eluted from the column in close agreement to the molecular weight expected from the known amino acid composition of the peptides.

Clinical laboratory applications of monoclonal antibodies

Monoclonal antibody (MAb) technology is well recognized as a significant development for producing specific serologic reagents to a wide variety of antigens in unlimited amounts. These reagents have provided the means for developing a number of highly specific and reproducible immunological assays for rapid and accurate diagnosis of an extensive list of diseases, including infectious diseases. The impact that MAbs have had in characterizing infectious disease pathogens, as well as their current and future applications for use in clinical microbiology laboratories, is reviewed. In addition, the advantages (and disadvantages) of the use of MAbs in a number of immunoassays, such as particle agglutination, radioimmunoassays, enzyme-linked immunosorbent assays, immunofluorescent-antibody assays, and immunohistology, are explored, including the use of these reagents in novel test system assays. Also, nucleic acid probe technology is compared with the use of MAbs from the perspective of their respective applications in the diagnosis of infectious disease agents. There is no question that hybridoma technology has the potential to alter significantly the methods currently used in most clinical microbiology laboratories.

DNA hybridization with oligodeoxyribonucleotide probes for identifying enterotoxin-producing Escherichia coli

The DNA hybridization method using oligodeoxyribonucleotide probes was compared with the GM, ELISA and the infant mouse assay for determining production of LT and ST, respectively, by 2000 strains of Escherichia coli. Sensitivity and specificity by DNA hybridization for LT were 98.7 and 99.8%, and for ST were 78.8 and 99.6%.

Evaluation of a nonisotopically labeled oligonucleotide probe to detect the heat-stable enterotoxin gene of Escherichia coli by the DNA colony hybridization test

A commercially available, alkaline-phosphatase-conjugated oligonucleotide probe for detecting the heat-stable enterotoxin gene of Escherichia coli was compared with cloned gene probes by examining E. coli isolates from traveler's diarrhea by DNA colony hybridization tests. The oligonucleotide probe was useful in specifically identifying the so-called STh gene. No deproteinization of sample was necessary to prepare the colony blots.

Blinded, two-laboratory comparative analysis of Escherichia coli heat-stable enterotoxin production by using monoclonal antibody enzyme-linked immunosorbent assay, radioimmunoassay, suckling mouse assay, and gene probes

Heat-stable enterotoxin (ST)-producing enterotoxigenic Escherichia coli (ETEC) can be identified by a variety of assays, including the suckling mouse assay (SMA), radioimmunoassay (RIA), polyclonal or monoclonal antibody enzyme-linked immunosorbent assay (ELISA), and DNA hybridization with STh and STp gene probes. To compare the sensitivity and reliability of these assays, 100 coded ETEC and non-ETEC isolates were blindly tested in two independent laboratories. SMA, RIA, and monoclonal ELISA were performed in Cincinnati, Ohio, while gene probe analysis was performed in Baltimore, Md. The method of storage of organisms had a profound effect on the stability of plasmids in certain strains. Hybridization experiments to determine the presence or absence of the enterotoxin gene showed that strains stored on Dorset egg medium at room temperature better retained their plasmids than strains stored frozen in skim milk. Forty-four of the 100 organisms obtained from the skim milk stock were found to produce STa in liquid culture by the RIA, SMA, and monoclonal ELISA (100% agreement). However, 50 of 54 of the strains stored on Dorset egg medium which were originally classified as STa+ or ST+ LT+ (positive for both heat-stable and heat-labile [LT] enterotoxins) were found to produce STa and retain the plasmid by each of these assays. Three additional strains were found which harbored the plasmid but did not elaborate STa by any of the assays (3% discrepancy). The monoclonal antibody ELISA appears to be highly reliable for determination of STa production by ETEC and can be easily scored visually even by untrained personnel. Furthermore, when this STa assay is coupled with a polyclonal antibody assay, it is possible to predict the genotype of STh- and STp-producing organisms.

Monoclonal antibodies against Escherichia coli heat-stable toxin (STa) and their use in a diagnostic ST ganglioside GM1-enzyme-linked immunosorbent assay

Seven monoclonal antibodies (MAbs) against heat-stable enterotoxin (ST) from a human Escherichia coli isolate were prepared and evaluated for their usefulness in an ST immunodetection assay, the ST ganglioside GM1-enzyme-linked immunosorbent assay (ELISA). This assay is based on the ability of STa, as present in, for example, culture filtrates from ST-producing E. coli, to inhibit specific anti-ST antibody from binding to solid-phase-bound ST ganglioside (GM1-bound ST-cholera B subunit). Four of the MAbs were of immunoglobulin G1 (IgG1), one was of IgG2b, and two were of IgM isotype. All the IgG1 MAbs could be completely inhibited by addition of free ST; 0.2 to 0.4 ng of purified ST inhibited binding of these MAbs by 50%. The non-IgG1 MAbs were, in contrast, not inhibited by 200-fold-higher amounts of purified ST, probably because they were directed against linkage epitopes or were of low affinity or both. When the IgG1 MAbs were tested in the ST GM1-ELISA, ST could be detected in culture filtrates from stock human E. coli isolates with 100% sensitivity and specificity. ST in filtrates from fresh stool cultures was demonstrated with higher sensitivity with the MAbs ST GM1-ELISA than with the conventional infant mouse test. Both subtypes of STa, STaI and STaII, could be detected by the ST GM1-ELISA by using either IgG1 MAb in the immunodetection step, whereas infant-mouse-active ST from Yersinia enterocolitica failed to react.

Simplified procedure for carrying out simultaneous multiple hydrogen fluoride cleavages of protected peptide resins

Methods have recently been presented which greatly increase the ability to synthesize large numbers of peptides. These advances make it essential to be able to cleave large numbers of protected peptide resins. Two different procedures are presented for carrying out cleavage of protected peptide resins. The first procedure enables multiple cleavages to be carried out with many existing HF apparatuses, while the second utilizes a new apparatus design. Using these procedures, at least 50 individual cleavages can be carried out per day.

Escherichia coli diarrhoea

Ever since Escherich (1885) first isolated the organism now known asEscherichia colifrom the stools of infants, medical microbiologists have been faced with the problem of distinguishing between those strains capable of causing diarrhoea and those that are harmless gut commensals. Epidemiological investigations were greatly facilitated by the description by Kauffmann (1947) of a serotyping scheme forE. coli, and Taylor (1961) later reported that 17 0 serogroups ofE. colihad been implicated as possible causes of epidemic infantile enteritis. These infantile enteropathogenicE. coli(EPEC), having been discovered by epidemiological studies using serotyping, belonged by definition to a restricted range of serogroups. More recently it was shown that otherE. colistrains may produce enterotoxins, and these enterotoxigenicE. coli(ETEC) usually belong to particular serogroups which are different from those associated with EPEC.E. colistrains belonging to a third range of serogroups may cause an illness resembling shigella dysentery, and these may be regarded as entero-invasiveE. coli(EIEC).E. colistrains that cause diarrhoea may therefore be considered as three groups, as follows.

Evaluation of a competitive enzyme-linked immunosorbent assay for porcine Escherichia coli heat-stable enterotoxin

A competitive enzyme-linked immunosorbent assay (ELISA) was compared with the conventional suckling mouse assay for the identification of heat-stable enterotoxin (STa) in samples from piglets suffering from diarrhea. A total of 110 Escherichia coli isolates, 22 primary cultures, and 26 fecal samples from piglets up to 8 weeks of age with diarrhea were compared in parallel by both assays. Of the 110 isolates tested, all gave consistent results by the ELISA and the suckling mouse assay; 60 strains were negative and 50 strains produced STa by both tests. Identical results were obtained when 22 primary agar cultures were screened for STa production by both methods; 6 were found to produce STa, while 16 did not. When 26 fecal samples were tested for the presence of STa, 10 were negative and 12 were positive by both assays. One of the remaining four samples gave questionable positive results by both the suckling mouse assay and the ELISA, but E. coli isolated from this sample gave positive results by both tests. The remaining three samples were negative by the suckling mouse assay, but gave questionable positive results by the ELISA. E. coli isolates from these three samples were always negative by both assays. The ELISA used in this study provides a reliable and convenient method for diagnosing STa-producing enterotoxigenic E. coli of porcine origin.

General method for the rapid solid-phase synthesis of large numbers of peptides: specificity of antigen-antibody interaction at the level of individual amino acids

A novel yet simple method is described that facilitates the synthesis of large numbers of peptides to the extent that the synthesis process need no longer be the limiting factor in many studies involving peptides. By using the methods described, 10-20 mg of 248 different 13-residue peptides representing single amino acid variants of a segment of the hemagglutinin protein (HA1) have been prepared and characterized in less than 4 weeks. Through examination of the binding of these analogs to monoclonal antibodies raised against residues 75-110 of HA1, it was found that a single amino acid, aspartic acid at position 101, is of unique importance to the interaction. Two other residues, aspartic acid-104 and alanine-106, were found to play a lesser but significant role in the binding interaction. Other single positional residue variations appear to be of little or no importance.

A completely synthetic toxoid vaccine containing Escherichia coli heat-stable toxin and antigenic determinants of the heat-labile toxin B subunit

The immunodeterminant regions of the Escherichia coli heat-labile toxin B subunit were identified by determining the antigenicity, by using enzyme-linked immunosorbent assays, of synthetically produced peptides corresponding to various segments of its 124-amino-acid sequence. The addition of the 18-amino-acid sequence of heat-stable toxin (ST) to some of these peptides enhanced their B subunit antigenicity. Peptide residues containing the 26 amino acids of B subunit sequence 58 to 83 joined to the 18-amino-acid sequence of ST yielded a 44-amino-acid peptide whose antigenicity was 50% that of both native B subunit and ST. This peptide was completely nontoxic when tested in Chinese hamster ovary tissue culture, suckling mouse, and rat ligated ileal loop assays. Peroral immunization of rats with the polymeric form of this peptide yielded a dose-dependent response of intestinal immunoglobulin A antitoxin titers to both the ST and B subunit components and provided strong protection against challenge with viable ST- and heat-labile toxin-producing E. coli strains. The immunogenicity of the synthetic peptide in rats was the same as that of ST and about 50% that of native B subunit. The completely synthetic peptide vaccine has the following advantages over previously described toxoid vaccines that consist of synthetic ST chemically cross-linked to native B subunit derived from bacterial cultures: it is produced by a single synthetic process, it is completely nontoxic, and it is immunogenic for both ST and B subunit.

Development of a competitive enzyme-linked immunosorbent assay (ELISA) for Escherichia coli heat-stable enterotoxin (STa)

A sensitive competitive enzyme-linked immunosorbent assay (ELISA) was developed to detect the low molecular weight heat-stable enterotoxin (STa) in culture supernatant fluids of enterotoxigenic Escherichia coli (ETEC). Competitive inhibition was observed between STa in solution and a glutaraldehyde-coupled STa-human serum albumin (HSA) conjugate bound to microtiter wells when antiserum raised against a glutaraldehyde-coupled STa-bovine serum albumin (BSA) conjugate was used as detecting antibody. No competition was observed with conjugates prepared using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide or dimethyl suberimidate and antisera raised against each conjugate. A biotin/avidin system increased the sensitivity of the assay such that 133 pg/ml of purified STa can be detected in less than 4 h. The assay was used to detect and quantify STa in culture supernatant fluids from human, porcine, and bovine ETEC isolates. No cross-reactivity was observed with the heat-labile enterotoxin (LT) or the form of ST with biological activity only in piglets (STb). Results from the quantitative STa ELISA showed good correlation (0.87) with the suckling mouse bioassay and a previously described radioimmunoassay. The quantitative assay was modified to reduce the total incubation time to less than 2 h. The qualitative STa ELISA provides a rapid and sensitive assay for clinical isolates of ETEC and should facilitate epidemiological studies on the incidence of STa-producing ETEC.

Properties of crude Campylobacter jejuni heat-labile enterotoxin

The amount of crude Campylobacter jejuni enterotoxin present in culture products was quantitated by comparing the response of these preparations with that of pure Escherichia coli heat-labile toxin (LT) in the Chinese hamster ovary assay and in enzyme-linked immunosorbent assays that used GM ganglioside or antisera to LT or both. Maximum C. jejuni enterotoxin production was achieved by growth at 42 degrees C for 24 h under agitation in supplemented GC medium. Adding polymyxin separately to either the broth supernatant or the cells enhanced the recovery of toxin; the yield from cell lysates was much lower. The quantity of C. jejuni enterotoxin produced by clinical isolates obtained locally or provided from Mexico varied widely, over a spectrum from none to large amounts; quantitative values for the amount of C. jejuni enterotoxin determined by the Chinese hamster ovary and enzyme-linked immunosorbent assays correlated with the degree of secretory potency of this material in ligated rat ileal loops. The cytotonic activity of C. jejuni enterotoxin in Chinese hamster ovary cells was abolished by heating at 96 degrees C for 10 min and by preincubation either with GM ganglioside or with LT or cholera toxin antisera. The secretory activity of C. jejuni enterotoxin in ligated rat ileal loops was passively neutralized by antiserum to LT, and immunizing rats with either LT or its B subunit significantly (P less than 0.001) reduced fluid response to active challenge with C. jejuni enterotoxin in ligated ileal loops. These observations indicate that strains of C. jejuni vary in their capacity to elaborate a heat-labile enterotoxin that has close immunological homology with LT and cholera toxin.