Pseudomonas aeruginosa exoenzyme S is an adhesion

Proteomics in the Study of Bacterial Keratitis

Bacterial keratitis is a serious ocular infection that can cause severe visual loss if treatment is not initiated at an early stage. It is most commonly caused by Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus pneumoniae, or Serratia species. Depending on the invading organism, bacterial keratitis can progress rapidly, leading to corneal destruction and potential blindness. Common risk factors for bacterial keratitis include contact lens wear, ocular trauma, ocular surface disease, ocular surgery, lid deformity, chronic use of topical steroids, contaminated ocular medications or solutions, and systemic immunosuppression. The pathogenesis of bacterial keratitis, which depends on the bacterium-host interaction and the virulence of the invading bacterium, is complicated and not completely understood. This review highlights some of the proteomic technologies that have been used to identify virulence factors and the host response to infections of bacterial keratitis in order to understand the disease process and develop improved methods of diagnosis and treatment. Although work in this field is not abundant, proteomic technologies have provided valuable information toward our current knowledge of bacterial keratitis. More studies using global proteomic approaches are warranted because it is an important tool to identify novel targets for intervention and prevention of corneal damage caused by these virulent microorganisms.

Contribution of Tamm–Horsfall protein to virulence of Pseudomonas aeruginosa in urinary tract infection

Tamm-Horsfall glycoprotein (THP) is the most abundant protein which is synthesized by renal tubular cells and excreted in urine. Its role in urinary tract infection has yet not been identified. In the present study, the contribution of THP towards adherence of Pseudomonas aeruginosa to uroepithelial cells and murine peritoneal macrophages was studied. Decreased adherence of THP-coated P. aeruginosa to UECs and phagocytes was observed in vitro. In vivo, P. aeruginosa showed increased renal bacterial load and tissue pathology in a mouse model of acute ascending pyelonephritis, when THP-coated P. aeruginosa was used to cause infection. This study shows that THP may not necessarily act as a host defense component; rather, it may help in renal colonization of P. aeruginosa in vivo.

Synthetic peptide vaccine and antibody therapeutic development: prevention and treatment of Pseudomonas aeruginosa

Pseudomonas aeruginosa and Pseudomonas maltophilia account for 80% of opportunistic infections by pseudomonads. Pseudomonas aeruginosa is an opportunistic pathogen that causes urinary tract infections, respiratory system infections, dermatitis, soft tissue infections, bacteremia, and a variety of systemic infections, particularly in patients with severe burns, and in cancer and AIDS patients who are immunosuppressed. Pseudomonas aeruginosa is notable for its resistance to antibiotics, and is therefore a particularly dangerous pathogen. Only a few antibiotics are effective against Pseudomonas, including fluoroquinolones, gentamicin, and imipenem, and even these antibiotics are not effective against all strains. The difficulty treating Pseudomonas infections with antibiotics is most dramatically illustrated in cystic fibrosis patients, virtually all of whom eventually become infected with a strain that is so resistant that it cannot be treated. Since antibiotic therapy has proved so ineffective as a treatment, we embarked on a research program to investigate the development of a synthetic peptide consensus sequence vaccine for this pathogen. In this review article we will describe our work over the last 15 years to develop a synthetic peptide consensus sequence anti-adhesin vaccine and a related therapeutic monoclonal antibody (cross-reactive to multiple strains) to be used in the prevention and treatment of P. aeruginosa infections. Further, we describe the identification and isolation of a small peptide structural element found in P. aeruginosa strain K (PAK) bacterial pili, which has been proven to function as a host epithelial cell-surface receptor binding domain. Heterologous peptides are found in the pili of all strains of P. aeruginosa that have been sequenced to date. Several of these peptide sequences have been used in the development of an consensus sequence anti-adhesin vaccine targeted at the prevention of host cell attachment and further for the generation of a monoclonal antibody capable of prevention and treatment of existing infections.

State of the art: why do the lungs of patients with cystic fibrosis become infected and why can't they clear the infection?

Cystic Fibrosis (CF) lung disease, which is characterized by airway obstruction, chronic bacterial infection, and an excessive inflammatory response, is responsible for most of the morbidity and mortality. Early in life, CF patients become infected with a limited spectrum of bacteria, especially P. aeruginosa. New data now indicate that decreased depth of periciliary fluid and abnormal hydration of mucus, which impede mucociliary clearance, contribute to initial infection. Diminished production of the antibacterial molecule nitric oxide, increased bacterial binding sites (e.g., asialo GM-1) on CF airway epithelial cells, and adaptations made by the bacteria to the airway microenvironment, including the production of virulence factors and the ability to organize into a biofilm, contribute to susceptibility to initial bacterial infection. Once the patient is infected, an overzealous inflammatory response in the CF lung likely contributes to the host's inability to eradicate infection. In response to increased IL-8 and leukotriene B₄ production, neutrophils infiltrate the lung where they release mediators, such as elastase, that further inhibit host defenses, cripple opsonophagocytosis, impair mucociliary clearance, and damage airway wall architecture. The combination of these events favors the persistence of bacteria in the airway. Until a cure is discovered, further investigations into therapies that relieve obstruction, control infection, and attenuate inflammation offer the best hope of limiting damage to host tissues and prolonging survival.

Purification and partial characterization of a 32-kilodalton sialic acid-specific lectin from Aspergillus fumigatus

Adherence of the opportunistic fungus Aspergillus fumigatus to the extracellular matrix components is considered a crucial step in the establishment of the infection. Given the high carbohydrate content of these glycoproteins and the role of carbohydrate-protein interactions in numerous adherence processes, the presence of a lectin in A. fumigatus was investigated. Different fungal extracts obtained by sonication or grinding in liquid nitrogen from resting or swollen conidia, as well as from germ tubes and mycelium, were tested by hemagglutination assays using rabbit erythrocytes. A lectin activity was recovered in all the extracts tested. However, sonication of resting conidia resulted in the highest specific activity. Purification of the lectin was achieved by gel filtration followed by ion-exchange and hydrophobic-interaction chromatographies. Analysis of the purified lectin by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed an apparent molecular mass of 32 kDa, which is similar to that of the alkaline protease already identified from different strains of A. fumigatus. However, as evidenced by the use of an alkaline protease-deficient mutant, the two activities were supported by distinct proteins. In addition, hemagglutination inhibition experiments using different saccharides and glycoproteins demonstrated the specificity of the lectin for sialic acid residues. Together these results suggest that this lectin may contribute to the attachment of conidia to the extracellular matrix components through the recognition of the numerous terminal sialic acid residues of their carbohydrate chains.

Pseudomonas aeruginosa and the in vitro and in vivo biofilm mode of growth

The biofilm mode of growth is the survival strategy of environmental bacteria like Pseudomonas aeruginosa. Such P. aeruginosa biofilms also occur in the lungs of chronically infected cystic fibrosis patients, where they protect the bacteria against antibiotics and the immune response. The lung tissue damage is due to immune complex mediated chronic inflammation dominated by polymorphonuclear leukocytes releasing proteases and oxygen radicals.

Invasion of human epithelial cells by Pseudomonas aeruginosa involves src-like tyrosine kinases p60Src and p59Fyn

Pseudomonas aeruginosa plays a major role in respiratory tract infections or sepsis in patients with cystic fibrosis or upon suppression of the immune system. Several P. aeruginosa strains have been shown to be internalized by human epithelial cells; however, the molecular mechanisms of the invasion process are poorly characterized. Here, we show that the internalization of P. aeruginosa into human epithelial cells results in and requires activation of the Src-like tyrosine kinases p59Fyn and p60Src and the consequent tyrosine phosphorylation of several eukaryotic proteins. The significance of Src-like tyrosine kinase activation is shown by an almost complete blockade of P. aeruginosa internalization, but not adhesion, upon inhibition of Src-like tyrosine kinases. Likewise, inhibition of P. aeruginosa binding to CFTR, which has been shown to block P. aeruginosa internalization, prevents Src and Fyn activation, supporting a pivotal role of Src-like tyrosine kinases for invasion by P. aeruginosa.

Prospects for the prevention and control of pseudomonal infection in children with cystic fibrosis

Most patients with cystic fibrosis (CF) experience recurrent and chronic endobronchial Pseudomonas aeruginosa infections. It is possible to prevent or delay the onset of these chronic infections in most patients with CF by eliminating cross-infection and by early aggressive antibiotic treatment of the first positive sputum culture and of subsequent intermittent colonisation. Lung tissue damage is caused by activation of the immunologically specific inflammatory defence mechanisms of the lungs, which are initiated by the antibody response and dominated by polymorphonuclear neutrophil leucocytes and their proteolytic and oxidative products. This inflammation induces a phenotypic shift from nonmucoid to mucoid, alginate-producing phenotypes of P. aeruginosa which then grow, endobronchially, as a biofilm. Such biofilms are impossible to eradicate with antibiotics. By using chronic suppressive antibiotic maintenance therapy and anti-inflammatory drugs it is however, possible to maintain the lung function of these patients for a number of years.

Comparison of pathogenic properties between two types of arginine-specific cysteine proteinases (gingipains-R) from Porphyromonas gingivalis

Two major arginine-specific cysteine proteinases (gingipains R) from Porphyromonas gingivalis have been compared with regard to their potential participation in the pathology of periodontal disease. Both the high and low molecular mass forms, HRgpA and RgpB, cleaved oligopeptide fluorogenic substrates at the P1-arginine residue with essentially identical specificity but different efficiencies, with HRgpA being about 1.5 to seven-fold less potent than RgpB. In contrast HRgpA, which occurs as a non-covalent complex of catalytic and hemagglutinin/adhesion domains, was about two-fold more active than RgpB in degrading fibrinogen and fibrin, while both enzymes activated prekallikrein with similar efficiency. These data indicate the likelihood that both activities could be involved in both the bleeding tendency and production of gingival crevicular fluid, which occur at infected periodontitis sites. Significantly, however, is the fact that HRgpA, but not RgpB, was able to bind phospholipids in the presence of calcium ions, the effect dramatically enhancing the activation of clotting factors by this proteinase. This suggests that HRgpA may play a more important role in the virulence of Porphyromonas gingivalis, relative to RgpB, almost certainly because of the presence of the hemagglutinin/adhesion domain which can bind phospholipid and apparently modulate enzyme activity.

Crystal structure of Pseudomonas aeruginosa PAK pilin suggests a main-chain-dominated mode of receptor binding

Fibers of pilin monomers (pili) form the dominant adhesin of Pseudomonas aeruginosa, and they play an important role in infections by this opportunistic bacterial pathogen. Blocking adhesion is therefore a target for vaccine development. The receptor-binding site is located in a C-terminal disulphide-bonded loop of each pilin monomer, but functional binding sites are displayed only at the tip of the pilus. A factor complicating vaccination is that different bacterial strains produce distinct, and sometimes highly divergent, pilin variants. It is surprising that all strains still appear to bind a common receptor, asialo-GM1. Here, we present the 1.63 A crystal structure of pilin from P. aeruginosa strain PAK. The structure shows that the proposed receptor-binding site is formed by two beta-turns that create a surface dominated by main-chain atoms. Receptor specificity could therefore be maintained, whilst allowing side-chain variation, if the main-chain conformation is conserved. The location of the binding site relative to the proposed packing of the pilus fiber raises new issues and suggests that the current fiber model may have to be reconsidered. Finally, the structure of the C-terminal disulphide-bonded loop will provide the template for the structure-based design of a consensus sequence vaccine.

[Interactions of the Pseudomonas aeruginosa outer membrane proteins with plasma fibronectins. Bacterial adhesin investigation]

Pseudomonas aeruginosa adherence is a complex phenomenon largely mediated by pili involving specific receptor-ligand interactions. Anti-fibronectin antibodies as well as plasmatic fibronectin are able to inhibit P. aeruginosa adherence onto A549 cells showing that matricial fibronectin is an actual receptor for this bacterium. Experiments performed in vitro with human plasmatic fibronectin used as receptor and outer membrane proteins of P. aeruginosa as ligands show the presence of four fibronectin-binding proteins. These proteins with molecular mass of 70 +/- 2, 60 +/- 2, 48 +/- 2 and 36 +/- 1 kDa should be adhesins of P. aeruginosa on epithelial cell matrix in a non-pilus mediated adherence.

Activation of blood coagulation factor X by arginine-specific cysteine proteinases (gingipain-Rs) from Porphyromonas gingivalis

The effect of two arginine-specific cysteine proteinases (gingipain Rs) from Porphyromonas gingivalis, a causative bacterium of adult periodontitis, on human blood coagulation was investigated. Activated partial thromboplastin time and prothrombin time were shortened by these proteinases, with a 95-kDa gingipain R containing adhesin domains being 5-fold more efficient in comparison to a 50-kDa gingipain R containing the catalytic domain alone. The 50-kDa enzyme reduced each coagulation time in several plasmas deficient in various coagulation factors, while it was ineffective in factor X-deficient plasma unless reconstituted with this protein. Each proteinase activated factor X in a dose- and time-dependent manner, with Michaelis constants (Km) being found to be lower than the normal plasma factor X concentration, strongly suggesting that factor X activation by gingipain Rs, especially the 95-kDa form which is strongly activated by phospholipids, could occur in plasma. This is the first report of factor X activation by bacterial proteinases and indicates that the gingipain Rs could be responsible for the production of thrombin and, indirectly, with the generation of prostaglandins, interleukin-1, etc., which have been found to be associated with the development of periodontitis induced by P. gingivalis infections. Furthermore, the data support the hypothesis that induction of blood coagulation by bacterial proteinases may be a causative agent in the pathogenesis of disseminated intravascular coagulation in sepsis.

Pseudomonas aeruginosa: assessment of risk from drinking water

Pseudomonas aeruginosa is an ubiquitous environmental bacterium. It can be recovered, often in high numbers, in common food, especially vegetables. Moreover, it can be recovered in low numbers in drinking water. A small percentage of clones of P. aeruginosa possesses the required number of virulence factors to cause infection. However, P. aeruginosa will not proliferate on normal tissue but requires previously organs. Further narrowing the risk to human health is that only certain specific hosts are at risk, including patients with profound neutropenia, cystic fibrosis, severe burns, and those subject to foreign device installation. Other than these very well-defined groups, the general population is refractory to infection with P. aeruginosa. Because of its ubiquitous nature, it is not only not practical to eliminate P. aeruginosa from our food and drinking water, but attempts to do so would produce disinfection byproducts more hazardous than the species itself. Moreover, because there is no readily available sensitive and specific means to detect and identify P. aeruginosa available in the field, any potential regulation governing its control would not have a defined laboratory test measure of outcome. Accordingly, attempts to regulate P. aeruginosa in drinking water would not yield public health protection benefits and could, in fact, be counterproductive in this regard.

Cell envelope characteristics of Helicobacter pylori: their role in adherence to mucosal surfaces and virulence

Helicobacter pylori colonises the gastric mucosa of humans and causes both antral gastritis and duodenal ulcer disease. Exactly how H. pylori causes disease is not known but several pathogenic determinants have been proposed for the organism. These include adhesins, cytotoxins and a range of different enzymes including urease, catalase and superoxide dismutase. Surface molecules of H. pylori such as flagella, lipopolysaccharide, the urease enzyme and outer membrane proteins are putative adhesin molecules. While phosphatidylethanolamine and the Lewis(b) blood group antigen have been proposed as receptor molecules for the organism the exact mechanism by which H. pylori adheres to the gastric mucosa has still to be identified. Characterisation of the adhesins of H. pylori could lead to the development of adhesin analogues for use in the inhibition of colonisation and improved therapy for ulcer disease. In vivo studies with isogenic mutants which are incapable of adhering to the gastric mucosa would greatly clarify the significance of adherence. Such mutants could possibly be useful as a vaccine against infection with wild-type organisms.

Potential of preventing Pseudomonas aeruginosa lung infections in cystic fibrosis patients: experimental studies in animals

In patients with cystic fibrosis (CF), respiratory tract infections caused by Staphylococcus aureus and Haemophilus influenzae are followed by Pseudomonas aeruginosa with increasing age. Chronic endobronchial lung infection with P. aeruginosa is the leading cause of morbidity and mortality. In Danish CF patients we noted that both onset of initial colonization and chronic lung infection with P. aeruginosa peaked during the winter months which is the season for respiratory virus infections. Virus may therefore pave the way for P. aeruginosa. We established a chronic P. aeruginosa lung infection in rats by embedding mucoid bacteria in seaweed alginate and installing the beads intratracheally into the lower part of the left lung. Although the rats did not suffer from CF, the antibody responses and the pathologic changes of the lungs mimicked the findings in CF patients. By using this model in normal and athymic rats we showed that the T-cell response during the "natural" course of the infection played no major role. In a model of acute P. aeruginosa pneumonia we found that the macroscopic inflammatory response of the lungs was immense and that the natural capacity to clear P. aeruginosa was very efficient and could not be improved by immunization, although high serum levels of IgM, IgG and IgA antibodies to P. aeruginosa alginate, LPS, exotoxin A and sonicate were induced. We developed a method for collecting and measuring IgA in saliva and noted that mucosal IgA antibodies were induced by vaccination; they did not significantly prevent inflammation, however. In the chronic rat model we succeeded to improve the survival significantly and to change the inflammatory response subsequent to vaccination from an acute type inflammation dominated by polymorphonuclear leukocytes (PMNs) as in CF patients to a chronic type inflammation dominated by mononuclear leukocytes. Furthermore, we found that rats immunized with an alginate containing vaccine had a significantly earlier cellular shift to a chronic type inflammation as well as a significant reduction in the severity of the macroscopic inflammation compared to two other vaccine groups and to nonimmunized controls. Similar results were obtained in rats treated with the TH1 cytokine, interferon-gamma (IFN-gamma). Several authors have shown that the lung tissue damage during chronic infection in CF patients is caused by a type III hypersensitivity reaction leading to release of elastase by PMNs surrounding the bacterial microcolonies. The cellular shift we have induced by vaccination and by IFN-gamma treatment therefore offers a possible new strategy for improving the clinical course in chronically infected CF patients.

Anti-receptor antibodies inhibit Pseudomonas aeruginosa binding to the cornea and prevent corneal perforation

A polyclonal antibody (pAb) against gangliotetraosylceramide (asialo GM1), a glycolipid to which bacterial pili and LPS bind, and a mAb against a 66 kDa pilus-binding protein purified from adult mouse corneal epithelium were used to determine if antibodies against host receptors for bacterial adhesins could inhibit bacterial binding to wounded corneal epithelium and protect ocularly challenged mice from corneal perforation when topically applied. Bacteria were mixed with anti-66 kDa mAb, a mixture of anti-asialo GM1 pAb and anti-66 kDa mAb, an irrelevant control mAb (anti-human histocompatibility Ag HLA-DR5) or PBS prior to application to scarified corneas in organ culture. The combination of the two antibodies or the anti-66 kDa mAb alone was effective in reducing bacterial adherence compared with either PBS or the antibody control. To determine if these antibodies were protective in vivo, corneas of C57BL/6J mice were scarified and inoculated with Pseudomonas aeruginosa. Eyes were treated topically with anti-asialo GM1 pAb, anti-66 kDa mAb, a mixture of the two or control mouse serum. More serum-treated corneas perforated compared to corneas from any other group (P < or = 0.005) by 30 days postinfection. Treatment with a combination of the two antibodies resulted in significantly less corneal pathology 30 days p.i. when compared to any other treatment (P < or = 0.005). These data provide evidence that antibodies against host corneal receptors significantly inhibit bacterial binding in vitro and when applied topically in vivo, lessen the severity of ocular disease characteristic of P. aeruginosa keratitis.

Genetic analysis of exoenzyme S expression by Pseudomonas aeruginosa

The dissemination of Pseudomonas aeruginosa to the bloodstream increases the likelihood of developing fatal sepsis. In experimental models, the ability to disseminate is linked to expression of the exoenzyme S pathway. Genetic and biochemical analysis of the pathway has led to the identification of the two structural genes encoding exoenzyme S, exoS and exoT. A key regulator of several loci of the pathway has been identified as a DNA-binding protein with transcriptional activation properties. Preliminary evidence suggests that exoenzyme S and the Yop virulence determinants of yersiniae share homology among proteins involved in their synthesis and secretion. With the addition of exoS and exoT to the molecular arsenal, questions concerning in vivo toxicity and target specificities of exoenzyme S can be directly addressed.

Characterization of Pseudomonas aeruginosa fliO, a gene involved in flagellar biosynthesis and adherence

Pseudomonas aeruginosa binds to eukaryotic cells via both pilus and nonpilus adhesins, while binding of P. aeruginosa to mucin is pilus independent. To characterize genes involved in non-pilus-mediated adherence, transposon mutants of the nonpiliated strain P. aeruginosa PAK-NP that are unable to bind to cells or mucins were isolated. Two such mutants, P. aeruginosa B164 and P. aeruginosa RR18, were identified previously as deficient in binding to eukaryotic cells or mucins as well as nonmotile. The transposon insertion in each of these strains was mapped to the same gene. Sequence analysis of both DNA flanking the transposons and plasmids that could complement the mutations indicated that this open reading frame encodes a putative protein homolog of both Escherichia coli FliO and Erwinia carotovora subsp. atroseptica MopB. The transposons in both of these mutants are nonpolar, since the addition of the P. aeruginosa fliO gene in trans restored adherence to both cells and mucins to these mutants. The cloned fliO gene also complemented the motility defect of both B164 and RR18. A 1.6-kb KpnI fragment from the PAK chromosome that contained the fliO gene was sequenced. The fliO gene appears to be part of an operon with a complete open reading frame upstream of the FliO homolog encoding a putative protein homolog of FliN of both E. coli and Salmonella typhimurium. The partial open reading frame downstream of fliO encodes a putative homolog of both E. coli and S. typhimurium FliP. The fliN gene is flanked on its 5'-end by the 3'-end of a homolog of a fliM gene. The P. aeruginosa FliN protein was identified with a T7 expression system, while all attempts to identify the P. aeruginosa FliO protein were unsuccessful. Homologs of P. aeruginosa FliO are involved in the biosynthesis of flagella, but the function of FliO in this biosynthetic process remains unknown. Further study should reveal the precise role of P. aeruginosa FliO in non-pilus-mediated adherence, which could include regulation of expression or localization of a nonpilus adhesin.

Adherence of Pseudomonas aeruginosa and Candida albicans to glycosphingolipid (Asialo-GM1) receptors is achieved by a conserved receptor-binding domain present on their adhesins

Pseudomonas aeruginosa, a gram-negative bacterium, and Candida albicans, a dimorphic yeast, are evolutionarily distant microorganisms which can utilize filamentous structures termed pili and fimbriae, respectively, to mediate adherence to glycosphingolipids (asialoganglioside-GM1) receptors. The mechanism of adherence to glycosphingolipid receptors was investigated in these studies. By using monoclonal antibodies (MAbs) against purified pili of P. aeruginosa PAK (PK99H) and monospecific anti-peptide antibodies against the PAK pilin peptides [anti-PAK(128-144) and anti-PAK(134-140)], we demonstrated that these antibodies agglutinated C. albicans whole cells and cross-reacted with C. albicans fimbriae in immunoblots. A control MAb, PKL1, and anti-PAK(75-84) peptide antibodies failed to agglutinate C. albicans whole cells or cross-react with the fimbrial proteins. Conversely, the anti-C. albicans fimbrial MAb Fm16, but not Fm34, agglutinated P. aeruginosa PAK whole cells and Western blots (immunoblots). The interactions between PK99H and Fm16 and their respective homologous antigens were competitively inhibited by heterologous antigens; this demonstrated that the interactions between the antibodies and the heterologous antigens, i.e., PK99H with C. albicans fimbriae and Fm16 with P. aeruginosa pili, were highly specific and suggested that both adhesins share a common antigenic determinant. The immunological cross-reactivity between Fm16 and P. aeruginosa PAK pilin is localized onto the PAK(134-140) region as shown by a competitive enzyme-linked immunosorbent assay. The PAK(134-140) region of PAK pilin contains the epitope recognized by PK99H and also constitutes part of the receptor-binding domain of the pilus adhesin. Thus, the results from these studies suggest that common cell surface receptors are recognized by the P. aeruginosa and C. albicans adhesins because of a conserved receptor-binding domain on the adhesins.

Pili and lipopolysaccharide of Pseudomonas aeruginosa bind to the glycolipid asialo GM1

This study investigated which adhesins of Pseudomonas aeruginosa interact with the glycolipid asialo GM1, using solid-phase binding and thin-layer chromatography assays. Radioiodinated pili and flagella contaminated with lipopolysaccharide (LPS) bound to the glycolipid. When LPS was reduced to acceptable levels in pilus and flagellum samples, only pili specifically bound to the glycolipid. Commercial, radiolabeled LPS as well as whole bacteria of strain ATCC 19660 also bound to asialo GM1. Binding was specific, competitive, and saturable. Organ cultures of whole mouse eyes and scanning electron microscopy techniques were used also, and strain ATCC 19660 was inhibited from corneal binding by exogenous pili or commercial LPS and inhibition was concentration dependent for both. Binding of radiolabeled strain ATCC 19660 bacteria to neutral lipids extracted from bovine corneal epithelial tissue showed that the bacteria bound to a glycolipid which migrated at a position similar to that of an asialo GM1 standard and that the glycolipid stained positively with an antibody specific for asialo GM1. The data provide evidence that pili (reduced LPS) and LPS of P. aeruginosa bind to asialo GM1 glycolipid and that the glycolipid is not restricted to the mouse cornea.

PA-I and PA-II lectin interactions with the ABO(H) and P blood group glycosphingolipid antigens may contribute to the broad spectrum adherence of Pseudomonas aeruginosa to human tissues in secondary infections

Pseudomonas aeruginosa may cause serious infections in most human tissues/organs. Its adherence to them is mediated by a battery of adhesins including the PA-I and PA-II lectins, which are produced in this bacterium in high quantities. PA-I binds to the D-galactose of the erythrocyte glycosphingolipids exhibiting highest affinities for B and Pk (followed by P1) antigens, while PA-II preferentially binds to the L-fucose of H, A and B antigens. Intact P. aeruginosa cells also exhibit a clear Pk and P1 over p preference. Such affinities for the most common human ABH and P system antigens may underlie the widespread tissue infectivity and pathogenicity of this bacterium.

Binding of the galactose-specific Pseudomonas aeruginosa lectin, PA-I, to glycosphingolipids and other glycoconjugates

The carbohydrate-binding specificity of Pseudomonas aeruginosa lectin I (PA-I) in iodinated or biotinylated form was studied. A large number of glycosphingolipids, as well as some glycoproteins and neoglycoproteins were used as ligands. Also, inhibition by free saccharides of PA-I binding to glycosphingolipids was tested. It was found that the lectin binds most strongly to terminal and nonsubstituted Gal alpha 3Gal- or Gal alpha 4Gal-structures.

Fimbria-mediated adherence of Candida albicans to glycosphingolipid receptors on human buccal epithelial cells

Candida albicans is an opportunist fungal pathogen that has the ability to adhere to host cell surface receptors via a number of adhesins. Yu et al. (L. Yu, K. K. Lee, K. Ens, P. C. Doig, M. R. Carpenter, W. Staddon, R. S. Hodges, W. Paranchych, and R. T. Irvin, Infect. Immun. 62:2834-2842, 1994) described the purification and initial characterization of a fimbrial adhesin from C. albicans. In this paper, we show that C. albicans fimbriae also bind to asialo-GM1 [gangliotetraosylceramide: beta Gal(1-3)beta GalNAc(1-4) beta Gal(1-4)beta Glc(1-1)Cer] immobilized on microtiter plates in a saturable and concentration-dependent manner. C. albicans fimbrial binding to exfoliated human buccal epithelial cells (BECs) was inhibited by asialo-GM1 in in vitro binding assays. The fimbriae interact with the glycosphingolipid receptors via the carbohydrate portion of the receptors, since fimbriae were observed to bind to synthetic beta GalNAc(1-4)beta Gal-protein conjugates and the disaccharide was able to inhibit binding of fimbriae to BECs in in vitro binding assays. We conclude from these results that the C. albicans yeast form expresses a fimbrial adhesin that binds to glycosphingolipids displayed on the surface of human BECs.

Isolation and characterization of a gene involved in hemagglutination by an avian pathogenic Escherichia coli strain

In this article, we report the isolation and characterization of a gene that may be important in the adherence of avian pathogenic Escherichia coli to the avian respiratory tract. The E. coli strain HB101, which is unable to agglutinate chicken erythrocytes, was transduced with cosmid libraries from the avian pathogenic E. coli strain chi 7122. Enrichment of transductants that could agglutinate chicken erythrocytes yielded 19 colonies. These isolates contained cosmids that encompassed four nonoverlapping regions of the E. coli chromosome. Only one group of cosmids, represented by pYA3104, would cause E. coli CC118 to agglutinate chicken erythrocytes. A 10-kb fragment of this cosmid was subcloned in pACYC184. Transposon mutagenesis of this fragment with Tn5seq1 indicated that a contiguous 4.4-kb region of cloned DNA was required for hemagglutination. In vitro transcription/translation assays indicated that this 4.4-kb region of DNA encoded one protein of approximately 140 kDa. The nucleotide sequence of this region was determined and found to encode one open reading frame of 4,134 nucleotides that would encode a protein of 1,377 amino acids with a deduced molecular weight of 148,226. This gene confers on E. coli K-12 a temperature-sensitive hemagglutination phenotype that is best expressed when cells are grown at 26 degrees C, and we have designated this gene tsh and the deduced gene product Tsh. Insertional mutagenesis of the chromosomal tsh gene in chi 7122 had no effect on hemagglutination titers. The deduced protein was found to contain significant homology to the Haemophilus influenzae and Neisseria gonorrhoeae immunoglobulin A1 proteases. These data indicate that (i) a single gene isolated from the avian pathogenic E. coli strain chi 7122 will confer on E. coli K-12 a hemagglutination-positive phenotype, (ii) chi 7122 contains at least two distinct mechanisms to allow hemagglutination to occur, and (iii) the hemagglutinin Tsh has homology with a class of proteins previously not known to exist in E. coli.

The effect of anti-exotoxin A on the adherence of Pseudomonas aeruginosa to hamster tracheal epithelial cells in vitro

One of the most important initial events of colonization and infection of epithelial tissues is the adherence of bacteria to mucosal surfaces. Bacterial adhesion to the epithelial cell may be mediated by a variety of adhesins, including exoproducts. One of these exoproducts, exotoxin A (EA) is a three-domain bacterial toxin that kills mammalian cells by gaining entry to the cytosol and inactivating protein synthesis. In the present study, HTE cultures, 2-4 weeks in vitro (containing both ciliated and non-ciliated cells), were treated for 1 hr with two different non-mucoid strains of Pseudomonas aeruginosa (1 x 10(8) organisms/ml) in the presence of anti-EA. 50 randomly selected fields were evaluated via SEM at x2500 magnification and the number of bacterial clusters/field quantitated. The results of this study indicate, first, that both piliated (ATCC15692) and non-piliated (PAKp) P. aeruginosa will bind to the HTE cells and, second, that treatment of HTE cells with either strain of P. aeruginosa in the presence of anti-EA will reduce bacterial binding by 25% to 50%. Thus, EA may participate in the adhesion of P. aeruginosa to respiratory tract epithelia.

The binding of Pseudomonas aeruginosa pili to glycosphingolipids is a tip-associated event involving the C-terminal region of the structural pilin subunit

Pili are one of the adhesins of Pseudomonas aeruginosa that mediate adherence to epithelial cell-surface receptors. The pili of P. aeruginosa strains PAK and PAO were examined and found to bind gangliotetraosyl ceramide (asialo-GM1) and, to a lesser extend, II3N-acetylneuraminosylgangliotetraosyl ceramide (GM1) in solid-phase binding assays. Asialo-GM1, but not GM1, inhibited both PAK and PAO pili binding to immobilized asialo-GM1 on the microtitre plate. PAO pili competitively inhibited PAK pili binding to asialo-GM1, suggesting the presence of a structurally similar receptor-binding domain in both pilus types. The interaction between asialo-GM1 and pili occurs at the pilus tip as asialo-GM1 coated colloidal gold only decorates the tip of purified pili. Three sets of evidence suggest that the C-terminal disulphide-bonded region of the Pseudomonas pilin is exposed at the tip of the pilus: (i) immunocytochemical studies indicate that P. aeruginosa pili have a basal-tip structural differentiation where the monoclonal antibody (mAb) PK3B recognizes an antigenic epitope displayed only on the basal ends of pili (produced by shearing) while the mAb PK99H, whose antigenic epitope resides in residues 134-140 (Wong et al., 1992), binds only to the tip of PAK pili; (ii) synthetic peptides, PAK(128-144)ox-OH and PAO(128-144)ox-OH, which correspond to the C-terminal disulphide-bonded region of Pseudomonas pilin are able to bind to asialo-GM1 and inhibit the binding of pili to the glycolipid; (iii) PK99H was shown to block PAK pilus binding to asialo-GM1.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for asialo GM1 as a corneal glycolipid receptor for Pseudomonas aeruginosa adhesion

Anti-gangliotetraosylceramide (anti-asialo GM1) and antiparagloboside monoclonal antibodies (MAbs) were used in immunofluorescence, immunoelectron-microscopic, and in vitro binding inhibition assays to determine whether either of the glycolipids was detectable in the normal cornea, whether levels changed following corneal scarification and either trypsin treatment or incubation in vitro with Pseudomonas aeruginosa, and whether either of the MAbs could competitively inhibit P. aeruginosa binding to cornea. No immunostaining above background for either glycolipid was observed in frozen, unfixed sections or in lightly fixed, K4M-embedded antibody-gold-labeled thin sections of normal cornea. In frozen sections of organ-cultured scarified cornea, no increased immunostaining for anti-asialo GM1 or antiparagloboside reactivity was noted immediately or 60 min after corneal scarification. However, at 60 min after scarification and in vitro incubation of the eye with either trypsin or P. aeruginosa, enhanced immunostaining for both glycolipids was associated with cells within or immediately adjacent to the wound site. Trypsin increased immunoreactivity in the wound site more markedly compared with incubation with P. aeruginosa, but immunostaining was similarly localized with either treatment. No staining above background was seen in control sections. Similarly, with immunoelectron microscopy, increased immunogold-MAb staining for both glycolipids was seen on the plasma membranes of the wound-site cells of eyes incubated with either trypsin or P. aeruginosa compared with controls that were similarly immunostained but with the primary antibody either omitted or substituted with a nonspecific MAb. Competitive binding inhibition assays, in which the bacterial inoculum or the eye in organ culture was incubated with anti-asialo GM1 MAb prior to topical ocular application of the bacteria, showed significantly decreased P. aeruginosa adhesion compared with preparations similarly treated with phosphate-buffered saline or antiparagloboside MAb. These data provide evidence to support the hypothesis that asialo GM1, not paragloboside, serves as a receptor for P. aeruginosa binding to the scarified cornea of the adult mouse and spatially localizes both glycolipids in the wound site.

Pulmonary clearance and inflammatory response in C3H/HeJ mice after intranasal exposure to Pseudomonas spp

The environmental release of engineered microorganisms has caused health and environmental concerns. In this study, an animal model was used to examine health effects following pulmonary exposure to environmental and clinical isolates. In order to rule out the possibility that an adverse response was caused by endotoxin, 50% lethal doses (LD50) were determined, when possible, with endotoxin-sensitive (C3HeB/FeJ) and endotoxin-resistant (C3H/HeJ) mice by using both environmental isolates (Pseudomonas aeruginosa BC16, BC17, BC18, and AC869 and Pseudomonas maltophilia BC6) and clinical isolates (P. aeruginosa PAO1 and DG1). The LD50 of strains AC869, DG1, and PAO1 are 1.05 x 10(7), 6.56 x 10(6), and 1.02 x 10(7) CFU, respectively, in C3HeB/FeJ mice and 1.05 x 10(7), 1.00 x 10(7), and 2.75 x 10(6) CFU, respectively, in C3H/HeJ mice. Strains BC17 and BC18 were not lethal to the animals. On the basis of the LD50 data, an appropriate sublethal dose (approximately 10(6) CFU) was selected. Animals were challenged intranasally with microorganisms, and clearance from the lungs and nasal cavity was determined. Strains BC17, BC18, and AC869 were not detected in lungs or nasal washes 14 days following treatment. Strains BC6, BC16, and DG1 were recovered from the nasal cavities at the end of the experiment. Only strain PAO1 was detected in lungs and in nasal cavities 14 days after treatment. At selected intervals following treatment, the percentages of polymorphonuclear leukocytes and lymphocytes in bronchoalveolar lavage samples were determined. P. aeruginosa AC869, PAO1, and DG1 elicited a relatively strong inflammatory response which was indirectly related to lung clearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Therapeutics used to alleviate peptic ulcers inhibit H. pylori receptor binding in vitro

Treatment with bismuth-containing remedies has been long associated with the alleviation of minor gastric ailments. Bismuth salts have a potent antimicrobial activity, and are part of the current standard regime used to treat Helicobacter pylori infection. H. pylori is considered to be the major etiological factor in the development of peptic ulcer disease. Earlier efficacious treatments for peptic ulcer included the oral administration of Tween detergents. We have found that these agents have an inhibitory effect on H. pylori adhesion to the lipid species phosphatidylethanolamine (PE) and gangliotetraosylceramide (Gg4) shown previously to be receptors for H. pylori binding in vitro. H. pylori binding to PE and Gg4 was inhibited after a thirty minute preincubation with different bismuth compounds: bismuth subsalicylate > bismuth subgallate > bismuth carbonate > colloidal bismuth subcitrate > tripotassium dicitrato bismuthate. No inhibitory effect on H. pylori binding was observed when bismuth salts were added directly into the binding assay. No changes in bacterial morphology and motility were observed after the thirty minute incubation. Pretreatment with Tween detergents also inhibited H. pylori receptor binding by up to 80% at concentrations as low as 0.0001%. These results suggest that inhibition of H. pylori/host cell adhesion might play a role in efficacious treatment for this infection.

Receptor affinity purification of a lipid-binding adhesin from Helicobacter pylori

Our previous work has shown that Helicobacter pylori specifically recognizes gangliotetraosylceramide, gangliotriaosylceramide, and phosphatidylethanolamine in vitro. This binding specificity is shared by exoenzyme S from Pseudomonas aeruginosa, and monoclonal antibodies against this adhesin prevent the attachment of H. pylori to its lipid receptors. We now report the use of a novel, versatile affinity matrix to purify a 63-kDa exoenzyme S-like adhesin from H. pylori which is responsible for the lipid-binding specificity of this organism.

Adhesins and receptors of Pseudomonas aeruginosa associated with infection of the respiratory tract

Substantial progress has been made in defining a number of Pseudomonas adhesins which may be involved in the pathogenesis of respiratory infection. As yet, it is unclear which of these adhesins are primarily responsible for initiating infection in CF. The findings that CF epithelial cells have increased numbers of receptors for P. aeruginosa attachment and that CF epithelia are less highly sialylated than normal epithelial cells is consistent with a role for Pseudomonas pili in the initial recognition of asialoganglioside receptors on epithelial cells. In addition, there is ample evidence supporting the presence of several classes of non-pilus adhesins. Adherence properties of P. aeruginosa clearly vary from strain to strain and it appears likely that all potential adhesions are not equally expressed. More importantly, the regulation of the expression of these adhesins is unlikely to be constitutive. Some may be expressed only when triggered by the appropriate environmental conditions as found in vivo. In reviewing the pathogenesis of Pseudomonas infection in the CF lung, several classes of receptors must be considered. Pseudomonas infection is limited to the bronchi in CF. The organisms do not invade the bronchial tissue, but remain in the airways forming a biofilm with associated microcolonies. Thus, it would seem reasonable to expect Pseudomonas receptors within respiratory mucin. However, to date, there is little confirmatory data to support the presence of specific receptors in mucin. Alternatively, it is possible that the failure of bacterial binding to mucin components may contribute to colonization as organisms which are not efficiently cleared by muco-ciliary function may persist in the airways long enough to find or expose cryptic epithelial binding sites. This hypothesis is supported by binding studies which demonstrate decreased Pseudomonas attachment to CF as compared with normal respiratory mucins. Based on the available data, there appears to be a hierarchy of adhesin expression. Multiple ligand-receptor interactions may occur in the respiratory tract and it may be difficult to analyze the effect of secondary adhesins in the presence of what appears to be the dominant ligand, i.e. pilin. Thus, the failure to find the expected sialylated receptor for Pseudomonas attachment may be due to methodologic problems such as studying strains under conditions in which pili are well expressed and affinities for asialylated receptors predominate. This may not be the situation in vivo after the initial contact of the infecting organisms with the epithelial surface. Not only must the organism attach initially, but it must then be able to persist within the lung. Further studies, based on genetically defined mutants should help define which P. aeruginosa gene products and which components of the CF but not the normal epithelium are responsible for this unique but ultimately fatal host/bacterium interaction.

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.

A murine model of chronic mucosal colonization by Pseudomonas aeruginosa

Chronic mucosal colonization by Pseudomonas aeruginosa is an integral part of the pathologic process associated with disease due to infection with this organism. We have adapted the streptomycin-treated murine model of chronic mucosal colonization by enteric pathogens to study colonization by P. aeruginosa. Mice first received 1 mg of streptomycin per ml of drinking water for 2 to 5 days and then ingested 10(7) CFU of P. aeruginosa per ml of drinking water for a minimum of 5 days. The result of this regimen was chronic mucosal colonization with P. aeruginosa for up to 10 weeks, which was determined by fecal cultures and confirmed by culture of the intestines after killing of the experimental animals. Bacterial counts were highest in the cecum and colon, with some evidence for extraintestinal bacterial translocation as well. Use of P. aeruginosa mutants deficient in the production of colonization factors such as pili and those dependent on the rpoN gene product resulted in a lower level of chronic colonization. Immune responses to type-specific lipopolysaccharide, pili, and flagellar antigens were measured, and increases in both serum and intestinal antibodies were usually elicited when a strain elaborated a given antigen. This model represents an easy method of routinely achieving chronic mucosal colonization by P. aeruginosa and should prove useful for the study of both bacterial virulence factors and host responses associated with this infectious process.

Genetic analysis of Pseudomonas aeruginosa adherence: distinct genetic loci control attachment to epithelial cells and mucins

Infection of mucosal tissues by the opportunistic pathogen Pseudomonas aeruginosa is initiated by attachment of the bacterium to host tissues. To gain a better understanding of this interaction, we used two methods to isolate mutants of P. aeruginosa with altered adherence to cultured A549 cells and to mucins. First, from a population of nonpiliated mutants of P. aeruginosa mutagenized with transposon Tn5G, we have isolated variants that are defective in binding to both A549 cells and respiratory mucins. Using a cloned transposon plus flanking DNA from one such mutant as a DNA probe, we have isolated plasmids from a cosmid bank, which, upon reintroduction to the original mutants, restored adhesion to both A549 cells and mucin. The second strategy to identify genes involved in adhesion used mutagenesis of P. aeruginosa N1G, an rpoN mutant which is unable to bind to either A549 cells or mucin, with transposon Tn5 containing an outward-directed promoter. From this bank of mutagenized P. aeruginosa N1G, two classes of adhesion variants were isolated; one class attached to A549 cells and to mucin, and the other class restored binding of the rpoN mutant to mucin but not to A549 cells. These findings suggest that P. aeruginosa can express at least two adhesins distinct from pili, one recognizing receptors shared by epithelial cells and mucins and the other recognizing mucins alone.