Interaction of mannose-containing oligosaccharides with the fimbrial lectin of Escherichia coli

Roles of glycoproteins and oligosaccharides found in human vaginal fluid in bacterial adherence

Adherence of type 1-piliated Escherichia coli to carbohydrate structures of vaginal mucosa plays a major role in the pathogenesis of ascending urinary tract infections in women. Colonization of the vaginal introitus is influenced by interactions between pathogens, vaginal fluid, and vaginal epithelium. In this study, the type and amount of carbohydrates and glycoproteins present in vaginal fluid were determined. Free and protein-bound oligosaccharides in vaginal fluid specimens were analyzed by fluorophore-assisted carbohydrate electrophoresis (FACE) and high-pressure liquid chromatography (HPLC). Two-dimensional electrophoretic separations of vaginal fluid glycoproteins were performed together with bacterial overlay assays. The results of FACE showed that the majority of the oligosaccharides are in the free state and the bound oligosaccharides are undetectable. HPLC analysis of free sugars revealed glucose as the major sugar (3.3 +/- 0.3 mM), and the concentrations of mannose and glucosamine were 0.065 +/- 0.04 and 0.02 +/- 0.001 mM, respectively. Radiolabeled E. coli bound three vaginal fluid glycoproteins with the following molecular masses and pIs: 82 kDa and pI 5.5, 55 kDa and pI 4.5, and 55 kDa and pI 6.5. The binding was inhibited by mannose and by deglycosylation of the proteins prior to the overlay assay. One of these putative receptors was identified to be the heavy chain of secretory IgA (S-IgA). These data suggest that the free mannose in the fluid is less than that required to affect E. coli-epithelial cell binding interactions and that S-IgA may bind E. coli in the vaginal introitus.

[Inhibition of peritoneal bacterial adhesion using oligosaccharides. An experimental model of peritonitis in rats]

BACKGROUND

Peritoneal colonization is a crucial event in the pathogenesis of peritonitis and its local complications. Adherence to the serosal mesothelium is mediated in a number of microorganisms derived from the digestive tract (especially E. coli) by type-1 fimbriae which have an oligosaccharide specificity.

PURPOSE

To evaluate the effect of repeated peritoneal washes with saline solution and oligosaccharides on E. coli peritoneal adherence in a rat peritonitis model.

METHODS

Sixty rats were randomized in 3 groups of 20. E. coli was inoculated at a constant concentration of 10(8)/mL per 100 g of weight. Then, peritoneal washes were achieved daily during three consecutive days (D1, D2, D3), with saline solution in Group I (control group), Methyl alpha-D-Mannoside (MADM) in Group II, and p-Nitro-phenyl alpha-D-Mannoside (pNADM) in Group III. Peritoneal samples were obtained before and after lavage at D1, D2, and D3. Microbial recovery was expressed as cfu/mg of tissue, and converted into a percentage of the initial value. A 10% threshold defined efficiency of the wash (inhibition of adherence for 90% of bacteries).

RESULTS

Compared with data from Group I, E. coli peritoneal adherence was significantly lower after washes in Group III (D1: p = 0.03; D2: p = 0.009; D3: p = 0.003). Repeated washes were more efficient in Group III than in Group II (D1: p = 0.1; D2: p = 0.5; D3: p = 0.001).

CONCLUSION

These results suggest that the addition of oligosaccharides, especially of pNADM, reduces the peritoneal adherence of E. coli when a peritoneal wash is performed for peritonitis.

Effect of shape, size, and valency of multivalent mannosides on their binding properties to phytohemagglutinins

Clusters of di-, tri-, and tetra-antennary alpha-D-mannopyranosides were synthesized in good yields based on the coupling of amine-bearing mono- or trisaccharide [Man alpha(1 --> 6)[Man alpha(1 --> 3)]Man] haptens to poly-isocyanate or -isothiocyanate tethering cores. The relative binding properties of the resulting multivalent ligands were determined by turbidimetric and solid phase enzyme-linked lectin assays (ELLA) using plant lectins (phytohemagglutinins) Concanavalin A (Con A) and Pisum sativum (pea lectin) having four and two carbohydrate binding sites, respectively. Rapid and efficient cross-linking between tetravalent Con A and mannopyranosylated clusters were measured by a microtiter plate version of turbidimetric analyses. In inhibition of binding of the lectins to yeast mannan, the best tetravalent monosaccharide (30) and trisaccharide (31) inhibitors were shown to be 140 and 1155 times more potent inhibitors than monomeric methyl alpha-D-mannopyranoside against pea lectin and Con A, respectively. Compounds 30 and 31 were thus 35- and 289-fold more potent than the reference monosaccharide based on their hapten contents. As a general observation, the ligands bearing the Man alpha(1 --> 6)[Man alpha(1 --> 3)]Man trimannoside structures were found to be more potent inhibitors for Con A than the ligands having single mannoside residues, whereas pea lectin could not discriminate between the two types of ligands.

A mannose-specific adherence mechanism in Lactobacillus plantarum conferring binding to the human colonic cell line HT-29

Two Lactobacillus plantarum strains of human intestinal origin, strains 299 (= DSM 6595) and 299v (= DSM 9843), have proved to be efficient colonizers of the human intestine under experimental conditions. These strains and 17 other L. plantarum strains were tested for the ability to adhere to cells of the human colonic cell line HT-29.L.plantarum 299 and 299v and nine other L. plantarum strains, including all six strains that belong to the same genetic subgroup as L. plantarum 299 and 299v, adhered to HT-29 cells in a manner that could be inhibited by methyl-alpha-D-mannoside. The ability to adhere to HT-29 cells correlated with an ability to agglutinate cells of Saccharomyces cerevisiae and erythrocytes in a mannose-sensitive manner and with adherence to D-mannose-coated agarose beads. L. plantarum 299 and 299v adhered to freshly isolated human colonic and ileal enterocytes, but the binding was not significantly inhibited by methyl-alpha-D-mannoside. Periodate treatment of HT-29 cells abolished mannose-sensitive adherence, confirming that the cell-bound receptor was of carbohydrate nature. Proteinase K treatment of the bacteria also abolished adherence, indicating that the binding involved protein structures on the bacterial cell surface. Thus, a mannose-specific adhesin has been identified in L. plantarum; this adhesin could be involved in the ability to colonize the intestine.

The Escherichia coli G-fimbrial lectin protein participates both in fimbrial biogenesis and in recognition of the receptor N-acetyl-D-glucosamine

The gafD gene encoding the N-acetyl-D-glucosamine-specific fimbrial lectin (adhesin) protein GafD of uropathogenic Escherichia coli was cloned and subjected to genetic analysis. The corresponding gene product was isolated as a MalE fusion protein. The lectin gene was identified with the aid of deletion mutagenesis; mutations in gafD impaired either receptor binding or both receptor binding and fimbria production, depending on the mutation created. All mutants converted to wild-type expressors when complemented in trans with the cloned intact gafD gene. The predicted 354-amino-acid sequence of GafD, deduced from the nucleotide sequence, is closely related to those of the fimbria-associated F17-G and F17b-G proteins coded for by enterotoxigenic and invasive E. coli strains. Isolated GafD was shown to recognize N-acetyl-D-glucosamine by virtue of specific binding to an immobilized receptor, thus proving directly that GafD is a sugar-binding protein. Our results indicate that GafD as such is sufficient for receptor recognition and that the protein also participates in fimbrial biogenesis.

Carbohydrate heterogeneity of human myeloma proteins of the IgA1 and IgA2 subclasses

Comparative studies of the N-linked carbohydrate chains of human myeloma proteins of the IgA1 and IgA2 subclasses were performed. The N-linked carbohydrate chains were released by hydrazinolysis from the polypeptide backbone, converted to radioactive oligosaccharides by sodium borotritide reduction after N-acetylation and separated into one neutral and two acidic fractions by paper electrophoresis. The acidic oligosaccharides were completely converted to neutral oligosaccharides by sialidase treatment, indicating that they were sialyl derivatives. The neutral and sialidase-treated acidic oligosaccharides were further fractionated by Bio-Gel P-4 column chromatography. Structural studies of each oligosaccharide by sequential exoglycosidase digestion and methylation analysis revealed that human myeloma IgA proteins contained significant amounts of biantennary complex-type carbohydrate chains in addition to a small amount of the high mannose-type. The results indicated that the oligosaccharide structures of human IgA1 and IgA2 display a high degree of heterogeneity not only in the number of carbohydrate chains, but also in their composition.

Type 1 fimbrial shafts of Escherichia coli and Klebsiella pneumoniae influence sugar-binding specificities of their FimH adhesins

The type 1 fimbriae of enterobacteria comprise FimA, which constitutes most of the fimbrial shaft, and a cassette of three minor ancillary subunits including FimH, the mannose-binding moiety. The sugar-binding specificities of Escherichia coli and Klebsiella pneumoniae type 1 fimbriae were examined by determining the relative activities of two aromatic mannosides in inhibiting the yeast aggregation caused by the fimbriated bacteria. 4-Methylumbelliferyl alpha-mannoside (MeUmb alpha Man) was approximately 10-fold more effective than p-nitrophenyl alpha-mannoside (p-NP alpha Man) in inhibiting the yeast aggregation caused by the recombinant expressing native E. coli type 1 fimbriae. In contrast, MeUmb alpha Man was only fourfold more effective than p-NP alpha Man in assays employing the recombinant expressing native K. pneumoniae type 1 fimbriae. In order to elucidate the molecular mechanisms underlying the sugar-binding specificities of type 1 fimbriae in the two species, transcomplementation studies were performed and resulted in the creation of recombinants expressing two types of hybrid fimbriae: one consisting of a cassette of minor subunits of E. coli fimbriae borne on a filamentous shaft of K. pneumoniae FimA subunits and the other consisting of a cassette of K. pneumoniae minor fimbrial subunits borne on a shaft of E. coli FimA subunits. Although the heterologous FimH was incorporated into the fimbrial filaments in amounts comparable to those observed in native fimbriae, the hemagglutination activities of recombinants expressing hybrid fimbriae were significantly lower than those of their counterparts bearing native fimbriae. The sugar-binding specificity of the recombinant expressing hybrid fimbriae consisting of an E. coli shaft bearing K. pneumoniae FimH was different from those of recombinants expressing native K. pneumoniae fimbriae in its affinity for the two aromatic sugars but was remarkably similar to the specificities exhibited by recombinants expressing native E. coli fimbriae. Conversely, the sugar-binding specificity of the recombinant expressing hybrid fimbriae consisting of a K. pneumoniae shaft bearing E. coli FimH was different from that of the recombinant expressing native E. coli fimbriae but was very similar to those of recombinants expressing native K. pneumoniae fimbriae. We conclude that the differences in the sugar-binding specificity between E. coli and K. pneumoniae FimH fimbrial subunits is influenced by the fimbrial shafts which carry the adhesin molecules in a functionally competent form at the distal tips.

The use of lipid-linked oligosaccharides (neoglycolipids) in the identification of carbohydrate receptors for microbial pathogens

Specific oligosaccharide chains on the host cell surface act as receptors for many microbial pathogens. Identification of receptor structures is an important step in the understanding of the pathogenesis of infection. Glycolipid receptors have been identified by direct binding assays. However, technical difficulties have prevented demonstration of bacterial binding to the oligosaccharides of glycoproteins; these have been identified mainly by inhibition assays. By a novel technique developed in our laboratory, oligosaccharides released from glycoproteins are linked to lipids to form neoglycolipids. These can be used in bacterial binding assays. The feasibility of this approach has been demonstrated using type 1 fimbriated Escherichia coli binding specifically to neoglycolipids rich in mannose residues. The application of the method has resulted in a demonstration of a new type of adhesive specificity for E. coli and differences in the binding specificities of E coli and Pseudomonas aeruginosa. Further application of this technique by generating oligosaccharides purified from mucus glycoproteins from patients with cystic fibrosis to use in binding assays with P aeruginosa is currently being undertaken. The basic knowledge gained by this approach may in time see the development of novel therapy in the form of receptor blocking agents.

Differences in the binding specificities of Pseudomonas aeruginosa M35 and Escherichia coli C600 for lipid-linked oligosaccharides with lactose-related core regions

Membrane glycolipids contain the lactose sequence (galactose linked to glucose), and the oligosaccharide is variously extended such that there is a cell-type-specific repertoire. In this study, binding of Pseudomonas aeruginosa M35 to lipid-linked lactose (Gal beta 1-4Glc [structure 1]), lacto-N-neotetraose (Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc [structure 2]), lacto-N-tetraose (Gal beta 1-3GlcNAc beta 1-3Gal beta 1-4Glc [structure 3]), and asialo GM1 (Gal beta 1-3GalNAc beta 1-4Gal beta 1-4Glc [structure 4]) was evaluated and compared with binding of Escherichia coli C600 to these compounds. Oligosaccharides were linked to the lipid phosphatidylethanolamine dipalmitoate, and the resulting neoglycolipids were resolved on thin-layer chromatograms or coated onto plastic microtiter wells. Lipid-linked structures 1 to 4 were bound by P. aeruginosa and E. coli in the chromatogram assay, but only structure 4 was bound in the microtiter well assay. As shown previously for E. coli binding to lipid-linked structures 1 to 3, binding to lipid-linked structure 4 was not inhibited with oligosaccharide, indicating a requirement for lipid and oligosaccharide. With few exceptions, sialylation and fucosylation of structures 1 to 4 resulted in impaired or abolished binding. Comparisons of binding intensities in the chromatogram assay indicated that recognition by P. aeruginosa and recognition by E. coli are not identical. Presence of the additional disaccharide unit, as in structure 2, resulted in enhanced binding of P. aeruginosa but diminished binding of E. coli relative to lactose binding; fucosylation at galactose of lactose resulted in markedly diminished binding of P. aeruginosa only. In the microtiter well assay, binding of E. coli to asialo GM1 was much weaker than P. aeruginosa binding. The saccharide-plus-lipid-dependent adhesion may be an important factor in increased susceptibility to infection of epithelia already damaged by microbial and chemical agents; the differing strengths of adhesion to the structural variants may relate to tissue tropism.

Chinese hamster ovarian cell glycoproteins that mediate type 1 piliated gram-negative bacterial adherence

We used Chinese hamster ovary (CHO) cell lines to define the structures of glycoproteins responsible for Type 1 piliated bacterial adherence. CSH 50 Escherichia coli, a Type 1 piliated bacteria, adhered significantly better than an isogenic nonpiliated E. coli to all CHO lines tested. CSH 50 E. coli adhered least well to CHO cells expressing intact complex type oligosaccharides on cell surface glycoproteins. CSH 50 adherence increased when shorter oligosaccharides were present and was maximal when mannose groups were present in terminal, nonreducing positions. Five high mannose type glycoproteins, with molecular weights of 79, 75, 55, 50, and 37 kD, were identified as high affinity ligands for Type 1 piliated bacteria. Our results suggest that alterations in cell surface carbohydrates may increase adherence of Type 1 piliated gram-negative bacteria to cells.

C-glycosyl compounds bind to receptors on the surface of Escherichia coli and can target proteins to the organism

A series of C-mannopyranosyl derivatives have been synthesized and their inhibitory activity towards the receptor-mediated adhesion of E. coli to yeast cells has been tested. Total inhibition of yeast-cell agglutination by C-glycosyl derivatives 4 and 9 is achieved at a concentration approximately one order of magnitude lower than that of methyl alpha-D-mannopyranoside, indicating that the binding affinity to the receptor is related to the hydrophobicity of the carbon-linked side chain. A biotin-linked C-glycosyl derivative of mannose (compound 9) has been synthesized and used to target avidin and streptavidin to the bacterial cell surface. Of the C-glycosyl derivatives tested in our study, the conjugate of compound 9 with avidin had the highest avidity for the bacterial receptors, inhibiting agglutination at a concentration three orders of magnitude lower than methyl alpha-D-mannopyranoside. The use of such bifunctional compounds as the mannose-biotin conjugate 9 is a general strategy to target molecules to pathogenic organisms via their cell-surface carbohydrate receptors and to change the antigenicity of the bacterial cell surface.

Persistence of Escherichia coli bacteriuria is not determined by bacterial adherence

The role of bacterial adherence in the persistence of bacteria in the human urinary tract was analyzed. Women with chronic symptomatic urinary tract infections were subjected to deliberate colonization with nonvirulent Escherichia coli, after eradication of their current infections. E. coli organisms were instilled into the bladder through a catheter. The strain used for colonization, E. coli 83972, was isolated from a patient with stable bacteriuria. It lacked expressed adherence factors and did not belong to the uropathogenic O:K:H serotypes. Strain 83972 was transformed with the pap and pil DNA sequences encoding Gal alpha 1-4Gal beta- and mannose-specific (type 1) adhesins. Patients were colonized with a mixture of the wild-type and the transformed strains. E. coli 83972 caused stable bacteriuria for greater than 30 days in 7 of 12 individuals. In contrast, the Gal alpha 1-4 Gal beta-recognizing or mannose-binding transformants were eliminated within 48 h. The consistent superiority of the wild-type strain in establishing stable bacteriuria when compared with the adhesive transformants did not appear to be due to differences in growth rates or to plasmid segregation. Rather, the transformants expressing the adhesin determinants were selectively eliminated by the host. This suggested that the acquisition of adherence factors is not sufficient to increase the fitness of E. coli for survival in the urinary tract of humans.

Mechanism of adherence of Moraxella (Branhamella) catarrhalis

We examined the mechanisms of adherence of Moraxella catarrhalis to nasopharyngeal epithelial cells. Fimbriae were detected by electron microscopy on most of the strains studied. A role of fimbriae in adherence was supported by the reduction in adherence by treatments denaturing the fimbriae or by antifimbrial antibodies. There was, however, no significant difference in adhesive capacity or hemagglutination between fimbriated and non-fimbriated strains. Furthermore, there was no correlation between hemagglutination and adherence. The possibility that receptor epitopes were provided by cell surface glycolipids was examined by thin-layer chromatography. Glycolipids from various sources, including nasopharyngeal cells were separated by thin layer chromatography plates and overlayed with bacteria. No binding was detected. The results suggest that lectin-glycolipid interactions do not explain the attachment of M. catarrhalis to epithelial cells.

Bacterial adherence as a virulence factor in urinary tract infection

Escherichia coli (E. coli) causes greater than 90% of urinary tract infections, UTI, in childhood. The capacity to adhere to urinary tract epithelial cells characterizes E. coli strains that cause acute pyelonephritis. Adherence of uropathogenic E. coli is the result of a specific interaction between bacterial adhesins and glycolipid receptors on the host cells, especially the globoseries of glycolipids which share the Galactose alpha 1-greater than 4Galactose beta disaccharide (Gal alpha 1-greater than 4Gal beta). In childhood UTI, Gal alpha 1-greater than 4Gal beta-binding bacteria caused significantly higher body temperature, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and pyuria, and lower renal concentrating capacity, than E. coli lacking this specificity. The Gal alpha 1-greater than 4Gal beta-binding bacteria thus appeared to be more potent inducers of inflammation than other strains. Since inflammation may lead to tissue damage we examined the relationship of infection with Gal alpha 1-greater than 4Gal beta-positive bacteria to renal scarring. The frequency of renal scarring was 5% in boys with Gal alpha 1-greater than 4Gal beta-positive and 40% in boys with Gal alpha 1-greater than 4Gal beta-negative E. coli. Bacterial binding to Gal alpha 1-greater than 4Gal beta can be detected with a commercially available test reagent. This reagent can thus be used as an effective predictor of risk for renal scarring. Interleukin-6 (IL-6) is a pyrogen and inducer of the acute phase reactants. It was shown to be produced locally in the urinary tract, in response to UTI, and to spread systemically. Mucosal challenge with dead bacteria was sufficient to induce the IL-6 response. Circulating IL-6, and/or IL-1 and tumor necrosis factor could explain the fever, as well as increased ESR and CRP found in association with acute symptomatic UTI.

Direct evidence that the FimH protein is the mannose-specific adhesin of Escherichia coli type 1 fimbriae

Type 1 fimbriae of Escherichia coli are surface organelles which mediate binding to D-mannose-containing structures. By direct binding of FimH to D-mannose attached to a carrier protein, we demonstrated that this protein was uniquely responsible for the receptor specificity. Furthermore, we show by receptor immunoelectron microscopy that the FimH protein is located laterally in the structure of the type 1 fimbriae.

Type I pili mediate gram-negative bacterial adherence to intact tracheal epithelium

We have investigated the role of pili in mediating gram-negative bacterial adherence to an intact tracheal epithelium. Type 1 pili, but not P or Pseudomonas pili, markedly increased bacterial adherence. The adherence-promoting effect of Type 1 pili was due to the mannose-binding Type 1 pili adhesin, as both alpha-methyl mannoside and concanavalin A blocked adherence of Type 1 piliated bacteria. The Type 1 pili-binding site on tracheal epithelium appears to be a mannose-containing glycoprotein. Clearance of Type 1 piliated bacteria from the lung parenchyma was assessed by depositing the bacteria into a lobe; no difference in clearance rates between Type 1 and nonpiliated bacteria was present. Type 1 pili may enhance the ability of gram-negative bacteria to adhere to and colonize the lower respiratory tract.

Characteristics of binding of Escherichia coli serotype O157:H7 strain CL-49 to purified intestinal mucin

Purified rat intestinal mucin was used as a model mucin to study the binding of Escherichia coli serotype O157:H7, a human pathogen associated with outbreaks of hemorrhagic colitis and hemolytic uremic syndrome. Of six O157:H7 strains, only one strain (designated CL-49) bound to rat (and other) intestinal mucins by a specific and saturable process. Binding was observed only after the bacteria were serially passaged to promote the expression of type 1 pili (fimbriae). Several other type 1-piliated E. coli strains, however, did not bind to mucin. Binding of E. coli CL-49 was inhibited by D-mannose and short oligomannosyl derivatives, particularly Man-alpha-1,3-Man, Man-alpha-1,2-Man, and Man-alpha-1,3-Man-beta-1,4-N-acetylglucosamine. Other inhibitors of binding included p-nitrophenol (10(-4) M), heating at 60 degrees C (to remove pili), an antibody to type 1 pili, and purified type 1 pili of E. coli CL-49 used as hapten inhibitors. A comparison of the hydrophobicity of piliated E. coli CL-49 with other type 1-piliated E. coli strains indicated that the former strain was much more hydrophobic than the others. These findings indicate that highly purified intestinal mucins possess specific mannosyl receptor sites for bacterial type 1 pili on E. coli CL-49, but that strong hydrophobic interactions between the mucin and the pili stabilize the mannose-dependent binding process. We speculate that the mucin receptors for type 1 pili reside in oligosaccharides of the 118-kilodalton "link" glycopeptide, since this is the only mucin component known to contain mannose.

Binding of Escherichia coli S fimbriae to cultured human endothelial cells

The binding of Escherichia coli adhesins to human umbilical vein endothelial cells was studied by a cell monolayer enzyme-linked immunosorbent assay. S fimbriae displayed a concentration-dependent and saturable binding to the endothelial cells which was mediated by their sialylgalactoside-specific lectin activity. P fimbriae exhibited only low binding, and type 1 fimbriae exhibited no binding to these cells.

New type of adhesive specificity revealed by oligosaccharide probes in Escherichia coli from patients with urinary tract infection

A series of oligosaccharides derived from glycoproteins or from human milk were coupled to lipid and used as probes of the binding specificities of Escherichia coli isolated from patients with urinary tract infections. Selective binding to the glycoprotein oligosaccharide probes rich in mannose residues (high-mannose type) was demonstrated with fimbriated E coli that give mannose-inhibitable haemagglutination. This observation is in accordance with predictions from inhibition studies. Binding studies with the human milk oligosaccharide probes, which resemble structures found on host-cell membranes, revealed adhesive specificity unrelated to the presence of fimbriae. This new type of host oligosaccharide receptor is affected by the presence of the blood group genetic markers. It involves the disaccharide sequence linked to the membrane-associated lipid moiety of host-cell glycolipids, and may have a role in initiation of infection on damaged epithelial cell membranes.

Identification of factors in human urine that inhibit the binding of Escherichia coli adhesins

Earlier studies on the binding of Escherichia coli adhesins to the human urinary tract have indicated that the ability to recognize binding sites on the urinary tract epithelial cells is not a characteristic for P fimbriae only, but is also shared by some other adhesins that are not associated with pyelonephritis, especially S fimbriae. In the present study we have investigated whether human urine contains inhibitors of the binding of E. coli adhesins. Normal human urine was found to inhibit hemagglutination by S and type 1 fimbriae but not P fimbriae. The major inhibitor of S fimbriae in normal urine was identified as Tamm-Horsfall glycoprotein, and the interaction with S fimbriae is probably mediated by its sialyloligosaccharide chains. No significant variation was observed in the inhibitory effect of T-H glycoprotein preparations originating from different individuals. In contrast to S fimbriae, the major inhibitors of type 1 fimbriae in urine were identified as low-molecular-weight compounds. Gel filtration and ion-exchange chromatography and alpha-mannosidase treatment indicated that they were neutral alpha-mannosides, probably manno-oligosaccharides with three to five saccharides. Studies of urine samples collected from several individuals indicated the common occurrence of these inhibitory alpha-mannosides. Type 1 fimbriae bound to immobilized T-H glycoprotein, but, unlike S fimbriae, their binding was poorly inhibited by soluble T-H glycoprotein. Some urine samples were also found to contain low-molecular-weight inhibitors for the O75X adhesin of E. coli. These results emphasize that to function as a virulence factor in human urinary tract infections, an adhesin must evidently recognize such receptor structures at the infection sites that are not excreted in soluble form in urine. This prerequisite is filled by P fimbriae but not by type 1 or S fimbriae.

Pathogenicity and virulence: another view

The concepts of pathogenicity and virulence have governed our perception of microbial harmfulness since the time of Pasteur and Koch. These concepts resulted in the recognition and identification of numerous etiological agents and provided natural and synthetic agents effective in therapy and prevention of diseases. However, Koch's postulates--the premier product of this view--place the onus of harmfulness solely on the microbial world. Our recent experiences with polymicrobic and nosocomial infections, legionellosis, and acquired immunodeficiency syndrome point to the host as the major determinant of disease. The principles of parasitism, enunciated by Theobold Smith, approximate more accurately the disturbances of the host-parasite equilibrium we designate as infection. Many complex attributes of microbial anatomy and physiology have been obscured by our dependency on the pure-culture technique. For example, bacterial attachment organelles and the production of exopolysaccharides enable microorganisms to interact with mammalian glycocalyces and specific receptors. In addition, selection, through the use of therapeutic agents, aids in the progression of environmental organisms to members of the intimate human biosphere, with the potential to complicate the recovery of patients. These factors emphasize further the pivotal significance of host reactions in infections. Parasitism, in its negative aspects, explains the emergence of "new" infections that involve harm to more than host organs and cells: we may encounter subtler infections that reveal parasitic and host cell nucleic acid interactions in a form of genomic parasitism.

Differences in adhesiveness among type 1 fimbriate strains of Enterobacteriaceae revealed by an in vitro HEp2 cell adhesion model

Ten type 1 fimbriate strains of Enterobacteriaceae were examined in an in vitro adhesion assay with HEp2 epithelial cells. The range of HEp2 cell adhesiveness, which was characteristic for each strain, was affected by motility, type 1 fimbriation and production of mannose sensitive haemagglutinin. Nevertheless, not all type 1 fimbriate strains adhered well in this model. The findings are discussed with regard to the possibility that different type 1 fimbriate enterobacteria, though all are mannose sensitive, recognize different mannose-containing receptors present or available on the surfaces of the HEp2 cells.

Identification of two new hemagglutinins of Escherichia coli, N-acetyl-D-glucosamine-specific fimbriae and a blood group M-specific agglutinin, by cloning the corresponding genes in Escherichia coli K-12

Genes encoding the Escherichia coli IH11165 hemagglutinins with specificity for terminal N-acetyl-D-glucosamine and blood group M antigen, respectively, were cloned by a cosmid cloning procedure. A 22-kilobase-pair subclone expressed both hemagglutination specificities in the nonhemagglutinating E. coli HB101 recipient strain. Derivatives obtained by insertion and deletion mutagenesis expressed either one of the two hemagglutination specificities. Both agglutinins were purified; the agglutinin recognizing terminal N-acetyl-D-glucosamine was associated with a new type of fimbria (G fimbria) with an apparent subunit molecular mass of 19.5 kilodaltons, whereas the blood group M agglutinin (M agglutinin) was nonfimbrial and had an apparent subunit mass of 21 kilodaltons.

Inhibitory effect of substituted aromatic hydrocarbons on adherence of Escherichia coli to human epithelial cells

Adherence of Escherichia coli to epithelial cells is postulated to be a necessary step in the pathogenesis of urinary tract infections. Investigations have focused on the role of carbohydrates in adherence because of the ability of mannose to inhibit adherence; however, there have been several reports of an additional hydrophobic receptor. Here we describe the inhibition of adherence mediated by substituted aromatic hydrocarbon compounds and the relationship of our findings to support the role of a postulated hydrophobic-binding domain.

Oligomannoside-type glycopeptides inhibiting adhesion of Escherichia coli strains mediated by type 1 pili: preparation of potent inhibitors from plant glycoproteins

Various structurally defined glycopeptides of natural origin were tested as inhibitors of guinea pig erythrocyte agglutination by enteropathogenic Escherichia coli strains expressing type 1 pili. Besides hybrid-type glycoasparagines from ovalbumin which were not active, large oligomannoside-type carbohydrate chains from legume storage glycoproteins moderately inhibited hemagglutinations, whereas the short oligomannoside-type glycoasparagine from ovalbumin Man alpha(1----6) [Man alpha(1----3)]Man alpha(1----6)[Man alpha(1----3)] Man beta(1----4)GlcNAc beta(1----4)GlcNAc beta(1----N)Asn exhibited a potent activity. These results strongly suggested that the nonsubstitution of the alpha(1----3)-linked mannosyl residue from the N-linked glycopeptide core structure is the key determinant in the minimal structural requirement specific to this fimbrial lectin. Such Man5GlcNAc2-containing glycopeptides were obtained from larger N-linked carbohydrate chains, occurring abundantly in natural sources. The ability of jack bean alpha-mannosidase to cleave the alpha(1----2)-linked mannoses more rapidly than the others allowed the controlled digestion of large oligomannoside-type glycopeptides from legume storage glycoproteins. Such shortened glycopeptides of plant origin were prepared which strongly inhibited guinea pig erythrocyte agglutinations as well as bacterial adhesion on human buccal cells, thus confirming their similarity (if not identity) with the receptor of type 1 pili on mammalian cells. The importance of this preparation of a receptorlike compound that inhibits bacterial adhesion with regard to the research on the role of type 1 pili in E. coli pathogenicity is discussed.

Monoclonal antibodies against the nonhemagglutinating fimbrial antigen 1C (pseudotype 1) of Escherichia coli

Hybridoma-derived monoclonal antibodies were produced with fimbrial preparations from Escherichia coli 20025 (04:K12:H-) with fimbrial (F) antigens 1C, 13, one related to 12, and one preliminarily termed y and from E. coli 2980 (018ac:K5:H-) with F antigens 1C and 8. Two clones of subclonal hybrid cells were studied which produced monoclonal antibodies (mc-20025-F2b, immunoglobulin G2b [IgG2b]; mc-2980-F2, IgG1) that were reactive with E. coli 20025, 2980, and a number of additional strains which exhibited the F1C antigen. Results of enzyme-linked immunosorbent assay and Western blot analysis indicated that the antibodies had F1C specificity, and competitive enzyme-linked immunosorbent assay with 125I-labeled antibodies showed that they recognized different epitopes on the fimbrial subunit. Neither of the antibodies agglutinated F1C-fimbriated E. coli but bound to the bacteria. There was no binding to E. coli without F1C fimbriae.

Role of fibronectin in attachment of Streptococcus pyogenes and Escherichia coli to human cell lines and isolated oral epithelial cells

We studied the binding of cells of Streptococcus pyogenes and mannose-sensitive Escherichia coli to human fibroblast cell lines and isolated buccal epithelial cells in relation to the cell-associated endogenous or exogenous fibronectin of the host cells. The degree of bacterial binding to cell lines correlated directly with the content of endogenous fibronectin on the surface of the cultured cells, although the correlation was better with S. pyogenes than with E. coli. The addition of exogenous plasma fibronectin to the cell lines or oral epithelial cells enhanced binding of S. pyogenes but suppressed binding of mannose-sensitive E. coli. These findings are consistent with the notion that exogenously acquired fibronectin on the surface of host cells modulates bacterial adherence by providing attachment sites for certain pathogens, such as S. pyogenes, and by blocking receptors for others, such as mannose-sensitive E. coli.

Effect of monosaccharides and ethyleneglycol on the interaction between Escherichia coli bacteria and Octyl-Sepharose

Combined effects of monosaccharides and reduced surface tension of the medium were studied in relation to the hydrophobic binding of Escherichia coli bacteria, with and without mannose-specific structures. Hydrophobic binding was analyzed by hydrophobic interaction chromatography on Octyl-Sepharose. The results showed that ethyleneglycol, as well as mannose, reduced the hydrophobic interaction of the bacteria with mannose-specific structures. This effect was potentiated by combining ethyleneglycol and mannose. No other monosaccharides tested (galactose and fucose) had any effect on the hydrophobic interaction of bacteria with mannose-specific structures. These results further strengthen the hypothesis that the mannose-specific interaction of Escherichia coli bacteria is, at least in part, mediated by hydrophobic forces.

Isolation and structural characterization of the equine erythrocyte receptor for enterotoxigenic Escherichia coli K99 fimbrial adhesin

The erythrocyte receptor for Escherichia coli K99 fimbrial adhesin was isolated from equine erythrocytes and characterized as Neu5Gc-alpha(2----3)-Galp-beta(1----4)-GLcp-beta(1----1)-Ceramide. This glycolipid acted as the receptor for K99 by four different experimental approaches: inhibition of equine erythrocyte hemagglutination by preincubation of K99-positive bacteria or purified K99 fimbriae with the isolated glycolipid; inhibition of attachment of K99-positive bacteria to porcine intestinal epithelial cells in the presence of the isolated glycolipid; induction of binding of K99-positive bacteria or purified K99 fimbriae to normally unreactive guinea pig erythrocytes by coating these cells with the isolated glycolipid; and isolation of the receptor by affinity chromatography with K99 coupled to CNBr-activated Sepharose 4B, indicating a strong interaction between K99 and the isolated glycolipid.

Carbohydrate-binding sites of the mannose-specific fimbrial lectins of enterobacteria

The combining sites of type 1 fimbrial lectins of various species of enterobacteria were studied by measuring the inhibitory activity of linear and branched oligosaccharides and several glycosides of D-mannose on the agglutination of yeast cells by the organisms. The results showed that all five strains of Escherichia coli tested possessed an elongated combining site best fitting a trisaccharide and including a hydrophobic region. Similar results were obtained with Klebsiella pneumoniae. Within the Salmonella genus, the combining sites of the six species tested were similar, but all differed significantly from those of the E. coli strains. The combining sites of Enterobacter cloacae and Enterobacter agglomerans were different from each other and from those of Salmonella sp. and E. coli. The results suggest that although classified under the general term "mannose-specific," bacterial lectins in the form of type 1 fimbriae on different genera exhibit differences in sugar specificities.

Antiadhesive properties of a quaternary structure-specific hybridoma antibody against type 1 fimbriae of Escherichia coli

The relationship between the structure and biological function of type 1 fimbriae of Escherichia coli was investigated using a set of monoclonal antibodies directed against conformation-specific antigenic determinants. Of three monoclonal antibodies tested, only one (clone CD3) prevented adhesion of the vaccine strain to epithelial cells or guinea pig erythrocytes. The antibody produced by CD3, but not that produced by the other two hybridoma clones (AA8 and GG1), precipitated isolated fimbriae by double diffusion in agar gel and was shown to bind in a highly discrete, periodic manner along the length of each of the fimbriae by immunoelectron microscopy. Immunoelectroblots of type 1 fimbrial subunits and polymers electrophoresed in SDS-gels indicated that the antibodies in AA8 and GG1 reacted only with fimbrial monomers (mol wt 17,000), whereas the antibody in CD3 reacted only with polymers of mol wt 102,000 (hexamers) or higher. ELISA inhibition assays demonstrated that dissociated fimbrial subunits lost their reactivity with antibody CD3 but gained reactivity with antibodies AA8 and GG1. Conversely, when allowed to reassemble in vitro in the presence of 5 mM MgCl2, the reassembled fimbriae lost their reactivity with antibodies AA8 and GG1 but regained reactivity with antibody CD3. These results demonstrated that certain antigenic epitopes are dependent on quaternary structural determinants, whereas others are independent of quaternary fimbrial structure and also are inaccessible for antibody binding in fimbriae once they have been assembled. These monoclonal antibodies should prove useful in studies of the structural determinants of the biological function of type 1 fimbriae as well as in studies of fimbrial synthesis, transport, and assembly.

Carbohydrate specificity of the surface lectins of Escherichia coli, Klebsiella pneumoniae, and Salmonella typhimurium

A large number of linear and branched oligosaccharides and several glycosides of D-mannose were tested for their inhibitory activity on the agglutination of yeast cells or guinea pig erythrocytes by three D-mannose-specific enteric bacteria possessing type 1 fimbriae. With Escherichia coli 346, the best inhibitors found are the alpha glycosides of the branched oligosaccharides alpha-D-Manp-(1 leads to 3)-[alpha-D-Manp-(1 leads to 6)]-alpha-D-Manp-(1 leads to 6)-alpha-D-Manp-(1 leads to 3)-D-Manp and alpha-D-Manp-(1 leads to 3)-[alpha-D-Manp-(1 leads to 6)]-alpha-D-Manp- (1 leads to 6)-[alpha-D-Manp-(1 leads to 2)-alpha-D-Manp-(1 leads to 3) ]-D-Manp and the trisaccharide alpha-D-Manp-(1 leads to 3)-beta-D-Manp-(1 leads to 4)-D-GlcNAc, all of which are 21-30 times more inhibitory than methyl alpha-D-mannopyranoside. The aromatic glycoside p-nitrophenyl alpha-D-mannopyranoside was also a strong inhibitor (30 times more inhibitory than methyl alpha-D-mannopyranoside), whereas the corresponding beta-D-glycoside was only a weak inhibitor (approximately as methyl alpha-D-mannopyranoside). A nearly identical pattern of inhibitory activity was observed with the fimbriae. This suggests that the combining site of the E. coli fimbrial lectin is in the form of an extended pocket on the surface of the lectin corresponding to the size of a trisaccharide and fitting best the structure alpha-D-Manp-(1 leads to 3)-beta-D-Manp-(1 leads to 4)-D-GlcNAc. Since p-nitrophenyl alpha-D-mannopyranoside is a strong inhibitor, the existence of a hydrophobic region in the combining site or close to it was assumed. The combining site of the Klebsiella pneumoniae fimbrial lectin is probably similar to that of E. coli, but that of the Salmonella typhimurium fimbrial lectin differs considerably. It appears that the combining sites of the three bacterial lectins tested exhibit preference for structures found in N-glycosylic oligomannoside units of mammalian cell surface glycoproteins.