Host CDK-1 and formin mediate microvillar effacement induced by enterohemorrhagic Escherichia coli

Enterohemorrhagic Escherichia coli (EHEC) induces changes to the intestinal cell cytoskeleton and formation of attaching and effacing lesions, characterized by the effacement of microvilli and then formation of actin pedestals to which the bacteria are tightly attached. Here, we use a Caenorhabditis elegans model of EHEC infection to show that microvillar effacement is mediated by a signalling pathway including mitotic cyclin-dependent kinase 1 (CDK1) and diaphanous-related formin 1 (CYK1). Similar observations are also made using EHEC-infected human intestinal cells in vitro. Our results support the use of C. elegans as a host model for studying attaching and effacing lesions in vivo, and reveal that the CDK1-formin signal axis is necessary for EHEC-induced microvillar effacement.

Characterizing interactions of Leptospira interrogans with proximal renal tubule epithelial cells

BACKGROUND

Leptospira interrogans is a pathogenic, spirochetal bacterium that is responsible for leptospirosis, an emerging worldwide zoonosis. Leptospires colonize the renal proximal tubules and chronically infect the kidney. Live bacteria are excreted into urine, contaminating the environment. While it is well known that leptospires can persist in the kidneys without signs of disease for several months, the interactions of leptospires with the proximal renal epithelial tubule cells that allow the chronic renal colonization have not been elucidated yet. In the present study, we compared the interactions between a virulent, low passage (LP) strain and a cultured-attenuated, high passage (HP) strain with renal proximal tubule epithelial cells (RPTECs) to elucidate the strategies used by Leptospira to colonize the kidney.

RESULTS

Kinetics analysis of kidney colonization in a mouse model of chronic infection performed by quantitative real-time PCR and immunofluorescence, showed that the LP strain reached the kidney by 3 days post infection (pi) and attached to the basal membrane side of the renal epithelial cells. At 10 days pi, some leptospires were attached to the luminal side of the tubular epithelia and the number of colonizing leptospires gradually increased. On the other hand, the HP strain was cleared during hematogenous dissemination and did not colonize the kidney. Transmission electron microscopy analysis of LP-infected kidneys at 25 days pi showed aggregated leptospires and membrane vesicles attached to the epithelial brush border. Leptospiral kidney colonization altered the organization of the RPTEC brush border. An in vitro model of infection using TCMK-1 cells, showed that leptospiral infection induced a host stress response, which is delayed in LP-infected cells.

CONCLUSIONS

After hematogenous dissemination, leptospires create protective and replicative niches in the base membrane and luminal sides of the RPTECs. During the long-term colonization, leptospires attached to the RPTEC brush borders and membrane vesicles might be involved in the formation of a biofilm-like structure in vivo. Our results also suggested that the virulent strain is able to manipulate host cell stress responses to promote renal colonization.

Immunohistochemical Detection of Porcine Rotavirus Using Immunogold Silver Staining (IGSS)

Immunogold silver staining (IGSS) was applied for the detection of porcine group A rotavirus in formalin-fixed paraffin-embedded tissue sections of small intestine. Prior to the application of IGSS, the reactivity of protein A-gold as a marker was tested with group-specific antiserum in immunogold electron microscopy. Immune aggregates were intensely and specifically labeled with the gold complex. Application of IGSS to tissue sections resulted in specific dark staining of villous enterocytes infected by group A rotavirus. This method also proved effective for the detection of rotaviral antigen in infected cultured cells. The IGSS method may be suitable for routine diagnostic detection of rotaviral infections and may have application for detection of other viral pathogens of veterinary importance.

Ultrastructural study on route of gut bacterial translocation in a rat after spinal cord injury

OBJECTIVE

To observe the ultrastructural change of the route of gut bacterial translocation in a rat with spinal cord injury (SCI).

METHODS

Forty Wistar rats were divided into the following groups: control group and 3 SCI groups (10 in each group). The rats in the SCI groups were established SCI model at 24 h, 48 h, and 72 h after SCI. Small intestine mucous membrane tissue was identified and assayed by transmission electron microscope, scanning electron microscope and immunofluorescence microscopy.

RESULTS

Small intestine mucous membrane tissue in control group was not damaged significantly, but those in SCI groups were damaged significantly. Proliferation bacteria in gut lumen attached on microvilli. The extracellular bacteria torn the intestinal barrier and perforated into the small intestinal mucosal epithelial cell. The bacteria and a lot of particles of the seriously damaged region penetrated into the lymphatic system and the blood system directly. Some bacteria were internalized into the goblet cell through the apical granule. Some bacteria and particles perforated into the submucosa of the M cell running the long axis of M cells through the tight junctions. In the microcirculation of mucosa, the bacteria that had already broken through the microvilli into blood circulation swim accompanying with erythrocytes.

CONCLUSION

The routes of bacterial translocation interact and format a vicious circle. At early step, the transcellular pathway of bacterial translocation is major. Following with the destroyed small intestine mucous, the routes of bacterial translocation through the lymphatic system and the blood system become direct pathways. The goblet cell-dendritic cell and M cell pathway also play an important role in the bacterial translocation.

Bacterial Composition of the Human Upper Gastrointestinal Tract Microbiome Is Dynamic and Associated with Genomic Instability in a Barrett's Esophagus Cohort

Background

The incidence of esophageal adenocarcinoma (EAC) has increased nearly five-fold over the last four decades in the United States. Barrett’s esophagus, the replacement of the normal squamous epithelial lining with a mucus-secreting columnar epithelium, is the only known precursor to EAC. Like other parts of the gastrointestinal (GI) tract, the esophagus hosts a variety of bacteria and comparisons among published studies suggest bacterial communities in the stomach and esophagus differ. Chronic infection with Helicobacter pylori in the stomach has been inversely associated with development of EAC, but the mechanisms underlying this association remain unclear.

Methodology

The bacterial composition in the upper GI tract was characterized in a subset of participants (n=12) of the Seattle Barrett’s Esophagus Research cohort using broad-range 16S PCR and pyrosequencing of biopsy and brush samples collected from squamous esophagus, Barrett’s esophagus, stomach corpus and stomach antrum. Three of the individuals were sampled at two separate time points. Prevalence of H. pylori infection and subsequent development of aneuploidy (n=339) and EAC (n=433) was examined in a larger subset of this cohort.

Results/Significance

Within individuals, bacterial communities of the stomach and esophagus showed overlapping community membership. Despite closer proximity, the stomach antrum and corpus communities were less similar than the antrum and esophageal samples. Re-sampling of study participants revealed similar upper GI community membership in two of three cases. In this Barrett’s esophagus cohort, Streptococcus and Prevotella species dominate the upper GI and the ratio of these two species is associated with waist-to-hip ratio and hiatal hernia length, two known EAC risk factors in Barrett’s esophagus. H. pylori-positive individuals had a significantly decreased incidence of aneuploidy and a non-significant trend toward lower incidence of EAC.

Bacterial community associated with the intestinal tract of Chinese mitten crab (Eriocheir sinensis) farmed in Lake Tai, China

Chinese mitten crab (CMC, Eriocheir sinensis) is an economically valuable species in South-East Asia that has been widely farmed in China. Characterization of the intestinal bacterial diversity of CMC will provide insights into the aquaculturing of CMCs. Based on the analysis of cloned 16S rRNA genes from culture-independent CMC gut bacteria, 124 out of 128 different clones reveal ＞95% nucleotide similarity to the species belonging to the four phyla of Tenericutes, Bacteroidetes, Firmicutes and Proteobacteria; one clone shows 91% sequence similarity to the member of TM7 (a candidate phylum without cultured representatives). Fluorescent in situ hybridization also reveals the abundance of Bacteroidetes in crab intestine. Electron micrographs show that spherical and filamentous bacteria are closely associated with the microvillus brush border of the midgut epithelium and are often inserted into the space between the microvilli using a stalk-like cell appendage. In contrast, the predominant rod-shaped bacteria in the hindgut are tightly attached to the epithelium surface by an unusual pili-like structure. Both 16S rRNA gene denaturing gel gradient electrophoresis and metagenome library indicate that the CMC Mollicutes group 2 appears to be present in both the midgut and hindgut with no significant difference in abundance. The CMC Mollicutes group 1, however, was found mostly in the midgut of CMCs. The CMC gut Mollicutes phylotypes appear to be most closely related to Mollicutes symbionts detected in the gut of isopods (Crustacea: Isopoda). Overall, the results suggest that CMCs harbor diverse, novel and specific gut bacteria, which are likely to live in close relationships with the CMC host.

A Tenebrio molitor GPI-anchored alkaline phosphatase is involved in binding of Bacillus thuringiensis Cry3Aa to brush border membrane vesicles

Bacillus thuringiensis Cry toxins recognizes their target cells in part by the binding to glycosyl-phosphatidyl-inositol (GPI) anchored proteins such as aminopeptidase-N (APN) or alkaline phosphatases (ALP). Treatment of Tenebrio molitor brush border membrane vesicles (BBMV) with phospholipase C that cleaves out GPI-anchored proteins from the membranes, showed that GPI-anchored proteins are involved in binding of Cry3Aa toxin to BBMV. A 68 kDa GPI-anchored ALP was shown to bind Cry3Aa by toxin overlay assays. The 68 kDa GPI-anchored ALP was preferentially expressed in early instar larvae in comparison to late instar larvae. Our work shows for the first time that GPI-anchored ALP is important for Cry3Aa binding to T. molitor BBMV suggesting that the mode of action of Cry toxins is conserved in different insect orders.

Targeting aminopeptidase N, a newly identified receptor for F4ac fimbriae, enhances the intestinal mucosal immune response

Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrhea in human and animal. In piglets, ETEC having F4 fimbriae (F4(+) ETEC) induce severe diarrhea, dependent on the presence of receptors for F4 (F4R). In this study, porcine aminopeptidase N (pAPN) was identified as an F4R by comparative proteomic analysis of brush border proteins of F4R(+) and F4R(-) pigs and by adherence/internalization experiments on pAPN-transfected cells. Binding of F4 fimbriae to pAPN depended on sialic acid containing carbohydrate moieties, and resulted in clathrin-mediated endocytosis of the fimbriae. Endocytosis via pAPN was not restricted to F4 fimbriae, but was also observed for anti-pAPN antibodies. Both F4 fimbriae- and pAPN-specific antibodies were taken up in vivo by porcine enterocytes and induced subsequently a rapid immunoglobulin A and G response. In conclusion, we identified pAPN as an endocytotic receptor for F4 fimbriae and highlight the opportunity to target vaccine antigens to this epithelial receptor.

Production of a subunit vaccine candidate against porcine post-weaning diarrhea in high-biomass transplastomic tobacco

Post-weaning diarrhea (PWD) in piglets is a major problem in piggeries worldwide and results in severe economic losses. Infection with Enterotoxigenic Escherichia coli (ETEC) is the key culprit for the PWD disease. F4 fimbriae of ETEC are highly stable proteinaceous polymers, mainly composed of the major structural subunit FaeG, with a capacity to evoke mucosal immune responses, thus demonstrating a potential to act as an oral vaccine against ETEC-induced porcine PWD. In this study we used a transplastomic approach in tobacco to produce a recombinant variant of the FaeG protein, rFaeG(ntd/dsc), engineered for expression as a stable monomer by N-terminal deletion and donor strand-complementation (ntd/dsc). The generated transplastomic tobacco plants accumulated up to 2.0 g rFaeG(ntd/dsc) per 1 kg fresh leaf tissue (more than 1% of dry leaf tissue) and showed normal phenotype indistinguishable from wild type untransformed plants. We determined that chloroplast-produced rFaeG(ntd/dsc) protein retained the key properties of an oral vaccine, i.e. binding to porcine intestinal F4 receptors (F4R), and inhibition of the F4-possessing (F4+) ETEC attachment to F4R. Additionally, the plant biomass matrix was shown to delay degradation of the chloroplast-produced rFaeG(ntd/dsc) in gastrointestinal conditions, demonstrating a potential to function as a shelter-vehicle for vaccine delivery. These results suggest that transplastomic plants expressing the rFaeG(ntd/dsc) protein could be used for production and, possibly, delivery of an oral vaccine against porcine F4+ ETEC infections. Our findings therefore present a feasible approach for developing an oral vaccination strategy against porcine PWD.

[Excretion of extracellular membrane nanovesicles by aeromonas]

AIM

Study of extracellular membrane nanovesicles production by Aeromonas hydrophila and Aeromonas salmonicida bacteria on a subcellular level.

MATERIALS AND METHODS

4 strains of A. hydrophila: 342-1, E 8-8, H 336 and H 1-6-05 and 1 strain of A. salmonicida A-450 as well as intact Wistar line rats were used. Methods of transmission electron microscopy: ultrathin sectioning and negative contrasting were used. RESULTS. A. hydrophila and A. salmonicida bacteria produced in pure cultures excrete into the environment extracellular membrane nanovesicles. The size of these vesicles varies from 20 to 200 nm in diameter. The process of gemmation from bacterial cell and possibility of obtaining isolated membrane nanovesicles preparations is shown. These vesicles are detected in ultrathin sections of apical surface of intact rat intestine among accumulations ofparietal microorganisms that colonize mucous membrane. Extracellular membrane nanovesicles excreted by aeromonas are analogous by size and ultrastructure to vesicles of other species of gram-negative bacteria described in the literature.

CONCLUSION

During production of A. hydrophila and A. salmonicida bacteria in vitro nanovesicles are formed from the outer membranes of the cells and excreted into the environment, the nanovesicles are similar to those detected in ultrathin sections of the surface of intestine of rats among accumulations of parietal microorganisms and in glycocalix between epitheliocyte microvilli.

Polymorphism and inheritance of swine small intestinal receptors mediating adhesion of three serological variants of Escherichia coli-producing K88 pilus antigen

Brush borders, enterocytes, or both preparations obtained from the small intestine of 345 pedigreed pigs, carrying components of seven breeds, were tested by adhesion assay in vitro with 6-32 enteropathogenic Escherichia coli strains, each expressing one of the three K88 pilus antigens, K88ab, K88ac and K88ad. With few exceptions, all pigs were classified as belonging to one of four adhesion phenotypes: I I--corresponding to K88ab(-),ac(-),ad(-); II--K88ab(-),ac(-),ad(+); III--K88ab(+),ac(+),ad(-); and IV--K88ab(+),ac(+),ad(+). The non-adhering phenotype I was found to be the most frequent among the pigs tested, with the exception of one commercial herd, and this phenotype seems to be inherited as a recessive trait. The remaining three phenotypes are adhering, or are susceptible to adherence by one K88 variant, K88ad (phenotype II), by two variants, K88ab, ac (phenotype III), or by all three K88 variants, K88ab,ac,ad (phenotype IV). Phenotype II was found to be at low frequency, whereas III and IV occurred with similar frequencies. While the prevailing phenomenon was the bacterial adhesion to all, or none, of the brush borders, some pigs exhibited both adhering and non-adhering brush borders, a mixed adherence phenotype. Preliminary segregation data, obtained from the F1 generation, seem to indicate that phenotypes III and IV correspond to two haplotypes with genes at two or three closely linked loci respectively. An alternative hypothesis is that the phenotypes III and IV are expressions of alleles at a single locus, each allele specifying a receptor able to bind two or three different serological types of K88 E. coli.

Infective colitis associated with human intestinal spirochetosis

AIM

Our study reports the detection and identification of intestinal spirochetosis in patients with colonic diseases in a tertiary-care hospital over a 12-year period, and includes a description of all cases we diagnosed.

METHODS

Our patients (8323) underwent colonoscopy and histopathological examinations including transmission electron microscopy (TEM) and light microscopy. Specimens from patients suspected of intestinal spirochetosis at histopathology (17 patients) underwent microbiological investigation performed by culture and molecular methods (16S restriction fragment length polymorphism-polymerase chain reaction [RFLP-PCR], nox RFLP-PCR assays).

RESULTS

Seventeen cases were diagnosed: seven patients were infected by B. aalborgi, one by B. pilosicoli, two by both species and four by Brachyspira spp. diagnosed both histopathology and microbiology (culture and molecular methods: 16S RFLP-PCR and nox RFLP-PCR assays). Three cases were referred to as Brachyspira spp. infections using only histopathology, including TEM.

CONCLUSIONS

Our results demonstrated that intestinal spirochetosis, although rarely occurring, might play a role in chronic diarrhea and suggested a pathogenetic mechanism of intestinal spirochetosis based on the destruction of colonic microvilli and colitis histologically documented, providing additional clinical and pathological information on this entity. This study suggests that metronidazole seems to be the drug of choice for the eradication of intestinal spirochetosis.

Plasmodium falciparum ookinetes require mosquito midgut chondroitin sulfate proteoglycans for cell invasion

Malaria transmission entails development of the Plasmodium parasite in its insect vector, the Anopheles mosquito. Parasite invasion of the mosquito midgut is the critical first step and involves adhesion to host epithelial cell ligands. Partial evidence suggests that midgut oligosaccharides are important ligands for parasite adhesion; however, the identity of these glycans remains unknown. We have identified a population of chondroitin glycosaminoglycans along the apical midgut microvilli of Anopheles gambiae and further demonstrated ookinete recognition of these glycans in vitro. By repressing the expression of the peptide-O-xylosyltransferase homolog of An. gambiae by means of RNA interference, we blocked glycosaminoglycan chain biosynthesis, diminished chondroitin sulfate levels in the adult midgut, and substantially inhibited parasite development. We provide evidence for the in vivo role of chondroitin sulfate proteoglycans in Plasmodium falciparum invasion of the midgut and insight into the molecular mechanisms mediating parasite-mosquito interactions.

An NSP4-dependant mechanism by which rotavirus impairs lactase enzymatic activity in brush border of human enterocyte-like Caco-2 cells

Lactase-phlorizin hydrolase (LPH, EC 3.2.1.23-62) is a brush border membrane (BBM)-associated enzyme in intestinal cells that hydrolyse lactose, the most important sugar in milk. Impairing in lactase activity during rotavirus infection has been described in diseased infants but the mechanism by which the functional lesion occurs remains unknown. We undertook a study to elucidate whether rotavirus impairs the lactase enzymatic activity in BBM of human enterocyte cells. In this study we use cultured human intestinal fully differentiated enterocyte-like Caco-2 cells to demonstrate how the lactase enzymatic activity at BBM is significantly decreased in rhesus monkey rotavirus (RRV)-infected cells. We found that the decrease in enzyme activity is not dependent of the Ca(2+)- and cAMP-dependent signalling events triggered by the virus. The LPH biosynthesis, stability, and expression of the protein at the BBM of infected cells were not modified. We provide evidence that in RRV-infected cells the kinetic of lactase enzymatic activity present at the BBM was modified. Both BBM(control) and BBM(RRV) have identical K(m) values, but hydrolyse the substrate at different rates. Thus, the BBM(RRV) exhibits almost a 1.5-fold decreased V(max) than that of BBM(control) and is therefore enzymatically less active than the latter. Our study demonstrate conclusively that the impairment of lactase enzymatic activity at the BBM of the enterocyte-like Caco-2 cells observed during rotavirus infection results from an inhibitory action of the secreted non-structural rotavirus protein NSP4.

CEACAM6 acts as a receptor for adherent-invasive E. coli, supporting ileal mucosa colonization in Crohn disease

The ileal mucosa of Crohn disease (CD) patients is abnormally colonized by adherent-invasive E. coli (AIEC) that are able to adhere to and invade intestinal epithelial cells. Here, we show that CD-associated AIEC strains adhere to the brush border of primary ileal enterocytes isolated from CD patients but not controls without inflammatory bowel disease. AIEC adhesion is dependent on type 1 pili expression on the bacterial surface and on carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6) expression on the apical surface of ileal epithelial cells. We report also that CEACAM6 acts as a receptor for AIEC adhesion and is abnormally expressed by ileal epithelial cells in CD patients. In addition, our in vitro studies show that there is increased CEACAM6 expression in cultured intestinal epithelial cells after IFN-gamma or TNF-alpha stimulation and after infection with AIEC bacteria, indicating that AIEC can promote its own colonization in CD patients.

Two specific sites for binding of K88ab Escherichia coli fimbriae to porcine intestinal brush border membranes

We have studied the characteristics of the binding of the K88ab Escherichia coli fimbrial antigen to porcine brush border membranes by solid phase binding assay. Binding of biotinylated K88ab to brush border membranes followed a sigmoidal dependence and was saturable, apparent saturation occurring with 0.8 ng of fimbriae (approx. 7 ng of fimbriae per microg of brush border protein) irrespective of incubation temperature in the range of room temperature to 4 degrees C. A Hill plot of log [(fimbriae bound)/(maximal binding-fimbriae bound)] vs. log free fimbriae gave a maximal slope of about 2, indicating the existence of two binding sites. From an analysis of an Scatchard plot, apparent binding constants (1)K(2) and (2)K(2) of 7.1 x 10(8) and 17.1 x 10(8)M(-1) were obtained at room temperature. Nor did temperature have any effect on the rate of binding or on receptor affinity (S(0.5)).

Effects of Saccharomyces boulardii on intestinal mucosa

Saccharomyces boulardii (S. boulardii) is a non-pathogenic biotherapeutic agent, widely prescribed in a lyophilized form in many countries over the world. S. boulardii acts as a shuttle liberating effective enzymes, proteins and trophic factors during its intestinal transit that improve host immune defenses, digestion, and absorption of nutrients. In addition, S. boulardii secretes during its intestinal transit polyamines, mainly spermine and spermidine that regulate gene expression and protein synthesis. In this review, we will focus on the interactions of the yeast with the host intestinal mucosa.

Expression of putative Escherichia coli heat-labile enterotoxin (LT) receptors on intestinal brush borders from pigs of different ages

Many strains of enterotoxigenic Escherichia coli (ETEC) that cause diarrhoea in young piglets secrete a heat-labile enterotoxin (LTp) that binds to specific glycoconjugates on porcine intestinal epithelial cells. Binding of LTp to an appropriate glycoconjugate facilitates the uptake and trafficking of the toxin into the cell, where it stimulates intracellular changes that promote fluid secretion and diarrhoea. The objective of the current study was to identify the LTp-binding glycoconjugates on porcine intestinal epithelial cells, the natural target cells for LTp. We found that LTp binds, in an age-correlated manner, to an acidic glycosphingolipid (GSL) that co-migrated with GM1 on thin-layer chromatography (TLC), a small acidic GSL that appears to be a sulphatide, a neutral GSL that co-migrated with neolactotetraglycosylceramide (nLc4) on TLC, and two glycoproteins (36 and 205 kDa). Of these potential LTp receptors, the GM1-co-migrating GSL was detected most intensely in young animals, while the other four LTp-binding glycoconjugates were detected most intensely in older pigs (> or= 4 weeks). Since ETEC primarily cause disease in young piglets, the GM1-co-migrating GSL is the most likely candidate for a functional LTp receptor.

Toxin-binding proteins from midgut epithelium membranes of Anopheles stephensi larvae

Proteins of 65 and 57 kD were isolated from the apical membranes of midgut epithelium of Anopheles stephensi larvae by affinity chromatography. These proteins can specifically bind endotoxin Cry11A and activate toxin Cry4B (Cry4B-tox) under conditions of ligand blotting, and both Cry proteins compete for this binding. At least in the case of Cry4B-tox, the binding with 65 and 57 kD proteins is reversible. The ability of the products of limited proteolysis of Cry11A and Cry4B to bind the 65 and 57 kD proteins correlates with their toxicity to A. stephensi larva. The N-terminal amino acid sequence of the 57 kD protein is unique and absent in the NCBI GenBank. The proteins of 65 and 57 kD share most of the properties studied with Aedes aegypti toxin-binding proteins. It is possible that they altogether represent a novel class (or classes) of delta-endotoxin receptors.

Histone H1 proteins act as receptors for the 987P fimbriae of enterotoxigenic Escherichia coli

The tip adhesin FasG of the 987P fimbriae of enterotoxigenic Escherichia coli mediates two distinct adhesive interactions with brush border molecules of the intestinal epithelial cells of neonatal piglets. First, FasG attaches strongly to sulfatide with hydroxylated fatty acyl chains. This interaction involves lysine 117 and other lysine residues of FasG. Second, FasG recognizes specific intestinal brush border proteins that migrate on a sodium-dodecyl sulfate-polyacrylamide gel like a distinct set of 32-35-kDa proteins, as shown by ligand blotting assays. The protein sequence of high performance liquid chromatography-purified tryptic fragments of the major protein band matched sequences of human and murine histone H1 proteins. Porcine histone H1 proteins isolated from piglet intestinal epithelial cells demonstrated the same SDS-PAGE migration pattern and 987P binding properties as the 987P-specific protein receptors from porcine intestinal brush borders. Binding was dose-dependent and shown to be specific in adhesion inhibition and gel migration shift assays. Moreover, mapping of the histone H1 binding domain suggested that it is located in their lysine-rich C-terminal domains. Histone H1 molecules were visualized on the microvilli of intestinal epithelial cells by immunohistochemistry and electron microscopy. Taken together these results indicated that the intestinal protein receptors for 987P are histone H1 proteins. It is suggested that histones are released into the intestinal lumen by the high turnover of the intestinal epithelium. Their strong cationic properties can explain their association with the negatively charged brush border surfaces. There, the histone H1 molecules stabilize the sulfatide-fimbriae interaction by simultaneously binding to the membrane and to 987P.

Interaction of enteropathogenic Escherichia coli with human intestinal mucosa: role of effector proteins in brush border remodeling and formation of attaching and effacing lesions

Enteropathogenic Escherichia coli (EPEC) strains deliver effector proteins Tir, EspB, Map, EspF, EspH, and EspG into host cells to induce brush border remodeling and produce attaching and effacing (A/E) lesions on small intestinal enterocytes. In this study, the role of individual EPEC effectors in brush border remodeling and A/E lesion formation was investigated with an in vitro human small intestinal organ culture model of EPEC infection and specific effector mutants. tir, map, espB, and espH mutants produced "footprint" phenotypes due to close bacterial adhesion but subsequent loss of bacteria; an espB mutant and other type III secretion system mutants induced a "noneffacing footprint" associated with intact brush border microvilli, whereas a tir mutant was able to efface microvilli resulting in an "effacing footprint"; map and espH mutants produced A/E lesions, but loss of bacteria resulted in a "pedestal footprint." An espF mutant produced typical A/E lesions without associated microvillous elongation. An espG mutant was indistinguishable from the wild type. These observations indicate that Tir, Map, EspF, and EspH effectors play a role in brush border remodeling and production of mature A/E lesions.

[Macromutations and evolution: fixation of Goldschmidt's macromutations as species and genus characters. Papillomatosis and appearance of macrovilli in the rodent stomach]

The cardiac portion of the stomach is lined with macrovilli in a few rodent genera. These are Mystromys (Cricetinae, Cricetidae), Myospalax (Myospalacinae, Cricetidae), Tachyoryctes (Tachyoryctinae, Cricetidae), and Cryptomys (Bathyergidae). The macrovilli favor the development of symbiotic flora and are called symbiovilli. Growth of the corneal epithelium of the cardiac portion of the stomach serves as a morphological basis of symbiovilli. Cases of a hereditary malignant neoplasm giving rise to the formation of multiple macrovilli in the cardiac portion of the stomach have been found in Microtus abbreviatus (Microtinae, Cricetidae), a vole endemic to St. Matthew Island in the Bering Sea. The macrovilli resulting from the papillomatosis mutation are morphologically and histologically identical to the macrovilli of the stomach of the four aforementioned genera. The voles affected with papillomatosis still survive long enough to reproduce. Therefore, the macromutation that leads to death in adult and old voles has been fixed as a species character in some rodent genera. At the early stages of papillomatosis, the pathogenic morphogenesis creates favorable conditions for the development of symbiotic microflora, which gives a selective advantage to the affected animals. It is assumed that mutations with pathogenic effects have been fixed as a species character as a result of heterochrony. The pathogenic neoplasm serves as a preadaptation for the growth of symbiotic flora in the stomach. The mechanisms of the fixation of Goldschmidt's "systemic mutations" during phylogeny are discussed.

Identification of MEK- and phosphoinositide 3-kinase-dependent signalling as essential events during Chlamydia pneumoniae invasion of HEp2 cells

The ability of Chlamydia pneumoniae to survive and cause disease is predicated on efficient invasion of cellular hosts. While it is recognized that chlamydial determinants are important for mediating attachment and uptake into non-phagocytic cells, little is known about the bacterial ligands and cellular receptors that facilitate invasion or host cell signal transduction pathways implicated in this process. We used transmission and scanning electron microscopy to demonstrate that attachment of bacteria to host cells induced the appearance of microvilli on host cell membranes. Invasion occurred 30-120 min after cell contact with the subsequent loss of membrane microvilli. Using an epithelial cell infection model, C. pneumoniae invasion caused a rapid and sustained increase in MEK-dependent phosphorylation and activation of ERK1/2, followed by PI 3-kinase-dependent phosphorylation and activation of Akt. Tyrosine phosphorylation of focal adhesion kinase (FAK) preceded its appearance in a complex with the p85 subunit of PI 3-kinase during chlamydial invasion and isoform-specific tyrosine phosphorylation of the docking protein Shc also occurred at the time of attachment and entry of bacteria. Chlamydia entry but not attachment could be abrogated with specific inhibitors of MEK, PI 3-kinase and actin polymerization, demonstrating the importance of these signalling pathways and an intact actin cytoskeleton for C. pneumoniae invasion. These results suggest that activation of specific cell signalling pathways is an essential strategy used by C. pneumoniae to invade epithelial cells.

Identification and partial purification of K88ab Escherichia coli receptor proteins in porcine brush border membranes

Six receptor proteins, with molecular masses ranging from 94 to 27 kDa, that bind to Escherichia coli K88ab fimbriae were recovered from brush border membranes and were detected after solubilization with Triton X-114. The recovery of these receptor proteins in the aqueous phase suggests their peripheral localization. The 63-, 60- and 33-kDa K88ab binding proteins were recovered using gel-filtration chromatography of the aqueous phase.

Phosphoserine modification of the enteropathogenic Escherichia coli Tir molecule is required to trigger conformational changes in Tir and efficient pedestal elongation

Enteropathogenic Escherichia coli (EPEC) virulence is correlated with intimate adherence to gut epithelial cells, loss of absorptive microvilli and reorganization of host cytoskeletal proteins into pedestal-like structures beneath the adherent bacteria. These processes depend on Tir (i) being inserted into the plasma membrane; (ii) being tyrosine phosphorylated; and (iii) interacting with the bacterial outer membrane protein, intimin. However, phosphorylation on other undefined residues leads to approximately 5 kDa and approximately 2 kDa increases in Tir apparent molecular mass within host cells. In this study, we show that equivalent shifts can be induced in vitro by phosphorylation of Tir on two serine (S434 and S463) residues by protein kinase A (PKA). Our data suggest that the sequential addition of two phosphate groups triggers conformational changes in Tir structure that may supply the energy to insert Tir into the plasma membrane. PKA was also shown to modify Tir within host cells on S434 to induce the approximately 5 kDa shift. Whereas modification of S434 was not essential to generate an actin-nucleating molecule, it was required for Tir to induce pedestal elongation efficiently. This study not only increases our understanding of the mechanism by which phosphorylation induces shifts in Tir apparent molecular mass and suggests a mechanism by which Tir may be inserted into the plasma membrane, but also reveals a role for non-tyrosine phosphorylation in Tir function and identifies the first kinase that can modify Tir in vitro or in vivo.

Effect of Bacillus cereus exocellular factors on human intestinal epithelial cells

To gain insight on the biological effects of the exocellular factors produced by Bacillus cereus, culture filtrate supernatants of different strains were coincubated with differentiated Caco-2 cells. Exocellular factors were able to detach enterocyte-like cells from the substratum after 1 h of incubation. In addition, microvilli effacing and dramatic changes on the cellular surface of enterocytes were found after incubation periods as short as 20 min. Since cell detachment was not inhibited by fetal calf serum, thiol activated cholesterol-binding cytolysin, cereolysin O, does not seem to be involved. Also, translocation of phosphatidylserine from the inner to the outer leaflets of the plasma membrane was demonstrated by using fluorescein isothiocyanate (FITC)-Annexin V. In contrast to the high capability of detaching Caco-2 cells shown by all the strains under study, the mitochondrial dehydrogenase activity was lowered by culture filtrate supernatants in a strain-dependent manner. For strain M2, the decrease in dehydrogenase activity was already evident after 30 min of incubation. Production of biologically active factors depends on the growth phase, and maximal activity was found in late exponential-early stationary phases. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of concentrated exocellular factors showed a very complex scenery supporting the multifactorial character of the biological activity of B. cereus.

Impairments in enzyme activity and biosynthesis of brush border-associated hydrolases in human intestinal Caco-2/TC7 cells infected by members of the Afa/Dr family of diffusely adhering Escherichia coli

Wild-type diffusely adhering Escherichia coli (DAEC) harbouring afimbrial adhesin (Afa) or fimbrial Dr and F1845 adhesins (Afa/Dr DAEC) apically infecting the human intestinal epithelial cells promote injuries in the brush border of the cells. We report here that infection by Afa/Dr DAEC wild-type strains C1845 and IH11128 in polarized human fully differentiated Caco-2/TC7 cells dramatically impaired the enzyme activity of functional brush border-associated proteins sucrase-isomaltase (SI) and dipeptidylpeptidase IV (DPP IV). Blockers of the transduction signal molecules, previously found to be active against the Afa/Dr DAEC-induced cytoskeleton injury, were inactive against the Afa/Dr-induced decrease in sucrase enzyme activity. In parallel, Afa/Dr DAEC infection promotes the blockade of the biosynthesis of SI and DPP IV without affection enzyme stability. The observation that no changes occurred in mRNA levels of SI and DPP IV upon infection suggested that the decrease in biosynthesis probably resulted from a decrease in the translation rate. When the cells were infected with recombinant E. coli strains expressing homologous adhesins of the wild-type strains, neither a decrease in sucrase and DPP IV enzyme activities nor an inhibition of enzyme biosynthesis were observed. In conclusion, taken together, these data give new insights into the mechanisms by which the wild-type Afa/Dr DAEC strains induce functional injuries in polarized fully differentiated human intestinal cells. Moreover, the results revealed that other pathogenic factor(s) distinct from the Afa/Dr adhesins may play(s) a crucial role in this mechanism of pathogenicity.

Localization of Tropheryma whippelii rRNA in tissues from patients with Whipple's disease

Whipple's disease is caused by a cultivation-resistant bacterium, Tropheryma whippelii. Ultrastructural studies of intestinal biopsy specimens from patients with Whipple's disease have shown that intracellular and extracellular bacteria are present, but the preferred site of growth is unknown. Tissue sections from 8 patients with Whipple's disease and from 19 healthy control subjects were analyzed by use of fluorescence in situ hybridization and laser scanning confocal microscopy, to determine the location of rRNA that would indicate the presence of metabolically active bacteria. T. whippelii rRNA was most prevalent near the tips of intestinal villi, in the lamina propria, just basal to epithelial cells. Most of the bacterial rRNA signal appeared to be located between cells and did not colocalize with the human intracellular protein vimentin. The location of bacterial rRNA in tissues from patients with Whipple's disease provides evidence that bacteria are growing outside cells and suggests that T. whippelii is not an obligate intracellular pathogen.

Escherichia coli strain RDEC-1 AF/R1 endogenous fimbrial glycoconjugate receptor molecules in rabbit small intestine

Escherichia coli strain RDEC-1 causes a diarrheagenic infection in rabbits with AF/R1 fimbriae, which have been identified as an important colonization factor in RDEC-1 adherence leading to disease. The AF/R1-mediated RDEC-1 adherence model has been used as a model systems for E. coli diarrheal diseases. In this study, RDEC-1 adhered specifically to small intestinal brush borders, with both sialic acid and beta-galactosyl residues apparently involved. The AF/R1-mediated adherence activity of [(14)C]-labeled RDEC-1 was analyzed quantitatively by using 24-well plates coated with purified brush borders and purified microvilli. Two microvillus membrane proteins (130 and 140 kDa) were individually isolated, and chicken antibody raised to each protein inhibited bacterial adherence. These same two proteins, previously shown to be recognized by AF/R1, were individually digested with trypsin, and the amino acid sequences of peptides were determined by reversed-phase capillary liquid chromatography-mass spectrometry tandem mass spectrometry (LC-MS). This LC-MS analysis indicated that these proteins are subunits of the rabbit sucrase-isomaltase protein (SI) complex. Guinea pig serum raised to purified rabbit SI complex inhibited bacterial adherence to microvilli. Additionally, as determined by high-performance thin-layer chromatography and autoradiography, RDEC-1 adhered selectively, via AF/R1 fimbriae, to a glycolipid tentatively identified as galactosylceramide (Gal beta 1-1Cer) in the lipid extract of rabbit small intestinal brush borders. RDEC-1 adherence to Gal beta 1-1Cer was partially inhibited in the presence of galactose. These combined results indicate that the endogenous receptor molecule for AF/R1 fimbriae of RDEC-1 is each individual component of the SI complex, although binding to glycolipid may be responsible for an additional adherence mechanism.

Escherichia coli heat stable enterotoxin receptors & guanylyl cyclase activity in the intestinal brush border membrane of hamsters & guinea pigs

BACKGROUND & OBJECTIVES

Although Escherichia coli heat stable enterotoxin (STa) causes diarrhoea in laboratory animals, no studies were done to find out the species specific variation of distribution of the STa receptors in laboratory animals. The present investigation evaluates the density of STa receptors and the guanylyl cyclase (GC) activity in the small intestinal epithelial cells of hamsters and guinea pigs.

METHODS

Brush border membrane (BBM) was prepared from the small intestines of hamsters and guinea pigs. Receptor binding assay, GC assay and autoradiography were performed to determine the density of STa receptors, the GC activity and molecular weights of the STa binding proteins respectively.

RESULTS

The receptor densities, per mg BBM protein at equilibrium, were found to be 4.1 x 10(9) and 1.5 x 10(12) in hamsters and guinea pigs respectively. The GC activity was found to be lower in STa treated hamster BBM compared to that of guinea pig. Scatchard analysis of the stoichiometric data showed a linear plot, and STa bound with association constants of 0.31 x 10(12) M-1 and 1.04 x 10(12) M-1 in hamsters and guinea pigs respectively. Autoradiographic analysis of the SDS-PAGE, revealed that 125I-STa bound apparently to a 45 kDa membrane protein in hamster and a 115 kDa membrane protein in guinea pig.

INTERPRETATION & CONCLUSIONS

It appears that a lower density of STa receptor exists in hamsters compared to that in guinea pigs. STa binds with a single population of STa receptors in each species with different ligand binding affinities. Also, the molecular weights of the STa binding proteins differ in these species. Moreover, the GC activity was found to be lower in hamsters than in guinea pigs.

Structural and functional lesions in brush border of human polarized intestinal Caco-2/TC7 cells infected by members of the Afa/Dr diffusely adhering family of Escherichia coli

Diffusely adhering Escherichia coli (DAEC) strains expressing F1845 fimbrial adhesin or Dr hemagglutinin belonging to the Afa/Dr family of adhesins infect cultured polarized human intestinal cells through recognition of the brush border-associated decay-accelerating factor (DAF; CD55) as a receptor. The wild-type Afa/Dr DAEC strain C1845 has been shown to induce brush border lesions by an adhesin-dependent mechanism triggering apical F-actin rearrangements. In the present study, we undertook to further characterize cell injuries following the interaction of wild-type Afa/Dr DAEC strains C1845 and IH11128 expressing fimbrial F1845 adhesin and Dr hemagglutinin, respectively, with polarized, fully differentiated Caco-2/TC7 cells. In both cases, bacterium-cell interaction was followed by rearrangement of the major brush border-associated cytoskeletal proteins F-actin, villin, and fimbrin, proteins which play a pivotal role in brush border assembly. In contrast, distribution of G-actin, actin-depolymerizing factor, and tubulin was not modified. Using draE mutants, we found that a mutant in which cysteine replaces aspartic acid at position 54 conserved binding capacity but failed to induce F-actin disassembly. Accompanying the cytoskeleton injuries, we found that the distribution of brush border-associated functional proteins sucrase-isomaltase (SI), dipeptidylpeptidase IV (DPPIV), glucose transporter SGLT1, and fructose transporter GLUT5 was dramatically altered. In parallel, SI and DPPIV enzyme activity decreased.

Brachyspira aalborgi infection diagnosed by culture and 16S ribosomal DNA sequencing using human colonic biopsy specimens

In this study we report on the isolation and characterization of the intestinal spirochete Brachyspira aalborgi using human mucosal biopsy specimens taken from the colon of a young adult male with intestinal spirochetosis. A selective medium, containing 400 microg of spectinomycin/ml and 5 microg of polymyxin/ml was used for the isolation procedure. A high degree of similarity, in terms of phenotypic properties and 16S ribosomal DNA sequence, was observed between the isolated strain, named W1, and the type strain, 513A, of B. aalborgi. A similarity of 99.7% in the nucleotide sequence was found between W1 and 513A(T), based on the almost-complete gene. A short segment of the 16S rRNA gene was amplified by PCR using genetic material enriched from paraffin-embedded biopsy specimens, which were taken from the patient on two occasions. The products showed 16S rRNA gene sequences virtually identical to that of strain 513A(T) in the actual region. Immunohistochemistry was performed on the colonic biopsy specimens with a polyclonal antibody raised against an intestinal spirochete isolated in a previous case of human intestinal spirochetosis. The antibody reacted strongly with the spirochete on the luminal epithelium. No immune reaction was seen within or below the surface epithelium. Routine histology did not reveal signs of colitis. Electron microscopy showed spirochetes attached end-on to the colonic mucosal surface. The isolate grew poorly on a commonly used selective medium for intestinal spirochetes, which may explain previous failures to isolate B. aalborgi.

Different patterns of Helicobacter pylori adherence to gastric mucosa cells in children and adults. An ultrastructural study

BACKGROUND

Infection with Helicobacter pylori in childhood may be the initiation of a lifelong coexistence between microorganisms and epithelial cells resulting in chronic inflammation. The adhesion pattern of H. pylori found in antral biopsies from a group of H. pylori-infected children with recurrent abdominal pain was compared with a group of H. pylori-infected adults suffering from dyspepsia, in an attempt to reveal differences in the type of adhesion.

METHODS

The histology of antrum biopsies and the ultrastructure of adherent H. pylori in biopsies from 26 children (median age, 10.1 years) were compared with organisms in biopsies from 19 adults (median age, 54.4 years).

RESULTS

More than 1000 adherent H. pylori were studied and divided into four types of adhesion: 1) contact to microvilli; 2) connection to the plasma membrane via filamentous material; 3) adhesive pedestal formation; and 4) abutting or making a depression in the plasma membrane. Contact to microvilli was significantly higher (69% versus 39%; P = 0.002) in children compared with adults and comprised two-thirds of all adherent organisms in children. The more intimate adhesion types as abutting or adhesive pedestals dominated in adults.

CONCLUSIONS

These results indicate a change in contact types between H. pylori and gastric epithelial cells in adults compared with children and this may be a natural development in the lifelong infection of humans.

Ultrastructural analysis of developmental events in Chlamydia pneumoniae-infected cells

Chlamydia pneumoniae is an obligate intracellular parasite with a developmental cycle believed to be common to all members of the genus Chlamydia. We present a detailed description based on transmission and scanning electron microscopy of temporal events and inclusion structures throughout the C. pneumoniae AR-39 developmental cycle.

Receptor-specific binding of purified F4 to isolated villi

Different procedures for preparing and purifying F4ac fimbriae of the enterotoxigenic Escherichia coli strain GIS 26 (O149:K91:F4ac LT+Sta+STb+) were performed and the purity and yield of F4ac were compared. Fimbriae were prepared by either mechanical shearing or heatshock treatment of concentrated bacterial suspensions (10(11) bacteria/ml). The mechanical shearing procedure resulted in approximately 1.7 mg fimbriae (i.e. 74.4% of the isolated protein) and 0.6 mg (25.6%) contaminating proteins per 10(12) bacteria, whereas the yield of fimbriae following heatshock treatment was lower (0.3 mg per 10(12) bacteria, i.e. 26.2%) and the relative contamination higher (1.0 mg per 10(12) bacteria, i.e. 73.8%). A further purification consisted of either anion exchange chromatography (AEC) or electro-elution from SDS-polyacrylamide gels. The electroelution procedure was performed under reducing and denaturing conditions, so that purified FaeG subunits, the major subunit of F4, were finally obtained. The binding activity of fimbriae, nonpurified as well as purified, and FaeG to F4-specific receptors on isolated intestinal villi was assessed in an inhibition adhesion assay. Native fimbriae as well as major subunits were able to bind to the receptors, and the specificity of the binding was demonstrated by blockage with F4ac-specific MAb.

Neisseria gonorrhoeae coordinately uses Pili and Opa to activate HEC-1-B cell microvilli, which causes engulfment of the gonococci

This study was undertaken to examine concomitant roles of pili and colony opacity-associated proteins (Opa) in promoting Neisseria gonorrhoeae adherence to and invasion of human endometrial HEC-1-B cells. Adherence of N. gonorrhoeae to cultured HEC-1-B cells was saturable, even though organisms adhered to <50% of the cells. During 4 to 6 h of incubation, adherent mono- and diplococci formed microcolonies on the surfaces of the cells. Microvilli of the HEC-1-B cells adhered by their distal ends to individual cocci within the microcolonies. When the microcolonies grew from isogenic pilus-negative (P-) Opa-, P- Opa+, or P+ Opa- gonococci, microvilli did not elongate, and the colonies were not engulfed. In contrast, the microvilli markedly elongated during exposure to P+ Opa+ gonococci. The microvilli adhered to the organisms along their full lengths and appeared to actively participate in the engulfment of the microcolonies. Internalized microcolonies, with P+ Opa+ gonococci, contained dividing cocci and appeared to be surrounded by cell membrane but were not clearly within vacuoles. In contrast, degenerate individual organisms were within vacuoles. Low doses of chloramphenicol, which inhibits protein synthesis by both prokaryotes and eukaryotes, prevented the microvillar response to and internalization of the P+ Opa+ gonococci; higher doses caused internalization without microvillus activation. Cycloheximide and anisomycin, which inhibit only eukaryotic protein synthesis, caused dose-dependent enhancement of uptake. Cytochalasins reduced engulfment; colchicine had no effect. These results show that gonococci must express both pili and Opa to be engulfed efficiently by HEC-1-B cells.

Enteropathogenic Escherichia coli: a pathogen that inserts its own receptor into host cells

Enteropathogenic Escherichia coli (EPEC) is a major cause of infant diarrhea, killing hundreds of thousands of children per year worldwide. Intimate attachment to the host cell leading to the formation of actin-rich pedestals beneath the adhering bacteria is an essential feature of EPEC pathogenesis. EPEC attaches to host cells via the outer membrane adhesin, intimin. It was recently shown that EPEC inserts its own receptor for intimate adherence, Tir (translocated intimin receptor) into the host cell membrane. The focus of this review is on the discovery and characterization of this novel receptor, and our current understanding of its role in pedestal formation. Gram-negative bacterial secretion systems, including type III secretion systems, are reviewed and discussed in the context of Tir delivery into the host cell membrane. The relationship and relevance of in vitro models compared to the actual in vivo situation is essential to understanding disease. We have critically reviewed the use of animal models in studying EPEC infection. Elucidating the function of Tir will contribute to our understanding of how EPEC mediates disease.

Characterization of outer membrane protein OmpU of Vibrio cholerae O1

The outer membrane protein OmpU of Vibrio cholerae O1 strain 86B3 was characterized with reference to colonization of the intestine by the organism. The purified OmpU exhibited a pI of 3.6. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, it migrated to 38, 32, and 110 kDa when the sample was heated at 100 degrees C for 2 min, 50 degrees C for 15 min, and room temperature for 30 min, respectively. The purified OmpU was not hemagglutinative. Anti-OmpU serum did not agglutinate strain 86B3 or other V. cholerae organisms. OmpU adhered to the brush border of the rabbit small intestine; adhesion of the organisms to the intestine treated in advance with OmpU was not inhibited. Treating the organisms in advance with anti-OmpU Fab did not inhibit adhesion to the intestine. These results obtained in vitro suggest that OmpU is not involved in the adhesion of V. cholerae to the intestinal epithelium.

Expression of mucin-type glycoprotein K88 receptors strongly correlates with piglet susceptibility to K88(+) enterotoxigenic Escherichia coli, but adhesion of this bacterium to brush borders does not

Three antigenic variants of the K88 fimbrial adhesin exist in nature, K88ab, K88ac, and K88ad. Enterotoxigenic Escherichia coli (ETEC) strains that produce these fimbriae cause life-threatening diarrhea in some but not all young pigs. The susceptibility of pigs to these organisms has been correlated with the adherence of bacteria to isolated enterocyte brush borders. Whether that correlation holds for multiple K88 variants and over a broad genetic base of pigs is unknown and was the impetus for this study. We also desired to examine the correlation of the expression of a porcine intestinal brush border mucin-type glycoprotein (IMTGP) which binds K88ab and K88ac with the susceptibility of piglets to K88(+) ETEC. Of 31 neonatal gnotobiotic pigs inoculated with K88ab+ or K88ac+ ETEC, 13 developed severe diarrhea, became dehydrated, and died or became moribund. Another pig became severely lethargic but not dehydrated. In vitro brush border adherence analysis was not possible for 10 of the severely ill pigs due to colonization by challenge strains. However, of the 17 pigs that did not become severely ill, 8 (47%) had brush borders that supported the adherence of K88ab+ and K88ac+ bacteria in vitro, suggesting a poor correlation between in vitro brush border adherence and piglet susceptibility to K88(+) ETEC. By contrast, the expression of IMTGP was highly correlated with susceptibility to K88(+) ETEC. Of the 12 pigs that produced IMTGP, 11 developed severe diarrhea. The other pig that produced IMTGP became lethargic but not severely diarrheic. Only 2 of 18 pigs that did not produce IMTGP became severely diarrheic. Colonizing bacteria were observed in histologic sections of intestines from all pigs that expressed IMTGP except for the one that did not develop severe diarrhea. However, colonizing bacteria were observed in histologic sections from only one pig that did not produce IMTGP. The bacterial concentration in the jejuna and ilea of pigs expressing IMTGP was significantly greater (P < 0.005) than that in pigs not expressing IMTGP. These observations suggest the IMTGP is a biologically relevant receptor for K88ab+ and K88ac+ E. coli or a correlate for expression for such a receptor.

Enteric bacterial pathogens, villus atrophy and microbial growth

The effects of three bacterial pathogens on the villus architecture of small intestines and the role that bacterial virulence factors play in pathogenesis are described. Bacterial pathogens cause a spectrum of effects ranging from severe tissue damage to a lack of perceptible damage. Enterotoxigenic Escherichia coli, which cause acute and severe diarrhea, does so by producing potent toxins, but these toxins act by altering the biological activity in epithelial cells. However, the cells are not damaged. Enteropathogenic E. coli and Salmonella, on the other hand cause various degrees of tissue damage. As part of their pathogenesis, they employ a type III protein secretion system to orchestrate internal changes in target cells. The expression of many virulence related genes is tightly regulated and appears to be turned on in response to cues found in the intestinal tract. The consequences of this level of regulation also is discussed.

The F41 adhesin of enterotoxigenic Escherichia coli: inhibition of adhesion by monoclonal antibodies

The anti-adhesive properties of 23 specific monoclonal antibodies (MAbs) against the F41 adhesive fimbrial antigen of enterotoxigenic Escherichia coli (ETEC) were studied in brush border adhesion inhibition tests and haemag-glutination inhibition tests with four F41-positive E. coli strains and purified F41 antigen. These MAbs recognize five epitope clusters, F41-1 to F41-5. It was proven that these epitope clusters were located on the 29 kDa F41 major fimbrial subunits. All nine MAbs against epitope cluster 1 inhibited the adhesion of F41-positive strains to brush border preparations of calf and pig intestines and the haemagglutination of sheep and guinea pig erythrocytes by the F41-positive strains and purified F41 antigen. The fourteen MAbs against the other four epitope clusters showed very little to no blocking of adhesion and haemagglutination. The results indicate that the adhesion of F41 to intestinal epithelial cells is mediated by the same domain of the 29 kDa F41 major fimbrial subunit(s) as the adhesion of F41 to erythrocytes. Irrespective of their epitope specificity F41 MAbs protected infant mice against a challenge with F41-positive ETEC. MAbs against all epitope clusters partly protected piglets against challenge with F41-positive ETEC in a similar way. Therefore, we conclude that direct blocking of the receptor binding site located on the major fimbrial subunit is not the main mechanism how antibodies protect against ETEC infection.

Chlamydial elementary bodies are translocated on the surface of epithelial cells

Infection of eukaryotic cells by intracellular pathogens such as chlamydia requires attachment to the host cell surface. Chlamydia are thought to attach to the tips of microvilli in confluent monolayers of polarized cells. In vitro evidence obtained from migrating epithelial cells suggested that during healing the route of pathogen uptake might be different from that in intact epithelia. The small size of infectious chlamydial elementary bodies (approximately 0.3 microm in diameter) has made it difficult, however, to analyze the early stages of pathogen-host cell interaction in living cells by conventional microscopy. Contrast-enhanced video microscopy was therefore used to examine the earliest events of host-pathogen interaction and test the hypothesis that chlamydial uptake into the healing epithelia can involve translocation over the host cell surface. Observations made in this way were validated by scanning and immunofluorescence microscopy. These studies revealed two fates for chlamydiae taken onto the lamellipodial surface: 1) some chlamydiae were moved in a random fashion on the cell surface or were detached into the culture medium, whereas 2) other chlamydiae were translocated across the lamellipodium in a highly directed manner toward the microvillous perinuclear region. After internalization, these latter chlamydiae were found within intracellular inclusions, which demonstrated that this route of attachment and location of uptake resulted in productive growth.

Intestinal mucosal lipid peroxidation and absorptive function in Salmonella typhimurium mediated intestinal infection

S. typhimurium infection is associated with neutrophil infiltration within the intestinal mucosa. Neutrophil activation provides a major source of reactive oxygen species (ROS). The mucosal pathology of S. typhimurium infection may be in part due to the excessive production of these reactive species. This study was carried out to investigate if ROS play a role in mediating the changes in the structural components and functional properties of brush border membrane (BBM) in rats during S. typhimurium infection. This was done by determining the changes in the BBM extent of lipid peroxidation and absorptive function. A significant increase in the extent of lipid peroxidation of BBM during S. typhimurium infection was observed as judged by malondialdehyde (MDA) and conjugated diene formation and depletion of alpha-tocopherol and protein associated thiol groups. A significant decrease in the BBMV (brush border membrane vesicle) transport of amino acids was also observed. However there was no change in the transport of D-glucose. The decrease in amino acid transport further led to a significant decrease in the enterocyte level of protein synthesis. Exposure of BBMV to a free radical donor, cumene hydroperoxide, also led to an increase in the extent of lipid peroxidation and a decrease in the amino acid transport. Possibly ROS might play a significant role in mediating the mucosal damage during S. typhimurium infection.

The haemagglutinin of Clostridium botulinum type C progenitor toxin plays an essential role in binding of toxin to the epithelial cells of guinea pig small intestine, leading to the efficient absorption of the toxin

Binding of the purified type C 7S (neurotoxin), 12S and 16S botulinum toxins to epithelial cells of ligated small intestine or colon of the guinea pig (in vivo test) and to pre-fixed gastrointestinal tissue sections (in vitro test) was analysed. The 16S toxin bound intensely to the microvilli of epithelial cells of the small intestine in both in vivo and in vitro tests, but did not bind to cells of the stomach or colon. The neurotoxin and 12S toxin did not bind to epithelial cells of the small intestine or to cells of the stomach or colon. Absorption of the toxins was assessed by determining the toxin titre in the sera of guinea pigs 6-8 h after the intra-intestinal administration of the toxins. When the 16S toxin [1 x 10(5) minimum lethal dose (MLD)] was injected, 200-660 MLD ml-1 was detected in the sera, whereas when the 12S toxin (2 x 10(5) MLD) or 7S toxin (2 x 10(5) MLD) was injected, little toxin activity was detected in the sera. Therefore, the haemagglutinin of type C 16S toxin is apparently very important in the binding and absorption of botulinum toxin in the small intestine.

Binding of diarrheagenic Escherichia coli to 32- to 33-kilodalton human intestinal brush border proteins

We have detected human intestinal brush border proteins to which Escherichia coli strains adhere by means of a blotting-nitrocellulose method in which the binding of radiolabeled bacteria to sodium dodecyl sulfate-polyacrylamide gel electrophoresis-separated intestinal cell membranes was evaluated. The brush border fraction contained several polypeptides that bound only adherent E. coli strains. The most prominent and consistent of these proteins had apparent molecular masses of 32 to 33 kDa. Additional polypeptides ranging from 50 to 70, from 105 to 130, and from 180 to 200 kDa were also recognized by adherent E. coli strains, although with less intensity (in accordance with the number of bound bacteria to these polypeptides). Independently of the pattern of adherence (localized [LA], diffuse [DA], or aggregative [AggA]) all HEp-2-adhering strains recognized, with different intensities, the 32- to 33-kDa brush border proteins, whereas nonadhesive strains did not. The relative avidity of an LA strain to bind to the 32- to 33-kDa proteins was approximately seven- and sixfold higher than the binding of strains with aggregative and diffuse adherence, respectively. Thus, it is reasonable to think that LA, DA, and AggA strains have a common adhesin that mediates binding to the 32- to 33-kDa bands. Inhibition experiments using HEp-2 cells demonstrated that isolated 32- to 33-kDa proteins or specific antiserum blocked preferentially bacterial adherence of the LA pattern. Delipidization and protein digestion of the human brush borders confirmed that E. coli bound to structures of a proteinaceous nature. Deglycosylation studies and sodium meta-periodate oxidation of the intestinal cell membranes decreased bacterial binding activity significantly, indicating that E. coli bound to carbohydrate moieties in the glycoproteins. These results suggest that binding of E. coli strains, mainly of the LA phenotype, to the 32- to 33-kDa proteins could play a role in colonization through adherence to the intestinal mucosa.

The early dynamic response of the calf ileal epithelium to Salmonella typhimurium

Ileal loops including Peyer's patch were prepared in five 28-day-old calves and infused Salmonella typhimurium strain ST4/74. Loops were fixed 5 minutes to 2 hours after inoculation, and the mucosa was examined by light and electron microscopy. Within 5 minutes, the bacteria were interacting with the follicle-associated epithelium (FAE); the surface of M cells changed to lamellipodia, engulfing many bacteria. This process proceeded rapidly to 30 minutes, involving most M cells above crypt level. Most cells were exfoliated, and many were packed with bacteria, and the domed villi became stunted. There was a rapid migration of neutrophils through the FAE into the lumen by 15 minutes. By 60 minutes, there was no further interaction between the bacteria and the FAE; at this time bacteria were present in macrophages in the lamina propria. Restitution of the FAE was complete by 2 hours in spite of the many bacteria in the cell debris overlying the epithelium. Interaction of bacteria with the absorptive villi was delayed compared with interaction with the FAE. After 15 minutes, bacteria were seen adhering to some enterocytes of the upper third of the villi; many bacteria were adhering to the surface of the enterocytes at 20 and 30 minutes, but few were seen thereafter. Adherence was patchy and largely confined to cells whose surfaces were depressed relative to others. The microvillous surface of these enterocytes was extensively remodelled. Tissue response, with uptake of bacteria into vacuoles, exfoliation of enterocytes containing bacteria, and subsequent stunting of the villi, began at 30 minutes and was severe and progressive to 2 hours. Following the initial attachment and uptake of the bacteria loss of enterocytes progressed from these initial sites; bacteria were associated with the lateral cell membrane of cells adjacent to cells being extruded and not with the microvilli of cells at new sites. In a calf 4 hours after dosing orally with the same strain, M cells were engulfing bacteria and their cell surface was changed as seen in the inoculated loops; absorptive enterocytes were also taking up bacteria as seen in the ileal loops, indicating the process seen in the loops and after oral dosage was similar. For this strain of S typhimurium, there was an initial concentration of bacilli around the domed villus epithelium. This distribution was not random but may have resulted from a specific attraction to the FAE.

Peyer's patch adherence of enteropathogenic Escherichia coli strains in rabbits

RDEC-1 (serotype O15) is an attaching and effacing strain of rabbit enteropathogenic Escherichia coli (REPEC) that causes diarrhea in postweanling rabbits. It expresses AF/R1 pili that mediate Peyer's patch M-cell adherence. We investigated Peyer's patch adherence, the presence of virulence genes, ileal brush border aggregation, and pilus expression in 9 strains representing several serotypes of REPEC as well as in two commensal strains. Postweanling rabbits were inoculated with 10(6) organisms and sacrificed at 24 h, and tissues were prepared for examination by light microscopy. Strains B10 and RDEC-1 were also studied at 12 and 72 h postinoculation. All REPEC strains were eaeA positive, expressed pili, and adhered to ileal brush borders. Both commensal strains expressed pili, and one strain adhered to brush borders. All REPEC strains demonstrated some degree of Peyer's patch lymphoid follicle adherence, ranging from diffuse coverage to small patches covering two to three dome epithelial cells. Strains C102 and C110 had genes homologous with the structural subunit gene of the AF/R1 pilus (afrA) of RDEC-1, which correlated with greater degrees of lymphoid follicle adherence and lesser degrees of ileal villus adherence. The observation that all REPEC strains adhere to Peyer's patch epithelium suggests the possibility that human strains of enteropathogenic E. coli (EPEC) might do likewise. EPEC strains might thus serve as mucosal vaccine vectors in humans. Better understanding of the molecular mechanism of REPEC adherence should provide a model for the targeting of the Peyer's patch in humans.

Apoptosis of enterocytes induced by inoculation of a strain of attaching and effacing Escherichia coli and verotoxin

When verotoxin (VT)-producing attaching and effacing Escherichia coli (AEEC, serotype O5: H-) were inoculated perorally into 10-day-old rabbits, attaching of the E. coli to enterocytes and effecting of their microvillous portion were observed extensively from the ileum to the colon. Subsequent apoptotic changes of the infected enterocytes were demonstrated by the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) reaction and electron microscopy. Apoptosis was also induced in cultured Vero cells by inoculation of VT extracted from the AEEC. This study clarified that VT-producing AEEC induce apoptosis of enterocytes, causing mucosal damage.

A novel developmental process of intestinal epithelial lesions in a calf infected with attaching and effacing Escherichia coli

A comparative study on the adhesion of attaching and effacing Escherichia coli (AEEC) to the enterocytes between the colon of a calf and the jejunum of a piglet showed differences in the developmental process of attaching and effacing (AE) lesions. In the calf, pedestals consisted of fused microvilli, while in the piglet they developed from the apical epithelial cell membranes after effacing microvilli. Microvilli adjacent to the AEEC attachment site were atrophic in the calf, whereas they were elongated in the piglet. The production of AE lesions in the calf may be indicative of a novel developmental process with AEEC infection.