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

Diarrheal Mechanisms and the Role of Intestinal Barrier Dysfunction in Campylobacter Infections

Campylobacter enteritis is the most common cause of foodborne bacterial diarrhea in humans. Although various studies have been performed to clarify the pathomechanism in Campylobacter infection, the mechanism itself and bacterial virulence factors are yet not completely understood. The purpose of this chapter is to (i) give an overview on Campylobacter-induced diarrheal mechanisms, (ii) illustrate underlying barrier defects, (iii) explain the role of the mucosal immune response and (iv) weigh preventive and therapeutic approaches. Our present knowledge of pathogenetic and diarrheal mechanisms of Campylobacter jejuni is explained in the first part of this chapter. In the second part, the molecular basis for the Campylobacter-induced barrier dysfunction is compared with that of other species in the Campylobacter genus. The bacteria are capable of overcoming the intestinal epithelial barrier. The invasion into the intestinal mucosa is the initial step of the infection, followed by a second step, the epithelial barrier impairment. The extent of the impairment depends on various factors, including tight junction dysregulation and epithelial apoptosis. The disturbed intestinal epithelium leads to a loss of water and solutes, the leak flux type of diarrhea, and facilitates the uptake of harmful antigens, the leaky gut phenomenon. The barrier dysfunction is accompanied by increased pro-inflammatory cytokine secretion, which is partially responsible for the dysfunction. Moreover, cytokines also mediate ion channel dysregulation (e.g., epithelial sodium channel, ENaC), leading to another diarrheal mechanism, which is sodium malabsorption. Future perspectives of Campylobacter research are the clarification of molecular pathomechanisms and the characterization of therapeutic and preventive compounds to combat and prevent Campylobacter infections.

Prediction of CTL epitope, in silico modeling and functional analysis of cytolethal distending toxin (CDT) protein of Campylobacter jejuni

Background

Campylobacter jejuni is a potent bacterial pathogen culpable for diarrheal disease called campylobacteriosis. It is realized as a major health issue attributable to unavailability of appropriate vaccines and clinical treatment options. As other pathogens, C. jejuni entails host cellular components of an infected individual to disseminate this disease. These host–pathogen interfaces during C. jejuni infection are complex, vibrant and involved in the nicking of host cell environment, enzymes and pathways. Existing therapies are trusted only on a much smaller number of drugs, most of them are insufficient because of their severe host toxicity or drug-resistance phenomena. To find out remedial alternatives, the identification of new biotargets is highly anticipated. Understanding the molecules involved in pathogenesis has the potential to yield new and exciting strategies for therapeutic intervention. In this direction, advances in bioinformatics have opened up new possibilities for the rapid measurement of global changes during infection and this could be exploited to understand the molecular interactions involved in campylobacteriosis.

Methods

In this study, homology modeling, epitope prediction and identification of ligand binding sites has been explored. Further attempt to generate strapping 3D model of cytolethal distending toxin protein from C. jejuni have been described for the first time.

Results

CDT protein isolated from C. jejuni was analyzed using various bioinformatics and immuno-informatics tools including sequence and structure tools. A total of fifty five antigenic determinants were predicted and prediction results of CTL epitopes revealed that five MHC ligand are found in CDT. The three potential pocket binding site are found in the sequence that can be useful for drug designing.

Conclusions

This model, we hope, will be of help in designing and predicting novel CDT inhibitors and vaccine candidates.

Role of Cytolethal Distending Toxin in Altered Stool Form and Bowel Phenotypes in a Rat Model of Post-infectious Irritable Bowel Syndrome

BACKGROUND/AIMS

Campylobacter jejuni infection is a leading cause of acute gastroenteritis, which is a trigger for post-infectious irritable bowel syndrome (PI-IBS). Cytolethal distending toxin (CDT) is expressed by enteric pathogens that cause PI-IBS. We used a rat model of PI-IBS to investigate the role of CDT in long-term altered stool form and bowel phenotypes.

METHODS

Adult Sprague-Dawley rats were gavaged with wildtype C. jejuni (C+), a C. jejunicdtB knockout (CDT-) or saline vehicle (controls). Four months after gavage, stool from 3 consecutive days was assessed for stool form and percent wet weight. Rectal tissue was analyzed for intraepithelial lymphocytes, and small intestinal tissue was stained with anti-c-kit for deep muscular plexus interstitial cells of Cajal (DMP-ICC).

RESULTS

All 3 groups showed similar colonization and clearance parameters. Average 3-day stool dry weights were similar in all 3 groups, but day-to-day variability in stool form and stool dry weight were significantly different in the C+ group vs both controls (P < 0.01) and the CDT- roup (P < 0.01), but were not different in the CDT- vs controls. Similarly, rectal lymphocytes were significantly higher after C. jejuni (C+) infection vs both controls (P < 0.01) and CDT-exposed rats (P < 0.05). The counts in the latter 2 groups were not significantly different. Finally, c-kit staining revealed that DMP-ICC were reduced only in rats exposed to wildtype C. jejuni.

CONCLUSIONS

In this rat model of PI-IBS, CDT appears to play a role in the development of chronic altered bowel patterns, mild chronic rectal inflammation and reduction in DMP-ICC.

The clinical importance of emerging Campylobacter species

A growing number of Campylobacter species other than C. jejuni and C. coli have been recognized as emerging human and animal pathogens. Although C. jejuni continues to be the leading cause of bacterial gastroenteritis in humans worldwide, advances in molecular biology and development of innovative culture methodologies have led to the detection and isolation of a range of under-recognized and nutritionally fastidious Campylobacter spp., including C. concisus, C. upsaliensis and C. ureolyticus. These emerging Campylobacter spp. have been associated with a range of gastrointestinal diseases, particularly gastroenteritis, IBD and periodontitis. In some instances, infection of the gastrointestinal tract by these bacteria can progress to life-threatening extragastrointestinal diseases. Studies have shown that several emerging Campylobacter spp. have the ability to attach to and invade human intestinal epithelial cells and macrophages, damage intestinal barrier integrity, secrete toxins and strategically evade host immune responses. Members of the Campylobacter genus naturally colonize a wide range of hosts (including pets, farm animals and wild animals) and are frequently found in contaminated food products, which indicates that these bacteria are at risk of zoonotic transmission to humans. This Review presents the latest information on the role and clinical importance of emerging Campylobacter spp. in gastrointestinal health and disease.

The role of Campylobacter jejuni cytolethal distending toxin in gastroenteritis: toxin detection, antibody production, and clinical outcome

The role of Campylobacter jejuni cytolethal distending toxin (CDT) on clinical outcome after gastroenteritis was investigated. Clinical data, blood serum samples, and Campylobacter spp. isolated, from each of 30 patients were collected over a period of 6 months. The CDT encoding genes, cdtABC, characterized by PCR, revealed that all but one of the C. jejuni strains had the wild-type sequence. Sequencing of cdtABC from this strain showed two major deletions. From all of the strains, CDT titers were determined, and toxin neutralizing antibodies were documented using an in vitro assay. Three of the thirty clinical isolates, including the one with the mutant cdtABC coding genes, did not have a detectable CDT activity. Analyzing the relationship between CDT titer, serum neutralization of CDT, and the clinical outcome showed that campylobacteriosis caused by CDT-negative strains was clinically indistinguishable from that of patients infected with an isolate that produced high levels of CDT. These results suggest that CDT does not solely determine severity of infection and clinical outcome.

Cross-reactivity of outer membrane proteins of Campylobacter species with cholera toxin

Campylobacter jejuni is a foodborne pathogen and a leading cause of diarrhoea worldwide. It is believed that a cholera toxin-like toxin (CTLT) produced by C. jejuni may mediate watery diarrhoea. However, the production of a CTLT by C. jejuni is controversial. A cholera toxin gene (ctx) homologue has not been identified in Campylobacter species. We investigated the identity of the CT cross-reactive antigen from Campylobacter species previously and the results are reviewed here. Filtrates of C. jejuni grown in four different liquid media, reported to promote CTLT production, were tested by Chinese hamster ovary (CHO) cell elongation assay for functional toxin and for reactivity with CT antibody using GM1 ganglioside ELISA (GM1 ELISA) and immunoblotting. Protein sequence of the CT antibody-reactive band was determined by matrix-assisted laser desorption ionization-time of flight (MALDI TOF-TOF). Non-jejuni species (C. coli, C. lari, C. foetus, C. hyointestinalis and C. upsaliensis) were investigated by CHO cell assay and immunoblotting. Filtrates from seven C. jejuni reference strains reported to produce CTLT and from 80 clinical strains were negative in the CHO cell assay. However, filtrates from three reference strains and 16 clinical strains were positive by GM1 ELISA. All strains irrespective of GM1 ELISA reactivity, possessed a 53-kDa protein which reacted with CT antibody by immunoblotting. This band was identified as the major outer membrane protein (PorA) of C. jejuni. CT antibody reacted with a C. jejuni recombinant PorA on immunoblotting. All non-C. jejuni strains were negative by CHO cell assay, but the common 53-kDa proteins reacted with CT antibody on immunoblots. The cross-reactivity of PorAs of Campylobacter species with CT may lead to the erroneous conclusion that Campylobacter species produce a functional CTLT.

Identification of hyperinvasive Campylobacter jejuni strains isolated from poultry and human clinical sources

Campylobacter jejuni causes gastroenteritis with a variety of symptoms in humans. In the absence of a suitable animal model, in vitro models have been used to study virulence traits such as invasion and toxin production. In this study, 113 C. jejuni isolates from poultry and poultry-related (n=74) environments as well as isolates from human cases (n=39) of campylobacteriosis and bacteraemia were tested for invasiveness using INT 407 cells. The method was sufficiently reproducible to observe a spectrum of invasiveness amongst strains. As a result, strains were classified as low, high and hyper-invasive. The majority of strains (poultry and human) were low invaders (82 % and 88 %, respectively). High invasion was found for 5 % of human strains and 11 % of poultry-related isolates. However, only 1 % of poultry strains were classified as hyperinvasive compared to 13 % of human isolates (P=0.0182). Of those isolates derived from the blood of bacteraemic patients, 20 % were hyperinvasive, though this correlation was not statistically significant. An attempt was made to correlate invasiveness with the presence of seven genes previously reported to be associated with virulence. Most of these genes did not correlate with invasiveness, but gene cj0486 was weakly over-represented, and a negative correlation was observed for the gene ciaB. This trend was stronger when the two genes were analysed together, thus ciaB(-) cj0486(+) was over-represented in high and hyperinvasive strains, with low invaders more commonly found to lack these genes (P=0.0064).

Major outer membrane proteins from many Campylobacter species cross-react with cholera toxin

We have previously shown that Campylobacter jejuni strains do not produce a functional cholera toxin-like toxin (CTLT) detectable in a Chinese hamster ovary cell assay. Instead, the 53-kDa major outer membrane protein (OMP) of C. jejuni, PorA, reacts with cholera toxin (CT) antibody on immunoblots. Here, we have extended this observation to other species of Campylobacter, including C. coli, C. lari, C. fetus, C. hyointestinalis, and C. upsaliensis, the common 53-kDa OMP of which reacted with CT antibody in immunoblotting assays. There were additional reactive bands for C. fetus. As with C. jejuni, this finding may lead to the erroneous conclusion that these additional species produce a functional CTLT. However, this common cross-reactive OMP can be explored as a vaccine candidate to prevent campylobacteriosis.

Characterization of genetically matched isolates of Campylobacter jejuni reveals that mutations in genes involved in flagellar biosynthesis alter the organism's virulence potential

Phenotypic and genotypic evidence suggests that not all Campylobacter jejuni isolates are pathogenic for humans. We hypothesized that differences in gene content or gene expression alter the degree of pathogenicity of C. jejuni isolates. A C. jejuni isolate (Turkey) recovered from a turkey and a second C. jejuni isolate (CS) recovered from a chicken differed in their degrees of in vitro and in vivo virulence. The C. jejuni Turkey isolate invaded INT 407 human epithelial cells and secreted the Cia (Campylobacter invasion antigen) proteins, while the C. jejuni CS isolate was noninvasive for human epithelial cells and did not secrete the Cia proteins. Newborn piglets inoculated with the C. jejuni Turkey isolate developed more severe clinical signs of campylobacteriosis than piglets inoculated with the C. jejuni CS isolate. Additional work revealed that flagellin was not expressed in the C. jejuni CS isolate. Microarray and real-time reverse transcription-PCR analyses revealed that all flagellar class II genes were significantly downregulated in the C. jejuni CS isolate compared to the C. jejuni Turkey isolate. Finally, nucleotide sequencing of the flgR gene revealed the presence of a single residue that was different in the FlgR proteins of the C. jejuni Turkey and CS isolates. Complementation of the C. jejuni CS isolate with a wild-type copy of the flgR gene restored the isolate's motility. Collectively, these findings support the hypothesis that critical differences in gene content or gene expression can alter the pathogenic potential of C. jejuni isolates.

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.

Campylobacter jejuni cytolethal distending toxin mediates release of interleukin-8 from intestinal epithelial cells

Live cells of Campylobacter jejuni and Campylobacter coli can induce release of interleukin-8 (IL-8) from INT407 cells. Additionally, membrane fractions of C. jejuni 81-176, but not membrane fractions of C. coli strains, can also induce release of IL-8. Membrane preparations from 81-176 mutants defective in any of the three membrane-associated protein subunits of cytolethal distending toxin (CDT) were unable to induce IL-8. The presence of the three cdt genes on a shuttle plasmid in trans restored both CDT activity and the ability to release IL-8 to membrane fractions. However, CDT mutations did not affect the ability of 81-176 to induce IL-8 during adherence to or invasion of INT407 cells. When C. jejuni cdt genes were transferred on a shuttle plasmid into a C. coli strain lacking CDT, membrane preparations became positive in both CDT and IL-8 assays. Growth of C. jejuni in physiological levels of sodium deoxycholate released all three CDT proteins, as well as CDT activity and IL-8 activity, from membranes into supernatants. Antibodies against recombinant forms of each of the three CDT subunit proteins neutralized both CDT activity and the activity responsible for IL-8 release. The data suggest that C. jejuni can induce IL-8 release from INT407 cells by two independent mechanisms, one of which requires adherence and/or invasion and the second of which requires CDT.

Detection and characterization of autoagglutination activity by Campylobacter jejuni

In several gram-negative bacterial pathogens, autoagglutination (AAG) activity is a marker for interaction with host cells and virulence. Campylobacter jejuni strains also show AAG, but this property varies considerably among strains. To examine the characteristics of C. jejuni AAG, we developed a quantitative in vitro assay. For strain 81-176, which shows high AAG, activity was optimal for cells grown for < or = 24 h, was independent of growth temperature, and was best measured for cells suspended in phosphate-buffered saline at 25 degrees C for 24 h. AAG activity was heat labile and was abolished by pronase or acid-glycine (pH 2.2) treatment but not by lipase, DNase, or sodium metaperiodate. Strain 4182 has low AAG activity, but extraction with water increased AAG, suggesting the loss of an inhibitor. Strain 6960 has weak AAG with no effect due to water extraction. Our study with clinical isolates suggests that C. jejuni strains may be grouped into three AAG phenotypes. A variant derived from strain 81116 that is flagellate but immotile showed the strong AAG exhibited by the parent strain, suggesting that motility per se is not necessary for the AAG activity. AAG correlated with both bacterial hydrophobicity and adherence to INT407 cells. Mutants which lack flagella (flaA, flaB, and flbA) or common cell surface antigen (peb1A) were constructed in strain 81-176 by natural transformation-mediated allelic exchange. Both AAG activity and bacterial hydrophobicity were abolished in the aflagellate mutants but not the peb1A mutant. In total, these findings indicate that C. jejuni AAG is highly associated with flagellar expression.

Milkborne campylobacter infection in Hungary

In April 1998, an annual 2-day animal farm sale was held in Hódmezóvásárhely, where 500 to 600 visitors consumed unpasteurized milk. The first signs of disease began 2 days after the end of the sale. Fifty-two people from a wide age range fell ill, primarily with inflammatory enteritis. These cases included 34 with Campylobacter positivity: 30 with Campylobacter jejuni and 4 with Campylobacter coli. Environmental samples (raw milk, udder swabs, and rectal swabs from 12 cows in the suspected herd) were tested 2 weeks after the first signs of the disease, and two rectal swabs were found to be positive for C. jejuni. Initially, the epidemic seemed to be sporadic and, accordingly, only 26 human and 2 animal Campylobacter isolates were reserved for randomly amplified polymorphic DNA analysis. This comparative analysis verified that fecally contaminated milk was the source of the outbreak. The DNA-banding patterns of 20 C. jejuni isolates (19 human and 1 animal) were identical. The antibiotic susceptibilities of the Campylobacter isolates were determined, and only six C. jejuni (human) isolates, one C. coli (human) isolate, and one C. jejuni (animal) isolate were resistant to tetracycline, both by disk diffusion and by E test (antimicrobial gradient strip for the quantitative determination of susceptibility or resistance of microorganisms). No plasmid was detected in these tetracycline-resistant isolates. The endotoxin production of Campylobacter isolates was examined via the cytopathogenic effect on the Vero cell line. This effect exhibited various degrees of positivity in 19 cases. Only two human C. jejuni isolates displayed + + + + positivity. Both isolates were from patients who had required antibiotic therapy and hospital care.

Detection of a novel campylobacter cytotoxin

The culture filtrates from 10 Campylobacter species were screened for the presence of cytotoxins on a variety of selected tissue culture cell lines. Some Campylobacter jejuni strains showed no effects on tissue culture cell lines compared with other C. jejuni strains, especially C. jejuni 81116, which consistently produced a cytotoxin that was lethal to tissue culture cells. It was observed that CHO cells were the most sensitive cell line in detecting campylobacter cytotoxins. Samples containing the culture filtrate of C. jejuni 81116 prepared at various growth stages were used to determine the subcellular location of the cytotoxin. This C. jejuni 81116 cytotoxin appears to be a heat-stable toxin that is secreted from the cell during stationary phase; cytotoxin activity can be abolished with proteolytic enzymes.

Detection of thermophilic Campylobacter spp. in blood-free enriched samples of inoculated foods by the polymerase chain reaction

The detection of thermophilic Campylobacter spp., as represented by Campylobacter jejuni, by the polymerase chain reaction (PCR) was investigated and compared with the selective agar isolation (SAI) method. Stationary-phase cultures of C. jejuni were inoculated into either blood-free enrichment broth (BFEB) or BFEB that contained 10% broccoli, crabmeat, mushroom, raw milk, and raw oyster rinses. Following a 48-h enrichment period, aliquots of food test portions were removed for simultaneous analysis by PCR and SAI. It was determined that the presence of charcoal and iron in the enrichment broth interfered with the PCR assay. Therefore, three DNA extraction techniques were developed and evaluated using a 16S rRNA primer pair in the PCR assay. The 50% end point (DL50) values (determined upon six initial C. jejuni spiking levels) were used to assess the frequency of isolation utilizing PCR versus SAI for the detection of this organism in the enrichment matrices. There were virtually no differences in detection of C. jejuni among enriched samples analyzed by PCR and SAI. Mean DL50 values (n = 3) for plain BFEB, broccoli, crabmeat, mushroom, raw milk, and raw oyster were, respectively, 0.02 (PCR) versus 0.01 (SAI), 0.01 versus 0.06, 0.07 versus 0.04, 0.03 versus 0.08, 0.01 versus 0.01, and 0.01 versus 0.01 CFU/5 g food. Significant variability in the detection limit of C. jejuni by PCR in the food enrichments was observed among DNA extraction techniques. Using 48-h enrichment cultures followed by PCR analysis could save 1 day of the time required for the presumptive identification of C. jejuni in suspected foods.

Pathophysiology of Campylobacter jejuni infections of humans

Campylobacter jejuni and closely related organisms are major causes of human bacterial enteritis. These infections can lead to extraintestinal disease and severe long-term complications. Of these, neurological damage, apparently due to the immune response of the host, is the most striking. This review examines current knowledge of the pathophysiology of the organism. Diversity of C. jejuni isolates in genotypic and phenotypic characteristics now is recognized and clinically relevant examples are presented. Expected future directions are outlined.

Formation of cytotoxins by enteric Campylobacter in humans and animals

Campylobacter (C.) jejuni from persons suffering from diarrhoea, from organs of poultry, C. jejuni and C. fetus ssp. fetus from the gastrointestinal tract of calves and adult cattle as well as a number of reference strains were examined for cytotoxin formation in a CHO-K1 cell culture test. During evaluation, three morphologically different pictures were observed. The first cytotoxin caused a formation of strikingly large, rounded or polymorphic and elongated cells which was associated with reduced growth. The progressive morphological changes corresponded to those described for the Cytolethal Distending Toxin (CLDT) and were assigned to it. The second cytotoxin produced a rounding of cells without a change in their size while at the same time, growth was reduced. In analogy to CLDT, this toxin was termed Cytolethal Rounding Toxin (CLRT). A third morphological picture consisted of cell changes characterized by enlarged polymorphic as well as by small rounded cells. These cell changes were considered as being distinct from the above mentioned ones and referred to as CLTD/CLRT effect. In none of the 39 Campylobacter strains isolated from humans and calves with diarrhoea, a noteworthy cytotonic activity could be detected that would indicate the presence of an enterotoxin.

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.

Outer membrane characteristics of Campylobacter jejuni grown in chickens

A type of in vivo phenotype of Campylobacter jejuni was obtained by maintaining bacteria in the peritoneal cavities of chickens for one week. These bacteria, which had not been subcultured on laboratory media, were used to prepare outer membranes for comparison with C. jejuni grown in vitro. Flagella with subunits of 65 kDa and a single porin with a protein subunit of 49 kDa were expressed constitutively; however, outer membrane proteins of 55, 35 and 20 kDa, and intermediate-chain lipopolysaccharide were only expressed by bacteria maintained in chickens.

Adhesion of enteroaggregative Escherichia coli to pediatric intestinal mucosa in vitro

Organ cultures of small- and large-intestinal mucosa from children were used to examine the interactions of enteroaggregative Escherichia coli (EAEC) with human intestine. Mucosae from patients aged between 3 and 190 months were cultured with five EAEC strains isolated from infants with diarrhea in the United Kingdom and with two well-described prototype EAEC strains, 17-2 and 221. The prototype strains adhered to jejunal, ileal, and colonic mucosae. The wild-type strains also adhered to this tissue but showed a variable pattern of adhesion: two adhered to all intestinal levels, one adhered to jejunum and ileum, one adhered to ileum only, and one adhered to ileum and colon. Adherence was in an aggregative or stacked-brick pattern, resembling that seen on HEp-2 cells. Electron microscopy of infected small intestinal mucosa revealed bacteria in association with a thick mucus layer above an intact enterocyte brush border, which contained extruded cell fragments. This mucus layer was not present on controls. EAEC adherence to colonic mucosa was associated with cytotoxic effects including microvillous vesiculation (but without evidence of an attaching/effacing lesion), enlarged crypt openings, the presence of intercrypt crevices, and increased epithelial cell extrusion. These results demonstrate that in vitro organ culture of intestinal mucosa from children can be used to investigate EAEC pathogenesis in childhood directly. EAEC strains appear able to colonize many regions of the gastrointestinal tract, without overt changes to small intestinal mucosa but with cytotoxic effects on colonic mucosa.

An environmentally regulated pilus-like appendage involved in Campylobacter pathogenesis

Examination of strains of Campylobacter jejuni, Campylobacter coli, and Campylobacter fetus by electron microscopy revealed that they produced peritrichous pilus-like appendages when the bacteria were grown in the presence of bile salts. Various bile-salt supplements were used and it was found that deoxycholate and chenodeoxycholic acid caused a significant enhancement of pilus production and resulted in a highly aggregative phenotype. Morphologically, the pili were between 4 and 7 nm in width and were greater than 1 micron in length. A gene, termed pspA, which encodes a predicted protein resembling protease IV of Escherichia coli, was identified in C. jejuni strain 81-176. A site-specific insertional mutation within this gene resulted in the loss of pilus synthesis as determined by electron microscopy. Insertions upstream and downstream of the gene had no effect on pilus production. The non-piliated mutant of strain 81-176 showed no reduction in adherence to or invasion of INT 407 cells in vitro. However, this mutant, while still possessing the ability to colonize ferrets, caused significantly reduced disease symptoms in this animal model.

Heat-labile and heat-stable haemolysins of Campylobacter jejuni

During studies on the virulence mechanisms of Campylobacter jejuni clinical isolates it became apparent that some strains produced one or more haemolysins and some did not. There was no great difference between Group C (cholera-like) strains and Group D (dysentery-like) strains. The protein haemolysin(s) showed a spectrum of activity against erythrocytes from different animals; with maximum activity against rabbit and minimal activity against chicken erythrocytes. The results suggested a two-stage activation mechanism for haemolysis which involved a multi-hit lytic activity. It was concluded that the C. jejuni haemolysins were not identical to those described in other organisms and they may be involved in iron acquisition in vivo.

Physical map of Campylobacter jejuni TGH9011 and localization of 10 genetic markers by use of pulsed-field gel electrophoresis

The physical map of Campylobacter jejuni TGH9011 (ATCC 43430) was constructed by mapping the three restriction enzyme sites SacII (CCGCGG), SalI (GTCGAC), and SmaI (CCCGGG) on the genome of C. jejuni by using pulsed-field gel electrophoresis and Southern hybridization. A total of 25 restriction enzyme sites were mapped onto the C. jejuni chromosome. The size of the genome was reevaluated and was shown to be 1,812.5 kb. Ten C. jejuni genetic markers that have been isolated in our laboratory were mapped to specific restriction enzyme fragments. Furthermore, we have accurately mapped one of the three rRNA operons (rrnA) and have demonstrated a separation of the 16S and 23S rRNA-encoding sequences in one of the rRNA operons.

Profiles of toxin production by thermophilic Campylobacter of animal origin

Seventy-five strains of Campylobacter jejuni and C. coli, which were isolated from a variety of animal species, primarily poultry, were examined for production of toxin. Polymyxin extracts were tested in in vitro assays using CHO-KI, FCL (foetal calf lung), Vero, HeLa and CEF (chicken embryo fibroblast) cells. The toxic effects observed were cell rounding and death. Extracts from almost all C. jejuni and C. coli strains were toxic to both CHO-KI and FCL cells and 69.0% of C. jejuni isolates and 75% of C. coli isolates were also toxic to CEF cells. 50.7% of C. jejuni extracts were toxic to Vero cells and 46.5% toxic to HeLa cells. None of the C. coli isolates were toxic to either of these cell lines. None of the strains tested produced cytotonic enterotoxin. No differences in toxigenicity patterns were evident between Campylobacter isolated from different sources.

Incidence of toxigenic Campylobacter strains in South Africa

Campylobacter strains can produce a heat-labile cytotonic toxin (CTON) and various cytotoxins (CTOX). Of 22 South African Campylobacter strains tested, 86% were toxigenic (77% produced CTON, 41% produced CTOX, and 32% produced both types) and 14% were toxin negative. Campylobacter jejuni strains were 67% CTON positive and 47% CTOX positive, whereas Campylobacter coli strains were 100 and 29% positive, respectively.

Virulence of Campylobacter jejuni for chicken embryos is associated with decreased bloodstream clearance and resistance to phagocytosis

The 11-day-old chicken embryo has been shown to be a useful animal model for comparing the virulence of human isolates of Campylobacter jejuni. Virulence in this system is associated with the ability to invade the chorioallantoic membrane and to survive and proliferate in vivo. In this study, the survival and multiplication of C. jejuni in the embryonic host was investigated. It was possible to enhance the virulence of a relatively avirulent C. jejuni strain by passaging it intravenously through the embryos. The resulting isogenic variants demonstrated enhanced abilities to survive in vivo but were still unable to invade when inoculated onto the chorioallantoic membrane. The bloodstream clearance of C. jejuni was studied, and virulent, but not avirulent, strains persisted and multiplied both in the bloodstream and in embryonic liver. Virulent strains also were cleared significantly more slowly from the bloodstream of adult BALB/c mice after intravenous challenge than were avirulent strains. C. jejuni strains which were cleared slowly in vivo were also ingested slowly in vitro by mouse peritoneal macrophages. Clearance studies in mice pretreated with cobra venom factor demonstrated that opsonization by serum complement was not a prerequisite for clearance of campylobacters from the murine bloodstream.

Evaluation of cytotoxic activity in fecal filtrates from patients with Campylobacter jejuni or Campylobacter coli enteritis

We sought to determine the prevalence of cytotoxic activity in fecal filtrates from persons with C. jejuni or C. coli enteritis. Stool specimens were collected from 20 persons with C. jejuni or C. coli enteritis, 20 persons with acute diarrheal illnesses of other causes, and 9 healthy, asymptomatic persons. Fecal filtrates were then incubated with Chinese hamster ovary (CHO) or HeLa cells. The fecal filtrate from 1 of the 20 (5%) persons with Campylobacter enteritis was cytotoxic for HeLa cells at a titer of 1:40, and 10 (50%) were cytotoxic for CHO cells at maximum titers of 1:20. Cytotoxic activity for CHO cells at a median titer of 1:20 was also present in 40% of the fecal filtrates from persons with diarrhea due to causes other than Campylobacter enteritis, and in 33% of filtrates from healthy, asymptomatic persons. The observed low level of cytotoxicity in fecal filtrates from all patient groups studied likely resulted from non-specific factors, unrelated to the pathogenesis of Campylobacter enteritis.

Partial purification and characterization of the enterotoxin produced by Campylobacter jejuni

Campylobacter jejuni enterotoxin was partially purified from culture supernatant. The purified fraction after gel filtration indicated three bands at 68, 54, and 43 kilodaltons on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). This fraction enhanced the adenylate cyclase activity of HeLa cell membranes by 1.5-fold over that of the control. The study with anti-cholera toxin immunoglobulin G (IgG) and ganglioside affinity column chromatographies revealed that the eluent from the anti-cholera toxin IgG column chromatography exhibited a single band (68 kDa) on SDS-PAGE and native PAGE, whereas the eluent from ganglioside column chromatography exhibited two bands (68 and 54 kDa) on SDS-PAGE. These suggest that the 68-kDa polypeptide should have an immunological relationship with cholera toxin, and the 68- and 54-kDa polypeptides might be responsible for the recognition of ganglioside.

Isolation, characterization, and host-cell-binding properties of a cytotoxin from Campylobacter jejuni

A 68,000-molecular-weight protein was isolated by polyacrylamide gel electrophoresis from the organism-free filtrate of a fully virulent clinical strain of Campylobacter jejuni. The eluted protein was heat labile, was inactivated at either pH 3.0 or 9.0, was sensitive to trypsin, and was lethal for fertile chicken eggs. It also had toxic effects on chicken embryo fibroblast, Chinese hamster ovary (CHO), and intestinal 407 (Int407) cells. A monoclonal antibody (CETPMAb4) raised to this eluted toxic protein (ETP) from C. jejuni abolished these toxic activities. Homology between C. jejuni ETP and Vibrio cholerae toxin was not observed in that specific antisera to each did not block their respective toxic activities. In enzyme-linked immunosorbent assays, ETP, unlike chlorea enterotoxin, did not bind to GM1 ganglioside. Furthermore, the C. jejuni toxin had cytotoxinlike properties and induced rounding of CHO cells. Binding of ETP to Int407 and primary chicken embryo fibroblast cells was maximal after 2 h as assessed by enzyme-linked immunosorbent assay, and this toxin adherence to host cell membranes was significantly reduced by prior treatment of the cells with proteolytic enzymes, neuraminidase, or glutaraldehyde but not by treatment with beta-galactosidase, lipase, Nonidet P-40, or sodium metaperiodate. In competitive binding assays, sugars, lectins, or GM1 ganglioside did not adversely influence uptake of ETP by these cells. These results suggest that the ETP produced by C. jejuni is a cytotoxin which binds to Int407 cells via a protein- or glycoproteinlike receptor on cell membranes and possesses properties dissimilar to those of V. cholerae toxin.

Enterotoxigenicity and frequency of Campylobacter jejuni, C. coli and C. laridis in human and animal stool isolates from different countries

Campylobacter jejuni and C. coli strains were collected during three different years from adult patients with enterocolitis in Sweden (n = 372) from 49 patients in Kuwait, and Campylobacter strains from hens from Mexico, Pakistan and Sweden (n = 107) and Swedish pigs (n = 47). C. jejuni was the predominant species in human and hen isolates, and C. coli in pigs C. coli was significantly more common in human isolates from Sweden, and more common in hen isolates from Pakistan, than in hens from Sweden and Mexico. C. laridis was only isolated from pigs (17%) and was in no case enterotoxigenic. Both in human and hen isolates, C. jejuni strains were more enterotoxigenic than C. coli strains. C. jejuni strains from Swedish hens were less enterotoxigenic than those from Pakistan and Mexico (P less than 0.001), and strains from pigs were less enterotoxigenic than those from hens (P less than 0.001). We conclude that C. jejuni are more often enterotoxigenic and possibly more virulent than c. coli and C. laridis. The relative frequency of C. jejuni and C. coli in humans and animals differs from one country to another.

Response of the chick embryo to live and heat-killed Campylobacter jejuni injected into the yolk sac

Graded doses of live and heat-killed cells of Campylobacter jejuni were injected into the yolk-sac of 5-day-old chick embryos, and the 50% lethal dose (LD50) was determined 7 days later. A strain dependent virulence was seen. In the diluted series of cultures the LD50 values for live campylobacter ranged from 10(6) c.f.u. beyond the last dilution showing growth, that is to less than one organism per embryo. When the 22 strains were tested as heat-killed cells, the chick embryo LD50 values retained the same relative order of toxicity obtained with viable cells, but the LD50 values were increased by +1 to +4 log units. Heat-killed cells from strains known to be invasive, but non-toxigenic, were still lethal for the embryos, suggesting that viability was not solely necessary for virulence. Semi-pure lipopolysaccharide from a non-virulent strain of C. jejuni was not toxic to the embryos, but semi-pure and ultracentrifuge-purified lipopolysaccharide from the most lethal campylobacter strains gave LD50 values in the order of 3.0 micrograms lipopolysaccharide per ml (0.6 microgram per embryo) in the yolk-sac assay. No relationship between serotype and lethality was seen. Injection into the yolk-sac appears to be an easy, rapid and reproducible in vivo assay of the virulence of C. jejuni.

Detection of salmonellas in animal feeds by electrical conductance

A comparison was made between standard culture methods and electrical conductance using a Malthus AT Microbiological Analyser for the examination of animal feeds for salmonella. Conductance testing with a selenite cystine/trimethylamine-N-oxide/dulcitol medium resulted in the detection of salmonellas in 49 of 55 known positive animal feeds, 13 of 19 spiked feed samples and 36 of 47 salmonella cultures. Testing with a lysine decarboxylase/glucose medium gave significantly better results (P less than 0.05) than with selenite cystine medium but five lysine decarboxylase negative strains of salmonella were undetected. When both media were used in parallel all salmonella positive samples were detected. No difference was found between preenrichment in buffered peptone water containing trimethylamine/mannitol and that containing lysine/glucose. Positive detection criteria for selenite medium of conductance peak at greater than or equal to 500 microsiemens (microS) with a rate of change of greater than or equal to 60 microS/h or 400-499 microS with a rate of change of greater than or equal to 40 microS/h and for lysine medium with a peak of greater than or equal to 100 microS have been established. The method offers savings in media and operating costs over conventional standard culture methods, provides results within 48 h and is recommended for statutory feed monitoring purposes.

A two-year study of the distribution of 'thermophilic' campylobacters in human, environmental and food samples from the Reading area with particular reference to toxin production and heat-stable serotype

The incidence of 'thermophilic' campylobacters in foods and environmental samples has been studied over a two-year period. Of 781 environmental samples, 529 (67%) were found to contain campylobacters, and campylobacters were isolated from 835 (39%) of 2116 food samples. Sewage was almost always contaminated with campylobacters (96.6% of samples) and of the food samples both poultry (55.5%) and offal (47.0%) were commonly contaminated. Determination of the heat-stable serotypes of all strains isolated from these sources and of 921 strains isolated from human faeces showed that there was a wide distribution of serotypes in most types of sample. Serotype Pen 2 was the commonest type found in human faeces (18.9%) and it was also commonest in offal (21.3%), beef (40.0%), sewage (17.7%) and was the third commonest type in poultry. A comparison of culture media and conditions for optimal production of both cytotoxic and cytotonic enterotoxins showed that Brucella Broth incubated under microaerobic conditions for 24 h at 42 degrees C was suitable for both toxins. Detection of cytotoxic activity was most sensitive using HeLa cells. The sensitivities of two ELISA systems and a Chinese Hamster Ovary tissue culture assay for detection of cytotonic enterotoxin were comparable. Not all strains isolated from cases of enteritis in human beings produced toxin; 23.1% produced cytotonic enterotoxin and 17.5% produced cytotoxin. There was no correlation between serotype and toxin production. The wide distribution of campylobacters, indistinguishable from those isolated from cases of enteritis in human beings, leads us to conclude that simplistic statements suggesting that one particular type of food is primarily responsible for cases of human disease should not be made.

Enterotoxin production and serogroups of Campylobacter jejuni and Campylobacter coli from patients with diarrhea and from healthy laying hens

Enterotoxin production, a possible virulence factor, was determined in Campylobacter jejuni and Campylobacter coli by two different techniques, the CHO cell test and the GM1 enzyme-linked immunosorbent assay. The frequency of enterotoxigenic Campylobacter strains was 32% in strains from both humans with acute enteritis and healthy laying hens, as measured by the CHO cell test. The CHO cell test was significantly more sensitive than the GM1 enzyme-linked immunosorbent assay in the detection of enterotoxigenic strains. Enterotoxin production was compared with the presence of heat-stable and heat-labile antigens. There was no significant correlation between enterotoxin production and serogroups for C. jejuni or C. coli. The difference in enterotoxigenicity between C. jejuni (34.1%) and C. coli (21.9%) was not significant.

Campylobacter jejuni isolations from Mexican and Swedish patients, with repeated symptomatic and/or asymptomatic diarrhoea episodes

The presence of different Campylobacter jejuni serotypes in Swedish patients with diarrhoea and in Mexican patients with or without diarrhoea was investigated with special reference to repeated isolations during the course of infection and to symptomatic and asymptomatic episodes. The study included 136 C. jejuni isolates from 62 Mexican children and 173 isolates from 68 Swedish patients. The bacteria were serotyped for heat-stable (HS) and heat-labile (HL) antigen. Swedish patients, all with symptoms, were in general only infected with one serotype and were rarely reinfected. Mexican patients on the other hand were in general infected with mixed serotypes and frequently reinfected without symptoms with new, different serotypes, a finding which is in concordance with a theory of an induced immunity to surface antigens.

Surface charge and hydrophobicity of Campylobacter jejuni strains in relation to adhesion to epithelial HT-29 cells

Hydrophobicity and surface charge of clinical isolates of Campylobacter jejuni strains were investigated by aqueous two-phase partitioning (one-step and counter-current distribution), ion exchange chromatography and hydrophobic interaction chromatography. There was a good correlation between the different physico-chemical methods reflecting the same bacterial property. All strains were negatively charged and exposed a hydrophobic surface, but to a varying extent. Bacteria with a high negative surface charge and a weak hydrophobic surface adhered better to human intestinal HT-29 cells than strains with less charge and a more hydrophobic surface. Highest adhesion was shown by a strain differing from all the others in charge properties. It was also found that the tendency to aggregate was higher among the strains showing the greatest degree of adherence.

In vitro model for Campylobacter pylori adherence properties

The adherence of 12 strains of Campylobacter pylori was studied on four cell lines. Immunofluorescence and scanning and transmission electron microscopy were used to visualize the bacteria. A heavy adherence to the epithelial cell line HEp-2 and to the intestinal cell line Int-407 was noted. By transmission electron microscopy, a close association between bacteria and cells in the form of cup-like structures was observed, but pedestals were not present.

Production of a Shiga-like cytotoxin by Campylobacter

Cell lysates and culture supernatants of 36 Campylobacter isolates from patients with enteritis were tested for cytotoxic activity on HeLa cells. Cytotoxic activity was considered Shiga-like if neutralized by monoclonal antibody to the B subunit of Shiga-like toxin I of Escherichia coli and rabbit anti-Shiga toxin. Fifteen of the Campylobacter isolates produced no detectable cytotoxin, 10 produced a non-neutralizable cytotoxin, and 11 produced low levels of a cell-associated SLT. However, under low stringency conditions no hybridization was observed between a DNA fragment containing cloned SLT-I genes and restriction enzyme-digested total DNA from a Campylobacter strain that produced low levels of a Shiga-like toxin I. The Shiga-like toxin neutralizing titers in sera from 15 patients with C. jejuni infections, 5 patients infected with S. sonnei, and 20 healthy persons were then determined. No rise in neutralizing titer between acute and convalescent sera of patients with C. jejuni infection or S. sonnei infection was observed, although 27% of C. jejuni-infected patients, 40% of S. sonnei-infected patients, and 30% of the healthy controls had neutralizing activity in their sera. These data indicate that low levels of Shiga-like toxin are produced by some Campylobacter isolates but that SLT is genetically distinct from the SLT-I toxin produced at high levels by certain E. coli. The findings also suggest that exposure to SLTs is common in the adult population but not as a consequence of infection with C. jejuni or S. sonnei.