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

Shigella toxin and the pathogenesis of shigellosis

Shigella dysenteriae 1 produces a periplasmic protein with multiple toxic effects in vivo and in vitro. These include neurotoxicity, cytotoxicity and enterotoxicity, as well as the ability to inhibit cell-free protein synthesis. The purified toxin is a protein of relative molecular mass (Mr) 64 000. It is composed of one catalytically active A subunit (Mr = 32 000) that inhibits protein synthesis, and a complex of five B monomers (Mr approximately 6500 each). Studies using subunit-specific antibodies demonstrate that the B subunit mediates the binding of toxin to toxin receptors in the cell membrane. In a model system in HeLa cell culture, the surface membrane receptor has been shown to be a glycoprotein, most probably asparagine-linked, and to contain oligomeric beta 1----4 linked N-acetyl-D-glucosamine. Studies with metabolic inhibitors and agents that disrupt the cytoskeleton, and/or alter the pH and function of acidic cytoplasmic vesicles, provide indirect evidence that toxin is transported from the cell surface to the cell interior. This process is probably receptor-mediated endocytosis, since it is also inhibited by amines that prevent receptor-mediated uptake of other ligands in well-characterized systems. The toxic action in the HeLa cell is due to the subsequent inhibition of protein synthesis which results from catalytic inactivation of the 60S ribosomal subunit and the cessation of polypeptide chain elongation. Inhibition of protein synthesis by toxin produced subsequent to bacterial invasion of colonic epithelial cells could explain the destructive lesions found in shigellosis. Although toxin can induce jejunal secretion in animal models, there is at present no clear explanation for the secretory response of the gut mucosa in shigella infection.

Rapid detection of Salmonella by polymerase chain reaction

Salmonella enterotoxin gene (stn) was sequenced from Salmonella enterica serotypes: Typhimurium, Typhi, Paratyphi A and B. The sequences from all the four serotypes showed complete homology with the already reported stn gene sequence of the serotype Typhimurium. As a tool for detection of this organism, four pairs of oligonucleotide primers were designed to amplify different fragments of this important pathological marker. The protocols were standardized with serotype Typhimurium in such a way so as to complete the PCR reaction in 75-90 min. These primers were found to generate specific amplicons with all the serotypes of Salmonella tested. The PCR protocols were found to be highly specific as no amplifications, specific or non-specific, were found when reactions were run using non-Salmonella DNA as template. The employment of a nested PCR markedly increased the sensitivity of the assay system in natural water samples. The protocol described herein is highly sensitive as it detects less than 10 cells of Salmonella in 250 microl of blood and approx. 1 cell in 1 ml of water without any enrichment. For the validation of this protocol, 72 coded samples of 11% skimmed milk spiked with different pathogens were received from NICED, Kolkata and analyzed for the presence of Salmonella. Our procedures detected correctly the presence of Salmonella in nine samples. 50 samples of raw milk were subjected to this PCR after enrichment for 8 h and 6 samples were found positive for Salmonella. The study indicates that Salmonella enterotoxin (stn) gene is highly conserved and the protocol devised in this study can be used as rapid and reliable method for detection of Salmonella spp. in water, milk and blood samples.

Most cited papers in Toxicon

Citation of a published work is one of the parameters considered in the analysis of relevance and importance of scientific contributions. In 2002, for the first time the Impact Factor of Toxicon has risen above 2.0, placing it at the 17th position among 76 journals in the 'toxicology' field. The aim of this article was to identify the most cited articles in Toxicon, that have contributed to the steady increase of its Impact Factor. The number of citations, complete reference and type of all documents appearing in Toxicon in the period 1963-2003 were retrieved from the ISI Web-of-Science homepage. The documents retrieved were sorted by the number of citations received. A 'citation index', defined as the number of citations divided by the number of years since publication, was calculated for each document. It was clearly seen that reviews in Toxicon received 4.4-fold more citations than articles. Unexpectedly, it was found that recent papers were proportionally more cited than old ones. A decrease in the proportion of papers dealing on 'snake*' through out the period and the broadened range of subjects of the most cited papers recently published in Toxicon reflects an increased 'visibility' in other fields of toxinology. Research on plant toxins gained its own space in Toxicon with newer publications showing high citation indexes. It can be postulated that these facts helped to increase Toxicon's Impact Factor from 1.248 in 1999 to 2.003 in 2002. With the increased number of issues in Toxicon as well as publications of subject-dedicated volumes containing mostly reviews, the Impact Factor of Toxicon is expected to keep rising in the near future.

The cytolytic effects of Salmonella enterica serovar Typhimurium on chicken heterophils

Mixing of chicken heterophils and Salmonella enterica serovar Typhimurium resulted in a rapid disappearance of heterophils when examined by scanning electron microscopy and trypan blue dye exclusion test. This disappearance appeared to be caused by a rapid degranulation of heterophils.

Salmonella-induced macrophage death: the role of caspase-1 in death and inflammation

Salmonella typhimurium invades host macrophages and can induce either an almost immediate cell death or establish an intracellular niche within the phagocytic vacuole. Rapid cell death depends on the Salmonella pathogenicity island SPI1 and the host protein caspase-1, a member of the pro-apoptotic caspase family of proteases. Caspase-1-dependent cell death leads to the activation of the potent pro-inflammatory cytokines interleukin (IL)-1beta and IL-18 to produce bioactive cytokines. Animal studies indicate that the activation of these cytokines is necessary for efficient colonization of the mouse gastrointestinal tract. Salmonella that reside in the phagocytic vacuole do not cause this early cell death and can trigger a macrophage death at a much later time point. This late-phase cell death is dependent on SPI2-encoded genes and ompR.

Differential bacterial survival, replication, and apoptosis-inducing ability of Salmonella serovars within human and murine macrophages

Salmonella serovars are associated with human diseases that range from mild gastroenteritis to host-disseminated enteric fever. Human infections by Salmonella enterica serovar Typhi can lead to typhoid fever, but this serovar does not typically cause disease in mice or other animals. In contrast, S. enterica serovar Typhimurium and S. enterica serovar Enteritidis, which are usually linked to localized gastroenteritis in humans and some animal species, elicit a systemic infection in mice. To better understand these observations, multiple strains of each of several chosen serovars of Salmonella were tested for the ability in the nonopsonized state to enter, survive, and replicate within human macrophage cells (U937 and elutriated primary cells) compared with murine macrophage cells (J774A.1 and primary peritoneal cells); in addition, death of the infected macrophages was monitored. The serovar Typhimurium strains all demonstrated enhanced survival within J774A.1 cells and murine peritoneal macrophages, compared with the significant, almost 100-fold declines in viable counts noted for serovar Typhi strains. Viable counts for serovar Enteritidis either matched the level of serovar Typhi (J774A. 1 macrophages) or were comparable to counts for serovar Typhimurium (murine peritoneal macrophages). Apoptosis was significantly higher in J774A.1 cells infected with serovar Typhimurium strain LT2 compared to serovar Typhi strain Ty2. On the other hand, serovar Typhi survived at a level up to 100-fold higher in elutriated human macrophages and 2- to 3-fold higher in U937 cells compared to the serovar Typhimurium and Enteritidis strains tested. Despite the differential multiplication of serovar Typhi during infection of U937 cells, serovar Typhi caused significantly less apoptosis than infections with serovar Typhimurium. These observations indicate variability in intramacrophage survival and host cytotoxicity among the various serovars and are the first to show differences in the apoptotic response of distinct Salmonella serovars residing in human macrophage cells. These studies suggest that nonopsonized serovar Typhimurium enters, multiplies within, and causes considerable, acute death of macrophages, leading to a highly virulent infection in mice (resulting in death within 14 days). In striking contrast, nonopsonized serovar Typhi survives silently and chronically within human macrophages, causing little cell death, which allows for intrahost dissemination and typhoid fever (low host mortality). The type of disease associated with any particular serovar of Salmonella is linked to the ability of that serovar both to persist within and to elicit damage in a specific host's macrophage cells.

Purification and characterization of novel toxin produced by Vibrio cholerae O1

Vibrio cholerae WO7 (serogroup O1) isolated from patients with diarrhea produces an extracellular toxin despite the absence of ctx, zot, and ace genes from its genome. The toxin elongates Chinese hamster ovary cells, produces fluid accumulation in ligated rabbit ileal loops, and agglutinates freshly isolated rabbit erythrocytes. Maximal production of this toxin (WO7 toxin) was seen in AKI medium with the pH adjusted to 8.5 at 37 degrees C under shaking conditions. We purified this toxin to homogeneity by sequential ammonium sulfate precipitation, affinity chromatography using a fetuin-Sepharose CL-4B column, and gel filtration chromatography, which increased the specific activity of the toxin by 1.6 x 10(6)-fold. The toxin is heat labile and sensitive to proteases and has a subunit structure consisting of two subunits with molecular masses of about 58 and 40 kDa as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Agglutination of GM1-coated sheep erythrocytes by toxin suggests that GM1 might be the physiologic receptor for WO7 toxin on the enterocytes. An immunodiffusion test between the antiserum raised against the purified WO7 toxin and the purified toxin gave a well-defined precipitation band. In the immunoblot assay, two bands were observed in the 58- and 40-kDa region. At the same time, antiserum against WO7 toxin failed to show any cross-reactivity with cholera toxin or Escherichia coli heat-labile toxin (LT1) in an immunodiffusion test or immunoblot assay. The enterotoxic activity of WO7 toxin could be inhibited by antiserum against purified WO7 toxin. Our results indicate that WO7 toxin is structurally and functionally distinct from other cholera toxins and that the enterotoxic activities expressed by WO7 toxin appear to contribute to the pathogenesis of disease associated with V. cholerae O1 strains.

Purification and characterization of a Chinese hamster ovary cell elongation factor of Vibrio hollisae

The halophilic bacterium Vibrio hollisae, isolated from patients with diarrhea, produces an extracellular toxin which elongates Chinese hamster ovary (CHO) cells. We purified this toxin to homogeneity by sequential ammonium sulfate precipitation, gel filtration with Sephacryl S-200, hydrophobic interaction chromatography with phenyl-Sepharose CL-4B, ion-exchange chromatography with DEAE-Sephadex A-50, and affinity chromatography. The toxin is heat labile and sensitive to proteases, with an isoelectric point of about 6.5 and molecular weights of about 83,000 and 80,000, as estimated by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, respectively. The toxin did not react with immunoaffinity-purified antibodies to cholera toxin in a plate enzyme-linked immunosorbent assay and in a Western blot, and its activity could not be neutralized by anti-cholrea toxin serum. Mixed gangliosides and gangliosides GM1, GD1a, GD1b, Gq1b, GT1b, GD2, GD3, GM2, and GM3 failed to block its activity. Elongation of CHO cells induced by the toxin was not accompanied by an increase in the levels of cyclic AMP. The toxin induced intestinal fluid accumulation in suckling mice. These results and the lack of homology between V. hollisae DNA and DNA coding for cholera toxin or the heat-labile toxin of Escherichia coli suggest that the V. hollisae toxin is structurally and functionally different from other CHO cell-elongating toxins.

Purification and characterization of enterotoxic moiety present in cell-free culture supernatant of Salmonella typhimurium

The enterotoxic moiety present in the cell-free culture supernatants of Salmonella typhiurium strains (p/536 and p/603) was purified to apparent homogeneity by salt precipitation with ammonium sulphate and successive chromatography through Sephadex G-100 and G-200 columns. It was non-dialysable, heat labile at 90 degrees C and active within pH 6-8. Its activity was completely lost on treatment with trypsin, protease and papain. The enterotoxin appeared to be of high molecular weight (100 kDa) and was highly immunogenic in rabbit. Antigenically, it was not related to cholera toxin, Shiga toxin or the heat labile enterotoxin of Escherichia coli. It did not bind to the GM1 ganglioside. The enterotoxic, delayed permeability and CHO cell elongation activities were attributed to a single protein moiety.

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.

Salmonella cytotonic and cytolytic factors: their detection in Chinese hamster ovary cells and antigenic relatedness

Thirty nine strains of Salmonella belonging to 14 different serotypes were screened for the production of cytotonic and cytolytic factors by assayed Chinese hamster ovary (CHO) cells. The cell-free culture supernatants (CFCS) of 32 isolates caused elongation and increase in size of CHO cells while the CFCSs completely lysed the cells. The cytotonic effect in CHO cells correlated precisely with fluid the CFCSs completely lysed the cells. The cytotonic effect in CHO cells correlated precisely with fluid accumulation in the rabbit ligated ileal assay in that 24 isolates yielded positive results in both assays and 13 were found negative in both. Antiserum to S. typhimurium enterotoxin, but not that to cholera toxin or Shiga toxin, neutralized the cytotonic activity present in the CFCS and reacted with the latter in immunodiffusion and coagglutination tests. The cytolytic factor produced by two strains reacted neither with antiserum to Salmonella enterotoxin nor with that the Shiga toxin.

Structural and functional changes in rabbit ileum by purified extracellular phospholipase A of Salmonella newport

As phospholipases of Salmonella species may play a role in the pathogenesis of gastrointestinal tract diseases. Salmonella newport, the causative agent of infantile diarrhoea was examined for the production of phospholipase. The enzyme was purified by gel filtration chromatography and was found to be a protein of molar mass ranging from 43 to 67 kDa. The purified enzyme alone or in combination with organisms, produced both structural and functional changes in rabbit ileum, contributing towards pathogenesis of diarrhoea due to this organism.

Fibronectin binding by Salmonella strains: evaluation of a particle agglutination assay

Thirty-five Salmonella strains isolated from human cases of salmonellosis were tested and compared for their fibronectin (fn) binding capacities by using two fn-particle agglutination assays (fn-PAAs) prepared by coating with human fn either (i) latex beads (Difco; 0.81-micron diameter) (L-fn-PAA) or (ii) heat-killed formalin-treated Staphylococcus aureus Cowan 1 cells (C-fn-PAA). Six S. aureus strains were also included in this study as controls. The strains were cultured on colonization factor antigen agar and blood agar and in tryptic soy broth and brain heart infusion broth. The Salmonella and S. aureus strains were cultured at 33 and 37 degrees C, respectively, for optimal expression of fn-binding proteins. Bacterial cells (approximately 10(10) cells per ml) harvested from growth in various culture media and suspended in 0.02 M potassium phosphate buffer (pH 6.8) agglutinated the fn-PAA reagents. These reactions were scored semiquantitatively from + to + depending on the speed or intensity of the reactions within 2 min. Maximum agglutination in fn-PAA systems was observed when the cells were grown in brain heart infusion broth, while tryptic soy broth proved to be least suitable media for culturing cells for fn-PAAS. Although a statistically highly significant correlation was obtained between results of assays of radiolabeled fn and 29-kDa fragment binding, no significant correlation was observed (i) between the results of strains cultured in different media or (ii) when semiquantitative score results of the two fn-PAA systems were compared with those of the conventional radiolabeled fn assay. To enhance the efficiency of the test system, the C-fn-PAA reagent was stained with methylene blue (2% in 0.17 M glycine-NaOH buffer [pH 6.8]). This facilitated easy interpretation of results, which could be performed on hydrophobic paper instead of glass slides. The results obtained with both unstained C-fn-PAA and stained C-fn-PAA were comparable to each other and reproducible. Although the fn-PAAs are simple and easy to perform, the results did not differentiate between negative, low, moderate, and high binding abilities when Salmonella strains were evaluated for fn binding, and the results were not comparable to those obtained by the conventional radiolabeling method.

Toxin profiles, and cell-surface properties of Salmonella strains isolated from Swedish travelers

Toxin production, cell-surface hydrophobicity and fibronectin-binding properties of 21 Salmonella strains of different species, isolated from Swedish travelers to different parts of the world, were studied. Cell sonicate supernatants from blood agar grown cultures of 80% of the strains induced rabbit skin permeability reaction in the form of induration and/or blueing while 33% of the strains also produced cell necrotizing factor on rabbit skin. Four strains were negative in the rabbit skin permeability test, while only two were negative when tested on CHO cells. When cultured on blood agar, a majority of the strains (17/21) showed low cell-surface hydrophobicity, showing no aggregation even at 1.5 M ammonium sulfate concentration in salt aggregation test (SAT), while only four strains showed high cell-surface hydrophobicity. Furthermore, these strains could be classified as low fibronectin binders due to their poor interaction with fibronectin or its 29 kDa N-terminal fragment.

Coagglutination test for rapid detection of Salmonella enterotoxin

The Staphylococcal Coagglutination (CoA) test using Staphylococcus aureus (Cowan type-1) cells coated with antiserum against purified Salmonella enterotoxin was standardized and carried out to screen Salmonella serotypes for their enterotoxigenicity. Of the 101 cell-free culture supernatants from an equal number of Salmonella strains belonging to 15 different serotypes tested, 76 were found to be enterotoxigenic. All of the 24 strains which gave positive reactions in the rabbit ligated ileal loop test were also positive with this test. As little as 7.5 ng of purified Salmonella enterotoxin could be detected by the CoA test. The presence of enterotoxin in polymyxin B extract of cells and cell-free preparation of a S. typhimurium strain was detected as early as after 1.5 and 3.0 h of incubation, respectively. Besides the test standardized with the antiserum to purified V. cholerae toxin (CT) could detect purified toxin in a quantity as little as 5.0 ng and also enterotoxigenicity in an E. coli strain (LT+). The usefulness of the test as a routine, rapid and economic one for the detection of enterotoxin of Salmonella, Vibrio cholerae and E. coli is discussed.

Production of a unique cytotoxin by Klebsiella oxytoca

Certain strains of Klebsiella oxytoca isolated from patients with hemorrhagic enterocolitis produced a unique cytotoxin. The cytotoxin induced rounding of tissue culture cells, such as HEp-2, Vero, CHO and HeLa cells. The induced morphologic changes were indistinguishable between cell types. Seventy to 80% of the rounded cells died in 48 h incubation. The cytotoxin was purified 1000-fold from culture supernatant by Sephadex G-25 and Bio-Gel P-2 gel filtration followed by reversed-phase high-performance liquid chromatography. The molecular weight of the purified cytotoxin was estimated to be less than or equal to 651 by mass spectrometry. The minimum concentrations of the purified cytotoxin required to cause 50% of rounding of cells were 0.6 micrograms/ml for HEp-2, 0.8 micrograms/ml for Vero, 0.8 micrograms/ml for CHO and 1.4 micrograms/ml for HeLa cells. The type strain of K. oxytoca, ATCC 13182, did not produce the cytotoxin and only the clinically isolated strains did, suggesting that the cytotoxin may play a role in the pathogenesis of the organisms.

Quantitative analysis and partial characterization of cytotoxin production by Salmonella strains

The pathogenesis of the wide-spectrum human disease caused by Salmonella species is poorly understood. Cytotoxin production by other enteric pathogens has been increasingly investigated recently, and data are accumulating regarding the role of cytotoxins in enteric infections and hemolytic uremic syndrome. We studied the cytotoxic activity of 131 Salmonella strains of the major serotypes, including 94 strains of Salmonella enteritidis, 12 strains of Salmonella typhi, and 25 strains of Salmonella choleraesuis. Cytotoxicity was quantitatively determined in sonic extracts by a [3H]thymidine-labeled HeLa cell assay. All Salmonella strains examined showed some degree of cytotoxic activity. The geometric means +/- standard deviations of the amounts of cytotoxin produced (50% cytotoxic dose per milligram of bacterial protein) were 27 +/- 2 for S. typhi, 65 +/- 2 for S. enteritidis, and 117 +/- 2 for S. choleraesuis. Analysis of variance showed that the differences in cytotoxin production by the three species were significant (P less than 0.001). No significant differences were found between stool isolates and invasive strains of the same species. Neutralization studies showed that the cytotoxins produced by all Salmonella strains were immunologically distinct from Shiga toxin and the closely related Shiga-like toxins produced by Escherichia coli. DNA hybridization studies with DNA probes for Shiga-like toxins of types I and II showed no hybridization. In each species the cytotoxin was heat labile and sensitive to trypsin treatment, which indicated that its active component was probably protein in nature. Upon ultrafiltration with Amicon membranes and gel filtration chromatography, cytotoxic activity was found in the molecular weight range of 56,000 to 78,000. Our findings indicate that salmonellae produce cytotoxin(s) that may play a role in the manifestations of the various species.

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.

Cell-surface properties of enterotoxigenic and cytotoxic Salmonella enteritidis and Salmonella typhimurium: studies on hemagglutination, cell-surface hydrophobicity, attachment to human intestinal cells and fibronectin-binding

Thirteen Salmonella enteritidis and S. typhimurium strains with smooth or rough colony morphology were investigated for their surface properties based on hemagglutination (HA), hydrophobicity, and fibronectin-binding profiles. The strains showed 5 different patterns of HA which was mannose-sensitive. The rough strains possessed comparatively greater number of fimbriae than the corresponding smooth strains and also attached to human intestinal cells in greater numbers. The Salmonella strains used in this study interacted with fibronectin and its 29-kDa N-terminal fragment to varied extents. These properties may be helpful in broadening the prospective interaction capabilities of Salmonella organisms with the host surfaces.

Unmasking of bacteriophage Mu lipopolysaccharide receptors in Salmonella enteritidis confers sensitivity to Mu and permits Mu mutagenesis

The human pathogen Salmonella enteritidis 3b was found to be highly resistant to phage P22 and Mu derivatives. The Mu sensitivity (musA1) allele from Salmonella typhimurium could be transferred to S. enteritidis 3b at low frequency by cotransduction with hisG::Tn10. Sensitivity to Mu resulted in a large reduction in the number of lipopolysaccharide core-region oligosaccharides that were substituted with O-antigen polysaccharide. The residual high-molecular-weight lipopolysaccharide appeared to be a hybrid displaying O antigens which were immunologically related to those of S. typhimurium and not to those of S. enteritidis. Consequently, Mu d1(Ap lac) could then be transduced into Mus strains forming stable lysogens. On temperature induction, Mu transposition could easily be used to generate mutations in genes coding for cell surface antigens including fimbriae, lipopolysaccharide, and flagella.

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.

Toxins, putative cell adhesins and fibronectin binding properties of Salmonella dublin

Fifty Salmonella dublin strains isolated from cattle and human diarrhoeal cases were assayed for toxin production, haemagglutination, cell-surface hydrophobicity and fibronectin-binding properties. Most strains (65% of tested) produced cytotonic toxins and cytotoxic factors when tested on Chinese hamster ovary (CHO) cells and rabbit skin test. However, only three strains produced a skin-permeability factor as determined in pig skin intra-dermal tests. None of the strains were positive in pig intestinal loop tests. Six of the 32 strains tested for 125I-fibronectin and its 125I-29 kDa N-terminal domain binding showed 10-17% and 6-10% binding, respectively. Most of the strains expressed mannose-sensitive haemagglutination (MSHA) (76%) and high cell-surface hydrophobicity (74%) when grown at 37 degrees C. At 20 degrees C the expression of MSHA and especially the expression of high cell-surface hydrophobicity were reduced. Twelve strains grown at 37 degrees C did not haemagglutinate erythrocytes from five animal species used in this study, while six of these strains expressed high cell-surface hydrophobicity. Salmonella dublin strains isolated in Denmark appeared to express a higher frequency of fimbriae type 1 (MSHA) and a lower frequency of high cell-surface hydrophobicity than the strains from external sources.

Cytotoxic and cytotonic factors produced by Campylobacter jejuni, Campylobacter coli, and Campylobacter laridis

Complete toxigenicity studies were performed on 341 strains of Campylobacter spp., including 23 nonhuman isolates. Toxin profiles based on both cytotonic and cytotoxic factors were determined after analyzing responses in Vero, HeLa, CHO and Y-1 cells. Suckling mouse assays were consistently negative for all culture filtrates tested. Toxin-producing strains were frequently encountered among both the human and nonhuman strains of Campylobacter jejuni, C. coli, and C. laridis investigated. Strains isolated from outbreaks demonstrated parallels in serotype, biotype, and toxigenicity profile, although no clear association could be demonstrated. Biphasic culture conditions conducive to the production of both toxic factors were delineated for the propagation of test Campylobacter strains. Cytotonic effects of Campylobacter culture filtrates were determined in Vero and CHO cells, and cyclic AMP accumulation in cells exposed to these culture filtrates was compared with that in cells exposed to reference toxigenic strains of Vibrio cholerae and Escherichia coli. Partial neutralization of C. jejuni enterotoxin was demonstrated by using antitoxins to cholera toxin and E. coli heat-labile enterotoxin. No neutralization of C. jejuni cytotoxin could be achieved by using antitoxins to either Clostridium difficile cytotoxin or E. coli Verotoxin (0157:H7).

Infectious diarrhea. Pathogenesis and risk factors

Our understanding of the pathogenesis of infectious, especially bacterial, diarrhea has increased dramatically. New etiologic agents, mechanisms, and diseases have become known. For example, Escherichia coli serogroup O157 is now known to cause acute hemorrhagic colitis. Also, E. coli serogroups that produce Shiga toxin are recognized as etiologic agents in the hemolytic-uremic syndrome. The production of bacterial diarrhea has two major facets, bacterial-mucosal interaction and the induction of intestinal fluid loss by enterotoxins. Bacterial-mucosal interaction can be described in stages: (1) adherence to epithelial cell microvilli, which is often promoted by or associated with pili; (2) close adherence (enteroadherence), usually by classic enteropathogenic E. coli, to mucosal epithelial cells lacking microvilli; and (3) mucosal invasion, as with Shigella and Salmonella infections. Further large strides in understanding infectious diarrhea are likely with the cloning of virulence genes if additional host-specific animal pathogens become available for study.

Enterotoxigenicity among Salmonella typhimurium strains isolated in France

Twenty strains of Salmonella typhimurium isolated in France from patients with diarrhea were tested for enterotoxins and cytotoxic factors by conventional bioassays. Eighteen of the strains produced enterotoxins to varying degrees and did not react with antisera to Escherichia coli heat-labile enterotoxin. Cytotoxic factors were present in two strains. These findings suggest that efforts to elucidate the virulence mechanisms of Salmonella spp. isolated in different parts of the world should be renewed.