Culture supernatants of Campylobacter jejuni induce a secretory response in jejunal segments of adult rats

A Systematic Review on the Role of Wildlife as Carriers and Spreaders of Campylobacter spp

Campylobacter spp. are important zoonotic pathogens and can cause one of the main bacterial diarrheal diseases worldwide. Research in the context of infection arising from transmission from other humans and other vertebrates has been extensive. A large fraction of these investigations has focused on domestic animals; however, there are also a number of publications which either totally, or at least in part, consider the role of wild or feral animals as carriers or spreaders of Campylobacter spp. Here, we carry out a systematic review to explore the role played by wild vertebrates as sources of Campylobacter spp. with a compilation of prevalence data for more than 150 species including reptiles, mammals and birds. We found that numerous vertebrate species can act as carriers of Campylobacter species, but we also found that some host specificity may exist, reducing the risk of spread from wildlife to domestic animals or humans.

Determination of toxicity of Campylobacter jejuni isolated from humans and from poultry carcasses acquired at various stages of production

AIM

The research focused on the determination of the toxicity variation associated with Campylobacter jejuni isolated from humans and chickens.

METHODS AND RESULTS

Campylobacter jejuni isolates were obtained from chicken carcasses and from humans exhibiting symptoms of campylobacteriosis. Using HeLa cells as the in vitro model, toxicity was determined for each isolate. The mean toxicity level of the chicken isolates was significantly lower than that of the human isolates (P < 0.001). There was a wide range of toxicity in C. jejuni isolated from chickens and the percentage of isolates exhibiting low toxicity remaining relatively constant. All C. jejuni isolates from humans possessed either medium or high levels of toxicity.

CONCLUSIONS

All wildtype C. jejuni isolates obtained from poultry carcasses may not be equally important as a human foodborne pathogen.

SIGNIFICANCE AND IMPACT OF STUDY

Campylobacter jejuni remains a primary foodborne pathogen and increased efforts are needed to determine the impact of wildtype isolates in causing human illness. The present research indicates that all isolates may not be equally important in regards to disease potential. The information found should be included in efforts to develop C. jejuni detection, control and infection modelling.

Toxin production by Campylobacter spp

Of all the virulence factors that were proposed for Campylobacter jejuni and related species to cause disease in humans, the discovery of toxin production was the most promising but led to a rather confusing and even disappointing stream of data. The discussion of whether proteinaceous exotoxins are relevant in disease remains open. One important reason for this lack of consensus is the anecdotal nature of the literature reports. To provide a basis for an unbiased opinion, this review compiles all described exotoxins, compares their reported properties, and provides a summary of animal model studies and clinical data. The toxins are divided into enterotoxins and cytotoxins and are sorted according to their biochemical properties. Since many Campylobacter toxins have been compared with toxins of other species, some key examples of the latter are also discussed. Future directions of toxin research that appear promising are defined.

Calcium and protein kinase C play an important role in Campylobacter jejuni-induced changes in Na+ and Cl- transport in rat ileum in vitro

The pathophysiological mechanism of Campylobacter jejuni (enterotoxigenic) induced secretory diarrhoea remains least understood. To investigate the mechanism(s) involved, the unidirectional fluxes of Na+ and Cl- were measured across the C. jejuni live culture infected and control (non infected) rat ileum (unstriped), in vitro by Ussing technique under short circuit conditions, in the presence or absence of: Ca2+ ionophore A23187 (5 microM), 1-verapamil (100 microM), calmodulin (CaM) antagonist W-7 (100 microM), dantrolene (25 microM), protein kinase C (PKC) activator PMA (100 ng/ml) and H-7 (60 microM), selective inhibitor of PKC. There was net absorption of Na+ and enhanced Cl- secretion in infected animals while in control animals there was net absorption of Na+ and marginal secretion Cl-.Ca2+ ionophore A23187 mimicked the effects of C. jejuni infection whereas 1-verapamil had significant antisecretory effect on Na+ and Cl- secretion in infected animals. In vitro measurement of undirectional 45Ca fluxes in Ussing chamber experiments revealed net absorption of Ca2+ in infected rat ileum as compared to net secretion of Ca2+ in control rat ileum. These observations clearly indicate that there is increased stimulation of Ca2+ uptake from extracellular milieu to the enterocytes during C. jejuni-induced diarrhoea. The intracellular calcium levels (Ca2+]i (as measured by fluorescent probe Fura-2AM) were found to be raised significantly (P < 0.0001) in enterocytes isolated from C. jejuni infected ileum as compared to the enterocytes from control ileum. The observed increase in [Ca2+]i in enterocytes isolated from C. jejuni live culture supernatant treated rat ileum further shows the involvement of enterotoxin in diarrhoeal process. Dantrolene decreased significantly C. jejuni-induced net Na+ and Cl- secretion but it could not reverse it to absorption suggesting the partial involvement of Ca2+ mobilised from intracellular stores in mediating secretion. W-7 failed to inhibit the C. jejuni-induced net Na+ and Cl- secretion. In addition the CaM activity estimated in intestinal microvillar core remained same in both the control and C. jejuni infected animals. This indicates that C. jejuni-induced diarrhoea is not mediated through the activation of Ca(2+)-CaM complex pathway of the Ca2+ messenger system. The PKC activator PMA, induced net secretion of Na+ and Cl- in the control animals but it could not enhance further the C. jejuni-induced Na+ and Cl- secretion, suggesting that there is overlapping effect of PMA and C. jejuni live culture infection.(ABSTRACT TRUNCATED AT 400 WORDS)

Impairment of Na+,K(+)-ATPase activity following enterotoxigenic Campylobacter jejuni infection: changes in Na+, Cl- and 3-O-methyl-D-glucose transport in vitro, in rat ileum

Unidirectional fluxes of Na+, Cl- and 3-O-methyl-D-glucose (3-MG) were measured in vitro across Campylobacter jejuni live culture-infected and control rat ileal short-circuited tissues by the Ussing Chamber technique. Net secretion of Na+ and enhanced secretion of Cl- ions was observed in the infected animals (P < 0.001, n = 6) as compared to the net absorption of Na+ and marginal secretion of Cl- ions in the control animals. There was a significant decrease in the mucosal-to-serosal fluxes of 3-MG in C. jejuni-infected rat ileum. The specific Na+,K(+)-ATPase activity when measured biochemically in the membrane-rich fraction of enterocytes was found to be significantly lower (58%) in the infected group as compared to the control group (P < 0.001). Our results therefore suggest that infection with an enterotoxigenic C. jejuni inhibits the Na+,K(+)-ATPase activity in rat enterocytes. The impairment of Na+,K(+)-ATPase activity thus appears to induce a secondary change in Na+,Cl- and 3-MG transport in vitro in rat ileum.

A cytotonic, cholera toxin-like protein produced by Campylobacter jejuni

1. Campylobacter jejuni is a major cause of gastroenteric infection. 2. This organism appears to produce both cytotonic and cytotoxic virulence factors. 3. We report here that culture filtrates of some clinical isolates of C. jejuni induce elongation of Chinese hamster ovary (CHO) cells in vitro but do not cause inhibition of fluid absorption in the rat ileum. 4. These culture filtrates contain low levels of a protein which cross-reacts immunologically with the cholera toxin. 5. The cholera toxin-like protein of C. jejuni behaved identically to cholera toxin on non-denaturing polyacrylamide gel electrophoresis. 6. Under denaturing conditions, however, this protein displayed no subunit structure and a molecular weight of approximately 50 kDa with many higher molecular weight aggregates. 7. In conclusion, isolates of C. jejuni produced small amounts of enterotoxin when grown in vitro. 8. The toxin cross-reacted immunologically with cholera toxin and has a similar native structure, but does not appear to possess subunits.

A new heat-labile cytolethal distending toxin (CLDT) produced by Campylobacter spp

A new heat-labile toxin cytolethal to CHO, Vero, HeLa, and HEp-2 cells and negative in Y-1 cells has been demonstrated in culture filtrates of many strains of Campylobacter spp. This new toxin was termed a cytolethal distending toxin (CLDT) to reflect the progressive cell distention and eventual cytotoxicity observed in all sensitive tissue cells. CLDT was distinct from previously reported cytotoxins and cholera-like enterotoxin produced by some Campylobacter spp. Since CHO elongation induced by either the Campylobacter enterotoxin or CLDT could not be differentiated after 24 h incubation, continuation of the assay for 96 h was essential for observation of CLDT-associated progressive morphological changes and cytolethal events. Specific assay conditions were required for demonstration of CLDT in Vero, HeLa, and HEp-2 cells. A 31-fold increase in cyclic AMP levels was observed in CHO cells exposed for 24 h to CLDT of catalase negative or weak positive Campylobacter. CLDT was detected in culture filtrates from strains of Campylobacter jejuni, C. coli, C. fetus subsp. fetus, C. laridis and catalase negative or weak positive Campylobacter. Of 718 strains investigated from both human and animal isolations, 295 (41%) were found to produce this toxin. Campylobacter CLDT was negative in adult rabbit ligated ileal loops, suckling mouse and rabbit skin tests. Hemorrhagic responses were observed in rat ligated ileal loop tests of CLDT-positive cultures. The new CLDT toxin could only be neutralized by homologous rabbit antitoxin, was trypsin-sensitive, nondialyzable and over 30,000 in molecular weight. CLDT-producing strains were observed in many serogroups and biotypes of Campylobacter spp. The strains tested originated from many countries and no clear association of toxigenicity with serotype or biotype could be established.

Production of a unique cytotoxin by Campylobacter jejuni

Campylobacter jejuni is an important diarrheal pathogen worldwide; the mechanisms by which it causes disease remain unclear. Because of its association with inflammatory diarrhea, we postulated that C. jejuni might produce a cytotoxin similar to that produced by Shigella sp., enterohemorrhagic Escherichia coli O157, or Clostridium difficile. Filtrates of 12 polymyxin-treated isolates of C. jejuni were placed on HeLa cells (sensitive to Shiga toxin cytotoxicity) and Chinese hamster ovary (CHO) cells. Of 12 isolates of C. jejuni tested, 5 killed 50% of the cells at greater than or equal to 1:4 dilutions of filtered suspensions of 10(9) bacteria per ml; killing was similar in HeLa and CHO cells (the CHO cells being insensitive to Shiga cytotoxin). One isolate produced a titer of 1:32 to 1:128. The relative potency in HeLa cells was comparable to that of E. coli strains that produce intermediate amounts of Shiga-like toxin. The other seven strains showed no cytotoxic effect, nor did the control diluents, polymyxin B, or supernatants of C. jejuni not treated with polymyxin B. Sonication also released active cytotoxin, but slightly less well than did polymyxin. The cytotoxic effect was dose dependent. Concentration of the C. jejuni in suspension by 10-fold before treatment with polymyxin B resulted in a 10-fold increase in the 50% cytotoxic dose. The cytotoxin effect was not neutralized by Shiga toxin immune serum against either Shiga-like toxin I or II or by anti-Clostridium difficile antiserum. The C jejuni cytotoxin was partially labile to trypsin (0.25%) and to heating to greater than or equal to 60 degrees C. Cytotoxicity was retained in Scientific Products dialysis tubing D1615-1 (Mr cutoff, 12,000 to 14,000). Some isolates of C. jejuni release a substance lethal to HeLa or CHO cells in vitro that is distinct from Shiga-like or Clostridium difficile toxin. This cytotoxin may contribute to the colonic mucosal invasive process that characterizes C. jejuni enteritis.

Campylobacter diarrhea in an adult mouse model

An adult mouse (18-20 g) model was developed for studying the pathogenesis of Campylobacter isolates. Iron-loaded BALB/c mice given 10(8)-10(9) Campylobacter colony forming units by intraperitoneal injection developed a severe mucoid diarrhea within 4 h. Severe diarrhea, consisting of unformed stools containing blood, mucus, and fecal leukocytes, persisted for 24 h. Diarrheal symptoms in surviving mice resolved gradually; no diarrhea was observed 5 days after inoculation. Mice not pretreated with iron developed no diarrheal symptoms, and no severe diarrhea was produced in mice inoculated orally. A transient (less than 24 h) bacteremia occurred in mice inoculated either orally or intraperitoneally. Liver, spleen, and kidney were positive for Campylobacter for 48 h; intestinal contents were positive for 5-7 days. Mice given greater than or equal to 10(10) colony forming units showed symptoms of endotoxemia (ruffled fur, inactivity, shaking, tearing, and hypothermia) and died without diarrheal symptoms. Mice given nonpathogenic Escherichia coli strain HB101, heat-killed C. jejuni cells (greater than 10(10)), C. jejuni lipopolysaccharide extract, or purified lipopolysaccharide from either Vibrio cholerae 569B or Salmonella typhimurium showed no diarrheal symptoms.

Association with HeLa cells of Campylobacter jejuni and Campylobacter coli isolated from human feces

We developed a rapid in vitro test for determining the association of Campylobacter jejuni and C. coli with HeLa cells. Association was expressed as a weighted mean of the number of bacteria associated with one cell in an association index (AI). The reproducibility of the AI was checked by repeating the test six times, using four strains chosen at random. Means and standard deviations of the means were 7.3 +/- 1.2, 6.8 +/- 0.9, 1.8 +/- 1.2, and 0.1 +/- 0.2. The experimental conditions for which the results are reliable have been standardized. Among 42 strains from human feces, two groups appeared: for 22 nonassociative strains (52%), AI values ranged from 0.0 to 2.1 (mean +/- SD, 0.5 +/- 0.6); for 20 associative strains (48%), AI values ranged from 3.5 to 8.3 (mean +/- SD, 6.2 +/- 1.4). Of these 42 strains, 17 were clinically documented. Diarrhea occurred more frequently in patients infected with associative strains than in those infected with noninvasive strains (7/7 versus 3/10, P = 0.01). Fever also occurred more frequently in patients infected with associative strains (6/7 versus 2/10, P = 0.03). Transmission electron microscopy and viable counts made after killing of extracellular bacteria by gentamicin support the fact that associated Campylobacter spp. are adherent to the cell membrane and are internalized into cytoplasmic vacuoles. The described test seems to be a convenient and rapid method for estimating the pathogenicity of a given strain.

Colonization and infection of athymic and euthymic germfree mice by Campylobacter jejuni and Campylobacter fetus subsp. fetus

Human clinical strains of Campylobacter jejuni and Campylobacter fetus subsp. fetus colonized the gastrointestinal tracts of both athymic (nu/nu) and euthymic (+/nu) germfree mice (BALB/c). Viable Campylobacter spp. (10(9) to 10(10) CFU/g [dry weight] of cecum and colon contents) were isolated on day 3 after oral challenge, and similar large numbers of viable cells were evident at several intervals during a 10-month experiment. The stomachs and upper small intestines of nu/nu and +/nu mice that were monoassociated for 224 days with C. jejuni 45100 contained 3 to 4 logs fewer viable bacteria than did their ceca or colons. Athymic mice that were monoassociated for 224 days with C. fetus subsp. fetus had 2 to 3 logs more viable Campylobacter spp. in their upper gastrointestinal tracts than did their +/nu littermates. Large viable populations (approximately 10(9)/g of contents) of C. fetus subsp. fetus were in the ceca and colons of both nu/nu and +/nu mice. All C. jejuni strains used in this study chronically infected the mesenteric lymph nodes of both nu/nu and +/nu mice. C. jejuni strains 24 and INN 73-83, which were cytotoxic for Chinese hamster ovary cells in vitro, were also more frequently isolated from the livers, spleens, and kidneys of nu/nu mice than was the weak cytotoxin-producing strain 45100. Additionally, heat-labile-enterotoxin-producing C. jejuni INN 73-83 was recovered more frequently from the internal organs of monoassociated +/nu mice than were any other Campylobacter spp. tested. Natural gastrointestinal colonization of neonatal nu/nu and +/nu mice (born to Campylobacter-colonized mothers) with Campylobacter spp. appeared to be delayed until approximately 1 to 2 weeks after birth. Conventionalization of C. jejuni 45100-monoassociated BALB/c mice with a complex mouse fecal microflora eliminated viable C. jejuni from the mesenteric lymph nodes by day 14 and from the cecum by day 78. These findings show that the gnotobiotic BALB/c mouse is a new model for studying acute and chronic host-Campylobacter sp. interactions.

Morphologic observations of experimental Campylobacter jejuni infection in the hamster intestinal tract

The authors have developed a model for the diarrhea and intestinal lesions seen in Campylobacter jejuni enterocolitis by colonizing the hamster ileum and cecum with C jejuni. Erythematous inflammation of the ileum and cecum and distention of the cecum with fluid were observed at autopsy. The cecal mucosa appeared edematous. Epithelial abnormalities observed by light microscopy included focal edema, occasional hyperplasia, diffuse hyperemia, and infiltration of the lamina propria with leukocytes. C jejuni-like bacteria penetrated the epithelium and were seen in the lamina propria of infected animals but not in uninfected controls. Diverse microvillus lesions, including elongation, shortening, blebbing, and denudation, were seen by transmission electron microscopy. Occasional cytoplasmic aberrations included vacuoles, some containing C jejuni-like bacteria, swollen endoplasmic reticulum, and enlarged mitochondria. Campylobacter structures were vibrio and S-shaped types. Some C jejuni organisms had corrugated screwlike structures wrapped around their circumferences.

Alterations of myoelectric activity associated with Campylobacter jejuni and its cell-free filtrate in the small intestine of rabbits

We evaluated the effects of a culture of Campylobacter jejuni and its cell-free filtrate on myoelectric activity of isolated ileal segments in New Zealand White rabbits. Hematoxylin and eosin staining and scanning electron microscopy were used to assess the association between histologic changes and alterations in intestinal myoelectric activity. A culture of C. jejuni was shown to cause a significant increase in repetitive bursts of action potentials (RBAPs) (6.9 +/- 1.2 RBAP/h; p less than 0.001) compared with controls (0.3 +/- 0.1). Cell-free filtrates of C. jejuni cultures were also observed to induce RBAPs (5.0 +/- 0.9 RBAP/h; p less than 0.001). The fraction within the filtrate that induces alterations in motility was not destroyed by heating to 100 degrees C for 15 min (6.3 +/- 1.2 RBAP/h). Although no gross histologic changes were noted by hematoxylin and eosin staining of intestine exposed to a culture of C. jejuni for 8 h, blunting of villi with a cellular infiltrate was noted in rabbits exposed for 24 h. Scanning electron microscopy disclosed patchy villous tip damage in 3 of 5 animals exposed to cell-free filtrates for 8 h. These studies suggest C. jejuni is pathogenic and produces a heat-stable substance that alters intestinal myoelectric activity in rabbits.

Receptors and recognition mechanisms in intestinal infection

Commensal and pathogenic micro-organisms of the alimentary tract exhibit outstanding specificity with respect to host species, phenotype and age, and often to the type and location of epithelial cells within the gut. Specificity in attachment to the gut is achieved most commonly by ligand-receptor interactions at the pathogen-epithelial interface, commonly a bacterial lectin interacting with specific saccharides of the intestinal microvillus membrane. These bacterial lectins are usually associated with specialized attachment organelles known as pili or fimbriae. A variety of different bacterial pili have now been characterized with respect to their sugar specificities. Similar molecular events are important in the production of diarrhoea, notably the interaction of enterotoxins (cholera toxin, Escherichia coli toxins) with glycolipid receptors on the intestinal cell surface. In most instances, toxin-gut interactions exhibit less impressive specificity than is evident for attachment of micro-organisms to the intestinal epithelium. Identification and characterization of these processes has, and will continue to have, important implications for the biological control of enteric infection, particularly with respect to vaccine development.

Properties of crude Campylobacter jejuni heat-labile enterotoxin

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

Cholera-like enterotoxin produced by Campylobacter jejuni. Characterisation and clinical significance

The presence and clinical significance of enterotoxins produced by Campylobacter jejuni were investigated. The supernatant of a prototype virulent strain grown in supplemented medium induced intraluminal fluid secretion in rat ileal loop but not in rabbit ileal loop or the infant mouse assay. It induced elongation and increased intracellular cyclic AMP levels in Chinese hamster ovary cells. Toxin activity was blocked by cholera antitoxin and was destroyed by heat and high or low pH; its molecular weight is in the range 10(4)-10(5) daltons. Toxin production was detected in 24 of 32 C jejuni strains from patients with diarrhoea and 1 of 6 from carriers. Antibody response to autologous C jejuni somatic antigen was investigated in 19 subjects for whom serial serum specimens were available. A fourfold rise was observed in all 10 patients with enterotoxigenic C jejuni diarrhoea, in 1 of 3 patients with non-enterotoxigenic C jejuni, and in none of the symptomless carriers of non-enterotoxigenic strains. These findings demonstrate that C jejuni produces an enterotoxin that may be important in pathogenesis of diarrhoea.