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.