Purification of the Escherichia coli type 1 pilin and minor pilus proteins and partial characterization of the adhesin protein

Strain and host-cell dependent role of type-1 fimbriae in the adherence phenotype of super-shed Escherichia coli O157:H7

Super-shed (SS) Escherichia coli O157 (E. coli O157) demonstrate a strong, aggregative, locus of enterocyte effacement (LEE)-independent adherence phenotype on bovine recto-anal junction squamous epithelial (RSE) cells, and harbor polymorphisms in non-LEE-adherence-related loci, including in the type 1 fimbriae operon. To elucidate the role of type 1 fimbriae in strain- and host-specific adherence, we evaluated the entire Fim operon (FimB-H) and its adhesion (FimH) deletion mutants in four E. coli O157 strains, SS17, SS52, SS77 and EDL933, and evaluated the adherence phenotype in bovine RSE and human HEp-2 adherence assays. Consistent with the prevailing dogma that fimH expression is genetically switched off in E. coli O157, the ΔfimHSS52, ΔfimB-HSS52, ΔfimB-HSS17, and ΔfimHSS77 mutants remained unchanged in adherence phenotype to RSE cells. In contrast, the ΔfimHSS17 and ΔfimB-HSS77 mutants changed from a wild-type strong and aggregative, to a moderate and diffuse adherence phenotype, while both ΔfimHEDL933 and ΔfimB-HEDL933 mutants demonstrated enhanced binding to RSE cells (p < 0.05). Additionally, both ΔfimHSS17 and ΔfimHEDL933 were non-adherent to HEp-2 cells (p < 0.05). Complementation of the mutant strains with their respective wild-type genes restored parental phenotypes. Microscopy revealed that the SS17 and EDL933 strains indeed carry type 1 fimbriae-like structures shorter than those seen in uropathogenic E. coli. Taken together, these results provide compelling evidence for a strain and host cell type-dependent role of fimH and the fim operon in E. coli O157 adherence that needs to be further evaluated.

Developments in Mannose-Based Treatments for Uropathogenic Escherichia coli-Induced Urinary Tract Infections

During their lifetime almost half of women will experience a symptomatic urinary tract infection (UTI) with a further half experiencing a relapse within six months. Currently UTIs are treated with antibiotics, but increasing antibiotic resistance rates highlight the need for new treatments. Uropathogenic Escherichia coli (UPEC) is responsible for the majority of symptomatic UTI cases and thus has become a key pathological target. Adhesion of type one pilus subunit FimH at the surface of UPEC strains to mannose-saturated oligosaccharides located on the urothelium is critical to pathogenesis. Since the identification of FimH as a therapeutic target in the late 1980s, a substantial body of research has been generated focusing on the development of FimH-targeting mannose-based anti-adhesion therapies. In this review we will discuss the design of different classes of these mannose-based compounds and their utility and potential as UPEC therapeutics.

Highly conserved type 1 pili promote enterotoxigenic E. coli pathogen-host interactions

Enterotoxigenic Escherichia coli (ETEC), defined by their elaboration of heat-labile (LT) and/or heat-stable (ST) enterotoxins, are a common cause of diarrheal illness in developing countries. Efficient delivery of these toxins requires ETEC to engage target host enterocytes. This engagement is accomplished using a variety of pathovar-specific and conserved E. coli adhesin molecules as well as plasmid encoded colonization factors. Some of these adhesins undergo significant transcriptional modulation as ETEC encounter intestinal epithelia, perhaps suggesting that they cooperatively facilitate interaction with the host. Among genes significantly upregulated on cell contact are those encoding type 1 pili. We therefore investigated the role played by these pili in facilitating ETEC adhesion, and toxin delivery to model intestinal epithelia. We demonstrate that type 1 pili, encoded in the E. coli core genome, play an essential role in ETEC virulence, acting in concert with plasmid-encoded pathovar specific colonization factor (CF) fimbriae to promote optimal bacterial adhesion to cultured intestinal epithelium (CIE) and to epithelial monolayers differentiated from human small intestinal stem cells. Type 1 pili are tipped with the FimH adhesin which recognizes mannose with stereochemical specificity. Thus, enhanced production of highly mannosylated proteins on intestinal epithelia promoted FimH-mediated ETEC adhesion, while conversely, interruption of FimH lectin-epithelial interactions with soluble mannose, anti-FimH antibodies or mutagenesis of fimH effectively blocked ETEC adhesion. Moreover, fimH mutants were significantly impaired in delivery of both heat-stable and heat-labile toxins to the target epithelial cells in vitro, and these mutants were substantially less virulent in rabbit ileal loop assays, a classical model of ETEC pathogenesis. Collectively, our data suggest that these highly conserved pili play an essential role in virulence of these diverse pathogens.

Fur-dependent MrkHI regulation of type 3 fimbriae in Klebsiella pneumoniae CG43

Type 3 fimbriae play a crucial role in Klebsiella pneumoniae biofilm formation, but the mechanism of the regulation of the type 3 fimbrial operon is largely unknown. In K. pneumoniae CG43, three regulatory genes, mrkH, mrkI and mrkJ, are located downstream of the type 3 fimbrial genes mrkABCDF. The production of the major pilin MrkA is abolished by the deletion of mrkH or mrkI but slightly increased by the deletion of mrkJ. Additionally, quantitative RT-PCR and a promoter-reporter assay of mrkHI verified that the transcription of mrkHI was activated by MrkI, suggesting autoactivation of mrkHI transcription. In addition, sequence analysis of the mrkH promoter region revealed a putative ferric uptake regulator (Fur) box. Deletion of fur decreased the transcription of mrkH, mrkI and mrkA. The expression of type 3 fimbriae and bacterial biofilm formation were also reduced by the deletion of fur. Moreover, a recombinant Fur was found to be able to bind both promoters, with higher affinity for P(mrkH) than P(mrkA), implying that Fur controls type 3 fimbriae expression via MrkHI. We also proved that iron availability can influence type 3 fimbriae activity.

Adhesive threads of extraintestinal pathogenic Escherichia coli

The ability to adhere to host surfaces is by far the most vital step in the successful colonization by microbial pathogens. Colonization begins with the attachment of the bacterium to receptors expressed by cells forming the lining of the mucosa. Long hair like extracellular appendages called fimbriae, produced by most Gram-negative pathogens, mediate specific attachment to the epithelial cell surface. Associated with the fimbriae is a protein called an adhesin, which directs high-affinity binding to specific cell surface components. In the last couple of years, an enormous amount of research has been undertaken that deals with understanding how bacterial pathogens adhere to host cells. E. coli in all probability is one of the best studied free-living organisms. A group of E. coli called Extraintestinal pathogenic E. coli (ExPEC) including both human and animal pathogens like Uropathogenic E. coli (UPEC), Newborn meningitic E. coli (NMEC) and Avian pathogenic E. coli (APEC), have been found to harbour many fimbriae including Type 1 fimbriae, P fimbriae, curli fibres, S fimbriae, F1C fimbriae, Dr fimbriae, afimbrial adhesins, temperature-sensitive haemagglutinin and many novel adhesin gene clusters that have not yet been characterized. Each of these adhesins is unique due to the recognition of an adhesin-specific receptor, though as a group these adhesins share common genomic organization. A newly identified putative adhesin temporarily termed ExPEC Adhesin I, encoded by gene yqi, has been recently found to play a significant role in the pathogenesis of APEC infection, thus making it an interesting candidate for future research. The aim of this review is to describe the role of ExPEC adhesins during extraintestinal infections known till date, and to suggest the idea of investigating their potential role in the colonization of the host gut which is said to be a reservoir for ExPEC.

Catch-bond mechanism of force-enhanced adhesion: counterintuitive, elusive, but ... widespread?

Catch bonds are bonds between a ligand and its receptor that are enhanced by mechanical force pulling the ligand-receptor complex apart. To date, catch-bond formation has been documented for the most common Escherichia coli adhesin, FimH, and for P-/L-selectins, universally expressed by leukocytes, platelets, and blood vessel walls. One compelling explanation for catch bonds is that force-induced structural alterations in the receptor protein are allosterically linked to a high-affinity conformation of its ligand-binding pocket. Catch-bond properties are likely to be widespread among adhesive proteins, thus calling for a detailed understanding of their underlying mechanisms and physiological significance.

Uropathogenic Escherichia coli outer membrane antigens expressed during urinary tract infection

Uncomplicated urinary tract infection (UTI) caused by uropathogenic Escherichia coli (UPEC) represents a prevalent and potentially severe infectious disease. In this study, we describe the application of an immunoproteomics approach to vaccine development that has been used successfully to identify vaccine targets in other pathogenic bacteria. Outer membranes were isolated from pyelonephritis strain E. coli CFT073 cultured under conditions that mimic the urinary tract environment, including iron limitation, osmotic stress, human urine, and exposure to uroepithelial cells. To identify antigens that elicit a humoral response during experimental UTI, outer membrane proteins were separated by two-dimensional gel electrophoresis and probed using pooled antisera from 20 CBA/J mice chronically infected with E. coli CFT073. In total, 23 outer membrane antigens, including a novel iron compound receptor, reacted with the antisera and were identified by mass spectrometry. These antigens also included proteins with known roles in UPEC pathogenesis, such as ChuA, IroN, IreA, Iha, IutA, and FliC. These data demonstrate that an antibody response is directed against these virulence-associated factors during UTI. We also show that the genes encoding ChuA, IroN, hypothetical protein c2482, and IutA are significantly more prevalent (P < 0.01) among UPEC strains than among fecal-commensal E. coli isolates. Thus, we suggest that the conserved outer membrane antigens identified in this study could be rational candidates for a UTI vaccine designed to elicit protective immunity against UPEC infection.

Secretory IgA and mucin-mediated biofilm formation by environmental strains of Escherichia coli: role of type 1 pili

Recent studies suggest the importance of secretory IgA (SIgA) and mucin in the mediation of biofilm formation by commensal bacteria within the mammalian gut. Studies using a variety of strains of Escherichia coli have indicated that the interaction between E. coli and SIgA is dependent on the type 1 pilus. In this study, the importance of the pilus in SIgA-mediated biofilm formation by a laboratory strain (MG1655) and environmental (fecal) strains of E. coli was evaluated. Transient expression of the type 1 pilus by the laboratory strain of E. coli failed to facilitate SIgA-mediated biofilm formation, whereas constitutive expression of the type 1 pilus by the laboratory strain was sufficient. In contrast, transient expression of the type 1 pilus was sufficient to facilitate SIgA-mediated biofilm formation by environmental isolates. The "threshold" for mucin-mediated biofilm formation appeared to be lower than that for SIgA-mediated biofilm formation, perhaps reflecting disparate roles of mucin and SIgA in mediating biofilm formation in the gut. These studies also provide the first procedures for the growth of bacterial biofilms on live epithelial cells in vitro, an important development that may facilitate future studies on the effects of bacterial biofilms on epithelial cells.

Major structural proteins of type 1 and type 3 Klebsiella fimbriae are effective protein carriers and immunogens in conjugates as revealed from their immunochemical characterization

Fimbriae are filamentous structures present on the cell surface of many bacteria, including genus Klebsiella. The use of fimbriae as protein carriers in conjugates may allow to formulate effective multivalent vaccines and suitable diagnostics. However, the evidences have been reported that fimbriae may enhance the inflammatory response. This prompted us to examine the degree of cytokine induction by the type 1 and type 3 Klebsiella fimbriae and their conjugates. Fimbriae were assessed as carrier proteins for Escherichia coli K12 endotoxin core oligosaccharide. MALDI-MS revealed the molecular mass of fimbrial monomer major protein, which was 15,847 Da for type 1 and 18,574 Da for type 3 fimbriae of Klebsiella. These two types of fimbriae were moderate inductors of IL-6 and interferon and almost inactive with regard to the stimulation of TNF when tested in human whole blood assay. Coupling of fimbriae with E. coli K12 core oligosaccharide gave immunogenic conjugates with respect to a saccharide ligand and protein carrier, although only 10% of the pilin monomers possessed the attached oligosaccharide. Rabbit antiserum reacted with a broad spectrum of lipopolysaccharides, as measured by ELISA and immunoblotting assays. The antibodies against glycoconjugates were bactericidal for the wild, S-type bacteria of some species. Regarding the induction of cytokines by conjugates only the TNF level was noticeably elevated. These results prompt for the practical use of fimbriae, as effective protein carriers for conjugates to obtain broad-spectrum antisera for diagnostic applications.

Resistance of broiler chickens to Escherichia coli respiratory tract infection induced by passively transferred egg-yolk antibodies

Egg-yolk antibodies induced by immunizing hens with selected Escherichia coli antigens were evaluated for their ability to protect broiler chickens against respiratory/septicemic disease caused by avian pathogenic E. coli (APEC). Seven groups of broiler breeder hens were vaccinated three times, 1 week apart with live E. coli, killed E. coli, E. coli antigens [lipopolysaccharide (LPS), type 1 pilus adhesin (FimH), P pilus adhesin (PapG), aerobactin outer membrane receptor (IutA)] or phosphate buffered saline (PBS). An O78 APEC strain was used for preparation of all the antigens. Egg yolk immunoglobulins (IgY) were purified from eggs of each group and antibody activity in serum and purified IgY was determined by enzyme-linked immunosorbent assay (ELISA). IgY (100mg) was injected intramuscularly into 11-day-old broiler chickens, which were challenged 3 days later with homologous (O78) or heterologous (O1 or O2) E. coli by the intra-air sac route. Mortality was recorded and surviving chickens were euthanized 1 week after the challenge and examined for macroscopic lesions. Passive antibodies against all antigens except FimH were protective (90-100%) against the homologous challenge, but only anti-PapG and anti-IutA were effective against heterologous challenge. Anti-PapG IgY provided the greatest protection against the three serogroups of E. coli used for challenge. Hence vaccination of broiler breeders to induce anti-PapG and anti-IutA antibodies may provide passive protection of progeny chicks against respiratory/septicemic disease caused by APEC.

Immunoglobulin-mediated agglutination of and biofilm formation by Escherichia coli K-12 require the type 1 pilus fiber

The binding of human secretory immunoglobulin A (SIgA), the primary immunoglobulin in the gut, to Escherichia coli is thought to be dependent on type 1 pili. Type 1 pili are filamentous bacterial surface attachment organelles comprised principally of a single protein, the product of the fimA gene. A minor component of the pilus fiber (the product of the fimH gene, termed the adhesin) mediates attachment to a variety of host cell molecules in a mannose inhibitable interaction that has been extensively described. We found that the aggregation of E. coli K-12 by human secretory IgA (SIgA) was dependent on the presence of the pilus fiber, even in the absence of the mannose specific adhesin or in the presence of 25 mM alpha-CH(3)Man. The presence of pilus without adhesin also facilitated SIgA-mediated biofilm formation on polystyrene, although biofilm formation was stronger in the presence of the adhesin. IgM also mediated aggregation and biofilm formation in a manner dependent on pili with or without adhesin. These findings indicate that the pilus fiber, even in the absence of the adhesin, may play a role in biologically important processes. Under conditions in which E. coli was agglutinated by SIgA, the binding of SIgA to E. coli was not increased by the presence of the pili, with or without adhesin. This observation suggests that the pili, with or without adhesin, affect factors such as cell surface rigidity or electrostatic repulsion, which can affect agglutination but which do not necessarily determine the level of bound immunoglobulin.

Major surface protein 2 of Anaplasma phagocytophilum facilitates adherence to granulocytes

Anaplasma phagocytophilum is an obligate intracellular bacterium that infects myeloid cells in the mammalian host. Msp2 (p44) is the major immunodominant outer-membrane protein of these bacteria. We hypothesized that Msp2 acts as an adhesin for A. phagocytophilum entry into granulocytes. This potential role was investigated by blocking binding with Msp2 monoclonal antibodies and by antagonizing binding and propagation with recombinant Msp2 (rMsp2) in vitro. With HL-60 cells, fresh human peripheral blood neutrophils, and a cell line devoid of the fucosylated platelet selectin glycoprotein ligand 1 (PSGL-1) receptor for A. phagocytophilum or one that was transfected to express this ligand, Msp2 monoclonal antibody and rMsp2 used as the antagonist caused concentration-dependent reductions in bacterial adhesion (P < 0.007 and P < 0.02, respectively) and propagation (P < 0.05 and P < 0.001), although inhibition of adhesion or propagation was moderate and incomplete. Likewise, rMsp2 bound to surfaces of the transfected cell at a level similar to that of extracellular A. phagocytophilum and significantly (P < 0.05) beyond that of nontransfected cells. Moreover, a dose-dependent reduction (P < 0.019) in PSGL-1 monoclonal antibody binding to HL-60 cells was elicited with rMsp2. We conclude that Msp2s of A. phagocytophilum are involved in bacterial adhesion to ligands on host myeloid cells before intracellular infection.

Bacterial adhesion to target cells enhanced by shear force

Surface adhesion of bacteria generally occurs in the presence of shear stress, and the lifetime of receptor bonds is expected to be shortened in the presence of external force. However, by using Escherichia coli expressing the lectin-like adhesin FimH and guinea pig erythrocytes in flow chamber experiments, we show that bacterial attachment to target cells switches from loose to firm upon a 10-fold increase in shear stress applied. Steered molecular dynamics simulations of tertiary structure of the FimH receptor binding domain and subsequent site-directed mutagenesis studies indicate that shear-enhancement of the FimH-receptor interactions involves extension of the interdomain linker chain under mechanical force. The ability of FimH to function as a force sensor provides a molecular mechanism for discrimination between surface-exposed and soluble receptor molecules.

Genetic characterization of Escherichia coli type 1 pilus adhesin mutants and identification of a novel binding phenotype

Five Escherichia coli type 1 pilus mutants that had point mutations in fimH, the gene encoding the type 1 pilus adhesin FimH, were characterized. FimH is a minor component of type 1 pili that is required for the pili to bind and agglutinate guinea pig erythrocytes in a mannose-inhibitable manner. Point mutations were located by DNA sequencing and deletion mapping. All mutations mapped within the signal sequence or in the first 28% of the predicted mature protein. All mutations were missense mutations except for one, a frameshift lesion that was predicted to cause the loss of approximately 60% of the mature FimH protein. Bacterial agglutination tests with polyclonal antiserum raised to a LacZ-FimH fusion protein failed to confirm that parental amounts of FimH cross-reacting material were expressed in four of the five mutants. The remaining mutant, a temperature-sensitive (ts) fimH mutant that agglutinated guinea pig erythrocytes after growth at 31 degrees C but not at 42 degrees C, reacted with antiserum at both temperatures in a manner similar to the parent. Consequently, this mutant was chosen for further study. Temperature shift experiments revealed that new FimH biosynthesis was required for the phenotypic change. Guinea pig erythrocyte and mouse macrophage binding experiments using the ts mutant grown at the restrictive and permissive temperatures revealed that whereas erythrocyte binding was reduced to a level comparable to that of a fimH insertion mutant at the restrictive temperature, mouse peritoneal macrophages were bound with parental efficiency at both the permissive and restrictive temperatures. Also, macrophage binding by the ts mutant was insensitive to mannose inhibition after growth at 42 degrees C but sensitive after growth at 31 degrees C. The ts mutant thus binds macrophages with one receptor specificity at 31 degrees C and another at 42 degrees C.

Functional flexibility of the FimH adhesin: insights from a random mutant library

Type 1 fimbriae are surface organelles of Escherichia coli which mediate D-mannose-sensitive binding to different host surfaces. This binding is conferred by the minor fimbrial component FimH. Naturally occurring variants of the FimH protein have been selected in nature for their ability to recognize specific receptor targets. In particular, variants that bind strongly to terminally exposed monomannose residues have been associated with a pathogenicity-adaptive phenotype that enhances E. coli colonization of extraintestinal locations such as the urinary bladder. In this study we have used random mutagenesis to specifically identify nonselective mutations in the FimH adhesin which modify its binding phenotype. Isogenic E. coli clones expressing FimH variants were tested for their ability to bind yeast cells and model glycoproteins that contain oligosaccharide moieties rich in either terminal monomannose, oligomannose, or nonmannose residues. Both the monomannose- and the oligomannose-binding capacity of type 1 fimbriae could be altered by minor amino acid changes in the FimH protein. The monomannose-binding phenotype was particularly sensitive to changes, with extensive differences in binding being observed in comparison to wild-type FimH levels. Different structural alterations were able to cause similar functional changes in FimH, suggesting a high degree of flexibility to target recognition by this adhesin. Alteration of residue P49 of the mature FimH protein, which occurs within the recently elucidated carbohydrate-binding pocket of FimH, completely abolished its function. Amino acid changes that increased the binding capacity of FimH were located outside receptor-interacting residues, indicating that functional changes relevant to pathogenicity are likely to be due to conformational changes of the adhesin.

Bacterial adhesins: function and structure

Specific adhesion to host tissue cells is an essential virulence factor of most bacterial pathogens. The fundamental processes that determine bacterial attachment to host tissue surfaces are mediated by microbial adhesins. Host specificity and tissue tropism are characteristics exhibited by different bacteria and are determined (at least in part) by the interaction between adhesins and their complementary receptors on host cell surfaces. A detailed picture of how bacteria are able to target to various receptors is emerging. A large number of bacterial adhesins with individual receptor specificities have been identified. Furthermore, recent research has shown that individual adhesins are prone to rapid microevolution that results in changes in the receptor specificity of individual adhesins. Microbial adhesins are often assembled into complex polymeric organelle structures, however non-organelle adhesins linked to the cell surface as monomers or simple oligomers also exist. This review gives an overview of bacterial adhesins and focuses on some general aspects of their biogenesis and role in bacterial colonization of host cell surfaces and as virulence factors.

X-ray structure of the FimC-FimH chaperone-adhesin complex from uropathogenic Escherichia coli

Type 1 pili-adhesive fibers expressed in most members of the Enterobacteriaceae family-mediate binding to mannose receptors on host cells through the FimH adhesin. Pilus biogenesis proceeds by way of the chaperone/usher pathway. The x-ray structure of the FimC-FimH chaperone-adhesin complex from uropathogenic Escherichia coli at 2.5 angstrom resolution reveals the basis for carbohydrate recognition and for pilus assembly. The carboxyl-terminal pilin domain of FimH has an immunoglobulin-like fold, except that the seventh strand is missing, leaving part of the hydrophobic core exposed. A donor strand complementation mechanism in which the chaperone donates a strand to complete the pilin domain explains the basis for both chaperone function and pilus biogenesis.

Bioaccumulation of heavy metals by fimbrial designer adhesins

Naturally occurring adhesins bind to specific molecular targets in a lock-and-key fashion due to the composition of the binding domain of the adhesin. By introduction of random peptide libraries in a suitable surface exposed carrier protein it is possible to create and select designer adhesins with novel binding affinities. Type 1 fimbriae are surface organelles of Escherichia coli which mediate D-mannose sensitive binding to different host surfaces through the FimH adhesin, an integral part of these organelles. We have studied the ability of the FimH adhesin to display random peptide sequences. By serial selection and enrichment procedures specific sequences were identified which conferred the ability on recombinant cells to adhere to various metal oxides (PbO2, CoO, MnO2, Cr2O3). The properties inherent in these sequences permitted the distinct recognition of metals to varying degrees, indicating that this system allow for the isolation of peptide sequences with a variety of binding avidities. These studies demonstrate the potential and versatility of the FimH display system for presenting random peptide sequences. In addition, the possibility exists for the construction of microorganisms for the bioaccumulation of heavy metals from the environment.

Probing the receptor recognition site of the FimH adhesin by fimbriae-displayed FimH-FocH hybrids

Type 1 fimbriae are surface organelles of Escherichia coli which mediate D-mannose-sensitive binding to different host surfaces. This binding is conferred by the minor fimbrial component FimH. The binding domain of the FimH adhesin has been studied by constructing hybrids of FimH and a homologous protein, FocH, originating from F1C fimbriae. F1C fimbriae do not bind to D-mannosides or confer agglutination of any known types of erythrocytes or yeast. It was previously shown that the FocH protein can be readily substituted by the FimH adhesin, resulting in hybrid fimbriae with the same binding characteristics as type 1 fimbriae. The receptor binding of fimbriae-presented chimeric FimH-FocH hybrids was studied. FimH-FocH fusions encompassing 72% of the N-terminus of FimH fused to the complementary sector of FocH conferred agglutination of erythrocytes and yeast cells at a comparable level to FimH. Surprisingly, it was also found that similar fusions containing between 56 and 66% FimH still conferred binding to yeast cells, D-mannose-BSA and D-mannose-beads but did not give rise to agglutination. The receptor binding capacity of fusions containing 50% or less of the FimH N-terminal region was virtually abolished. The results point to the presence of a D-mannose-receptor-binding core domain in FimH, the affinity of which is modulated by other sectors of the protein to enable binding to extended mannose-containing targets.

Characterisation of epitopes of type 1 fimbriae of Salmonella using monoclonal antibodies specific for SEF21 fimbriae of Salmonella enteritidis

Monoclonal antibodies (mAbs) were used to identify and characterise epitopes of type 1 (SEF21) fimbriae of Salmonella enteritidis. The distribution of the epitopes among salmonellas and other enterobacteria was investigated, as well as the influence of growth media and temperatures on their expression. At least four different epitope clusters were identified on SEF21 fimbriae of S. enteritidis. Two of these clusters were associated with fimbrial haemagglutinins that were either common to all salmonellae tested, or restricted only to S. enteritidis and S. dublin. The four epitope clusters were identified on type 1 fimbriae of most Salmonella serotypes, as well as non-haemagglutinating type 2 fimbriae of S. pullorum and S. gallinarum, and on many other enterobacterial species. The expression of the epitopes was affected by growth conditions.

Specificity of the high-mannose recognition site between Enterobacter cloacae pili adhesin and HT-29 cell membranes

Enterobacter cloacae has been implicated as one of the causative agents in neonatal infection and causes a septicemia thought to be initiated via the gastrointestinal tract. The adhesion of radiolabeled E. cloacae to HT-29 cells was concentration and temperature dependent and was effectively blocked by unlabeled bacteria or by millimolar concentrations of alpha-mannosides and micromolar concentrations of high-mannose oligosaccharides. A variety of well-characterized mannose oligosaccharides were tested as inhibitors of adhesion. The best inhibitor was the Man9(GlcNAc)2-tyrosinamide, which was considerably better than other tyrosinamide-linked oligosaccharides such as Man7(GlcNAc)2, Man6(GlcNAc)2 or Man5(GlcNAc)2. Further evidence that the bacteria preferred Man9(GlcNAc)2 structures was obtained by growing HT-29 cells in the presence of glycoprotein processing inhibitors that block mannosidase I and increase the amount of protein-bound Man9(GlcNAc)2 at the cell surface. Such cells bound 1.5- to 2-fold more bacteria than did control cells. The adhesin involved in binding to high-mannose structures was purified from isolated pili. On sodium dodecyl sulfate-gels, a 35-kDa protein was identified by its specific binding to a mannose-containing biotinylated albumin. The amino acid sequences of several peptides from the 35-kDa subunit showed over 85% identity to FimH, the mannose-specific adhesin of Salmonella typhimurium. Pili were labeled with 125I and examined for the ability to bind to HT-29 cells. Binding showed saturation kinetics and was inhibited by the addition of Man9(GlcNAc)2-tyrosinamide but not by oligosaccharides with fewer mannose residues. Polyclonal antibody against this 35-kDa protein also effectively blocked adhesion of pili or E. cloacae, but no effect was observed with nonspecific antibody. These studies demonstrate that the 35-kDa pilus subunit is a lectin whose specificity is directed toward Man, (GlcNAc)2 oligosaccharides.

Assembly proteins of CS1 pili of enterotoxigenic Escherichia coli

Some strains of enterotoxigenic Escherichia coli associated with human diarrhoeal disease produce a class of pili represented by those called CS1. For the assembly of the major-pilin subunit, CooA, into pili, each of four linked genes, cooB, A, C, and D, is required. In this study, we have determined the subcellular localization of CooB, C and D, and investigated the molecular interactions of these proteins using specific antisera. CooD appears to be an integral pilus protein because it co-purifies with, and is strongly associated with, CS1 pili. In keeping with its role as an assembly protein, the CooD minor pilin (when overexpressed in CS1-piliated strains) was detected in periplasmic intermolecular complexes with the major-pilin subunit CooA. CooB is an assembly protein found exclusively in the periplasm of CS1-piliated strains. CooB also forms periplasmic intermolecular complexes with CooA, but does not constitute part of the final pilus structure. Immunoblot analysis of cell fractions showed that CooC is an outer membrane protein of CS1-piliated E. coli. Based on this information, we have proposed a model for CS1-pilus assembly which is very similar to the model for polymerization of the PapA pilin of uropathogenic E. coli. As the assembly proteins of Pap and CS1 pili are structurally unrelated, this may represent a case of convergent evolution.

Adhesion of bovine enterotoxigenic Escherichia coli (ETEC) by type 1-like fimbriae

Enterotoxigenic Escherichia coli (STa+) strains were isolated from adult bovine with diarrhea. These strains did not express any known ETEC-specific adhesins. Although hemagglutination with rat and sheep erythrocytes was observed in the presence of D-mannose (MRHA), these strains also showed mannose-sensitive hemagglutination (MSHA) with guinea-pig erythrocytes. Electron microscopic studies revealed the presence of fimbria-like structures (provisionally called "F43ms") on bacterial cells grown at 37 degrees C but not on cells grown at 18 degrees C. However, it was observed by SDS-PAGE that the J-1 strain (F43ms+) produces a protein similar to F1 fimbriae, and this strain hybridized with a DNA probe for F1 fimbriae. Immunogold-labelling techniques indicated that a rabbit anti-serum is specific for F43ms fimbrial structures, but not for Type 1 fimbriae. The immunofluorescence test carried out with semipurified F43ms on bovine brush borders suggests that the fimbria-like structures are responsible for the adhesion to bovine epithelial cells.

Linker insertion analysis of the FimH adhesin of type 1 fimbriae in an Escherichia coli fimH-null background

The gene encoding the Escherichia coli FimH adhesin of type 1 fimbriae has been subjected to linker insertion mutagenesis. Amino acid changes were introduced at a number of positions spanning the entire sequence in order to probe the structure-function relationship of the FimH protein. The effect of these mutations on the ability of bacteria to express a D-mannose binding phenotype was assessed in a fimH null mutant (MS4) constructed by allelic exchange in the E. coli K-12 strain PC31. Mutations mapping at amino acid residues 36, 58 and 279 of the mature FimH protein were shown to completely abolish binding to D-mannose receptors. Differences in the level of fimbriation were also observed as a result of some of the mutations in the fimH gene. These mutants may prove useful in dissecting receptor-ligand interactions by defining regions of the FimH protein that are important in erythrocyte binding.

Quantitative differences in adhesiveness of type 1 fimbriated Escherichia coli due to structural differences in fimH genes

Type 1 fimbriae are heteropolymeric surface organelles responsible for the D-mannose-sensitive (MS) adhesion of Escherichia coli. We recently reported that variation of receptor specificity of type 1 fimbriae can result solely from minor alterations in the structure of the gene for the FimH adhesin subunit. To further study the relationship between allelic variation of the fimH gene and adhesive properties of type 1 fimbriae, the fimH genes from five additional strains were cloned and used to complement the FimH deletion in E. coli KB18. When the parental and recombinant strains were tested for adhesion to immobilized mannan, a wide quantitative range in the ability of bacteria to adhere was noted. The differences in adhesion do not appear to be due to differences in the levels of fimbriation or relative levels of incorporation of FimH, because these parameters were similar in low-adhesion and high-adhesion strains. The nucleotide sequence for each of the fimH genes was determined. Analysis of deduced FimH sequences allowed identification of two sequence homology groups, based on the presence of Asn-70 and Ser-78 or Ser-70 and Asn-78 residues. The consensus sequences for each group conferred very low adhesion activity, and this low-adhesion phenotype predominated among a group of 43 fecal isolates. Strains isolated from a different host niche, the urinary tract, expressed type 1 fimbriae that conferred an increased level of adhesion. The results presented here strongly suggest that the quantitative variations in MS adhesion are due primarily to structural differences in the FimH adhesin. The observed differences in MS adhesion among populations of E. coli isolated from different host niches call attention to the possibility that phenotypic variants of FimH may play a functional role in populations dynamics.

The export systems of type 1 and F1C fimbriae are interchangeable but work in parental pairs

Type 1 and F1C fimbriae are surface organelles of Escherichia coli which mediate receptor-specific binding to different host surfaces. Such fimbriae are found, among others, on strains associated with urinary tract infections. Biosynthesis of type 1 and F1C fimbrial organelles requires individual, specialized two-component assembly systems. The organization of the fim and foc gene clusters encoding these fimbriae, as well as the structure of the organelles, is very similar; however, the actual sequence homology of the structural elements is not remarkable (34 to 60%). Both gene clusters encode a periplasmically located chaperone and an usher protein, located in the outer membrane, required for organelle biogenesis. Deletion of either element causes abolishment of fimbriation. The present report addresses the question of promiscuity in fimbrial biogenesis. Our data indicate that the two-component export systems of the two organelle systems are reciprocally interchangeable; however, they seem to function only in parental pairs.

FimH family of type 1 fimbrial adhesins: functional heterogeneity due to minor sequence variations among fimH genes

We recently reported that the type 1-fimbriated Escherichia coli strains CSH-50 and HB101(pPKL4), both K-12 derivatives, have different patterns of adhesion to yeast mannan, human plasma fibronectin, and fibronectin derivatives, suggesting functional heterogeneity of type 1 fimbriae. In this report, we provide evidence that this functional heterogeneity is due to variations in the fimH genes. We also investigated functional heterogeneity among clinical isolates and whether variation in fimH genes accounts for differences in receptor specificity. Twelve isolates obtained from human urine were tested for their ability to adhere to mannan, fibronectin, periodate-treated fibronectin, and a synthetic peptide copying the 30 amino-terminal residues of fibronectin. CSH-50 and HB101(pPKL4) were tested for comparison. Selected isolates were also tested for adhesion to purified fragments spanning the entire fibronectin molecule. Three distinct functional classes, designated M, MF, and MFP, were observed. The fimH genes were amplified by PCR from chromosomal DNA obtained from representative strains and expressed in a delta fim strain (AAEC191A) transformed with a recombinant plasmid containing the entire fim gene cluster but with a translational stop-linker inserted into the fimH gene (pPKL114). Cloned fimH genes conferred on AAEC191A(pPKL114) receptor specificities mimicking those of the parent strains from which the fimH genes were obtained, demonstrating that the FimH subunits are responsible for the functional heterogeneity. Representative fimH genes were sequenced, and the deduced amino acid sequences were compared with the previously published FimH sequence. Allelic variants exhibiting >98% homology and encoding proteins differing by as little as a single amino acid substitution confer distinct adhesive phenotypes. This unexpected adhesive diversity within the FimH family broadens the scope of potential receptors for enterobacterial adhesion and may lead to a fundamental change in our understanding of the role(s) that type 1 fimbriae may play in enterobacterial ecology or pathogenesis.

Pap pili as a vector system for surface exposition of an immunoglobulin G-binding domain of protein A of Staphylococcus aureus in Escherichia coli

Fusion genes between papA, the gene coding for the major Pap pilus subunit, and fragments coding for an immunoglobulin G-binding domain of the Staphylococcus aureus protein A were constructed in such a way that the spa fragments were inserted following either codon 7 or 68 of the coding sequence for the mature portion of PapA. Peptides in the area of amino acids 7 and 68 of PapA are localized at the external side of the pilus. A set of pL expression plasmids containing papA and derivatives suitable for insertion were constructed. A papA gene carrying a spa insert following codon 68 was cloned back into the pap operon. The presence of this altered operon in a bacterial strain allowed the detection of immunoglobulin G-binding activity at the surfaces of the bacterial cells.

T-cell-independent stimulation of immunoglobulin secretion in resting human B lymphocytes by the mannose-specific adhesin of Escherichia coli type 1 fimbriae

Purified Escherichia coli type 1 fimbriae have been shown previously to stimulate T-cell-independent proliferation of human B lymphocytes. The response is mediated by the mannose-specific, lectin-like adhesin protein FimH. Here we show that type 1 fimbriae also stimulate immunoglobulin (Ig) secretion by B cells. The response was maximal at three days of culture and consisted predominantly of the IgM isotype. It was independent of serum components, T lymphocytes, monocytes, and natural killer cells. Highly purified resting B cells were induced to proliferate and secrete Ig in response to the fimbriae. The role of FimH in the response was shown by the failure of FimH- type 1 fimbriae to stimulate and by inhibition of the response with alpha-methyl mannoside. In light of the fact that carbohydrate-binding adhesins have been found on a wide variety of microorganisms, these studies suggest the possibility that responses of other cell types to other microbial adhesins will be discovered.

FimC, a chaperone-like periplasmic protein of Escherichia coli involved in biogenesis of type 1 fimbriae

The product of the fimC gene of Escherichia coli K12 is required for the biogenesis of type 1 fimbriae. Mutations within the fimC gene abolish fimbrial synthesis. The FimC protein was found to be processed and the mature version was located in the periplasm. Unlike similar fimbrial systems, the major type 1 fimbriae structural protein FimA was found to be significantly resistant to proteolytic degradation when present in the periplasm in a fimC- host background. The fimC gene was sequenced, and the deduced primary structure of the FimC protein was compared to other similar known proteins involved in the biogenesis of various fimbriae.

Lesions in two Escherichia coli type 1 pilus genes alter pilus number and length without affecting receptor binding

We describe the characterization of two genes, fimF and fimG (also called pilD), that encode two minor components of type 1 pili in Escherichia coli. Defined, in-frame deletion mutations were generated in vitro in each of these two genes. A double mutation that had deletions identical to both single lesions was also constructed. Examination of minicell transcription and translation products of parental and mutant plasmids revealed that, as predicted from the nucleotide sequence and previous reports, the fimF gene product was a protein of ca. 16 kDa and that the fimG gene product was a protein of ca. 14 kDa. Each of the constructions was introduced, via homologous recombination, into the E. coli chromosome. All three of the resulting mutants produced type 1 pili and exhibited hemagglutination of guinea pig erythrocytes. The latter property was also exhibited by partially purified pili isolated from each of the mutants. Electron microscopic examination revealed that the fimF mutant had markedly reduced numbers of pili per cell, whereas the fimG mutant had very long pili. The double mutant displayed the characteristics of both single mutants. However, pili in the double mutant were even longer than those seen in the fimG mutant, and the numbers of pili were even fewer than those displayed by the fimF mutant. All three mutants could be complemented in trans with a single-copy-number plasmid bearing the appropriate parental gene or genes to give near-normal parental piliation. On the basis of the phenotypes exhibited by the single and double mutants, we believe that the fimF gene product may aid in initiating pilus assembly and that the fimG product may act as an inhibitor of pilus polymerization. In contrast to previous studies, we found that neither gene product was required for type 1 pilus receptor binding.

Isolation and characterization of conditional adherent and non-type 1 fimbriated Salmonella typhimurium mutants

Mutations in the genes encoding the type 1 fimbriae of Salmonella typhimurium were isolated by selecting for the deletion of Tn10 inserted adjacent to the chromosomal fim+ genes and screening for the loss of mannose-sensitive haemagglutination (HA) activity. S. typhimurium strains with Tn10 insertions in ahp were hypersensitive to peroxides, and tetracycline-sensitive derivatives of ahp::Tn10 mutants displayed two fim mutant phenotypes. The predominant class of fim mutants did not synthesize type 1 fimbriae. A second type of fim mutant synthesized type 1 fimbriae and exhibited a conditional lipoic acid requirement for HA. A fim-lip conditional mutant synthesized type 1 fimbriae when grown in Mueller-Hinton broth but the haemagglutinating activity of the fimbriae was dependent upon the addition of lipoic acid to the growth medium. Independently isolated lip mutations did not demonstrate a similar pleiotropic effect on HA. Western blots of fimbriae extracted from a fim-lip conditional mutant that was grown under permissive and restrictive conditions indicated the presence of 33 and 36.6 kDa proteins in HA+ fimbriae that were absent in HA- fimbriae. The HA+ phenotype of both conditional and non-fimbriated mutants was restored by transformation with cloned genes encoding S. typhimurium type 1 fimbriae.

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.

Genetic control of flocculation inEscherichia coli

Escherichia coli cells form flocs or aggregates by overproducing type 1 pili. When the pil operon is placed under the control of a tac or lac promoter-operator sequence, the bacterial cells can be induced to form flocs by adding isopropyl-beta-D-thiogalactopyranoside to the culture medium. This phenomenon of genetically induced flocculation can aid in the downstream of biological products. This paper describes the construction of two artificially controlled plasmids which cause cell flocculation. Cell aggregates 50 microns in mean diameter were obtained 1 h after the cells were induced.

Bacterial etiologic agents in the pathogenesis of urinary tract infection

Most of the information available concerning virulence factors of uropathogens is based on studies of Escherichia coli, the commonest cause of urinary tract infections. Earlier studies revealed several phenotypic Escherichia coli virulence factors that influenced both the anatomic level and severity of urinary tract infection. Virulence factors included O antigen serotype, presence and quantity of K capsular polysaccharide, adherence to uroepithelial cells, resistance to serum bactericidal activity, hemolysin, and aerobactin production. The introduction of DNA hybridization methodology has provided a valuable tool for reevaluation of the epidemiology of Escherichia coli infection as well as an alternative to the conventional phenotypic approach for studying the genotypic basis for virulence.

The hemagglutinating adhesin HA-Ag2 of Bacteroides gingivalis is distinct from fimbrilin

We carried out a series of immunoblots with antigenic preparations from the periodontal pathogen Bacteroides gingivalis using antisera of restricted specificity for the hemagglutinating adhesin HA-Ag2, and for the major structural subunit of the fimbriae (fimbrilin). We have been able to show that these 2 antigens are distinct. The fimbrilin subunit had an apparent molecular weight of 42 kDa in all of the bacterial preparations tested. HA-Ag2 occurred as a pair of bands at 43 and 49 kDa in outer membranes prepared as extracellular vesicles, and at 33 and 38 kDa in glass-bead-EDTA extracted antigens and in sheared-cell outer membranes prepared in the presence of EDTA. No HA-Ag2 was found in an enriched fimbrial preparation. The 2 antigens could thus be distinguished on the basis of their behaviour when subjected to different extraction techniques. The lower apparent molecular weight of HA-Ag2 (a pair of bands at 33 and 38 kDa) was invariably associated with the presence of EDTA in the buffers used to prepare the extracts, and the effect could be partially prevented by adding MgCl2 to the extraction buffer. The difference in apparent molecular weight of HA-Ag2 in the different extracts can thus be attributed either to an EDTA-sensitive tertiary conformation of its component polypeptides, or to an EDTA-sensitive linkage of each of these polypeptides to an unknown component of approximately 10 kDa.

Virulence factors in Escherichia coli urinary tract infection

Uropathogenic strains of Escherichia coli are characterized by the expression of distinctive bacterial properties, products, or structures referred to as virulence factors because they help the organism overcome host defenses and colonize or invade the urinary tract. Virulence factors of recognized importance in the pathogenesis of urinary tract infection (UTI) include adhesins (P fimbriae, certain other mannose-resistant adhesins, and type 1 fimbriae), the aerobactin system, hemolysin, K capsule, and resistance to serum killing. This review summarizes the virtual explosion of information regarding the epidemiology, biochemistry, mechanisms of action, and genetic basis of these urovirulence factors that has occurred in the past decade and identifies areas in need of further study. Virulence factor expression is more common among certain genetically related groups of E. coli which constitute virulent clones within the larger E. coli population. In general, the more virulence factors a strain expresses, the more severe an infection it is able to cause. Certain virulence factors specifically favor the development of pyelonephritis, others favor cystitis, and others favor asymptomatic bacteriuria. The currently defined virulence factors clearly contribute to the virulence of wild-type strains but are usually insufficient in themselves to transform an avirulent organism into a pathogen, demonstrating that other as-yet-undefined virulence properties await discovery. Virulence factor testing is a useful epidemiological and research tool but as yet has no defined clinical role. Immunological and biochemical anti-virulence factor interventions are effective in animal models of UTI and hold promise for the prevention of UTI in humans.

Isolation and characterization of mutants with lesions affecting pellicle formation and erythrocyte agglutination by type 1 piliated Escherichia coli

The product of the pilE (also called fimH) gene is a minor component of type 1 pili in Escherichia coli. Mutants that have insertions in the pilE gene are fully piliated but unable to bind to and agglutinate guinea pig erythrocytes, a characteristic of wild-type type 1 piliated E. coli. In this paper we describe the isolation of 48 mutants with point lesions that map to the pilE gene. Such mutants were isolated by using mutT mutagenesis and an enrichment procedure devised to favor the growth of individuals that could form a pellicle in static broth containing alpha-methylmannoside, an inhibitor of erythrocyte binding and pellicle formation. Results indicated that the enrichment favored mutants expressing pilE gene products that were defective in mediating erythrocyte binding. Characterization of 12 of the mutants in greater detail revealed that certain lesions affected pilus number and length. In addition, a mutant that was temperature sensitive for erythrocyte binding was isolated and used to provide evidence that pellicle formation relies on the intercellular interaction of pilE gene products. Our results suggest a molecular explanation for the old and paradoxical observations connecting pellicle formation and erythrocyte agglutination by type 1 piliated E. coli.

Mannose-sensitive haemagglutination in the absence of piliation in Escherichia coli

The relationship between type 1 pilus structure and the mannose-sensitive adhesin was investigated by analysing the properties of an 11.2 kb fragment of DNA derived from the chromosomal pil region of a type 1 piliated uropathogenic strain of Escherichia coli. The recombinant plasmids pHA9 and pSJH9, containing the cloned fragment, conferred a mannose-sensitive haemagglutination (MSHA)-positive but non-piliated phenotype on recipient cells of ORN104. Most of the DNA sequences homologous to the pilA and hyp genes were not present in the 11.2 kb insert, and the genetic information necessary for MSHA in the absence of piliation spanned a 6.5 kb region of the cloned fragment. The polypeptides expressed by pSJH9 were examined in minicells and Tn1000 insertions in three genes encoding proteins of molecular weights 90 kD, 29 kD and 17 kD abolished the MSHA phenotype.

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.

Purification and characterization of a Bacteroides loeschei adhesin that interacts with procaryotic and eucaryotic cells

The adhesin of Bacteroides loeschei PK1295 that mediates coaggregation with Streptococcus sanguis 34 and hemagglutination of erythrocytes was purified to electrophoretic homogeneity. The lectinlike protein has an estimated native Mr of 450,000 and consists of six subunits of identical molecular weight (Mr 75,000). The purified adhesin appears to be a basic protein with a pI between 7.4 and 8.0. Amino acid and N-terminal sequence analyses were carried out with the purified protein. These indicated that the protein contains a large number of Asx and Glx residues as well as basic amino acid residues. The binding site of the pure adhesin retained its native configuration during purification. When preincubated with streptococcal partner cells at pH 4.6, the adhesin prevented B. loeschei cells from coaggregating with the streptococci. An adhesin preparation adjusted to a pH of 6.8 rapidly agglutinated both streptococci and neuraminidase-treated erythrocytes. Galactosides inhibited the agglutination reactions.

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.

The major subunit of Escherichia coli type 1 fimbriae is not required for D-mannose-specific adhesion

Type 1 fimbriae are surface organelles on Escherichia coli, which mediate specific binding to D-mannose-containing structures. These fimbriae are heteropolymers composed of a major building element, the FimA protein, and small amounts of the FimF, FimG and FimH proteins. The FimH protein is uniquely responsible for the D-mannose receptor binding. In this work data are presented which indicate that the major subunit of type 1 fimbriae is dispensable for D-mannose-specific binding. A recombinant strain was studied which harboured an insertional deletion in the fimA gene, and was thereby unable to produce type 1 fimbriae; however, it was still able to express a D-mannose-binding phenotype. However, the deletion resulted in a 25-fold reduction of the adhesive potential, as measured by binding to D-mannose-coated Sepharose beads. Serological and specific receptor binding evidence is presented that suggests that the FimH adhesion is capable of being exposed on the bacterial surface without being an integral part of the fimbriae.

Cloning and expression in Escherichia coli of LKP pilus genes from a nontypeable Haemophilus influenzae strain

Nontypeable Haemophilus influenzae HF0295, isolated by aspiration from the middle ear of a patient with otitis media, expresses long, thick, and hemagglutinating pili of a single serotype (LKP1) on its surface. An intact pilus vaccine consisting of the LKP1 serotype protected chinchillas against experimental otitis media (C. C. Brinton, Jr., M. J. Carter, D. B. Derber, S. Kar, J. A. Kramarik, A. C. C. To, S. C. M. To, and S. W. Wood, Pediatr. Infect. Dis. J. 8:554-561, 1989; R. B. Karasic, D. J. Beste, S. C. M. To, W. J. Doyle, S. W. Wood, M. J. Carter, A. C. C. To, K. Tanpowpong, C. D. Bluestone, and C. C. Brinton, Jr., Pediatr. Infect. Dis. J. 8:562-565, 1989). The genes encoding LKP1 pili were cloned from a genomic library of the clinical strain as a 12.5-kilobase insert on a plasmid vector and inserted into Escherichia coli K-12. Transposon mutagenesis and deletion constructs mapped the pilus-coding region within a 7-kilobase region of insert DNA. The recombinant bacteria were found by electron microscopy to express pili morphologically similar to LKP1 pili. Purified pilus rods from the recombinant and its parental strain were composed of a single detectable protein with an apparent molecular weight of 27,500. Antibodies raised against LKP1 pili purified from H. influenzae immunologically reacted with pili from the recombinant bacteria. Pili from both strains also adhered to human erythrocytes and buccal cells with the same specificity.