Pasteurella multocida enters polarized epithelial cells by interacting with host F-actin

We investigated the interaction of an avian strain of Pasteurella multocida with the cytoskeleton of MDCK cells, which formed a polarized epithelium when grown on type I collagen coated filters. Bacteria were incubated with MDCK cells for 30 min. 2, 4 and 6 hours and their location and association with the cell cytoskeleton determined by double-label immunofluorescence confocal microscopy. Cells were stained with a polyclonal antiserum to the outer-membrane proteins of P. multocida and with rhodamine phalloidin which specifically binds filamentous (F) actin. Confocal microscopy revealed that bacteria entered the cells by 30 min, and that by 6 hours there was a marked alteration in the actin cytoskeleton in which long filaments were reorganized to discrete foci of short actin filaments, within which were one or more bacteria. Electron microscopy demonstrated that by 2 hours, each bacterium was associated with many short 5-6 nm filaments. Treatment of MDCK cells with cytochalasin D for either 30 minutes or 24 hours prior to infection disrupted the actin cytoskeleton and inhibited entry of P. multocida.

Distribution of K88 Escherichia coli-adhesive and nonadhesive phenotypes among pigs of four breeds

Enterotoxigenic Escherichia coli expressing K88 fimbrial adhesins often cause diarrhea in young pigs. However, some pigs are inherently resistant to colibacillosis, because they lack receptors on their epithelial cell brush borders to which the fimbriae bind. Phenotypic diversity with respect to the binding of E. coli expressing K88 of the three variant types (K88ab, K88ac, and K88ad) was reported by Bijlsma et al. (1982), and binding specificities for each phenotype were described: A (adhesive to all three variants), B (adhesive to K88ab and K88ac), C (adhesive to K88ab and K88ad), D (adhesive to K88ad) and E (nonadhesive). Because brush border adhesiveness has been correlated with disease susceptibility, swine K88 adhesive phenotypes are of significance in the control of enteric disease. To determine the prevalence of the various K88 adhesive phenotypes in the swine population in the Midwestern United States, we tested epithelial cell brush borders of 24 purebred pigs from each of four breeds (Chester White, Duroc, Hampshire and Yorkshire) for adhesiveness to each of the K88 variants. Four, 4-week-old pigs (the largest and smallest healthy female littermates from two litters) were collected from each of 24 farms. Brush border vesicles from the pigs were tested for ability to bind E. coli expressing each K88 variant. The five brush border adherence patterns described for phenotypes A-E were observed. In addition, brush borders from some pigs only bound K88ab + bacteria. Nearly three quarters of the pigs whose brush borders tested, were found to be phenotype A (43%) or phenotype E (28%). These were the most common phenotypes in each breed, except Hampshire, in which case phenotypes C (17%) and D (25%) were more common than E (8%). There appeared to be no relationship between the phenotype of a pig and its weight relative to its littermate.

Phenotypic and genotypic profiles of human, canine, and porcine spirochetes associated with colonic spirochetosis correlates with in vivo brush border attachment

A group of phenotypically and genotypically distinct weakly beta-hemolytic intestinal spirochetes (WBHIS) have been associated with a diarrheal disease of humans, dogs and swine, designated colonic spirochetosis (CS). Because attachment of spirochetes to the brush border of colonic enterocytes is a consistent feature of CS, it may represent an important virulence mechanism. In this study, pure cultures of WBHIS obtained from humans, dogs, and swine with clinical signs or lesions of CS were compared with Serpulina innocens using biochemical, genotypic and an in vivo brush border attachment assay CS-associated WBHIS did not form genotypic and an in vivo brush border attachment assay CS-associated WBHIS did not form indole, but hydrolyzed hippurate. Analysis of genomic DNA using arbitrarily primed-PCR (AP-PCR) revealed that the CS-associated WBHIS had a closely related pattern which was distinctly different from that of S. innocens. For in vivo brush border attachment assays, one-day old chicks were inoculated by crop gavage with either sterile trypticase soy broth or broth containing either S. innocens or CS-associated WBHIS. On day 7 post-inoculation, the ceca of sham-inoculated control chicks and S. innocens-inoculated chicks had tall columnar enterocytes without spirochetes, and no spirochetes were isolated by culture on selective medium. Focal to segmental attachment of spirochetes to the brush border of superficial enterocytes was present in the ceca of chicks inoculated with WBHIS, and weakly beta-hemolytic spirochetes with effacement of the microvillous brush border of colonic enterocytes. Complete agreement between hippurate hydrolysis, specific- and AP-PCR assays and in vivo brush border attachment studies confirms the enteropathogencity of CS-associated WBHIS.

Pathotypes of bovine verotoxigenic Escherichia coli isolates producing attaching/effacing (AE) lesions in the ligated intestinal loop assay in rabbits

Effacement of the microvilli and intimate attachment to the enterocytes (AE lesions) are two common properties of enteropathogenic (EPEC) and many verotoxigenic (VTEC) E. coli isolates from humans and animals. However not all of the several chromosomal and plasmidic genes and loci involved in the pathogenesis of the human EPEC strain E2348/69 are present in EPEC and VTEC isolates from animal species. We here report that in addition to verotoxin-encoding genes, bovine VTEC isolates harbour a variant of the original eaeA gene, confirming previous results, but neither the eaf nor the hfp loci which are involved in early attachment stage, and that not all of them possess an eaeB gene, as determined by the colony hybridization assay. Have these bovine VTEC isolates lost some of the loci or are they not necessary for the production of AE lesions in vivo? We also report the results of the ligated intestinal loop assay in rabbits with several bovine VTEC isolates. The production of AE lesions was correlated with the presence of an eaeA gene, but not with the presence of an eaeB gene, and was of course independent of the presence of the eaf and bfp loci. The eaeA-negative VTEC isolates produced no AE lesions. Either the eaeB gene is unnecessary for the production of AE lesions in the rabbit ligated intestinal loop assay or bovine VTEC possess other loci coding for similar functions. As to the adhesins involved in the early attachment step of bovine VTEC, they are most probably specific to cattle.

Principles of ex ovo competitive exclusion and in ovo administration of Lactobacillus reuteri

The data that have been presented indicate that the in ovo use of competitive exclusion (CE) agents is feasible for both chickens and turkeys. However, there are many pitfalls that await the use of in ovo application of CE agents, including the use of nonspecies-specific intestinal microbes and the use of harmful proteolytic, gas-producing and toxin-producing intestinal microbes. Of the potential CE agents that have posthatch application, only Lactobacillus reuteri has been shown to be safe and effective in terms of not affecting hatchability and in having a prolonged effect in the hatched chick or poult. Lactobacillus reuteri administration in ovo increases its rate of intestinal colonization and decreases the colonization of Salmonella and Escherichia coli in both chicks and poults. Additionally, mortality due to in-hatcher exposure to E. coli or Salmonella is reduced with in ovo L. reuteri. Use of antibiotics in ovo may preclude the use of co-administered CE agents, but Gentamicin and L. reuteri are a compatible mixture when administered in ovo in separate compartments. Nevertheless, the intestinal morphology can be affected by both the CE agent and by antibiotics. Lactobacillus reuteri both in ovo and ex ovo will increase villus height and crypt depth, and Gentamicin in ovo causes a shortening and blunting of the villus. Both Gentamicin and L. reuteri in ovo suppress potentially pathogenic enteric microbes, but with diminished antibiotic effects shortening and blunting of the intestinal villi does not correct itself. Goblet cell numbers increase significantly on the ileum villus of chicks treated with Gentamicin in ovo, and this is presumably due to the increase in potentially pathogenic bacteria in the intestinal tract. Diminishing antibiotic effects posthatch would then negatively affect the absorption of nutrients and reduce growth at least in a transitory manner. Thus, L reuteri administration in ovo singly or in combination with Gentamicin followed by L reuteri via drinking water or feed appears to have potential to control many enteric pathogens in poultry. Additional work in the use of in ovo CE cultures is mandated because there is a world-wide movement to reduce antibiotic use in poultry due to increased microbial resistance to antibiotics. Use of naturally occurring intestinal bacterial cultures, either in mixed culture or as single well-defined cultures, has potential for immediate use in the poultry industry.

Interactions between the enteric pathogen and the host. An assortment of bacterial lectins and a set of glycoconjugate receptors

Bacteria have been associated with a wide variety of syndromes in animals and humans. These include enteropathies, urinary infections, meningitis and septicemia. Among the distinct set of tactics to prevail within the host, is the ability of bacteria to adhere to cellular targets. Adhesion to the gut by enteric bacteria occurs via several types of adhesins. During the last 15 years, much information has become available on bacterial adhesins and mechanisms governing bacteria-host interactions. Due to their location on the cell surface, establishing a carbohydrate frontier, and their inherent variability, glycosphingolipids and glycoproteins provide a wide range of binding sites for bacteria, toxins and more generally lectins. Bacterial lectins are localized either on the tip or along fimbrial filaments or on nonfimbrial structures. We examine in this short review, a collection of pathogen lectins, through their different receptor specificities. For sialic acid-binding lectins, the conformation of terminal sialic acid is essential for adhesion, whereas for other bacterial lectins, complementary sugars may be arranged in specific linear and/or branched sequences. Finally, it appears that the composition and structure of cell carbohydrates could in part explain the bacterial tropism and susceptibility or resistance of the host to enteric diseases.

A three-receptor model for the interaction of the K88 fimbrial adhesin variants of Escherichia coli with porcine intestinal epithelial cells

Four phenotypes of pigs distinguished by the variant(s) of K88 fimbrial adhesin (K88ab, K88ac, K88ad) that bind to their intestinal epithelial cells (I-none of the variants, II-K88ad, III-K88ab and K88ac, and IV-all three variants) have been identified. We hypothesize that the differences between the phenotypes are defined by the presence or absence of K88 adhesin receptors. We propose a three-receptor model to account for the observed phenotypes: 1) Receptor bed which binds all three variants and is found in phenotype IV, 2) Receptor be which binds K88ab and K88ac and is found in phenotype III and IV, and 3) Receptor d which binds K88ad and is found in phenotype II. We have identified the be receptor activity as a pair of mucin-type sialoglycoproteins (210 and 240 kDa). Although neither the bcd nor d receptor has been identified biochemically, their presence has been established using both blocking and receptor localization studies. Blocking studies using phenotype IV brush borders demonstrated that K88ab and K88ac fimbriae block the binding of E. coli expressing any of the K88 variants, but K88ad fimbriae block only K88ad E. coli binding. These results indicate that two receptors (bcd and bc) exist in the phenotype IV animals. Receptor localization studies on intestinal sections from phenotype IV animals showed that K88ab and K88ac adhesin binding is continuous from the crypt to the tip of the villus. The binding of the K88ad adhesin binding is multifocal in phenotype IV pigs, but continuous from crypt to tip of the villus in sections of phenotype II pigs. These studies verify the presence of two receptors (bcd and bc) in phenotype IV animals, and indicate that the K88ad receptor in phenotype IV animals (bcd) is different than in phenotype II animals (d).

Dynamics of Escherichia coil infection in experimentally inoculated chickens

In order to study the dynamics of avian colibacillosis, commercial broiler chickens were inoculated with a pathogenic Escherichia coli strain (01:K1:H7) into the left caudal thoracic air sac. Chickens were euthanatized at different times from 3 to 48 hr postinoculation and examined for bacterial counts and macroscopic and microscopic lesions. The E. coli strain colonized the air sacs, lungs, and trachea and was recovered from blood and all tested extrarespiratory organs of inoculated birds. A gradual increase in bacterial counts in the trachea, lungs, air sacs, and liver was observed from 3 to 12 hr. Clinical signs and macroscopic lesions of colibacillosis were observed in all inoculated birds. Moderate to severe lesions of airsacculitis, pericarditis, perihepatitis, and splenic hypertrophy were observed. Microscopically, inflammatory cell infiltration, serious to fibrinous exudate, and cellular debris on serosal surfaces were present in the liver, spleen, and air sacs. In air sacs, heterophils were present in low numbers perivascularly 3 hr after inoculation and became more numerous by 24 hr postinoculation. Ultrastructurally, epithelial cells in the air sacs and in air capillary regions of the lung were swollen and vacuolated beginning at 3 hr postinoculation. Bacteria were adherent to and present within the epithelial cells at 3 hr postinoculation and were also seen in phagocytic cells and, rarely, in the connective tissue of these organs at 24 hr postinoculation. These results indicate that both air sacs and lungs can be the portal of entry for E. coli into the systemic circulation, probably via damaged epithelium.

Attaching and effacing enteropathogenic Escherichia coli O18ab invades epithelial cells and causes persistent diarrhea

A case of persistent diarrhea following Escherichia coli O18ab gastroenteritis is reported. Electron microscopy of a biopsy of the small intestine showed effacement of the brush border, attachment of bacteria to the epithelial cells with pedestal formation, and bacteria within the enterocytes. The bacterial isolate was an enteropathogenic E. coli isolate which did not contain the adherence factor (EAF) but possessed the attaching-effacing eae gene, was able to invade HeLa cells in a gentamicin invasion assay, and also invaded rabbit intestinal cells. Results suggest that E. coli organisms of the O18ab serotype may cause diarrhea by an as yet unknown pathogenic mechanism, involving attaching to and effacing of enterocytes followed by invasion of the epithelial cells.

Experimental inoculation of foals and pigs with an enterotoxigenic E. coli isolated from a foal

Hemolytic E. coli strain 807-13, O149:NM:K88(STb+, LT+), was isolated from the feces of a neonatal diarrheic foal. E. coli 807-13 was examined for adhesion to brush border membranes (BBM) from foals, adult horses and pigs, and its pathogenicity was assessed in neonatal foals and pigs. E. coli 807-13 did not adhere to equine BBM but adhered to pig BBM. It did not cause diarrhea nor did it colonize the intestinal epithelium of 3 colostrum-deprived and 3 suckled foals challenged at 24 h of age. Acute ulcerative gastritis and acute suppurative gastritis were observed in 2 colostrum-deprived challenged foals, and acute neutrophilic enteritis was observed in 1 colostrum-deprived and in 1 suckled challenged foal. No similar histopathologic lesions were detected in the control foals. Both gnotobiotic and suckled pigs developed diarrhea after challenge exposure to E. coli 807-13 and the intestinal epithelium of the pigs was colonized. Histopathologic evidence of gastritis and enteritis among the foals indicated some complicity of E. coli 807-13 in foal enteric disease.

Adhesion of Helicobacter pylori to polarized T84 human intestinal cell monolayers is pH dependent

Epithelial cells, which form tight polarized monolayers on porous substrates, constitute ideal model systems to study bacterial adhesion and invasion. The binding of Helicobacter pylori to the apical membrane of T84 cells, an epithelial cell line derived from a human colon carcinoma, was assessed biochemically and morphologically. Attachment was rapid, and binding remained constant over time, with a significant (P < 0.01, Mann-Whitney U test) ca. fourfold increase at pH 5.4 (76% +/- 22%) compared with pH 7.4 (18% +/- 7%). In contrast, adhesion of enteropathogenic Escherichia coli was not enhanced at pH 5.4. The transepithelial electrical resistance of the T84 cell monolayers was not affected by pH or by H. pylori. Following binding, H. pylori induced a reorganization of the brush border as reflected by actin condensation, facilitating the intimate association of the bacteria with the apical plasma membrane. H.pylori was not internalized, as shown by confocal microscopy. Some bacteria, found in deep invaginations of the apical membrane, were probably inaccessible to gentamicin, thus accounting for the observed tolerance to the antibiotic. These data provide the first evidence that an acidic environment favors Helicobacter adhesion and that binding is followed by survival of the survival of the bacteria in pockets of the apical membrane.

Porcine 987P glycolipid receptors on intestinal brush borders and their cognate bacterial ligands

Certain strains of enterotoxigenic Escherichia coli adhere to piglet intestinal epithelial cells by means of the 987P fimbriae. The 987P fimbrial structure consists of a helical arrangement of three fimbrial proteins, namely, the major subunit FasA and two minor subunits, FasF and FasG. FasG, which is located at the fimbrial tip and at various positions along the fimbriae, mediates 987P binding to glycoprotein receptors. In this study, we isolated and analyzed the structure of piglet glycolipid brush border receptors and characterized their cognate ligands on the 987P fimbriae. Two major glycolipid bands recognized by 987P fimbrial probes in thin-layer chromatography overlay assays were further purified by high-performance thin-layer chromatography and shown to comigrate with control galactosylceramide containing hydroxylated fatty acids and with sulfatide. Their structures were confirmed by fast atom bombardment mass spectrometry, which detected homologous series of ceramide monohexoside and sulfatide with hydroxylated fatty acyl chains ranging from h16:0 to h24:0. Assembled 987P fimbriae, pre- and postassembly dissociated fimbrial subunits, and Fab fragments of specific anti-FasG, -FasF, and -FasA were used to inhibit 987P-mediated bacterial binding to the two identified piglet glycolipids and corresponding isoreceptor controls. Only assembled fimbriae and anti-FasG Fab fragments were significantly able to inhibit bacterial binding to sulfatide, indicating that in addition to glycoproteins, FasG recognizes a specific glycolipid of piglet brush borders. In contrast, only anti-FasA Fab fragments were significantly able to inhibit bacterial binding to galactosylceramide with hydroxylated fatty acids and piglet hydroxylated ceramide monohexoside, indicating that FasA may determine a third type of ligand-receptor interaction in the piglet intestines. Since these bacterial adhesins recognize their respective glycolipid receptors only after being assembled in their final fimbrial quaternary structure, adhesin binding may involve cooperative interactions and the subunits by themselves may have very low binding affinities. Alternatively, conformation-sensitive domains of these subunits present in the assembled fimbriae may be required for glycolipid binding.

Differentiation-associated antimicrobial functions in human colon adenocarcinoma cell lines

We report that the enterocytic cells of the HT-29 glc-/+ cell subpopulation strongly expressed two antimicrobial enzymes: the lysozyme and alpha1-antitrypsin. Moreover, we found that 20 to 30% of these cells expressed positive immunoreactivity using the mAbs directed against the gut porcine PR-39 and cecropin P1 antimicrobial peptides, but did not express immunreactivity against the human antimicrobial polymorphonucleated neutrophil-associated HNP 1-3 defensin and the Xenopus skin magainin. The HT-29 glc-/+ cell subpopulation develops bacteriolytic activity against the enterovirulent diffusely adhering C1845 Escherichia coli characterized by dramatic alterations of the bacterial cell, suggesting lysis, and bacterial death. In contrast, no expression of immunoreactivity against the antimicrobial peptides and no C1845 bacterial alteration were found in the cultured human embryonic undifferentiated INT407 cells and the colon adenocarcinoma T84 crypt cells. The development of the bacterial alteration and the expression of the antimicrobial components were examined as a function of the cell differentiation using the Caco-2 cell line which spontaneously differentiates in culture. We found that the bacterial alteration and the expression of the PR-39 immunoreactivity are differentiation-associated events. Altogether, our results suggest that in the intestine the enterocytes could develop antimicrobial defenses participating in the protection of the gut epithelium against enterovirulent microorganisms.

Probiotics, cecal microflora, and aberrant crypts in the rat colon

Our hypothesis was that administration of bifidobacteria, Lactobacillus acidophilus or both to rats will minimize the numbers of aberrant crypts in the distal colon that develop in response to the carcinogen 1,2-dimethylhydrazine (DMH). A series of experiments was designed to test this hypothesis where the treatments used were as follows: skim milk controls (Skim-Basal), skim milk + bifidobacteria (Bifido-Basal), skim milk + fructooligosaccharide (Skim-FOS), and skim milk + bifidobacteria + fructooligosaccharide (Bifido-FOS). In two experiments, bifido-bacteria + FOS administration significantly decreased the number of aberrant crypts that developed, but there was no clear relationship of aberrant crypts to numbers of bifidobacteria or Clostridium perfringens. In the third experiment, the Bifido-FOS treatment led to significantly fewer aberrant crypts and aberrant crypt foci than the Bifido-Basal treatment. The Skim-FOS group had significantly more cecal bifidobacteria than the Skim-Basal group and significantly fewer C. perfringens than the Skim-Basal and Bifido-Basal. In a fourth experiment, L. acidophilus was added as an additional treatment. The number of aberrant crypts was not significantly different among the groups. However, the number of C. perfringens was significantly decreased by the addition of bifidobacteria, L. acidophilus or the combination of the two, whereas the numbers of bifidobacteria and L. acidophilus were not affected by treatment. A significant correlation (R2 = 0.84, P < 0.01) was noted between the body weight of rats at DMH administration and the magnitude of the difference in aberrant crypts between the Skim-Basal rats and the Bifido-FOS rats. The results suggest that there is variability in the effects of bifidobacteria and L. acidophilus administration on both aberrant crypt formation and C. perfringens.

Penetration of M cells and destruction of Peyer's patches by Yersinia enterocolitica: an ultrastructural and histological study

Yersinia enterocolitica is enteropathogenic for man and rodents. Previous studies provided evidence that Y. enterocolitica invades the lymphoid follicles of the Peyer's patches (PP) of the small intestine. In this study Y. enterocolitica-induced tissue alterations of the follicle-associated epithelium (FAE) and the underlying PP tissue were analysed by scanning (SEM) and transmission electron microscopy (TEM) as well as by conventional histological examination. For this purpose, an experimental mouse infection model including orogastric infections as well as ileal loop experiments were used. A rapid and selective colonisation of the FAE after orogastric yersinia infection was observed by SEM. TEM studies confirmed that Y. enterocolitica adhered closely to the FAE including M cells and enterocytes. Histological studies and TEM revealed that Y. enterocolitica selectively invaded the PP via M cells but not via other cells of the FAE. One day after Y. enterocolitica infection the FAE was altered and small micro-abscesses comprising yersiniae expressing the major outer-membrane protein YadA were observed immediately beneath the FAE. Adjacent villi were dilated from lymphangiectasis and transmigrating polymorphonuclear leucocytes (PMNL) were found within the epithelium. At 5-7 days after infection the FAE and parts of PP were destroyed. Profound alterations of the cyto-architecture of the PP were due to the enormous recruitment of PMNL. By day 5 after infection, abscesses were found in the mesenteric lymph nodes. However, TEM studies revealed evidence that Y. enterocolitica may disseminate from the PP not only via the lymphatics but also by invasion of blood vessels. Taken together, the results of this study demonstrate that the FAE is the primary site of host-pathogen interaction in Y. enterocolitica infection and that this pathogen penetrates M cells and subsequently induces destruction of the PP.

Helicobacter pylori attachment to gastric cells induces cytoskeletal rearrangements and tyrosine phosphorylation of host cell proteins

The consequences of Helicobacter pylori attachment to human gastric cells were examined by transmission electron microscopy and immunofluorescence microscopy. H. pylori attachment resulted in (i) effacement of microvilli at the site of attachment, (ii) cytoskeletal rearrangement directly beneath the bacterium, and (iii) cup/pedestal formation at the site of attachment. Double-immunofluorescence studies revealed that the cytoskeletal components actin, alpha-actinin, and talin are involved in the process. Immunoblot analysis showed that binding of H. pylori to AGS cells induced tyrosine phosphorylation of two host cell proteins of 145 and 105 kDa. These results indicate that attachment of H. pylori to gastric epithelial cells resembles that of enteropathogenic Escherichia coli. Coccoid H. pylori, which are thought to be terminally differentiated bacterial forms, are capable of binding and inducing cellular changes of the same sort as spiral H. pylori, including tyrosine phosphorylation of host proteins.

Genotypic and phenotypic characterization of Escherichia coli isolates from dogs manifesting attaching and effacing lesions

Thirteen Escherichia coli isolates from dogs manifesting attaching and effacing lesions were characterized genetically with respect to the presence of the following virulence determinants associated with human enteropathogenic E. coli (EPEC): eaeA, encoding the outer membrane protein intimin; eaeB, which is necessary for inducing signal transduction; bfpA, encoding the bundle-forming pilus; and the EAF (stands for EPEC adherence factor) plasmid. These isolates were also analyzed phenotypically with respect to adherence to mammalian cells in vivo and in vitro. Nine of these 13 isolates were found to be eaeA positive by PCR: four of these nine were eaeB positive. The 5' end, but not the 3' end, of the eaeA gene was amplified by PCR when primers derived from the eaeA gene of EPEC were used. Six and eight of these 13 isolates were found to be bfpA positive and EAF positive, respectively. The bfpA gene and EAF locus were found on high-molecular-weight plasmids, whereas the eaeA and eaeB genes were chromosomally located when present. Only one canine E. coli isolate, 4221, which was positive for eaeA, eaeB, bfpA, and EAF, adhered to HEp-2 cells in a localized manner and was positive in the fluorescence actin staining test. The nine eaeA-positive isolates adhered to the mucosal surface of piglet ileal explants and induced some microvillus effacement. However, when tested in experimentally inoculated gnotobiotic piglets, isolate 4221 did not induce attaching and effacing lesions at any level of the intestinal tract. Our results indicate that canine E. coli isolates associated with attaching and effacing lesions share some properties with human EPEC but form a heterogeneous group.

Segmented filamentous bacteria associated with lymphoid tissues in the ileum of horses

Segmented filamentous bacteria preferentially attached to the follicle-associated epithelium overlying the lymphoid tissue in samples of the terminal ileum from seven horses examined by scanning electron microscopy. The bacteria adhered to the apical membrane of the enterocytes by a holdfast segment. Each filament tended to be of uniform diameter, but the filaments ranged from 0.7 to 1.4 microns in diameter. The bacteria were usually absent from the adjacent villous epithelium.

Two stages of enteropathogenic Escherichia coli intestinal pathogenicity are up and down-regulated by the epithelial cell differentiation

Pathogens and eucaryotic cells are active partners during the process of pathogenicity. To gain access to enterocytes and to cross the epithelial membrane, many enterovirulent microorganisms interact with the brush border membrane-associated components as receptors. Recent reports provide evidence that intestinal cell differentiation plays a role in microbial pathogenesis. Human enteropathogenic Escherichia coli (EPEC) develop their pathogenicity upon infecting enterocytes. To determine if intestinal epithelial cell differentiation influences EPEC pathogenicity, we examined the infection of human intestinal epithelial cells by JPN 15 (pMAR7) [EAF+ eae+] EPEC strain as a function of the cell differentiation. The human embryonic intestinal INT407 cells, the human colonic T84 cells, the human undifferentiated HT-29 cells (HT-29 Std) and two enterocytic cell lines, HT-29 glc-/+ and Caco-2 cells, were used as cellular models. Cells were infected apically with the EPEC strain and the cell-association and cell-entry were examined by quantitative determination using metabolically radiolabeled bacteria, as well as by light, scanning and transmission electron microscopy. [EAF+ eae+] EPEC bacteria efficiently colonized the cultured human intestinal cells. Diffuse bacterial adhesion occurred to undifferentiated HT-29 Std and INT407 cells, whereas characteristic EPEC cell clusters were observed on fully differentiated enterocytic HT-29 glc-/+ cells and on colonic crypt T84 cells. As shown using the Caco-2 cell line, which spontaneously differentiates in culture, the formation of EPEC clusters increased as a function of the epithelial cell differentiation. In contrast, efficient cell-entry of [EAF+ eae+] EPEC bacteria occurred in recently differentiated Caco-2 cells and decreased when the cells were fully differentiated.(ABSTRACT TRUNCATED AT 250 WORDS)

A plasmid-encoded surface protein on Enterococcus faecalis augments its internalization by cultured intestinal epithelial cells

Aggregation substance, a plasmid-encoded Enterococcus faecalis surface protein, plays a role in mediating the formation of mating aggregates, resulting in plasmid transfer. The role of aggregation substance in the internalization of E. faecalis by cultured intestinal epithelial cells, namely HT-29 cells, was analyzed. It was associated with a significant increase in endocytosis of E. faecalis by HT-29 cells: Numbers of internalized enterococci were fewer than of an invasive strain of Listeria monocytogenes, similar to Salmonella typhimurium and another L. monocytogenes strain, and greater than relatively noninvasive strains of E. faecalis, Proteus mirabilis, and Escherichia coli. Electron microscopy confirmed aggregation substance on the surface of strains interacting with the enterocyte microvillous surface, and intracellular enterococci were localized within membrane-bound vacuoles in the enterocyte cytoplasm. Thus, aggregation substance may facilitate E. faecalis internalization by host epithelial cells.