Assay, characterization, and localization of an enterotoxin produced by Salmonella

Effects of carbon and nitrogen sources, sodium chloride and culture conditions on cytotoxin production by Salmonella choleraesuis

The effects of carbon and nitrogen sources, incubation temperature, shaking speed, initial pH of culture broth as well as various concentration of NaCl on the production of cytotoxin by Salmonella choleraesuis SC-5 were evaluated in the present study. Results reveal that the optimal temperature, initial medium pH and shaking speed for cytotoxin production was 37 degrees C, pH 6.0-8.0 and 100 rpm, respectively. Tryptone was the best of the eight nitrogen sources tested for toxin production by S. choleraesuis. Among the nine carbon sources tested, S. choleraesuis produced a higher amount of cytotoxin in media containing glucose, fructose, galactose, sorbitol or mannitol as the carbon source. No toxin was detected in broths containing 4.0% or more sodium chloride in Tryptic soy broth (TSB). Cultures of S. choleraesuis in the medium containing 2.0% tryptone, 0.5% NaCl, 0.25% K2HPO4 and 0.25% of the best carbon source under the optimal conditions for 14 h resulted in the highest cytotoxin production. The Vero cell CD50 of S. choleraesuis lysate of cells grown under these optimal conditions was a titer of 589-758 per mg of lysate protein.

Occurrence of the toxin dehydroabietic acid in Salmonella typhimurium

Many strains of Salmonella typhimurium studied in our lab demonstrated marked differences in the pathogenicity for guinea pig, chicken and Hela cells. As a result, a pathogenic strain of S. typhimurium, strain 9SR2, was evaluated for lipophilic components that may be associated with virulence using gas chromatography/mass spectrometry. The hydroxylated fatty acids 2-hydroxytetradecanoic acid (2-OH-14:0) and 3-hydroxytetradecanoic acid (3-OH-14:0) often present in lipid A, a potent endotoxin, were observed as their methyl esters. The cyclic fatty acids methylene-hexadecanoic acid (C17delta) and methyleneoctadecanoic acid (C19delta) also were detected. The nephrotoxic and neurotoxic diterpenoid resin acid, dehydroabietic acid, was observed for the first time from S. typhimurium in both the total lipid and diglyceride fractions and determined as its methyl ester at m/z 314.2246. Due to its previously established toxicity, dehydroabietic acid may be a factor associated with virulence of S. typhimurium.

Enterotoxin and cytotoxin production by Salmonella enteritidis strains isolated from gastroenteritis outbreaks

Seventy-six Salmonella enteritidis, three Salmonella virchow and one Salmonella bradenrup strains were screened for enterotoxigenicity by using the Chinese hamster ovary (CHO), Y1 adrenal, Vero and HeLa cell tests. All the strains gave positive reactions for enterotoxin production, except one, and the relative sensitivity to the toxin exhibited by the different cell lines was evaluated. An enterotoxic activity has been identified in sonicated extracts of Salm. enteritidis. This enterotoxin was purified on Agarose A-5m (Bio-Rad) and Superose 12 HR 10/30 column. The enterotoxic activity was eluted from the Superose column in the first peak. Like Vibrio cholerae toxin CT and Escherichia coli enterotoxin LT, it was blocked by GM1 ganglioside, but at a higher concentration. In addition, a cytotoxic factor has been partially identified. The procedure for isolating the cytotoxin included ammonium sulphate precipitation, size-exclusion chromatography and anion exchange chromatography. This cytotoxin factor caused inhibition of protein synthesis in cultured cells, as determined by flow cytometry and [3H]-leucine incorporation. Flow cytometry analysis also showed an activation of CHO cells when exposed to this cytotoxic factor resulting in a state of active growth. Cytotoxic activity was not blocked by gangliosides.

The pef fimbrial operon of Salmonella typhimurium mediates adhesion to murine small intestine and is necessary for fluid accumulation in the infant mouse

We investigated the role of the pef operon, containing the genes for plasmid-encoded (PE) fimbriae of Salmonella typhimurium, in adhesion to the murine small intestine. In an organ culture model, a mutant of S. typhimurium carrying a tetracycline resistance cassette inserted in pefC was found to be associated in lower numbers with murine small intestine than the wild-type. Similarly, heterologous expression of PE fimbriae in Escherichia coli increased the bacterial numbers recovered from the intestine in the organ culture model. Adhesion to villous intestine mediated by PE fimbriae was further demonstrated by binding of an E. coli strain expressing PE fimbriae to thin sections of mouse small intestine. The contribution of pef-mediated adhesion on fluid accumulation was investigated in infant mice. Intragastric injection of S. typhimurium 14028 and SR-11 caused fluid accumulation in infant mice. In contrast, pefC mutants of S. typhimurium 14028 and SR-11 were negative in the infant mouse assay. Introduction of a plasmid containing pefBACD and orf5, the first five genes of the pef operon, into the pefC mutant complemented for fluid accumulation in the infant mouse assay. However, heterologous expression of PE fimbriae in E. coli did not result in fluid accumulation in the infant mouse, suggesting that factors other than fimbriae are involved in causing fluid accumulation.

Alternate routes of invasion may affect pathogenesis of Salmonella typhimurium in swine

Transmission of Salmonella typhimurium in swine is traditionally believed to occur by the fecal-oral route, with invasion through the intestinal wall and Peyer's patches. However, involvement of the upper respiratory tract may be equally important. An esophagotomy was performed on 6- to 8-week-old pigs. Esophagotomized pigs were challenged intranasally with 10(9) CFU of S. typhimurium cells and necropsied at 3, 6, 12, and 18 h postinoculation (p.i.). By 3 h p.i., S. typhimurium was recovered from cecum, colon, head, and thoracic tissues and from the middle ileum involving a large number of Peyer's patches. The ileocolic lymph nodes and ileocolic junction were not positive for S. typhimurium until 6 and 12 h p.i., respectively. Additional pigs were inoculated transthoracically with 10(9) CFU of S. typhimurium and necropsied at 3 and 18 h p.i. By 3 h p.i., all tissues were positive for S. typhimurium. Tonsil explants seeded with 10(9) CFU of S. typhimurium indicated that within 6 h p.i., S. typhimurium was located within the tonsilar crypts. These data show that after intranasal inoculation, S. typhimurium rapidly appears in the gut tissues and suggest that the tonsils and lung may be important sites for invasion and dissemination of Salmonella species.

The Salmonella dublin virulence plasmid mediates systemic but not enteric phases of salmonellosis in cattle

Plasmid-bearing and plasmid-free isolates and a plasmid-cured strain of Salmonella dublin were compared for virulence in calves. The plasmid-bearing strains were highly virulent, causing severe enteric and systemic disease with high mortality. In contrast, the plasmid-free strains caused diarrhea but only low mortality. The infection kinetics of a wild-type and a derivative plasmid-cured strain were compared. Both strains were isolated in high numbers from intestinal sites at 3 and 6 days after oral challenge and were isolated at comparable frequencies from systemic sites at 3 days, but not at 6 days, when the wild-type strain was predominant. The strains were equally invasive in intestinal epithelia with and without Peyer's patch and elicited comparable secretory and inflammatory responses and intestinal pathology in ligated ileal loops. The effect of the virulence plasmid on growth kinetics and on the outer membrane protein profile was assessed in an in vivo growth chamber. The virulence plasmid did not influence either extracellular growth or the expression of major outer membrane proteins. These observations demonstrate that the virulence plasmid is not involved in either the enteric phase of infection or the systemic dissemination of S. dublin but probably mediates the persistence of S. dublin at systemic sites.

Current perspectives in salmonellosis

Salmonellosis remains an important human and animal problem worldwide and, despite extensive research effort, many of the details of its pathogenesis are not known. While there have been recent advances in some aspects of pathogenesis, other areas are not understood. The host adaptation shown by several serotypes and the recent dramatic changes in the predominance of particular serotypes are examples. Molecular techniques using in vitro model systems have identified several genes involved in adhesion and invasion, though their function and even their relevance to disease remain poorly defined. Similarly, several potential toxins have been identified and the genes cloned, although their significance is far from clear. Some of the essential genes on the large virulence plasmids have been defined, and these are known to be necessary for the establishment of systemic infection. Two of these genes are regulatory, but the function of the other genes is unknown. A general theme has been the identification of gene systems involved in regulation of virulence. New vaccines, based on 'rational attenuation' are being designed, and these have also been used to carry heterologous antigens; such vaccines are currently undergoing trials. The improved understanding of the pathogenesis of salmonellosis may also provide a model of wide applicability to a more general understanding of bacterial pathogenesis. New techniques, including the polymerase chain reaction, are being applied to diagnose salmonellosis.

Pathogenicity of Salmonella enteritidis in poultry

Salmonella enteritidis is a common pathogen of all species of mammals and fowls. The recent increase in the number of outbreaks of food poisoning due to S. enteritidis in man was epidemiologically analysed, and it was considered that contaminated eggs or egg products were the major source of this infection. To assist in prevention and eradication of human food poisoning many investigators have studied the pathogenicity of S. enteritidis in poultry. Gross pathological observations after natural and experimental infections with S. enteritidis in poultry revealed that this organism may cause systemic infection in chicks and laying hens accompanied by prolonged faecal shedding. Some variations in the mortality rates, clinical symptoms, faecal shedding and frequency of production of contaminated eggs were observed in the chicks and hens experimentally infected with S. enteritidis isolates. Choice of bacterial strain, phage type, age of bird and inoculum size may affect the outcome of an infection. Moreover, isolation of the organisms from the ovaries, oviducts and egg contents indicates the possibility of transovarian infection of S. enteritidis in chickens. Some virulence factors associated with S. enteritidis are also reviewed in the present paper.

Location of the enterotoxin gene from Salmonella typhimurium and characterization of the gene products

The enterotoxin gene (stn) in Salmonella typhimurium (Q1 strain) was confined to an 800 bp ClaI-EcoRI genomic DNA fragment (pCE3) that coded for two polypeptides (25 and 12 kDa) under the control of the T7 RNA polymerase/promoter system. The appearance of the 25 kDa protein corresponded to the enterotoxic activity, as determined by elongation of Chinese hamster ovary (CHO) cells, fluid accumulation in rabbit intestinal loops, and altered vascular permeability in rabbit skin. The stn gene products (STN) caused an elevation of intracellular cAMP in CHO cells. These values were at control levels in stn mutants devoid of enterotoxicity, and the 25-kDa protein concurrently disappeared. The biological activity of the heat-labile enterotoxin was blocked by GM1 ganglioside and neutralized by affinity-purified antibodies made against cholera toxin. The 12 kDa protein however was not correlated with an enterotoxic response.

Expression and characterization of the cloned Salmonella typhimurium enterotoxin

Earlier, our laboratory reported the cloning of a chromosomally encoded cholera toxin (CT)-like enterotoxin gene from Salmonella typhimurium Q1 into pBR322. Cell lysates from the plasmid clone pC1, containing a 4.8 kb EcoR1 DNA fragment from Salmonella, caused elongation of Chinese hamster ovary (CHO) cells and this biologic activity was neutralized by anti-CT. However, this cloned gene product did not elicit fluid secretion in the rabbit intestinal loop (RIL) model, because of poor expression. We report here, subcloning of a 4.8 kb EcoRI and a 2.7 kb HindIII/Eco Rl fragment into a high expression T7 RNA polymerase/promoter system. Cell lysates from these clones elicited fluid secretion in the RIL model, caused firm induration in rabbit skin and elongated CHO cells. These biological activities were neutralized by anti-CT. SDS-PAGE and subsequent fluorographic analysis of Escherichia coli, harboring recombinant plasmids in a T7 expression system, revealed the presence of two prominent 35S-labeled polypeptides of 25 and 12 kDa, which were immunoprecipitated with anti-CT. The enterotoxin appeared to be 125 kDa in size, based on chromatography on a P-300 column, had a pl of 6.6 to 6.8, and was heat-labile (60 degrees C/5 min). Unlike cloned CT and heat-labile enterotoxin (LT-l), which were localized in the periplasm, the Salmonella enterotoxin was cytoplasmic in nature.

Toxicity of cyst extract of Sarcocystis fusiformis from buffalo in rabbits and mice

The toxic effect of cysts of Sarcocystis fusiformis (of buffalo origin) in rabbits and mice have been studied. It is shown that inoculation of a 2 mg ml-1 concentration of protein of the macrosarcocyst extract (ME) into rabbits and mice was lethal. The toxic substance was thermolabile at greater than or equal to 60 degrees C for 30 min. Protease and trypsin caused inactivation, while papain did not affect the toxicity. ME was found to be non-dialysable, but precipitable. There was also no effect of a pH of 6-9, while pH 4-5 altered the toxicity and pH 10 only partially affected the toxic effect.

Biological and immunological characterization of a cloned cholera toxin-like enterotoxin from Salmonella typhimurium

A chromosomal DNA fragment, encoding an enterotoxin gene of Salmonella typhimurium Q1, was cloned into bacteriophage EMBL3 and plasmid vector pBR322. The recombinant clones lambda B8 and pC1 were identified using a synthetic oligonucleotide probe made to the B subunit region of the cholera toxin gene (ctx). Cell lysates of Escherichia coli VCS257 [lambda B8] induced fluid secretion in rabbit intestinal loops, while lysates of E. coli DH5 alpha [pC1] failed to elicit an enterotoxic response in this model. Both lysates and partially purified preparations elongated Chinese hamster ovary (CHO) cells, elevated cellular cAMP and PGE2, and bound to ganglioside GM1. The biological activity associated with the cloned enterotoxin was neutralized by monospecific antiserum to cholera toxin (CT). Immunoblots of pC1 and lambda B8 lysates probed with anti-CT, exhibited a 30 kDa protein similar to that of pJM17, which carried the ctx gene. Under non-dissociating conditions, anti-CT immunoblots of the same lysates revealed two proteins, one corresponding in size to the holotoxin and the other to CT-A. When analysed by DNA-directed protein synthesis in vitro, both pC1 and lambda B8 DNA expressed two unique proteins (30 and 11 kDa) similar to that of pJM17.

Enterotoxic, cytotoxic, necrotic and lethal activities in cell-free extracts of Salmonella strains isolated from humans

Unconcentrated cell-free sonic extracts from thirty Salmonella strains isolated from the faeces and blood of humans were investigated for the production of enterotoxins in various tests (Vero cell, infant mouse, rabbit skin permeability and rabbit ileal loop), as well as for lethal activity in adult mice. Sonic extracts from 23 (76.7%) strains were lethal for mice, 21 (70%) increased skin permeability and 3 (10%) showed necrotizing activity for the rabbit skin. No Salmonella strain producing typical Escherichia coli toxins, such as thermolabile (LT) or thermostable (STa) enterotoxins, Verotoxin (VT) or cytotoxic necrotizing factor (CNF) cytotoxins, were detected. Non-repetitive fluid accumulation in rabbit loops was obtained when unconcentrated sonic extracts from 10 selected strains were assayed in seven rabbits. Growth of Salmonella in casamino acid yeast extract medium, followed by treatment of bacterial cells with polymyxin B, was demonstrated to be a rapid and sensitive method for releasing the delayed permeability factor.

Molecular cloning of a Salmonella typhi LT-like enterotoxin gene

Diarrhoea is a common event during typhoid fever; nevertheless, the possible participation of a diarrhoea-inducing enterotoxin has not been described (Roy et al., 1985). Recombinant bacteriophage lambda FDC1 was isolated from a genomic library of Salmonella typhi, the causal agent of typhoid fever, by screening with a probe for the B subunit gene of the heat-labile, cholera-like, Escherichia coli enterotoxin (LT). Lambda FDC1 codes for an enterotoxin that causes secretion in rat ileal loops, that elongates Chinese hamster ovary (CHO) cells, that is recognized by antibodies against LT, and does not bind in vitro to ganglioside GM1. These results should allow further studies towards elucidating a possible role for the S. typhi enterotoxin in the pathogenesis of typhoid fever.

Immunogenic and antigenic characteristics of Salmonella heat-labile enterotoxin

The intramuscular immunization of rabbits with enterotoxin of S. weltevreden failed to provide protection against challenges with homologous Salmonella enterotoxin as well as heterologous enterotoxins (cholera toxin or E. coli LT). Similar results were obtained in rabbits immunized with cholera toxin, choleragenoid and E. coli LT. However, Salmonella antitoxin contained neutralizing antibodies against Salmonella enterotoxin (but not against cholera toxin) and thus was capable of neutralizing Salmonella enterotoxin when tested for skin permeability reaction. Immunodiffusion experiments showed that antitoxin prepared against the enterotoxin of one of the strains of S. weltevreden formed precipitin bands with enterotoxin preparations of 5 strains of S. weltevreden and 2 strains of S. anatum. However, Salmonella antitoxin failed to form precipitin bands with enterotoxins of other heterologous Salmonella species (S. dublin, S. enteritidis, S. hindmarsh and S. newport), cholera toxin and E. coli LT. The immunoelectrophoretic studies corroborated the results obtained by double immunodiffusion experiments. However, both Salmonella and cholera toxins migrated electrophoretically toward the cathode and resembled globulin in this respect. Salmonella enterotoxin, though immunogenic, yet proved unprotective through the parenteral route and appears to be antigenically distinct from cholera and E. coli enterotoxins.

Bacterial gastroenteritis

Acute diarrhea is a major cause of childhood morbidity. Important advances in the understanding of bacterial gastroenteritis have been made in the past two decades. This article reviews the epidemiology, pathogenesis, and methods of diagnosis of bacterial gastroenteritis. Bacterial enteric pathogens common to North America are discussed in more detail.

Evaluation of immuno-dot-blot assay for detection of cholera-related enterotoxin antigen in Salmonella typhimurium

Twenty-five strains of Salmonella typhimurium isolated in India were examined for the presence of cholera/coli-related enterotoxin antigen by a previously described latex particle agglutination test and by a newly developed immuno-dot-blot test using immunopurified goat antibody against the cholera-related enterotoxin isolated from an Escherichia coli strain of human origin. The immuno-dot-blot assay could detect 0.02 ng of purified enterotoxin. The amount of toxin antigen detected varied widely from strain to strain. Fourteen of the 25 polymyxin B-treated extracts of bacteria harvested from 6-h Casamino Acids-yeast extract broth cultures gave positive results in both serologic assays as well as in rabbit skin tests for delayed permeability factor. An additional strain was positive only in the immuno-dot-blot. Five of six stool isolates and six of seven blood isolates tested gave positive reactions. Two isolates of Salmonella enteritidis tested were also positive. The immuno-dot-blot test appears to be a simple, rapid, and reliable method for detection of cholera-related enterotoxin antigen in S. typhimurium. The demonstration of a cholera-related enterotoxin, even in small amounts, in a facultative intracellular pathogen raises interesting questions regarding its potential role in pathogenesis both of diarrheal disease and systemic infections caused by salmonellae.

Competitive enzyme-linked immunosorbent assay for cholera-related enterotoxins in Salmonella typhimurium

We report a rapid competitive enzyme-linked immunosorbent assay to screen Salmonella typhimurium strains for cholera-related enterotoxin antigens. Polymyxin B extracts of bacterial cells from syncase-glucose broth cultures of 7 of 15 strains gave positive results. The specificity of the test was confirmed with known heat-labile-enterotoxin-positive and -negative Escherichia coli strains which gave significantly different values.

Pathophysiology of neonatal calf diarrhea

Neonatal calf diarrhea caused by bacterial enterotoxins, bacterial or parasitic-induced inflammation, or virus-induced villous atrophy leads to intestinal hypersecretion, malabsorption, or both. Mechanisms of secretion and malabsorption differ depending on the agent, suggesting that different modes of treatment must be employed to be effective. Currently, oral rehydration solutions and the pharmacologic blockade of secretory processes are being evaluated in these various diseases.

Pathology of the alimentary tract in Salmonella typhimurium food poisoning

The pathology of the alimentary tracts of nine patients dying of Salmonella typhimurium infection is reviewed. Two patients had previous gastric operations, supporting previous reports that such patients are more susceptible to food poisoning. Four had no parietal (oxyntic) cells in the gastric mucosa, suggesting hypo- or anacidity. Only one had acute gastritis. None had acute enteritis, but in half of the patients, subtle histological changes suggested an 'enteropathy'. Acute diffuse colitis with abundant crypt abscesses, without stromal abscesses in the lamina propria, was the most constant finding and reparative features started very early, and occurred in later deaths. Under ideal circumstances this crypt abscess is readily distinguished from that of idiopathic ulcerative colitis, but can be confused with the crypt abscess of acute bacillary (sonne) dysentery. While the florid colonic changes may have settled in the late deaths, active inflammation is commonly present in the appendix mucosa on histology. The pathology of the alimentary tract in S typhimurium infection differs from that of S typhi and S paratyphi infections. There is little evidence of gastroenteritis, although subtle changes occur in the stomach and small intestine. The features are those of acute diffuse colitis with histological appendicitis, distinguishable from idiopathic ulcerative colitis.

Nonfluid therapy and selected chemoprophylaxis of acute diarrhea

Various available forms of therapy can decrease morbidity and mortality associated with acute diarrhea. Oral fluids represent the cornerstone of therapy of all cases. A variety of agents acting nonspecifically can decrease diarrhea and improve other worrisome symptoms associated with enteric infection. Kaopectate makes the stool more formed but has little additional effects. Bismuth subsalicylate, an antisecretory agent, reduces the number of stools passed by about 50 percent and improves other associated symptomatology. The drugs that affect motility such as loperamide and diphenoxylate are the most active of the nonspecifically acting drugs. They must be avoided in patients with significant fever and dysentery. Trimethoprim/sulfamethoxazole is now considered the drug of choice for shigellosis due to the presence of ampicillin-resistant Shigella strains in most regions of the world. Trimethoprim/sulfamethoxazole is also an effective form of therapy for enterotoxigenic Escherichia coli infection and for traveler's diarrhea without definable cause. Erythromycin, although not proved to be effective against Campylobacter, probably shortens the disease. Furazolidone, although not dramatically effective, has a spectrum of activity that includes Shigella, enterotoxigenic E. coli, Campylobacter, and Giardia lamblia. It may not be effective in severely ill (hospitalized) patients with diarrhea. The various forms of available therapy can be administered empirically, depending on symptomatology. Mildly ill patients (one to three unformed stools in 24 hours with minimal additional symptoms) probably are best treated with fluids only. Mild to moderately ill persons (three to six unformed stools in 24 hours) can be treated with a drug that acts nonspecifically, such as bismuth subsalicylate or loperamide. Those with severe diseases (six or more unformed stools with moderate to severe associated symptoms), particularly when associated with fever and the passage of bloody mucoid stools, may be given an antimicrobial agent. The antimicrobial drug given will be determined by ancillary laboratory tests (dark-field examination or examination of a wet-mount preparation for motile Campylobacter or stool culture for Shigella, Campylobacter, or Salmonella) or may be administered on an empiric basis. Traveler's diarrhea can be eliminated in selected persons by the administration of a pharmacologic agent. Liquid bismuth subsalicylate is effective in large doses, which may be impractical. Studies with the tablet formulation suggest that it is partially effective in preventing the illness. Doxycycline and trimethoprim/sulfamethoxazole are more effective, particularly when admini

Enterotoxin-induced fluid accumulation during experimental salmonellosis and cholera: involvement of prostaglandin synthesis by intestinal cells

Challenge of rabbit intestinal loops with Salmonella typhimurium or Vibrio cholerae resulted in significant elevation of mucosal cyclic adenosine monophosphate (cAMP) and prostaglandin concentrations. This effect could be reproduced in vitro by exposing either isolated epithelial cells from normal rabbits or Chinese hamster ovary cells to purified cholera toxin or cell-free lysates of Salmonella. Indomethacin treatment of animals challenged with Salmonella resulted in less fluid accumulation, in addition to lower concentrations of intestinal cAMP and prostaglandins, compared to that of similarly changed loops in normal animals. Likewise, intestinal loop challenge of indomethacin-treated rabbits with V. cholerae or purified cholera toxin also resulted in decreased fluid secretion and diminished levels of tissue cAMP and prostaglandins. Intestinal loop tissue from normal animals challenged with V. cholerae displayed 10-fold higher levels of prostaglandins than tissue from uninfected animals. Prostaglandin levels in Salmonella-infected intestinal loops were similarly elevated, but by only 2-3 fold. Chinese hamster ovary cell monolayers were simultaneously exposed to either 10 ng of cholera toxin or 20 microliter of Salmonella lysate and varying concentrations of indomethacin ranging from 1 ng/ml to 10 micrograms/ml. Indomethacin decreased both cAMP and prostaglandin levels in Chinese hamster ovary cells. At high indomethacin concentrations, the cells lost their ability to respond to stimulation with either cholera toxin or Salmonella lysate, while retaining greater than 95% viability as determined by trypan blue exclusion. The prostaglandin and cAMP content of epithelial cells from Salmonella-challenged loops was increased in crypt epithelial cell fractions. Prostaglandin concentrations were elevated in isolated intestinal epithelial cells exposed to purified cholera toxin in vitro. These data indicate that prostaglandins synthesized by the epithelial cells are involved in the pathogenesis of both experimental cholera and salmonellosis. The data are consistent with an enterotoxin-mediated mechanism for both diarrheal diseases and argue against the role of inflammatory cells as the source of elevated cAMP and prostaglandins appearing in the intestinal mucosa during experimental salmonellosis.

Pathogenesis of experimental salmonellosis: inhibition of protein synthesis by cytotoxin

Salmonella cytotoxin present in cell lysates inhibited protein synthesis in both Vero cells and isolated rabbit intestinal epithelial cells. A time-course experiment with Vero cells revealed progressive inhibition of protein synthesis beginning as early as 1 h after exposure to the Salmonella cell lysate. Significant loss of membrane integrity of Vero cells (measured by release of [3H]uridine) did not appear before 24 h. To demonstrate inhibited protein synthesis in intestinal tissue during experimental salmonellosis, we isolated rabbit epithelial cells from Salmonella-infected and control intestinal loops. Measurement of [3H]leucine incorporation showed a similar decrease in protein synthesis in epithelial cells from the Salmonella-infected intestinal loop as that from an adjacent control loop. A similar pattern of protein synthesis inhibition was observed when isolated epithelial cells from normal rabbit intestine were exposed to the Salmonella cell lysate. The inhibited protein synthesis in the intestinal cells provides a molecular basis for the cellular damage caused by Salmonella cytotoxin during experimental salmonellosis.

Effect of lipopolysaccharide mutations on the pathogenesis of experimental Salmonella gastroenteritis

Lipopolysaccharide mutants of Salmonella typhimurium provoked diminished amounts of fluid in rabbit ileal loops as compared with the response to the wild type. The responses elicited by these mutants ranged from 0 to 60% of that caused by the parent strain. Two completely rough mutants and one leaky rough mutant were chosen for further study. Purified lipopolysaccharide from the parent and the mutant strains failed to stimulate fluid exsorption in ileal loop experiments. Histological studies revealed that the three lipopolysaccharide mutants were less invasive than wild type and were less able to generate an inflammatory reaction in the rabbit ileum. A Salmonella enterotoxin was present in culture filtrates from one rough mutant and the wild type; however, the rough mutant appeared to produce less toxin. Enterotoxic activity was absent in culture filtrates from the two other rough mutants. These results suggest that reductions in both invasiveness and the ability to produce Salmonella enterotoxin decreased the ability of these mutants to provoke fluid exsorption. Also, the results indicate that lipopolysaccharide mutations can have a profound effect on the enteropathogenic properties of S. typhimurium.

Cytotonic enterotoxins and cytotoxic factors produced by Salmonella enteritidis and Salmonella typhimurium

Strains of Salmonella enteritidis and Salmonella typhimurium isolated from human diarrheal cases produced heat-labile enterotoxin(s) and cytotoxic factor(s) which elongated, lysed or deformed Chinese hamster ovary cells in tissue culture. The toxin(s) caused fluid accumulation in ligated rabbit gut loops and produced increased skin permeability. Salmonella toxin produced by these strains does not cross-react immunologically with high titer Vibrio cholerae toxin antisera or heat-labile Escherichia coli enterotoxin antisera used in this study and does not bind to galactose--Sepharose gel. The activity of the toxin was not inhibited by GM1-ganglioside.

Cell-free extracts of Salmonella inhibit protein synthesis and cause cytotoxicity in eukaryotic cells

Cell-free, unconcentrated sonic extracts of several serotypes of Salmonella caused extensive detachment of intact Vero cells. Undiluted sonic extracts of these strains exhibited cell detachment in the range 20-50%. Upon dilution, the extract preparations caused a linear, dose-related cytotoxic effect on Vero cell monolayers. The heat-lability (100 degrees C for 30 min) of much of the cytotoxic activity in the extract ruled out the possible involvement of endotoxin in this toxic effect for eukaryotic cells and suggested that this toxic factor is probably a protein. It was demonstrated that these sonic extracts also inhibited the incorporation of 3H-leucine by Vero-cells and that the inhibitory events occurred 1-2 hr after exposure. When subjected to heating at 100 degrees C for 30 min, the ability of Salmonella extracts to inhibit protein synthesis of Vero cells was significantly but only partially destroyed. Because of Salmonella extract-treated Vero cells did not release 3H-uridine until 24-48 hr after addition of sonic extracts, cell lysis was considered to be a secondary event resulting from the early shutdown of protein synthesis, rather than a direct effect of the toxic factor on membrane integrity. Further studies are needed to determine if these two biological activities of Salmonella sonic extracts are due to a single toxic molecule or result from two distinct toxin molecules.

Experimental Salmonella anatum infection in horses

Salmonella anatum was given orally to 8 horses on 11 occasions in doses ranging from 9.5 X 10(6) to 8.8 X 10(11) organisms. Four distinct syndromes were induced based upon clinical, laboratory and pathological findings: (1) asymptomatic; (2) moderate clinical signs with or without changes in faecal consistency; (3) fever, depression, anorexia with unstructured or diarrhoeic faeces; and (4) septicaemia with or without diarrhoea, and peripheral circulatory failure. All animals excreted the organism. The peak temperature preceded the onset of diarrhoea by 1 or 2 days. Changes in faecal consistency were associated with direct isolation of the organism. The degree of neutropaenia increased with the dosage. Blood cultures were unsatisfactory, only 1 of 33 samples being positive. The serological responses were not significant although one animal displayed a significant seroconversion consistent with the clinical reaction. Indomethacin was not of value in moderating intestinal fluid secretion in one animal. The distribution and quantitation of positive cultures at autopsy closely reflected the type of syndrome induced. The invasiveness of the organism was confirmed by frequent direct recoveries from intestinal wall and draining lymph node samples. S. anatum appears to be of similar pathogenicity to S. typhimurium in the horse, at least under experimental conditions.

Enterotoxigenicity and invasiveness of Salmonella species

A large number of enterotoxigenic strain was encountered in a group 56 Salmonella cultures belonging to 8 species viz., S. alachua, S. anatum, S. dublin, S. Enteritidis, S. hindmarsh, S. newport, S. typhimurium, S. weltevreden, and 5 serotypes of S. arizona (16:z4:--; 48:1,v:z56; 53:z52:z53; 60:r:z; 60:i:z53). These cultures were isolated mainly from humans and animals suffering from gasteroenteritis. The enterotoxigenic (diarrhoeagenic) Salmonella cultures possess capacities for both skin permeation and epithelial penetration (invasiveness). Preliminary characterization revealed that Salmonella enterotoxin is a heat-labile protein of high molecular weight. It is suggested that enterotoxigenic and invasive properties play a vital role in the pathogenesis of Salmonella diarrhoea.

Effect of pH on the production of the Kanagawa hemolysin by Vibrio parahaemolyticus

Production of the Kanagawa hemolysin by patient strains of Vibrio parahaemolyticus was found to respond to the pH rather than to the type of carbohydrate present in the growth medium. Regardless of the carbohydrate present, hemolysin production in peptone broth cultures occurred only when the pH was between 6.5 and 5.5. Mannitol, the sugar used in the Wagatsuma agar, lowered the pH to within this range, thus providing optimal conditions for hemolysin production. Glucose and mannose, although readily metabolized, lowered the pH below this range, inhibiting growth and hemolysin production. Alkaline cultures either without carbohydrates or containing non-metabolizable sugars showed little hemolytic activity because the pH always remained alkaline. In pH-stat cultures maintained at pH 6.2, higher hemolysin yields were produced irrespective of the presence or absence of mannitol. We conclude that the production of the Kanagawa hemolysin is under pH control. Marine strains of V. parahaemolyticus, which are Kanagawa negative, did not express detectable amounts of hemolysin under those conditions shown to stimulate hemolysin production by Kanagawa-positive strains.

Characterization of Salmonella toxin released by mitomycin C-treated cells

The enzyme-linked immunosorbent assay and the Chinese hamster ovary floating cell assay for cholera toxin have proven to be sensitive and reliable tests for determining the antigenic and biological characteristics of Salmonella toxin, respectively. The addition of mitomycin C to the culture media 3 h after inoculation resulted in increased amounts of Salmonella toxin in culture filtrates but had the reverse effect on cell sonic extracts. Our data suggested that the increased amounts of Salmonella toxin culture filtrates caused by mitomycin C were due to cell lysis, resulting in the release of intracellular toxin, rather than to an increase in the synthesis of Salmonella toxin. The biological activity of Salmonella toxin was heat labile at 100 degrees C. The antigenic structure of the toxin appeared to remain intact after exposure to temperatures as high as 100 degrees C but was altered somewhat when the toxin was subjected to autoclaving. The toxin had an isoelectric point in the pH range from 4.3 to 4.8 and an estimated molecular weight which appeared to be more than 110,000. With the exception of the range for its isoelectric point, its molecular weight, and its low concentration in filtrates and sonic extracts, Salmonella toxin was very similar in biological and antigenic characteristics to cholera toxin. The antigenic and biological assays described here provide an effective basis for extending our study of Salmonella toxin.

Pyridine nucleotide cycle of Salmonella typhimurium: in vitro demonstration of nicotinamide adenine dinucleotide glycohydrolase, nicotinamide mononucleotide glycohydrolase, and nicotinamide adenine dinucleotide pyrophosphatase activities

Extracts of Salmonella typhimurium were chromatographed by using Sephadex G-150 to separate the various enzymes involved with pyridine nucleotide cycle metabolism. This procedure revealed a previously unsuspected nicotinamide adenine dinucleotide (NAD) glycohydrolase (EC 3.2.2.5) activity, which was not observed in crude extracts. In contrast to NAd glycohydrolase, NAD pyrophosphatase (EC 3.6.1.22) was readily measured in crude extracts. This enzyme possessed a native molecular weight of 120,000. Other enzymes examined included nicotinamide mononucleotide (NMN) deamidase (EC 3.5.1.00), molecular weight of 43,000; NMN glycohydrolase (EC 3.2.2.14), molecular weight of 67,000; nicotinic acid phosphoribosyl transferase (EC 2.4.2.11), molecular weight of 47,000; and nicotinamide deamidase (EC 3.5.1.19), molecular weight of 35,000. NMN deamidase and NMN glycohydrolase activities were both examined for end product repression by measuring their activities in crude extracts prepared from cells grown with and without 10(-5) M nicotinic acid. No repression was observed with either activity. Both activities were also examined for feedback inhibition by NAD, reduced NAD, and NADP. NMN deamidase was unaffected by any of the compounds tested. NMN glycohydrolase was greatly inhibited by NAD and reduced NAD, whereas NADP was much less effective. Inhibition of NMN glycohydrolase was found to level off at an NAD concentration of ca. 1 mN, the approximate intracellular concentration of NAD.

Cholera toxin-like toxin released by Salmonella species in the presence of mitomycin C

Several serotypes of Salmonella were shown to release increased amounts of a cholera toxin-like toxin during culture in vitro with mitomycin C (MTC). Filter-sterilized culture supernatants containing the toxin caused elongation of Chinese hamster ovary cells, which could be blocked by heating the supernatants at 100 degrees C for 15 min or by adding mixed gangliosides or monospecific cholera antitoxin. When MTC was not added to the Salmonella cultures, little or no toxin was detected in crude, unconcentrated culture supernatants. Optimal production of toxin was observed in the presence of 0.5 micrograms of MTC per ml in shake flask cultures of Casamino Acids-yeast extract medium, Syncase, or peptone saline at 37 degrees C. Meat infusion media (heart infusion and brain heart infusion) plus MTC resulted in poor toxin yield. Culture filtrates frequently could be diluted 1:8 and still result in elongation of Chinese hamster ovary cells.

Systemic and gastrointestinal candidiasis of infant mice after intragastric challenge

Systemic and gastrointestinal infection can be established in infant mice after intragastric challenge with Candida albicans. Differences in virulence of the six strains tested were noted. As early as 3 h after infection, some but not all livers, spleens, and kidneys contained C. albicans, but the peak number of colony-forming units in these organs was seen at 6 h. The early colonization of the organs could not be attributed to aspiration of the inoculum since about 90% of lungs and livers tested yielded no colony-forming units at 10 to 15 min postinfection. In animals with systemic infections, lungs, livers, kidneys, and spleens showed similar numbers of colony-forming units within the organs during the first 6 h postinfection- and then the number declined progressively up to 72 h. The gastrointestinal tract was colonized throughout a 20-day period of study. Counts made at intervals beyond day 1 yielded between 10(5) and 10(6) colony-forming units in the stomach, ileum, and cecum. Preparatory techniques for scanning electron microscopy preserved the yeast, intestinal mucus layer, and epithelial surface and made it possible to visualize the association between the pathogen and host tissues within the digestive tract.

Studies on experimental enteric salmonellosis in ponies

Clinical, bacteriological, serological and haematological observations were made on 13 adult ponies orally inoculated with Salmonella typhimurium. The results were compared to two control ponies and four others infected by accidental transmission. The clinical responses in inoculated ponies included pyrexia lasting four days and neutropaenia during the first five days after inoculation followed by a neutrophilia. Pyrexia and neutropaenia was associated with maximal shedding of organisms in the rectal faeces. Changes in the character of the faeces occurred between one and two days after inoculation and appeared to be associated with the serological response. Serological responses occurred in all the infected ponies except one. At necropsy, of the 14 ponies with positive cultures in the colon, seven had negative cultures in the rectal faeces. Serological studies performed on 43 clinically normal horses indicated a correlation between age and salmonella agglutination titre.

Isolation of the membranes of an enterotoxigenic strain of Escherichia coli and distribution of enterotoxin activity in different subcellular fractions

The intracellular localization of enterotoxin in Escherichia coli AP1, a strain of porcine origin which produces high levels of heat-labile, but no heat-stable enterotoxin, has been examined. The cytoplasmic and outer membranes of this strain both contained enterotoxin activity, while the membranes isolated from a serologically related non-enterotoxigenic strain (E. coli AP2) also of porcine origin, did not show enterotoxin activity. The periplasmic fraction isolated from the enterotoxigenic strain contained considerable enterotoxin activity, but this activity was associated with outer membrane fragments present in the periplasmic fraction. Thus, of the total cellular enterotoxin activity, about 55%, 15% and 30% were present in the outer membrane, cytoplasmic membrane and the cell cytoplasm, respectively. The specific activity of enterotoxin was 20 units per mg protein in the cytoplasm and 90 and 150 units per mg protein in the cytoplasmic and outer membranes, respectively.

Production and partial purification of Salmonella enterotoxin

By using a strain of Salmonella typhimurium, we detected the presence of an enterotoxin, as determined by the rabbit ileal loop assay, in various complex and defined media. The enterotoxin was concentrated by ultrafiltration of culture supernatant fluids and eluted in and adjacent to the void volume of a Sephadex G-100 column. This suggested that the enterotoxic factor was of a relatively high molecular weight, and additional evidence indicated it was heterogeneous in size. Further chromatography, using a diethylaminoethyl-cellulose anion exchanger, facilitated at least a 50-fold purification of the Salmonella enterotoxin.

Heat-stable enterotoxin from Escherichia coli: factors involved in growth and toxin production

Six enterotoxigenic strains of Escherichia coli produced variable levels of heat-stable enterotoxin (ST) when grown under pH control at 8.5 in a simple synthetic medium containing neither amino acids nor vitamins. Bacterial growth and ST production were at levels as high as or higher than those observed in complex media. ST elaboration was detectable in the early logarithmic phase of growth and appeared to be related to disappearance of glucose in the growth medium. The results of this study did not suggest pH-dependent release of ST. Imposition of pH control in complex media resulted in increased growth rates, earlier detectable ST synthesis, and elevated levels of ST. In synthetic medium, attainment of the stationary growth phase was followed by a significant decrease in culture density and a concomitant increase in ST. Cellular autolysis experiments revealed that as much as 20% of the total ST activity was present in a cell-associated form.