Stimulation of steroidogenesis in tissue culture by enterotoxigenic Escherichia coli and its neutralization by specific antiserum

Impact of diagnostic methods on efficacy estimation - a proof-of-principle based on historical examples

INTRODUCTION

Accurate diagnostic methods are essential for evaluating treatment efficacy in clinical trials, including vaccine trials. Although a plethora of studies assessing novel or modified treatment options is available, clinical trials evaluating the sensitivity and specificity of diagnostic methods in compliance with the demands of drug registration trials are scarce. We assessed the accuracy of diagnostic methods in two vaccine trials conducted in 1995 and 2009 to demonstrate the impact of sensitivity and specificity on efficacy estimations.

METHODS

We applied the sensitivity- and specificity-adjusted vaccine efficacy estimator of Lachenbruch for modelling the impact of test characteristics on the outcome of the two vaccine trials by varying diagnostic specificity.

RESULTS

Because of non-ideal diagnostic sensitivity and specificity, the estimation of vaccine efficacy is compromised. We demonstrate the impact of diagnostic accuracy on efficacy estimations with increasing confidence limits.

CONCLUSIONS

Because sensitivity and specificity less than one have a direct impact on efficacy estimations in clinical trials, evaluation of diagnostic methods should lead to a level of evidence comparable with the efficacy assessment of novel treatment options. Furthermore, statistical methods adjusted for sensitivity and specificity of diagnostic methods should be applied for efficacy estimations, or this lack of confidence has to be taken into account when interpreting the results of trials.

Cross-reactivity and avidity of antibody responses induced in humans by the oral inactivated multivalent enterotoxigenicEscherichia coli (ETEC) vaccine ETVAX

We investigated whether the oral inactivated, multivalent enterotoxigenic Escherichia coli (ETEC) vaccine ETVAX, consisting of four E. coli strains over-expressing the colonisation factors (CFs) CFA/I, CS3, CS5 and CS6, combined with the toxoid LCTBA, could induce cross-reactive antibodies to CFs related to the CFA/I and CS5 families. We also evaluated the avidity of vaccine induced antibodies against the toxoid and CFs. Cross-reactivity was analysed in mucosal (faecal and antibodies in lymphocyte supernatants, ALS) samples, and antibody avidity in serum and ALS samples, from two phase I trials: a primary vaccination study, where two oral doses of ETVAX were given±the double mutant heat labile toxin (dmLT) adjuvant at a 2-week interval, and a booster vaccination study, where a single booster dose of ETVAX was given 13-23months after primary vaccinations. We found that 65-90% of subjects who had responded to CFA/I in ALS or faecal specimens also developed cross-reactive antibodies to the related CFs tested, i.e. CS1, CS14 and CS17, and that approximately 80% of those responding to CS5 also responded to the closely related CS7. For subjects who had developed cross-reactive antibodies, the magnitudes of responses against vaccine CFs and related non-vaccine CFs were comparable. Using both a simple method of antibody avidity determination based on limiting antigen dilution, as well as a chaotropic ELISA method, we found that the avidity of serum and ALS antibodies to key vaccine antigens increased after a late booster dose compared to after primary vaccination. Our results suggest that the cross-reactive antibody responses against multiple CFs may result in expanded ETEC strain coverage of ETVAX and that repeated vaccinations induce vaccine-specific antibodies with increased binding capacity.

Safety and immunogenicity of an improved oral inactivated multivalent enterotoxigenic Escherichia coli (ETEC) vaccine administered alone and together with dmLT adjuvant in a double-blind, randomized, placebo-controlled Phase I study

BACKGROUND

We have developed a new oral vaccine against enterotoxigenic Escherichia coli (ETEC), which is the most common cause of bacterial diarrhea in children in developing countries and in travelers.

METHODS

The vaccine was tested for safety and immunogenicity alone and together with double-mutant heat-labile toxin (dmLT) adjuvant in a double-blind, placebo-controlled Phase I study in 129 Swedish adults. The vaccine consists of four inactivated recombinant E. coli strains overexpressing the major ETEC colonization factors (CFs) CFA/I, CS3, CS5, and CS6 mixed with an LT B-subunit related toxoid, LCTBA. Volunteers received two oral doses of vaccine alone, vaccine plus 10 μg or 25 μg dmLT or placebo. Secretory IgA antibody responses in fecal samples and IgA responses in secretions from circulating intestine-derived antibody secreting cells were assessed as primary measures of vaccine immunogenicity.

RESULTS

The vaccine was safe and well tolerated; adverse events were few and generally mild with no significant differences between subjects receiving placebo or vaccine with or without adjuvant. As many as 74% of subjects receiving vaccine alone and 83% receiving vaccine plus 10 μg dmLT showed significant mucosal IgA responses to all five primary vaccine antigens and about 90% of all vaccinees responded to at least four of the antigens. Subjects receiving vaccine plus 10 μg dmLT responded with significantly increased intestine-derived anti-CS6 responses compared to subjects receiving vaccine alone.

CONCLUSIONS

The vaccine was safe and broadly immunogenic. dmLT further enhanced mucosal immune responses to CF antigens present in low amounts in the vaccine. Based on these encouraging results, the vaccine will be tested for safety and immunogenicity in different age groups including infants in Bangladesh and for protective efficacy in travelers.

Escherichia coli: a brief review of diarrheagenic pathotypes and their role in diarrheal diseases in Iran

Diarrheagenic Escherichia coli have developed different strategies for establishment of infection in their host. Understanding these pathogenic mechanisms has led to the development of specific diagnostic tools for identification and categorization of E. coli strains into different pathotypes. This review aims to provide an overview of the various categories of diarrheagenic Escherichia coli and the data obtained in Iran pertaining to these pathotypes.

Enterotoxigenic Escherichia coli in developing countries: epidemiology, microbiology, clinical features, treatment, and prevention

ETEC is an underrecognized but extremely important cause of diarrhea in the developing world where there is inadequate clean water and poor sanitation. It is the most frequent bacterial cause of diarrhea in children and adults living in these areas and also the most common cause of traveler's diarrhea. ETEC diarrhea is most frequently seen in children, suggesting that a protective immune response occurs with age. The pathogenesis of ETEC-induced diarrhea is similar to that of cholera and includes the production of enterotoxins and colonization factors. The clinical symptoms of ETEC infection can range from mild diarrhea to a severe cholera-like syndrome. The effective treatment of ETEC diarrhea by rehydration is similar to treatment for cholera, but antibiotics are not used routinely for treatment except in traveler's diarrhea. The frequency and characterization of ETEC on a worldwide scale are inadequate because of the difficulty in recognizing the organisms; no simple diagnostic tests are presently available. Protection strategies, as for other enteric infections, include improvements in hygiene and development of effective vaccines. Increases in antimicrobial resistance will dictate the drugs used for the treatment of traveler's diarrhea. Efforts need to be made to improve our understanding of the worldwide importance of ETEC.

Serum antibody response induced in mice after oral administration of three different antigens of enterotoxigenic Escherichia coli in enteric coated microparticles

BACKGROUND

Gastric digestion of these antigens plays an important role, decreasing the ability to deliver antigens to the gut-associated lymphoid tissue. To overcome this obstacle, microencapsulated antigens from enterotoxigenic Escherichia coli (ETEC) were evaluated for oral immunization of mice.

METHODS

Four groups of 10 each received 3 series of 3 doses each of (1) B subunit of cholera toxin (CTB), similar to heat-labile toxin of ETEC, (2) formalin-killed whole cell ETEC H10407 (FK-ETEC), (3) crude preparation of colonization factor antigen I (CFA/I), or (4) placebo. Serum antibody was measured on day 0 and 60 by ELISA.

RESULTS

In group 1 a CTB antibody response was induced in all mice, 3 with 1:105 titer and 7 with 1:106. These antibodies neutralized cholera toxin-induced steriodogenesis of Y-1 adrenal cells. In group 2, 8 mice developed a whole H10407 bacteria antibody titer of 1:100, one 1:200 and one showed no immune response. In the same group, an anti-CFA/I response was observed in 6 mice and anti-LPS in 4 mice as determined by Western blot. All mice in group 3 showed > 1:104 anti-CFA/I antibody titer. Group 4 mice did not develop an immune response to any ETEC antigens.

CONCLUSIONS

Microencapsulation appears to be a suitable approach for oral vaccination against ETEC and Vibrio cholerae.

Importance of ADP-ribosylation in the morphological changes of PC12 cells induced by cholera toxin

Cholera toxin (CTX) is composed of two subunits, subunit A, which possesses ADP-ribosyltransferase activity, and subunit B, which is responsible for receptor binding. It has previously been shown that agents that increase cyclic AMP (cAMP) levels in cells induce differentiation of PC12 cells into neurite-like cells. In this report, we show that as little as 100 pg of CTX per ml induces such changes. CTX was found to ADP-ribosylate at least four membrane proteins of PC12 cells in vitro and in vivo and to increase intracellular cAMP levels. We have developed an inducible ctx gene expression system in Vibrio cholerae by using the tac promoter. The culture medium of the CTX-producing bacteria was able to induce the morphological changes and the ADP-ribosylation of the PC12 cell membrane proteins. We have constructed two CTX-cross-reactive mutant proteins (CTX-CRM) by site-directed mutagenesis. The choice of glutamic acid 29 as the target amino acid was based on sequence similarities with other bacterial toxins. CTX-CRM-E29 delta, in which the Glu-29 of the A subunit was deleted, showed strongly reduced ADP-ribosyltransferase activity and did not induce significant morphological changes of PC12 cells. In contrast, CTX-CRM-E29D, in which the Glu-29 was replaced by an aspartic acid, was as active as the wild-type protein. We conclude that the ADP-ribosylation activity of CTX is important for the toxin-induced differentiation of PC12 cells. Pertussis toxin, which had no visible effect on PC12 cell morphology, was also able to ADP-ribosylate a membrane-bound protein(s) in vitro and in vivo. Pertussis toxin alone did not significantly increase cAMP levels in PC12 cells, but it acted synergistically with CTX.

Quantitative determination of lymphocyte ACTH1-39

A method was developed for quantitative measurement of ACTH1-39, produced by human lymphocytes. It was shown that pH adjustment to 2 was essential for processing of the precursor molecule proopiomelanocortin (POMC). Linearity between time of incubation and ACTH production was shown. The existence of specific endopeptidases in lymphocytes for processing of the POMC molecule remains doubtful.

Enteroadherent Escherichia coli as a cause of diarrhea among children in Mexico

Enteropathogenic Escherichia coli (EPEC) often exhibits localized adherence or diffuse adherence to HEp-2 cells. We recently provided evidence that HEp-2 cell-adherent or enteroadherent E. coli (EAEC) not belonging to EPEC serogroups was the cause of diarrhea among U.S. travelers to Mexico. In the present study, we looked for EAEC and EPEC in stool specimens from 154 children with acute diarrhea and 137 well children seen at several outpatient clinics in Guadalajara, Mexico. EAEC showing localized adherence (EAEC-L) was isolated from 13.0% of the patients and 0.7% of the controls (P less than 0.0001). EAEC showing diffuse adherence (EAEC-D) was recovered from 20.8% of the patients and 7.3% of the controls (P less than 0.001). EPEC was isolated from 4.5 and 6.7% of the patients and controls, respectively. Among all enteropathogens, only enterotoxigenic E. coli occurred as commonly (21.4%) as EAEC-D and EAEC-L did in children with diarrhea. Of the EAEC-L strains isolated from children with diarrhea, 20% belonged to recognized EPEC serogroups, and 3.1% of EAEC-D strains belonged to recognized EPEC serogroups. This study suggests that EAEC may be an important pediatric enteropathogen in Mexican children with diarrhea and further supports the observation that adherence to HEp-2 cells may be a marker of virulence independent of EPEC serogroup among E. coli strains.

Natural and experimental infection with an attaching and effacing strain of Escherichia coli in calves

Gnotobiotic calves were inoculated with an O5:K4:H-, urease-positive strain of Escherichia coli isolated from a 2-day-old calf with diarrhea. The calves developed elevated temperatures and passed loose mucoid feces, with or without blood. The E. coli strain was negative for heat-stable and heat-labile enterotoxins but produced high levels of Shiga-like toxin. Bacteria attached diffusely to the epithelium of the large intestine and multifocally to the epithelium of the ileum. The duodenum and jejunum were not affected. At the sites of bacterial attachment, microvilli were effaced, enterocytes were degenerate, and necrosis and exfoliation had occurred. These results confirm a previous report from England that calves may naturally contract infections similar to those caused by enteropathogenic E. coli strains pathogenic to humans or rabbits. This suggests that the calf bacterial strains, like some enteropathogenic E. coli strains, produce high levels of Shiga-like toxin and cause attachment and effacement lesions in the colonic epithelium of the infected host.

Production of extracellular enzymes and cytotoxicity by Vibrio vulnificus

Thirty-three strains of Vibrio vulnificus of clinical and environmental origin were examined for production of 12 extracellular enzymes of potential importance to the virulence of this bacterium. Strains of Vibrio vulnificus were consistent in their production of protease, mucinase, lipase, chondroitinase, hyaluronidase, DNase, sulfatase, and hemolysin. No differences between clinical and environmental isolates were noted. Although none of the enzymes appeared to correlate with the ability of these strains to produce lethality in mice, the production of hemolysin and of a protease with activity against native serum albumin may be significant in the pathogenesis of the potentially fatal infections produced by this organism. The production of several of these exoenzymes also appeared to correlate with pathogenicity in the seven other Vibrio species examined. Culture filtrates of all virulent strains of Vibrio vulnificus were cytotoxic for Chinese hamster ovary cells, whereas those of the strains of Vibrio parahaemolyticus and Vibrio alginolyticus examined lacked this activity.

Concurrent infection of pigs with enterotoxigenic Escherichia coli of different serogroups

Naturally occurring dual infections with Escherichia coli of different serogroups occurred in 12 pigs 2 to 14 days of age. In each case, one isolate was hemolytic and produced K88 pili and the other was nonhemolytic and produced either K99 or 987P pili.

Evaluation of BW942C, a novel antidiarrheal agent, against enterotoxins of Escherichia coli and Vibrio cholerae

BW942C, an enkephalin-like pentapeptide with anti-diarrheal activity, was tested against crude toxins of Escherichia coli and Vibrio cholerae in the Y-1 adrenal cell assay, rabbit ileal loop assay, and suckling mouse assay. The effects of BW942C on in vitro ion transport were measured in rabbit ileum mounted in Ussing chambers. In vitro, BW942C decreased basal short-circuit current (2.26 and 3.15 mueq cm-2 h-1 in experimental samples and controls, respectively; n = 7, P less than 0.05) and increased basal net Cl absorption (1.59 and 0.50 mueq cm-2 h-1 in experimental samples and controls, respectively; P less than 0.025). Net Na absorption was also increased, but not significantly. BW942C did not block the secretory response to a maximal dose of purified heat-stable toxin. BW942C directly enhanced intestinal fluid absorption. In the Y-1 adrenal cell assay, 5 mg of BW942C per ml inhibited the cytopathic effect caused by cholera toxin or heat-labile enterotoxin of E. coli. In the rabbit ileal loop assay, E. coli heat-stable toxin, E. coli heat-labile enterotoxin, and cholera toxin were inhibited 35 to 70% by administration of BW942C. With the suckling mouse model, the fluid accumulation caused by E. coli heat-stable toxin was ablated by prior treatment with BW942C. The drug is currently being evaluated in patients with acute secretory diarrhea to determine its effect on clinical symptoms.

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.

An outbreak of gastroenteritis due to a heat-labile enterotoxin-producing strain of Escherichia coli

In April 1981, an outbreak of gastroenteritis, characterized by diarrhea and abdominal cramps, occurred in 282 of approximately 3,000 personnel at a large metropolitan hospital in San Antonio, Tex. There was a significant association between illness and eating at the hospital cafeteria (P = 0.0008), but no specific food could be incriminated. Stools or rectal swabs from 54 ill individuals produced almost pure cultures of Escherichia coli. Cultures from 51 of these subjects had identical antibiotic sensitivity patterns, and 38 had the same biotype. Isolates from 45 persons were tested for production of heat-stable and heat-labile enterotoxins, using the suckling mouse and Y-1 adrenal cell assays, respectively. Of 45 isolates, 41 produced heat-labile enterotoxins, while 0 of 45 produced heat-stabile enterotoxins. Two isolates were rough, and 34 of the remaining 43 were serotype O25:H-. Two strains were O25:H+. None of the 45 strains possessed hemagglutination patterns typical of colonization factor antigens I or II. Six of seven O25:H- heat-labile enterotoxin-positive strains selected at random were piliated as seen by electron microscopy but did not agglutinate with anti-colonization factor antigens I or II antisera.

A corticotropin (ACTH) related peptide with cytotoxic activity

A commercially available preparation of corticotropin was found to have potent cytotoxic activity for several established cell lines. Neither synthetic corticotropin nor alpha melanocyte stimulating hormone demonstrated this cytotoxic activity. Gel filtration allowed separation of a 2100 dalton cytotoxic peptide from the actual corticotropin present in the commercially prepared material. The structural relatedness of the cytotoxic peptide to corticotropin was demonstrated by neutralization with antisera to alpha melanocyte stimulating hormone. These studies indicate the existence of a newly identified ACTH related peptide with cytotoxic activity.

Evaluation of different cell cultures for the detection of heat-labile enterotoxins of Escherichia coli strains isolated from pigs

The sensitivity of various cell cultures to heat-labile enterotoxins (LT) and Verocytotoxin (VT) of fifteen E. coli strains isolated from cases of pig colibacillosis in Poland was estimated and compared with the effect of enterotoxins of four standard E. coli strains. Of ten tested cell cultures, only the following were susceptible: CHO, Vero, GMK, and HeLa. Eight strains showed CTE in He La and CHO cells and five of these reacted in Vero cells. The results appear to suggest that some of the tested E. coli strains isolated from pigs produced VT enterotoxin. Morphological changes caused by the above mentioned E. coli toxins in Vero and GMK cells took the form of cell rounding, followed by cell dissolution.

GM1 ganglioside enzyme-linked immunosorbent assay for detection of heat-labile enterotoxin produced by human and porcine Escherichia coli strains

Human and porcine enterotoxigenic strains of Escherichia coli were cultivated in tryptone-yeast extract medium or brain heart infusion broth and tested for production of heat-labile enterotoxin by the GM1 ganglioside enzyme-linked immunosorbent assay (GM1-ELISA) and the Y1 adrenal cell assay. When testing for enterotoxigenicity by the GM1-ELISA technique, homologous antisera for human and porcine heat-labile enterotoxins had to be used to detect enterotoxigenic strains of human and porcine origin, respectively. This observation indicates a serological difference between the heat-labile enterotoxins produced by human and porcine strains. Furthermore, brain heart infusion broth was found to have an inhibitory effect on detection of enterotoxin both in the GM1-ELISA and in a toxin-binding modification of the Y1 adrenal cell test, but not in the conventional adrenal cell assay.

Vibrio parahaemolyticus and related halophilic Vibrios

Approximately 30 years have elapsed since Dr. Fujino's original discovery that Vibrio parahaemolyticus (then termed Pasteurella parahemolytica) was the cause of "summer diarrhea" in Japan. Since that finding, V. parahaemolyticus has been established as a cause of gastroenteritis in numbers and places approaching global proportions. It has been isolated in marine and estuarine areas almost worldwide and despite its halophilic nature, V. parahaemolyticus has been isolated from saline-free waters. The relationship of this organism to the environment reveals a close association with other marine organisms especially copepods on which the Vibrios depend for survival in winter months and growth in summer months. There is a uniquely provocative disparity between human strains of V. parahaemolyticus which are Kanagawa phenomenon (KP) positive and the environmental strains which to a large extent are KP negative, the significance being that pathogenicity is measured according to the Kanagawa phenomenon (hemolytic activity) reaction. The hemolysin of the pathogenic strains is a thermostable, cardiotoxic protein, which thus far has not been implicated in the mechanism(s) which causes human gastroenteritis. The interest in this organism has been widened in recent years by the finding that similar organisms, V. alginolyticus, lactose positive vibrios and group F vibrios also cause serious disease in humans.

Immunological cross-reactivity of enterotoxins of Aeromonas hydrophila and cholera toxin

Pre-incubation with anticholera toxin (ACT) significantly reduced intestinal secretion induced by cell-free broth preparations of heat-labile toxins (LT) of Escherichia coli and Aeromonas hydrophila in jejunal perfusion experiments in rats in vivo. Pre-incubation with ACT also prevented cytotoxicity by E. coli LT in the Y1 cell culture system. Pre-incubation had no effect on cytotoxicity in Y1 and L132 cell lines or on haemolytic activity with cell-free preparations of A. hydrophila. In another series of experiments rats were immunized with cholera toxin given as an intraperitoneal priming dose followed 12 days later by intraduodenal boosting. Immunization significantly protected against net intestinal fluid secretion induced by enterotoxigenic E. coli and A. hydrophila and by cholera toxin.

Human lymphocyte production of corticotropin and endorphin-like substances: association with leukocyte interferon

Human leukocyte interferon (hIFN-alpha) preparations contain immunologically and biologically recognizable endorphin and corticotropin-like (ACTH-like) activities. The ACTH bioactivity was demonstrable only after pepsin or acid treatment. Highly purified hIFN-alpha was composed of two molecular species of interferon (18,500 and 23,000 daltons). Endorphin activity was associated with both of these molecules. Pepsin treatment of the 23,000-dalton but not the 18,500-dalton hIFN-alpha generated ACTH activity. In acid, the 23,000-dalton hIFN-alpha broke down into the 18,500-dalton form and ACTH (4500 daltons). The ACTH derived from hIFN-alpha by pepsin digestion comigrated with a purified ACTH standard in NaDodSO4/polyacrylamide gel electrophoresis. hIFN-alpha-producing lymphocytes showed positive immunofluorescence after staining with highly specific antisera to ACTH alpha-(1-13) and gamma-endorphin. Essentially 100% of the human peripheral lymphocytes were capable of producing both ACTH and gamma-endorphin-related substances, presumably associated with hIFN-alpha. These results strongly suggest a circuit between the immune and neuroendocrine systems which involves neuroendocrine hormone-like substances, some of which are associated with hIFN-alpha

Probing for enterotoxigenicity among the salmonellae: an evaluation of biological assays

Sixty-eight Salmonella strains representing 39 serotypes were variously screened for enterotoxigenicity by using the Chinese hamster ovary (CHO), Y1 adrenal, and Vero cell tests, rabbit skin tests for delayed permeabiltity factor (DPF) and rapid permeability factor (RPF), the rabbit ileal loop test, and the infant mouse test. An iron-sufficient medium, YT-1, and a deferrated medium, DF, were compared. Of the culture supernatant fluids of strains grown in DF medium, 66% yielded positive reactions in the CHO cell test compared with only 10% with TY-1 medium. The corresponding performances with supernatant fluids of DF medium cultures in Y1 adrenal and Vero cell tests were 85 and 69% positive, respectively. The overall agreement between the Y1 adrenal or CHO cell test and the rabbit skin test for DPF, i.e., positive or negative in both tests, was about 70%. Positivity in DPF tests was a better predictor of positivity in either the Y1 adrenal or rabbit ileal loop test than vice versa. CHO cell, DPF, and rabbit ileal loop reactivities of unheated culture filtrates were each neutralized by anticholera antitoxin. Only four strains gave positive reactions in the infant mouse test, whereas up to 66% were positive for RPF in rabbit skin, based on positivity in Ty-1 or DR medium or both. DPF and RPF were produced by 35% of the strains. Of the 28 isolates from human stools, 82 and 92% and all of 11 strains tested were positive in the DPF, Y1 adrenal cell, and rabbit ileal loop tests, respectively. The corresponding data for 17 sewage isolates, representing 17 different serotypes rarely isolated from human stools in Sweden, were 63 and 69% and 8 of 8 tested. On the basis of this investigation, rabbit skin tests for both DPF and RPF provide the most reliable means of screening for enterotoxigenicity among salmonellae.

Effect of fractions of Ethiopian And Norwegian colostrum on rotavirus and Escherichia coli heat-labile enterotoxin

Samples of colostrum from both Ethiopian and Norwegian women contained antirotavirus activities of immunoglobulin and non-immunoglobulin nature. No significant differences in rotavirus immunoglobulin A or in rotavirus-inhibiting activity were found between samples from the two countries. The non-immunoglobulin inhibitory activity was trypsin sensitive and heat stable (100 degrees C for 10 min). Escherichia coli heat-labile enterotoxin antibodies were measured in the colostrum samples by enzyme-linked immunosorbent assay. No E. coli enterotoxin-specific immunoglobulin A was detected, possibly due to the high background caused by the nonspecific adsorption of immunoglobulin A to the enzyme-linked immunosorbent assay plates in the absence of toxin. A total of 5 of 15 Ethiopian colostrum samples and 0 of 11 Norwegian colostrum samples neutralized the effect of E. coli heat-labile enterotoxin on YI adrenal cells. Both the Ethiopian and the Norwegian colostrum samples contained a non-immunoglobulin enterotoxin-inhibitory activity when the toxin was measured by enzyme-linked immunosorbent assay. This inhibitory activity was not trypsin sensitive, and extraction by chloroform-methanol indicated that the inhibitor was of a lipid nature.

Actions of cholera toxin and the prevention and treatment of cholera

The drastic intestinal secretion of fluid and electrolytes that is characteristic of cholera is the result of reasonably well understood cellular and biochemical actions of the toxin secreted by Vibrio cholerae. Based on this understanding it is possible to devise new techniques for the treatment and prophylaxis of cholera to complement those based on fluid replacement therapy and sanitation.

Diarrhea caused by Shigella, rotavirus, and Giardia in day-care centers: prospective study

We conducted a 19-month prospective study of children attending 20-day-care centers to determine the occurrence, causes, and transmission of gastroenteritis among children, staff, and family members. Nine centers had 15 outbreaks of diarrhea involving 195 patients. An enteropathogen was identified in all outbreaks. Shigella was detected in five outbreaks, rotavirus in two, giardia in one, and in the remaining seven multiple enteropathogens were identified. Rotavirus and Giardia occurred only in children less than 3 years of age; shigellosis occurred at all ages. In six DCC 68 single cases of diarrhea were not associated with an outbreak; an enteropathogen was identified in only three (4%) persons. Thirty-four family members (11%) developed diarrhea associated with the occurrence of gastroenteritis in children in six DCC evaluated for this problem. Secondary attack rates of diarrhea in families according to organisms identified in the DCC outbreaks were: Shigella 26%, rotavirus 15%, and G. lamblia 17%. DCC may play an important role in the epidemiology and transmission of gastroenteritis in the United States.

Interferon and adrenocorticotropic hormone induction of steroidogenesis, melanogenesis and antiviral activity

Adrenocorticotropic hormone (ACTH) and mouse but not human interferon caused a steroidogenic response and induced antiviral activity in mouse adrenal tumor (Y-1) cells. ACTH and human but not mouse interferon caused induction of melanin synthesis and antiviral activity in human melanoma cells. ACTH did not induce antiviral activity in mouse L or human amnion (WISH) cells. The hormonal activities of interferon were neutralized by specific rabbit anti-interferon sera. Thus, interferon has species-specific hormonal activity and ACTH has cell-specific antiviral activity. These results are discussed in terms of the possible natural functions of interferon polypeptide hormones.

Human leukocyte interferon: structural and biological relatedness to adrenocorticotropic hormone and endorphins

Anti-alpha-corticotropin [anti-ACTH alpha (1-13)](also alpha-melanotropin) and anti-gamma-endorphin antisera neutralized human leukocyte interferon activity but not fibroblast interferon activity. Human leukocyte interferon was not neutralized by anti-human lutenizing hormone (lutropin) or follicle-stimulating hormone (follitropin) antisra. Conversely, antisera to human leukocyte interferon neutralized ACTH activity. The neturalization of human leukocyte interferon by anti-human leukocyte interferon serum was partially blocked by ACTH. These studies show strong antigenic relatedness among human leukocyte interferon, ACTH, and endorphins, implying that there are underlying structural similarities. Structural relatedness is shown by pepsin cleavage of ACTH activity from human leukocyte interferon. The implication for the natural functions of human leukocyte interferon are discussed.

Non-antibody components in human milk inhibit Escherichia coli heat labile enterotoxin measured by an enzyme-linked immunosorbent assay

Milk from 11 Norwegian women was fractionated by ammonium sulphate precipitation and column chromatography. The milk samples inhibited the binding of heat labile E. coli enterotoxin to antibodies coated on microtiter plates in an enzyme-linked immunosorbent assay. Inhibiting activity was not detected when the toxin was measured in an adrenal cell assay. The inhibiting activity was of a non-immunoglobulin nature with an apparent molecular weight of greater than 400 000 in gel filtration experiments.

Hemagglutination and adhesiveness of toxigenic Escherichia coli isolated from humans

Toxigenic strains of Escherichia coli isolated from humans were studied for adherence to human buccal mucosal epithelial cells. The E. coli strains were labeled with 3H-amino acids or fluorescein isothiocyanate. Toxigenic E. coli strains varied in their ability to adhere in the presence of mannose. Of 32 toxigenic strains examined, 52% bound to the buccal cells, whereas none of 8 control strains did so (Mann-Whitney U test, P =0.007). The control strains were nontoxigenic E. coli isolates from humans, enterotoxigenic E. coli isolates from animals, and E. coli K-12 containing the K88 or K99 plasmid; these strains exhibited only background-level adherence in this assay. Among the toxigenic E. coli strains that bound to human buccal mucosal cells, there was no correlation with mannose-resistant hemagglutination (MR-HA) of guinea pig and human erythrocytes. Screening 32 strains, we found the following phenotypes: (i) MR-HA+, buccal adherent; (ii) MR-HA+, buccal nonadherent; (iii) MR-HA-, buccal adherent. Presumably the third group represents strains with another type(s) of surface attachment components not involved in the MR-HA reaction. Our findings indicate that a number of bacterial surface structures can function in MR-HA and buccal adherence.

Adaptation of the staphylococcal coagglutination technique for detection of heat-labile enterotoxin of Escherichia coli

Protein A-containing staphylococci coated with specific antiserum were tested for heat-labile enterotoxin of Escherichia coli. The immunological cross-reactivity of E. coli heat-labile enterotoxin with Vibrio cholerae toxin (choleragen) was the basis for sensitizing stabilized suspensions of the Cowan I strain of Staphylococcus aureus with anticholeragen. Unconcentrated culture supernatant fluid containing E. coli heat-labile enterotoxin produced macroscopic agglutination when mixed with sensitized staphylococci in capillary tubes. A total of 15 toxigenic and 61 nontoxigenic isolates were tested by the staphylococcal coagglutination technique in a coded fashion and found to be in agreement with previous results of the Chinese hamster ovary cell assay and the passive immune hemolysis test. The staphylococcal coagglutination technique is simple, relatively inexpensive to perform, and requires the immunoglobulin fraction of anticholeragen as the only specific reagent. The staphylococcal coagglutination technique appears to have potential for routine use in diagnostic microbiology laboratories.

Nutritional requirements for synthesis of heat-labile enterotoxin by enterotoxigenic strains of Escherichia coli

Optimal growth conditions have been established for production of heat-labile enterotoxin (LT) by both porcine and human strains of enterotoxigenic (ENT(+)) Escherichia coli. There were no unusual growth factor requirements, and some strains produced fairly high levels of LT in a basal salts medium containing 0.5% glucose if the pH was carefully controlled. Several amino acids markedly stimulated LT synthesis when added to the basal salts-glucose medium. Methionine and lysine were the most stimulatory for both human and porcine strains. Either aspartic acid or glutamic acid further enhanced LT synthesis in the presence of methionine and lysine, with aspartic acid being more stimulatory for porcine strains and glutamic acid more stimulatory for human strains. There were no apparent vitamin requirements and no unusual cations needed for toxin synthesis except that Fe(3+) was slightly stimulatory for porcine strains. The stimulation by Fe(3+) was observed only in the presence of the three amino acids, suggesting that the effect was indirect rather than on toxin synthesis. The carbon source also influenced the yield of LT. Glucose supported maximal synthesis, but other carbon sources which exhibit a high degree of catabolite repression also supported high levels of synthesis. Little or no LT was released below pH 7.0; therefore, because the pH drops during growth from 7.5 to 6.8, even in highly buffered media, it was necessary to adjust the pH to 8.0 to effect complete release of cell-associated toxin. The defined medium containing three amino acids reduced the amount of UV-absorbing material in culture supernatants about fivefold and increased LT activity for various strains from two- to fivefold over a complex Casamino Acids-yeast extract medium. Conditions found to be optimal for synthesis of LT were inhibitory for the heat-stable enterotoxin.

Demonstration of shared and unique immunological determinants in enterotoxins from Vibrio cholerae and Escherichia coli

Immunodiffusion and biological neutralization studies demonstrated that the heat-labile enterotoxin (LT) from Escherichia coli has antigenic determinants in common with each of the isolated subunits (A and B) of the enterotoxin (choleragen) from Vibrio cholerae. Each of the enterotoxins also possesses unique antigenic specificities. Monospecific antiserum to LT was prepared by immunization with antigens derived by immune precipitation of E. coli cell-free supernatant with isolated specific anticholeragenoid antibodies. This antiserum neutralized the biological acitivity of both LT and cholera enterotoxin and recognized antigens of both in immunodiffusion. This antiserum was adsorbed with choleragenoid to remove antibodies directed against the shared "B" immunological determinants. The neutralizing effect of the antiserum on cholera toxin was completely removed, but the neutralizing activity against the E. coli preparations was retained, although somewhat reduced. Antisera to the isolated subunits (A and B) of cholera enterotoxin neutralized the biological activity of cholera enterotoxin and LT. These antisera also recognized the homologous and heterologous antigens in immunodiffusion. Multiple forms or conformations of LT and its components may explain the diversity of the properties which have been reported for it.

Cytotoxic activity of Aeromonas hydrophila

Most strains of Aeromonas hydrophila tested demonstrated cytotoxic activity on several tissue-cultured cell lines. The cytotoxin is heat-labile, non-dialyzable, and immunologically distinct from that of Shigella dysenteriae and Clostridium perfringens. None of the aeromonas isolates was found to be enterotoxigenic by either tissue culture or rabbit ileal loop assays.

Prospective study of enteropathogens in children with diarrhea in Houston and Mexico

During a 22-month period, 595 children with diarrhea and 210 age-matched controls attending clinics in Houston (367 children) and Mexico (438) were prospectively evaluated for enteric pathogens. Enteropathogens associated with disease were Shigella (18%), rotavirus (14%), Salmonella (9%), toxigenic Escherichia coli (6%), and others (12%), including 14 Proteus isolates that caused rounding of adrenal cells. Enteropathogens were isolated from a greater (P less than 0.001) number of children with diarrhea (59%) than from asymptomatic controls (6%). Paired sera tested for antibody to heat-labile toxin of E. coli rarely demonstrated a fourfold rise during episodes of diarrhea. This study demonstrates: (1) more striking illness in children from Mexico; (2) more common occurrence of Shigella in Houston, and of rotavirus and Salmonella in Mexico; (3) lack of seasonal occurrence of rotavirus isolation in either population and a summertime occurrence of Shigella in Houston; (4) lack of toxigenic E. coli isolation in endemic diarrhea of either population; and (5) a significant (P less than 0.001) age-related acquisition of E. coli LT antibodies.

Immunological relationship of different preparations of coliform enterotoxins

Antisera raised in rabbits to ultrafiltrate toxin preparations containing either the heat-labile (LT) toxin form obtained from whole cell lysates or broth filtrates or the heat-stable (ST) toxin form prepared from broth filtrates from nontoxigenic and toxigenic strains of Escherichia coli and Klebsiella were examined for their ability to neutralize the secretory effect on water transport of these toxins in the rat jejunum as determined by the in vivo marker perfusion technique. Antisera to the heat-labile toxin derived from whole cell lysate preparations from nontoxigenic strains had no neutralizing effect. Antisera to both types of LT preparation from both toxigenic strains neutralized, with several exceptions, all of the homologous and heterologous LT toxins as well as a heat-labile toxin preparation derived from sequential ultrafiltration of cell-free whole cell lysates which had a defined molecular weight of between 30,000 and 100,000. These antisera also neutralized homologous and heterologous ST preparations obtained from broth filtrates, but they had no neutralizing effect on low-molecular-weight, ST toxin material obtained during the sequential ultrafiltration of cell lysates. Antisera to ST prepared from broth filtrates had no neutralizing capacity against either LT or ST toxin preparations. These observations (i) indicate that the immunological relationship of E. coli and Klebsiella LT and ST toxins extends to antisera raised against LT prepared by several different methods, (ii) raise the possibility that, based on the response to antisera to LT, there may be several immunologically heterogeneous forms of low-molecular-weight ST toxin, and (c) confirm the lack of immunogenicity of ST.

Mechanism of action of choleragen

Choleragen exerts its effect on cells through activation of adenylate cyclase. Choleragen initially interacts with cells through binding of the B subunit of the toxin to the ganglioside GM1 on the cell surface. Subsequent events are less clear. Patching or capping of toxin on the cell surface may be an obligatory step in choleragen action. Studies in cell-free systems have demonstrated that activation of adenylate cyclase by choleragen requires NAD. In addition to NAD, requirements have been observed for ATP, GTP, and calcium-dependent regulatory protein. GTP also is required for the expression of choleragen-activated adenylate cyclase. In preparations from turkey erythrocytes, choleragen appears to inhibit an isoproterenol-stimulated GTPase. It has been postulated that by decreasing the activity of a specific GTPase, choleragen would stabilize a GTP-adenylate cyclase complex and maintain the cyclase in an activated state. Although the holotoxin is most effective in intact cells, with the A subunit having 1/20th of its activity and the B subunit (choleragenoid) being inactive, in cell-free systems the A subunit, specifically the A1 fragment, is required for adenylate cyclase activation. The B protomer is inactive. Choleragen, the A subunit, or A1 fragment under suitable conditions hydrolyzes NAD to ADP-ribose and nicotinamide (NAD glycohydrolase activity) and catalyzes the transfer of the ADP-ribose moiety of NAD to the guandino group of arginine (ADP-ribosyltransferase activity). The NAD glycohydrolase activity is similar to that exhibited by other NAD-dependent bacterial toxins (diphtheria toxin, Pseudomonas exotoxin A), which act by catalyzing the ADP-ribosylation of a specific acceptor protein. If the ADP-ribosylation of arginine is a model for the reaction catalyzed by choleragen in vivo, then arginine is presumably an analog of the amino acid which is ADP-ribosylated in the acceptor protein. It is postulated that choleragen exerts its effects on cells through the NAD-dependent ADP-ribosylation of an arginine or similar amino acid in either the cyclase itself or a regulatory protein of the cyclase system.

Sensitivity of strains of enteropathogenic Escherichia coli to tobramycin and other antibiotics

The sensitivity patterns of strains of enteropathogenic Escherichia coli associated with diarrhoeal disease of infants to tobramycin and other antibiotics were estimated. The activity of tobramycin and of gentamicin alone and in combinations against recent isolates of enteropathogenic Escherichia coli was investigated. It was found that all the strains included in the present study were sensitive to tobramycin and gentamicin and most of them were sensitive to colistin and furazolidone. No significant differences in minimal inhibitory concentrations (MICs) and rates of killing were found between tobramycin and gentamicin, and they acted in an additive manner against most of the strains tested.

Enzyme-linked immunosorbent assay for detection of Escherichia coli heat-labile enterotoxin

The development of an enzyme-linked immunosorbent assay (ELISA) for the detection of heat-labile Escherichia coli enterotoxin is described. The assay, which is based on the immunological similarity between Vibrio cholerae toxin and heat-labile E. coli enterotoxin, is similar in design to a radioimmunoassay but utilizes enzyme-labeled rather than radioactive isotope-labeled reagents. The ELISA system is as sensitive as both radioimmunoassay and the y-1 adrenal cell assay for the detection of heat-labile E. coli enterotoxin but requires neither radioactive reagents nor tissue culture techniques. The ELISA is easy to perform and is adaptable for use in small laboratories.

Immunological interrelationships between cholera toxin and the heat-labile and heat-stable enterotoxins of coliform bacteria

Cholera toxin (CT) and the heat-labile (LT) toxin of Escherichia coli are known to share antigenic properties. The present study examined the immunological relationship of CT and the LT and heat-stable (ST) toxins of E. coli, Klebsiella pneumoniae, and Enterobacter cloacae. The neutralizing capacity of equine CT antiserum and of antiserum raised in rabbits to the LT toxin of the three species of coliform bacteria was evaluated by determining their capacity to inhibit the action of purified CT and semipurified ultrafiltration preparations of the coliform LT and ST toxins in inducing water secretion as assayed by the in vivo marker perfusion technique in the rat jejunum. One milliliter of antiserum to CT and to E. coli and Klebsiella LT completely neutralized the secretory action of each of these three toxins; effective serial dilutions of CT antiserum extended to 1 to 4, whereas those of the antisera to LT were limited to 1 to 2 in most instances. One milliliter of antiserum to E. cloacae LT partially neutralized each of the three coliform LT toxins; serial dilutions were inactive. Antiserum to E. cloacae LT did not neutralize CT. Antiserum to CT and to each of the three coliform LT toxins also had a weak neutralizing effect on the ST toxins of E. coli and Klebsiella, but they did not affect E. cloacae ST. Adsorption of the antiserum to CT and to each of the three LT toxins by incubation with a heat-inactivated preparation of either the homologous or a heterologous LT toxin completely abolished the neutralizing capacity of the antisera towards both LT and ST. These observations indicate that the immunological interrelationship of CT and E. coli LT extends to the LT toxins of Klebsiella and E. cloacae and, further, that these immunological properties are shared to a lesser extent by the ST toxins of E. coli and Klebsiella.

Effect of Staphylococcus aureus delta toxin on Chinese hamster ovary cell morphology and Y-1 adrenal cell morphology and steroidogenesis

Since Staphylococcus aureus delta toxin previously had been shown to increase the cyclic adenosine 3',5'-monophosphate (cAMP) content of guinea pig ileum, the effect of delta toxin on such cAMP-mediated responses as morphogenesis and steroidogenesis in cultured tissue cells was examined. In contrast to cholera toxin, delta toxin did not cause spindling of Chinese hamster ovary cells. Unlike adrenocorticotropin or cholera toxin, delta toxin was unable to cause rounding of Y-1 adrenal cells or to promote steroid production by the cells. S. aureus alpha toxin and enterotoxin B were also unable to cause rounding of Y-1 adrenal cells. Omission of Ca2+ from the media still allowed for increased steroid production by adrenocorticotropin but not by delta toxin. Delta toxin at concentrations greater than 10 micrograms/ml did cause lysis of both Chinese hamster ovary and Y-1 adrenal cells. These findings suggest that the increase in intestinal cAMP levels caused by delta toxin is mediated through a mechanism different from that initiated by cholera toxin.

Humoral immune response to the heat-labile enterotoxin of Escherichia coli in naturally acquired diarrhea and antitoxin determination by passive immune hemolysis

Acute- and convalescent-phase sera from 132 students attending a university in rural Mexico were assayed for antibody against the heat-labile enterotoxin (LT) of Escherichia coli by neutralization of LT activity in the Y-1 adrenal cell assay and by passive immune hemolysis of LT-sensitized sheep erythrocytes. The two titration methods produced comparable results with respect to antitoxin responses detected. An inverse relationship was found between acute geometric mean antitoxin titer and the occurrence of diarrhea associated with LT-producing E. coli, especially in newly arrived students from the U.S.A. A significant correlation (P less than 0.00 5) was found between a rise in antitoxin titer detectable by the passive immune hemolysis technique and diarrhea with LT-producing E. coli isolated. Thus, humoral antitoxin titers appear to be a useful indicator of immune status with respect to enterotoxigenic (LT) E. coli diarrhea.

Direct serological assay for the heat-labile enterotoxin of Escherichia coli, using passive immune hemolysis

Sheep erythrocytes sensitized with the heat-labile enterotoxin (LT) of Escherichia coli exhibited passive immune hemolysis (PIH) when exposed to specific antitoxin and complement. Thus, PIH serves as the basis for an in vitro serological assay for LT that is sufficiently specific and sensitive to differentiate LT-positive and LT-negative E. coli isolates. The PIH assay for E. coli LT has been performed with the standard Microtiter system and also by a tube method employing the spectrophotometric determination of hemoglobin release. The spectrophotometric method enhances the sensitivity, accuracy, and objectivity of the PIH assay. The increased sensitivity of the spectrophotometric method also facilitates the identification of LT-positive cultures employing polymyxin "mini-extracts" of whole overnight (18 h) broth cultures of 2.0% Casamino Acid-0.6% yeast extract-salts medium rather than mini-extracts of cells derived from 3.5-h subcultures. Thus, large numbers of E. coli isolates can be individually tested for LT in less than 24 h after broth inoculation by a rapid in vitro assay which requires anti-LT serum as the only specific reagent.

Assay of Escherichia coli heat-labile enterotoxin with vero cells

The continuous cell line of African green monkey kidney, Vero, showed characteristic morphological changes in response to culture filtrates from toxigenic strains of Escherichia coli. The response compared favorably with that of Y-1 (mouse adrenal) and CHO (Chinese hamster ovary) cells. Vero cells were the simplest and most economical to maintain in the laboratory.