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PubMed1981

Plasmids coding for colonization factor antigen I and heat-stable enterotoxin production isolated from enterotoxigenic Escherichia coli: comparison of their properties.

We examined seven enterotoxigenic Escherichia coli strains which produced colonization factor antigen I (CFA/I). Four of these strains were from South Africa (three serotype O78:H12 and one serotype O63:H-), one was from Ethiopia (O78:H12), and two were from Bangladesh (O78:H11 and O78:H12). Plasmids coding for CFA/I were mobilized from six of these strains by using resistance or enterotoxin factors. No plasmid was mobilized from the serotype O78:H12 Bangladesh strain. The transconjugants obtained from crosses with the O78 strains also produced heat-stable enterotoxin (ST), and additional investigations showed that CFA/I and ST were coded for by a single non-autotransferring plasmid. These plasmids were fertility inhibition negative, did not restrict any of the coliphages with which they were tested, and were incompatible with each other. Four had molecular weights of approximately 60 X 10(6), and one had a molecular weight of 52 X 10(6). Like the other CFA/I plasmids, the CFA/I plasmid transferred from the O63:H- strain coded for ST, but this plasmid also coded for heat-labile enterotoxin. In most other respects the properties of this plasmid were similar to those of the CFA/I-ST plasmids previously described. The molecular weight of this plasmid was 65 X 10(6). The IncT R-factor Rtsl was marked with a transposon for tetracycline resistance and then transferred into the two Bangladesh wild-type strains. Plasmids which coded for tetracycline resistance, CFA/I, and ST were transferred from these strains. These plasmids were incompatible with Rtsl and with the CFA/I-ST plasmids described above and were recombinants between Rtsl and a CFA/I-ST plasmid. Their properties are also described.

Antigens, Bacterial↗

PubMed1981

Nonimmunoglobulin fraction of human milk inhibits bacterial adhesion (hemagglutination) and enterotoxin binding of Escherichia coli and Vibrio cholerae.

Human milk and colostrum samples were divided into an immunoglobulin and a nonimmunoglobulin fraction by immunosorbent chromatography. The ability of these fractions to inhibit bacterial cell adhesion and enterotoxin receptor binding of Vibrio cholerae and various Escherichia coli isolates was then tested by in vitro assays. The strongest effect was generally seen with the nonimmunoglobulin fractions, which were shown to significantly inhibit E. coli cell adhesion (hemagglutination) mediated by CFA/I, CFA/II, or K88 fimbriae (but not type 1 pili) and V. cholerae hemagglutination, as well as the binding of cholera toxin and E. coli heat-labile enterotoxin to GM1 ganglioside. Also, the immunoglobulin fractions had significant inhibitory activity in some of these systems. The results are interpreted to suggest that human milk and colostrum may contain secreted structure analogs of the cell receptors for some bacterial adhesions and enterotoxins; this might contribute to the protective effect of milk against enteric infections.

Bacterial Physiological Phenomena↗

PubMed1982

Comparison of heat-labile enterotoxins from porcine and human strains of Escherichia coli.

Heat-labile enterotoxins (LTs) from porcine EWD299) and human (H74-114) enterotoxigenic strains of Escherichia coli were isolated by a single-step galactose elution procedure. Although both strains had similar amounts of LT in their whole-cell lysates, H74-114 yielded a smaller quantity of purified LT than did EWD299. Immunodiffusion studies with specific antisera revealed that although the two LTs shared major antigenic determinants each also had unique antigens. Both also had shared and unique specificities in comparison with the cholera enterotoxin (choleragen). Differences also exist in the apparent molecular weights of their B-subunit oligomers (coligenoid) as well as in the B-subunit monomers. The monomer molecular weights are 11,500 for EWD299 porcine LT and 12,700 for H74-114 human LT. The results suggest that either this isolated human LT has a tetrameric coligenoid or it moves differently in sodium dodecyl sulfate gels for other reasons. The A-subunits of both LTs were similar in size (28,000 daltons), and both LTs were activated by mild proteolytic processing. Amino acid analysis showed a threefold increase in the level of tryptophan and two- and fourfold decreases in the levels of glutamic acid and methionine, respectively, in H74-114 LT compared with EWD299 LT. These structural and antigenic differences may prove to be significant in immunoprophylaxis of the cholera-coli family of enterotoxins. Further studies to define the extent of evolutionary drift of these toxins are needed.

Amino Acids↗

PubMed1982

Genetic and molecular studies of plasmids coding for colonization factor antigen I and heat-stable enterotoxin in several escherichia coli serotypes.

Plasmids coding for colonization factor antigen I (CFA/I) and heat-stable enterotoxin (ST) were identified in 10 strains of human enterotoxigenic Escherichia coli. The strains, which belonged to serogroups O63, O114, O128, and O153, were isolated in Bangladesh, Latin America, Spain, and South Africa. Two strains produced heat-labile enterotoxin in addition to ST. CFA/I-ST plasmids were mobilized from two O128 strains into E. coli K-12 with the R factor R1-19K-. Like the prototype CFA/I-ST plasmid NTP113, mobilized previously from an E. coli O78 strain into K-12, these two plasmids were non-autotransferring. All 10 CFA/I-ST plasmids were incompatible with NTP113 and had molecular weights ranging from 59 X 10(6) to 72 X 10(6). The molecular properties of seven of these plasmids were compared with those of six CFA/I-ST plasmids previously mobilized from O78 strains from Ethiopia, South Africa, and Bangladesh and with those of one plasmid coding for CFA/I, ST and heat-labile enterotoxin from a South African strain of serogroup O63. Digestion with the restriction endonuclease HindIII showed that several plasmids had very similar fragment patterns and two were identical. Generally, a larger proportion of HindIII fragments were of common size in digests of plasmids identified in strains from related geographical areas, regardless of serogroup. However, all except one plasmid shared five or six HindIII fragments of the same size, one of which had been shown previously to be involved in CFA/I production. There was at least 90% DNA homology between CFA/I-ST plasmids with a molecular weight of about 58 X 10(6) from O78 strains from different sources. Most of the DNA sequences of these plasmids were present in a larger CFA/I-ST plasmid (72 X 10(6) from an O128 strain. The results of genetic and molecular studies suggest that CFA/I and ST production is determined by very similar plasmids in different serogroups of human enterotoxigenic E. coli from several sources.

Antigens, Bacterial↗

PubMed1982

Isolation of hybridoma cell lines and characterization of monoclonal antibodies against cholera enterotoxin and its subunits.

Hybridoma cell lines which produced monoclonal antibodies against cholera toxin were isolated. These cell lines were detected with an enzyme-linked immunosorbent assay screening procedure with purified cholera toxin or subunit A of cholera toxin. Seven cell lines were characterized with respect to their reactivity with cholera toxin subunits by Western blot analysis. Five clones produced antibodies which were directed against subunit A, and two clones produced antibodies which reacted with subunit B. These antibodies were also characterized by Western blot analysis for reactivity with the heat-labile enterotoxin produced by porcine and human enterotoxinogenic strains of Escherichia coli. Monoclonal antibodies which reacted with subunit A of cholera toxin also reacted with subunit A of both porcine and human heat-labile enterotoxins. In contrast, monoclonal antibodies to subunit B of cholera toxin did not react with subunit B of the heat-labile enterotoxin. Antibodies directed against subunit B neutralized the biological activity of cholera toxin in vitro in the S49 mouse lymphosarcoma assay. In contrast to polyclonal anti-subunit A antisera, monoclonal anti-subunit A from four of five clones had small but measurable neutralizing capacities in vitro.

Animals↗

PubMed1982

Clostridium perfringens type A enterotoxin: characterization of the amino-terminal region.

The amino-terminal region of the enterotoxin of Clostridium perfringens was investigated by automated sequence analysis. The primary structure results revealed that the enterotoxin is composed of a single polypeptide amino acid sequence. Computer comparison of a 20-residue sequence with a sequence library of reported proteins revealed no significant chemical similarities, indicating that the enterotoxin represents a unique polypeptide primary structure.

Amino Acid Sequence↗

PubMed1982

Synergistic protective effect of antibodies against Escherichia coli enterotoxin and colonization factor antigens.

We studied the ability of antisera against different Escherichia coli surface antigens, both alone and in combination with anti-enterotoxin, to decrease fluid secretion induced by intestinal challenge with enterotoxigenic E. coli in rabbits. Antiserum against lipopolysaccharide protected significantly against O group homologous bacteria. Monospecific antisera against pilus-associated colonization factor antigens CFA/I and CFA/II were also effective, giving highly significant protection against enterotoxigenic E. coli strains bearing the corresponding colonization factor antigens. Protection was also observed with Fab fragments of the CFA/I antibodies. Addition of the anti-lipopolysaccharide serum to a protective antiserum against purified heat-labile enterotoxin resulted in an antisecretory effect which slightly exceeded the sum of the effects obtained with each preparation alone. The combination of antiserum against CFA/I or CFA/II with anti-enterotoxin gave protection that equaled the product of the effects obtained with each antiserum alone; i.e. the antisera cooperated synergistically.

Animals↗

PubMed1982

Failure to detect conventional enterotoxins in classical enteropathogenic (serotyped) Escherichia coli strains of proven pathogenicity.

Ammonium sulfate-precipitated supernatants of classical enteropathogenic Escherichia coli strains were negative when investigated for enterotoxin production in rabbit ligated ileal loops, rabbit skin vascular permeability factor tests, suckling mice, and Y-1 adrenal cells. They also failed to stimulate guanylate cyclase activity in homogenates of rabbit, rat, and infant mouse intestines. Furthermore, DNA from enteropathogenic E. coli lacked sequences that encode heat-labile and heat-stable enterotoxins. These studies fail to show conventional enterotoxin synthesis by classical enteropathogenic E. coli.

Animals↗

PubMed1983

Sequence of the amino-terminal part of enterotoxin from Clostridium perfringens type A: identification of points of trypsin activation.

The sequence of the first 66 amino acids of the amino-terminal part of the enterotoxin from Clostridium perfringens type A is presented. The trypsin activation of the enterotoxin involves hydrolysis of Lys15-Glu16 and Lys25-Thr26 bonds. The N-terminal sequence of the trypsin-activated enterotoxin has limited homology with the sequence of the N-terminal region of the cholera toxin B subunit.

Amino Acid Sequence↗

PubMed1983

Synthesis of plasmid-coded heat-labile enterotoxin in wild-type and hypertoxinogenic strains of Escherichia coli and in other genera of Enterobacteriaceae.

The effect of host determinants on expression of plasmid-coded heat-labile enterotoxin (LT) was examined. A collection of LT plasmids was introduced into isogenic strains of Escherichia coli K-12 strains containing the wild type or hypertoxinogenic (htx-2) allele. For each plasmid tested, production of LT increased by approximately 1.5- to 3-fold in the host containing htx-2, indicating that the htx-2 allele affects a regulatory function for LT production that is common to many different enterotoxin plasmids. LT plasmids from E. coli were also introduced into strains of Shigella flexneri, Shigella sonnei, Citrobacter freundii, Enterobacter cloacae, Klebsiella pneumoniae, and Salmonella typhimurium. The plasmids were stably maintained and determined production of LT in those genera, although the amounts of LT produced varied by more than 50-fold. These observations demonstrate that host factors have an important role in determining the level of expression of plasmid-coded LT genes and support the hypothesis that interspecific, conjugal transfer of enterotoxin plasmids may confer enterotoxigenicity to a wide variety of potentially pathogenic enteric bacteria.

Alleles↗

PubMed1983

Immunological properties of purified Klebsiella pneumoniae heat-stable enterotoxin.

Klebsiella pneumoniae heat-stable enterotoxin was purified to apparent homogenicity by the same techniques used to purify Escherichia coli heat-stable enterotoxin. The two toxins had the same potency in the suckling mouse assay and showed immunological cross-reactivity in enzyme-linked immunosorbent assay, neutralization of secretory activity by specific hyperimmune antisera, and protection against active challenge in rats immunized with a vaccine containing synthetically produced E. coli heat-stable enterotoxin.

Animals↗

PubMed1984

Purified Shigella enterotoxin does not alter intestinal motility.

A purified Shigella enterotoxin (pST) and a cell-free lysate with pST removed (CFL-pST) from the whole-cell lysate of Shigella dysenteriae 60 R were used to study their effect on the myoelectric activity and mucosal integrity of rabbit ileal segments. We have previously defined two myoelectric patterns: the migrating action potential complex and repetitive bursts of action potentials that occur in response to certain bacteria and their enterotoxins. The in vivo model consisted of isolated ileal segments in male New Zealand White rabbits. The segments were infused with sterile saline (1 ml/h), pST (2.4-micrograms injection), or CFL-pST (1 ml/h). Myoelectric activity in the segments exposed to pST was similar to that with the saline infusion, but CFL-pST induced significant alterations in myoelectric activity in the form of repetitive bursts of action potentials. The mucosa of the segments exposed to pST showed only mild inflammatory changes. In contrast, CFL-pST caused moderate to severe inflammatory changes with enterocyte necrosis. These studies show that pST, a known enterotoxin, did not alter myoelectric activity and had no significant effect on the integrity of ileal mucosa, as determined by light microscopy. CFL-pST caused both inflammation and tissue necrosis with significant alterations in motor activity. These studies suggest that S. dysenteriae 60 R produces a substance or substances other than pST that cause florid in vivo cytotoxicity and alter myoelectric activity.

Action Potentials↗

PubMed1984

Sealed adult mice: new model for enterotoxin evaluation.

Outbred, inbred, and congenic strains of conventional mice which were ano-rectally occluded with cyanoacrylate ester glue and converted to sealed adult mice (SAM) were given, per os, crude cholera enterotoxin (CT) in 10% NaHCO3. At 6 h when the response was maximal, mice were killed, the small intestines were removed, and gut weight/body weight ratios were calculated. Experimental mice gave a linear response after receiving 1.5 to 60 micrograms of CT. Purified heat-stable enterotoxin from Escherichia coli and purified heat-labile enterotoxins from E. coli, Vibrio cholerae, and Clostridium difficile all elicited vigorous fluid outpouring as did culture filtrates from Vibrio fluvialis with cytotoxic activity. Active and passive immunization with crude CT completely or partially neutralized fluid secretion due to CT. Monospecific anti-CT incubated with CT before feeding also eliminated the response. Mice pretreated with penicillin, held in barrier cages, converted to SAM, and fed live vibrios, showed fluid responses similar to those seen with low doses of CT. Each of six different strains of inbred mice fed a half-maximal fluid accumulation response dose of CT gave fluid accumulation ratios which varied fourfold. There was no correlation of fluid accumulation with body weight, gut length, age, or sex. All poor responders were of H-2k haplotype and all good responders were H-2b. BALB congenic mice which differed only in H-2 haplotypes showed the same correlations, and body weights and gut lengths of all haplotypes were not significantly different.

Animals↗

PubMed1984

Characterization of monoclonal antibodies to heat-labile enterotoxin encoded by a plasmid from a clinical isolate of Escherichia coli.

Eight selected hybridoma cell lines that produced monoclonal antibodies against heat-labile enterotoxin from an Escherichia coli strain of human origin (LTh) were characterized. Antibodies produced by these cell lines were tested for binding specificity in a series of solid-phase radioimmunoassays and Western blots by using as test antigens LTh, the A, A1, A2, and B polypeptides of LTh, the heat-labile enterotoxin from an E. coli strain of porcine origin, and cholera toxin. The monoclonal antibodies were also tested for isotype and ability to neutralize LTh. Two of the anti-LTh monoclonal antibodies cross-reacted with cholera toxin, and six were specific for determinants of LTh that were not present on cholera toxin. One was specific for a unique epitope of LTh that was not shared by the heat-labile enterotoxin from an E. coli strain of porcine origin or cholera toxin. Four antibodies specific for epitopes on the B subunit of LTh (LTh-B) reacted with pentameric LTh-B but did not react in Western blots with monomeric LTh-B. The remaining four antibodies were specific for epitopes on LTh-A; two of these antibodies bound to A1, one reacted with A2, and one recognized only intact LTh-A. Only one monoclonal antibody had detectable neutralizing activity, and it was specific for LTh-A.

Animals↗

PubMed1985

Production of neutralizing monoclonal antibodies to Escherichia coli heat-stable enterotoxin.

In an effort to develop new approaches to the study and control of infectious diarrhea, we prepared murine monoclonal antibodies to the Escherichia coli heat-stable enterotoxin (STa). The toxin was purified from E. coli culture media and conjugated to bovine serum albumin. The STa-bovine serum albumin conjugate was used to immunize BALB/c mice, and the immune spleen cells from these mice were fused with SP2/0 myeloma cells. Resultant hybridomas were screened in an enzyme-linked immunosorbent assay protocol against 500 ng of STa-bovine serum albumin bound to microtiter wells as the solid-phase antigen. Five stable clones were selected and grown further in ascites fluid, which demonstrated anti-STa activity at dilutions of up to 1:500,000 in the enzyme-linked immunosorbent assay for heat-stable enterotoxin. In a competitive enzyme-linked immunosorbent assay format, the antibodies recognized several human and porcine strains of STa to various extents, but did not recognize E. coli heat-labile toxin, cholera toxin, or staphylococcal enterotoxin B. The antibodies were all able to bind lactoperoxidase-labeled [125I]STa, and antibody 20B3 was also able to dissociate [125I]STa bound to toxin receptors on rat jejunal villous cells. Preincubation of STa with antibodies 20B3 or 20F5 led to a concentration-dependent neutralization of toxin activity in a suckling mouse intestinal secretion assay. These antibodies are likely to provide new tools for the continued study of STa structure-function relationships and may lead to improved diagnosis and treatment of E. coli-induced infectious diarrhea.

Animals↗

PubMed1985

Revised amino acid sequence for a heat-stable enterotoxin produced by an Escherichia coli strain (18D) that is pathogenic for humans.

The amino acid sequence of heat-stable enterotoxin produced by enterotoxigenic Escherichia coli 18D has been revised. Amino acids originally assigned to positions 11 and 18, i.e., Tyr and Asn, respectively, were found to occupy positions 18 and 11, respectively. Thus all heat-stable enterotoxins composed of 18 amino acids sequenced to date from human, porcine, and bovine isolates of E. coli have identical primary structures, i.e., Asn-Thr-Phe-Tyr-Cys-Cys-Glu-Leu-Cys-Cys-Asn-Pro-Ala-Cys-Ala-Gly-Cys-Tyr. Furthermore, all 18- and 19-amino-acid heat-stable enterotoxins from E. coli share an almost identical core sequence, i.e., 14 of the 15 carboxy-terminal amino acid residues are identical.

Amino Acid Sequence↗

PubMed1985

Escherichia coli contains plasmids coding for heat-stable b, other enterotoxins, and antibiotic resistance.

Plasmid DNAs obtained from 18 Escherichia coli isolates that hybridized with the heat-stable b (ST-b) enterotoxin gene probe were examined by Southern blot analysis for genes coding for heat-labile, ST-a, and ST-b enterotoxins with specific radiolabeled DNA probes. Four E. coli isolates contained plasmids coding for both heat-labile and ST-b enterotoxins, and one isolate contained a plasmid coding for ST-a and ST-b. Five of 11 isolates of antibiotic-resistant enterotoxigenic E. coli isolates containing ST-b-coding DNA transferred a plasmid coding for both antibiotic resistance and ST-b to E. coli K-12, suggesting that the widespread use of antibiotics could increase the distribution of genes coding for ST-b.

Anti-Bacterial Agents↗

PubMed1972

Antigenic cross-reactivity of staphylococcal enterotoxins.

The antigenic cross-reactivity of staphylococcal enterotoxins types A, B, and C was assessed using anti-A and anti-B antitoxins in the solid-phase radioimmunoassay test. Heterologous reactions were observed. At the 33% inhibition level, B was 18,000 and 5,400 times more effective as an inhibitor in its homologous system than were the heterologous enterotoxins A and C, respectively. Similarly, in the A system, A enterotoxin was 55,000 and 25,000 times more effective than were B and C toxins, respectively, in inhibiting A-anti-A reactions.

Animals↗