Bacterial lectins, cell-cell recognition and infectious disease

Numerous bacterial strains produce surface lectins, commonly in the form of fimbriae that are filamentous assemblies of protein subunits. Among the best characterized of these are the type 1 (mannose specific) fimbrial lectins of Escherichia coli that consist almost exclusively of one class of subunit with a molecular mass of 17 kDa. They possess an extended combining site corresponding to a trisaccharide and preferentially bind carbohydrate units of oligomannose or hybrid type. Type 1 fimbriae also possess a hydrophobic region close to the carbohydrate-binding site, since aromatic alpha-mannosides inhibit strongly (up to 1000-times more than methyl alpha-mannoside) the agglutination of yeasts by the bacteria and the adherence of the latter to pig ileal epithelial cells. The combining sites of type 1 fimbriae of the salmonellae and of other enteric bacteria are different from those of E. coli in that they are smaller and do not possess a hydrophobic region. The various bacterial surface lectins appear to function primarily in the initiation of infection by mediating bacterial adherence to epithelial cells, e.g. in the urinary and gastrointestinal tracts. The mannose specific lectins also act as recognition molecules in lectinophagocytosis (i.e. phagocytosis of the bacteria in the absence of opsonins) by mouse, rat and human peritoneal macrophages, and human polymorphonuclear leukocytes. Affinity chromatography of membrane lysates from human polymorphonuclear leukocytes on immobilized type 1 fimbrial lectin, using methyl alpha-mannoside as eluent, showed that glycoproteins with apparent molecular masses of 70-80, 100 and 150 kDa act as receptors for the bacteria. Inhibition experiments with monoclonal antibodies suggest that the glycoprotein bands of 100 and 150 kDa may be identical with the alpha and beta subunits of leukocyte complement receptors and adhesion glycoproteins involved in complement-mediated opsonophagocytosis. The systems described serve as a fine illustration for the biological role of lectin-carbohydrate interactions. Further studies of these systems will lead to a deeper understanding of the molecular basis of infectious diseases, and perhaps also to new approaches for their prevention.     

The genetic determinant of adhesive function in type 1 fimbriae of Escherichia coli is distinct from the gene encoding the fimbrial subunit.

The role of type 1 fimbriae in the mannose-sensitive attachment of Escherichia coli to eucaryotic cells was investigated by deletion mutation analysis of a recombinant plasmid, pSH2, carrying the genetic information for the synthesis and expression of functional type 1 fimbriae. A mutant, pUT2002, containing a deletion remote from the structural gene encoding the 17-kilodalton subunit protein of type 1 fimbriae failed to agglutinate guinea pig erythrocytes even though the bacteria expressed fimbriae morphologically and antigenically indistinguishable from those produced by the intact recombinant plasmid. Fimbriae isolated from pUT2002 failed to agglutinate guinea pig erythrocytes, but reacted with a monoclonal antibody specific for quaternary structural determinants of type 1 fimbriae. Moreover, the dissociated fimbrial subunits from this mutant were indistinguishable from normal fimbriae by their migration during electrophoresis in sodium dodecyl sulfate-polyacrylamide gels, by their reactivity with a monoclonal antibody directed against a subunit-specific epitope, and in enzyme-linked immunosorbent assays with monospecific antisera. These results indicate that the adhesive functions in type 1 fimbriae are dependent on a factor(s) encoded by a gene other than those required for synthesis, assembly, and expression of the structural 17-kilodalton subunit.     

Molecular and structural aspects of fimbriae biosynthesis and assembly in Escherichia coli

Abstract: Fimbriae are long filamentous polymeric protein structures located at the surface of bacterial cells. They enable the bacteria to bind to specific receptor structures and thereby to colonise specific surfaces. Fimbriae consist of so-called major and minor subunits, which form, in a specific order, the fimbrial structure. In this review emphasis is put on the genetic organisation, regulation and especially on the biosynthesis of fimbriae of enterotoxigenic Escherichia coli strains, and more in particular on K88 and related fimbriae, with ample reference to the well-studied P and type 1 fimbriae. The biosynthesis of these fimbriae requires two specific and unique proteins, a periplasmic chaperone and an outer membrane located molecular usher ('doorkeeper'). Molecular and structural aspects of the secretion of fimbrial subunits across the cytoplasmic membrane, the interaction of these subunits with the periplasmic molecular chaperone, their translocation to the inner site of the outer membrane and their interaction with the usher protein, as well as the (ordered) translocation of the subunits across the outer membrane and their assembly into a grwoing fimbrial structure will be described. A model for K88 fimbriae is presented.     

Precise and rapid assessment of Escherichia coli adherence to vaginal epithelial cells by flow cytometry

BACKGROUND: In the pathogenesis of Escherichia coli urinary tract infections (UTIs) in women, infecting bacteria adhere to vaginal and periurethral epithelial cells prior to ascending to the bladder and causing infection. Complex interactions among specific bacterial adhesins and various host factors appear to influence adherence of E. coli to mucosal surfaces such as the urogenital epithelium. To conduct population-based studies assessing host epithelial cell determinants that influence bacterial attachment, a method of measuring bacterial adherence utilizing clinically derived epithelial cell samples is needed. METHODS: We developed and standardized an efficient, accurate, high-throughput method for analyzing the adherence of uropathogenic E. coli to clinical samples containing a large number of exfoliated vaginal epithelial cells (VEC). Three wild-type E. coli strains isolated from women with UTI (IA2 expressing pap-encoded, class II fimbriae only; F24 expressing pap-encoded, class II and type 1 fimbriae; and F20, without pap-encoded or type I fimbriae) were transformed with gfpmut3, encoding green fluorescent protein, incubated with VECs, and analyzed by flow cytometry. RESULTS: Enumeration of the binding of each E. coli strain to 10,000 VECs showed reproducible, highly significant strain-dependent differences in adherence to VECs. Differential analysis of the relative contributions of type 1 pili and P fimbrial-mediated binding to the adherence phenotype was performed. It demonstrated that IA2 binding was dependent entirely on P fimbriae, whereas F24 binding was dependent on both P and type 1 fimbriae. CONCLUSIONS: This method has great potential for use in high-throughput analyses of clinically derived epithelial cell samples and will be valuable in population-based investigations of host-parasite interactions in UTI utilizing VECs collected from specific patient groups.     

A possible association between CFA (I) fimbriae and K99 fimbriae on Escherichia coli and bacterial adherence to human lymphocytes

We have explored a possible association between Escherichia coli binding to human lymphocytes and plasmid coded fimbriae on the bacterial surface. E. coli with or without the plasmid coded membrane CFA(I), K99 and K88 were mixed with freshly-drawn human peripheral blood lymphocytes. When the lymphocytes were mixed with E. coli possessing the CFA(I) fimbriae, 59% of the lymphocytes bound bacteria onto the surface, whereas only 22% of the lymphocytes bound the CFA(I)- derivative. The lymphocytes bound 53% and 56% of two K9+ strains, whereas 22% and 8% of the lymphocytes adhered the same strains without the K99 fimbriae. Twelve per cent and 7% of lymphocytes bound bacteria when the strain was K88+ or K88-, respectively. Likewise a low (8%) adherence to lymphocytes was found when the E. coli did not possess fimbriae or flagella.     

Identification of two ancillary subunits of Escherichia coli type 1 fimbriae by using antibodies against synthetic oligopeptides of fim gene products.

We have chemically synthesized oligopeptides corresponding to the NH2-terminal stretch of two gene products, designated FimG and FimH, of the fim gene cluster of Escherichia coli. These synthetic peptides, designated S-T1FimG(1-16) and S-T1FimH(1-25)C, evoked antibodies in rabbits that reacted with 14- and 29-kilodalton subunits, respectively, of dissociated fimbriae encoded by the recombinant plasmid pSH2 carrying the genetic information for the synthesis and expression of functional type 1 fimbriae. Neither of these fimbrial proteins was detected in dissociated fimbrial preparations from nonadhesive E. coli cells carrying the mutant plasmid pUT2002, containing a restriction site-specific deletion of fimG and fimH. Anti-S-T1FimH(1-25)C inhibited the adherence of type 1 fimbriated E. coli to epithelial cells. Immunoelectron microscopy revealed that anti-S-T1FimH(1-25)C, but not anti-S-T1FimG(1-16), bound to intact type 1 fimbriae of E. coli at the fimbrial tips and at long intervals along the fimbrial filaments. Anti-S-T1FimG(1-16) appeared to be directed at epitopes not accessible on the intact fimbriae and consequently failed to bind to intact fimbriae or to block fimbrial attachment. Our results suggest that the fimG and fimH gene products are components of type 1 fimbriae and that FimH may be the tip adhesin mediating the binding of type 1 fimbriated E. coli to D-mannose residues on mucosal surfaces.     

Kidney bean lectin-induced Escherichia coli overgrowth in the small intestine is blocked by GNA, a mannose-specific lectin

The reversible and dose-dependent hyperplastic growth of the small intestine and accelerated epithelial cell turnover caused by feeding rats with diets containing kidney bean lectin (PHA) increased the proportion of immature cells on the villi whose membrane and/or cytoplasm contained mainly simple, polymannosylated glycans. These new α-linked mannosyl terminals, particularly of the damaged epithelium, facilitated the preferential adherence of opportunistic Escherichia coli with mannose-sensitive Type 1 fimbriae, and other coliforms, to the glycocalyx. Accordingly, the growth of the gut was accompanied by a reversible and PHA dose-dependent overgrowth with E.coli. As expected from their common carbohydrate specificity, the inclusion in the diet of the mannose-specific agglutinin from snowdrop ( Galanthus nivalis ) bulbs (GNA) significantly reduced the extent of E.coli overgrowth, but abolished neither the growth nor the damage caused by PHA to the small intestine. Thus, GNA and perhaps other mannose-specific lectins, especially when used in a preventive mode, can be used to specifically block the proliferation of Type 1 E.coli in the small intestine.     

A rapid bioluminescence method for quantifying bacterial adhesion to polystyrene

Bioluminescence ATP analysis has been used to assess bacterial adhesion with hydrophobic polystyrene tubes as the attachment surface. The assay was performed at 37 degrees C and pH 6.8 with a 10 min incubation period. A variation of more than 200-fold was observed in the adherence capacity of 34 urinary isolates of Escherichia coli, and organisms could be classified as strongly or weakly adherent. All strains capable of strong adhesion possessed both type 1 fimbriae and flagella, and maximum adhesion was expressed during the exponential growth phase. Attachment was in all cases virtually eliminated by addition of 2.5% (w/v) D-mannose to the incubation buffer. Conversely, strains which were deficient in type 1 fimbriae or flagella, or both, were weakly adherent during all phases of growth. There was no correlation between adherence of E. coli to polystyrene and adherence to buccal or uroepithelial cells, but there was a significant association with adherence to uromucoid (P less than 0.002).     

Use of the coagglutination reaction of yeast-like Candida maltosa fungi for detecting fimbriae in intestinal bacteria

The capacity of nonpathogenic yeast-like C. maltosa strains to coagglutinate Escherichia coli has been studied. C. maltosa cells have also been shown to coagglutinate E. coli possessing mannose-sensitive adhesins in a wide range of their concentrations (5-140 bacterial cells per C. maltosa cell). Strains belonging to types CFA/I and CFA/II with fimbriae, similarly to their corresponding paired genetically related strains without these adhesins, are practically incapable of agglutinating C. maltosa cells, while strains K88 and B41 react with them. The reaction occurs at a concentration of 9.5-37.0 and 38.0-55.5 bacteria respectively per C. maltosa cell and is not inhibited by 1% d-mannose. The suggestion that C. maltosa cell surface glycoproteins contain not only receptors for E. coli fimbriae, type I, but also components similar in their structure to receptors specific to the mannose-resistant adhesins of strains K88, K99 and 41, has been confirmed by hemagglutination inhibition with C. maltosa surface antigens as inhibiting agents.     

Characterization of fimbriae produced by enteropathogenic Escherichia coli.

Enteropathogenic Escherichia coli (EPEC) express rope-like bundles of filaments, termed bundle-forming pili (BFP) (J. A. Girón, A. S. Y. Ho, and G. K. Schoolnik, Science 254:710-713, 1991). Expression of BFP is associated with localized adherence to HEp-2 cells and the presence of the EPEC adherence factor plasmid. In this study, we describe the identification of rod-like fimbriae and fibrillae expressed simultaneously on the bacterial surface of three prototype EPEC strains. Upon fimbrial extraction from EPEC B171 (O111:NM), three fimbrial subunits with masses of 16.5, 15.5, and 14.7 kDa were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Their N-terminal amino acid sequence showed homology with F9 and F7(2) fimbriae of uropathogenic E. coli and F1845 of diffuse-adhering E. coli, respectively. The mixture of fimbrial subunits (called FB171) exhibited mannose-resistant agglutination of human erythrocytes only, and this activity was not inhibited by alpha-D-Gal(1-4)-beta-Gal disaccharide or any other described receptor analogs for P, S, F, M, G, and Dr hemagglutinins of uropathogenic E. coli, which suggests a different receptor specificity. Hemagglutination was inhibited by extracellular matrix glycoproteins, i.e., collagen type IV, laminin, and fibronectin, and to a lesser extent by gangliosides, fetuin, and asialofetuin. Scanning electron microscopic studies performed on clusters of bacteria adhering to HEp-2 cells revealed the presence of structures resembling BFP and rod-like fimbriae linking bacteria to bacteria and bacteria to the eukaryotic cell membrane. We suggest a role of these surface appendages in the interaction of EPEC with eukaryotic cells as well as in the overall pathogenesis of intestinal disease caused by EPEC.     

Detection of Shiga-like toxin on the outer membranes of Shigella species and Escherichia coli K-12

Abstract Outer membranes of Shigella species and E. coli K-12 carrying large invasive plasmids and isogenic non-invasive strains without plasmids were analyzed by SDS-PAGE. The immunoblotting analysis of the outer membrane proteins of these bacteria was performed with monoclonal antibody (mAb) made against A and B subunits of Shiga-like toxin (SLT). The SLT was detected in the outer membranes of S. dysenteriae 1 IDBM11, S. sonnei PNS20, S. flexneri M90T, S. dysenteriae 60R, and E. coli K-12 strain AB2463. The two other E. coli K-12 strains, C600 and 933J were included as controls for low and high toxin producers respectively. The outer membrane protein band of molecular weight 70 kDa was common to all bacterial strains studied. The most prominent band of 70 kDa protein was seen to be present in the high toxin producing plasmidless strain of S. dysenteriae 60R and the lysogenic strain of E. coli 933J. The invasive strains of S. dysenteriae 1 and S. flexneri M90T which carry the large invasive plasmids showed the least prominent band of 70 kDa protein.
The immunoblotting analysis of Shiga-toxin partially purified from the S. dysenteriae 60R strain revealed the absence of 70 kDa band on SDS-PAGE, instead the two dissociated subunits were seen. Furthermore, periplasmic Shiga-toxin proteins also showed the complete dissociation into A and B subunits. However, under the same denaturing conditions, the 70 kDa protein band cross-reacting with mAb against A and B subunits was still present in the outer membranes of all different strains.     

Carbohydrates as future anti-adhesion drugs for infectious diseases

Adhesion of pathogenic organisms to host tissues is the prerequisite for the initiation of the majority of infectious diseases. In many systems, it is mediated by lectins present on the surface of the infectious organism that bind to complementary carbohydrates on the surface of the host tissues. Lectin-deficient mutants often lack the ability to initiate infection. The bacterial lectins are typically in the form of elongated submicroscopic multi-subunit protein appendages, known as fimbriae (or pili). The best characterized of these are the mannose-specific type 1 fimbriae, the galabiose-specific P fimbriae and the N-acetylglucosamine-specific fimbriae of Escherichia coli. Soluble carbohydrates recognized by the bacterial surface lectins block the adhesion of the bacteria to animal cells in vitro. Aromatic alpha-mannosides are potent inhibitors of type 1 fimbriated E. coli, being up to 1000 times more active than MealphaMan, with affinities in the nanomolar range. This is due to the presence of a hydrophobic region next to the monosaccharide-binding site of the fimbriae, as recently demonstrated by X-ray studies. Polyvalent saccharides (e.g., neoglycoproteins or dendrimers) are also powerful inhibitors of bacterial adhesion in vitro. Very significantly, lectin-inhibitory saccharides have been shown to protect mice, rabbits, calves and monkeys against experimental infection by lectin-carrying bacteria. Since anti-adhesive agents do not act by killing or arresting the growth of the pathogens, it is very likely that strains resistant to such agents will emerge at a markedly lower rate than of strains that are resistant to antibiotics. Suitable sugars also inhibit the binding to cells of carbohydrate-specific toxins, among them those of Shigella dysenteriae Type 1, and of the homologous Verotoxins of E. coli, specific for galabiose. Appropriately designed polyvalent ligands are up to six orders of magnitude stronger inhibitors of toxin binding in vitro than the monovalent ones, and they protect mice against the Shigella toxin. The above data provide clear proof for the feasibility of anti-adhesion therapy of infectious diseases, although this has not yet been successful in humans. All in all, however, there is little doubt that inhibitors of microbial lectins will in the near future join the arsenal of drugs for therapy of infectious diseases.     

Interactions between Mytilus haemocytes and different strains of Escherichia coli and Vibrio cholerae O1 El Tor: role of kinase-mediated signalling

Marine bivalves accumulate large amounts of bacteria from the environment (mainly Vibrionaceae and coliforms). Although persistence of different bacteria in bivalve tissues largely depends on their sensitivity to the bactericidal activity of circulating haemocytes and haemolymph soluble factors, the mechanisms involved in bacteria-host cell interactions in these invertebrates are largely unknown. In the mussel Mytilus, differences in interactions between haemocytes and different Escherichia coli and Vibrio cholerae strains [E. coli MG155, a wild-type strain carrying type 1 fimbriae, and its unfimbriated derivative, AAEC072 Deltafim; V. cholerae O1 El Tor biotype strain N16961, carrying the mannose-sensitive haemagglutinin (MSHA), and its MSHA mutant] lead to differences in bactericidal activity in the presence of serum. Here we show that different bacteria induced distinct patterns of phosphorylation of mitogen-activated protein kinases (MAPKs), in particular of the stress-activated MAPKs involved in the immune response. Differences in phosphorylation of PKC-like proteins were also observed. The results support the hypothesis that, like in mammalian host cells, different bacteria can modulate the signalling pathways of mussel haemocytes. The lower anti-bacterial activity towards the mutant E. coli strain and wild-type V. cholerae compared with wild E. coli may result from a reduced capacity of activating MAPKs. Moreover, the mutant V. cholerae strain that was the most resistant to the haemocyte bactericidal activity induced downregulation of cell signalling and showed the strongest effect on lysosomal membrane stability, evaluated as a marker of bivalve cell stress. These data suggest that certain bacteria could evade the bactericidal activity of mussel haemocytes through disruption of the host signalling pathways.     

The Escherichia coli biofilm-promoting protein Antigen 43 does not contribute to intestinal colonization

Abstract Escherichia coli is a versatile organism capable of causing a variety of intestinal and extraintestinal diseases, as well as existing as part of the commensal flora. A variety of factors permit specific attachment to host receptors including fimbrial adhesins and outer membrane proteins such as autotransporters. One of the better characterized autotransporters is Antigen 43 (Ag43), the major phase-variable surface protein of E. coli. Ag43 is associated with bacterial cell-cell aggregation and biofilm formation. Nevertheless, the precise biological significance and contribution to intestinal colonization remain to be elucidated. Here we investigated the contribution of Ag43 to E. coli adherence to intestinal epithelial cells and colonization of the mouse intestine. These investigations revealed that Ag43 increased in vitro adherence of E. coli to epithelial cells by promoting bacterial cell-cell aggregation but that Ag43 did not promote specific interactions with the mammalian cells. Furthermore, Ag43 did not contribute significantly to colonization of the mouse intestine and expression of Ag43 was lost a few days after colonization of the mouse was established. Unexpectedly, considering its similarity to other adhesins, our findings suggest that Ag43 does not act as a direct colonization factor by binding to mammalian cells.     

A key role for type 1 pili in enterobacterial communicability

Up to 80% of faecal Escherichia coli strains are able to produce type 1 pili. These filamentous bacterial surface organelles, which mediate mannose-sensitive attachment to mammalian epithelial cells, are also conserved throughout the Enterobacteriaceae. As a potential explanation for their prevalence among intestinal isolates of enteric bacteria, it has been widely speculated that type 1 pili are important for adherence to the host's intestinal mucosa. However, conclusive evidence for this idea is lacking, and there are reasonable grounds for doubting such an effect. Permanent interruption of type 1 piliation in previously pil+ E. coli (by directed mutagenesis of pilA, the gene coding for the major structural subunit of type 1 pili) does not diminish the density of intestinal colonization in individual animals. Rather, as we demonstrate here, this lesion results in a dramatic decrease in transmission of E. coli K1 from experimentally colonized neonatal rats to their littermates. The enhanced communicability associated with type 1 piliation suggests a heretofore unrecognized explanation for the prevalence of type 1 pili among intestinal E. coli; one that does not necessarily require the direct action of these organelles at the intestinal mucosa.     

Binding of intimin from enteropathogenic Escherichia coli to Tir and to host cells

Enteropathogenic Escherichia coli (EPEC) induce characteristic attaching and effacing (A/E) lesions on epithelial cells. This event is mediated, in part, by binding of the bacterial outer membrane protein, intimin, to a second EPEC protein, Tir (translocated intimin receptor), which is exported by the bacteria and integrated into the host cell plasma membrane. In this study, we have localized the intimin-binding domain of Tir to a central 107-amino-acid region, designated Tir-M. We provide evidence that both the amino- and carboxy-termini of Tir are located within the host cell. In addition, using immunogold labelling electron microscopy, we have confirmed that intimin can bind independently to host cells even in the absence of Tir. This Tir-independent interaction and the ability of EPEC to induce A/E lesions requires an intact lectin-like module residing at the carboxy-terminus of the intimin polypeptide. Using the yeast two-hybrid system and gel overlays, we show that intimin can bind both Tir and Tir-M even when the lectin-like domain is disrupted. These data provide strong evidence that intimin interacts not only with Tir but also in a lectin-like manner with a host cell intimin receptor.     

Characterization of a pattern recognition protein, a masquerade-like protein, in the freshwater crayfish Pacifastacus leniusculus

A multifunctional masquerade-like protein has been isolated, purified, and characterized from hemocytes of the freshwater crayfish, Pacifastacus leniusculus. It was isolated by its Escherichia coli binding property, and it binds to formaldehyde-treated Gram-negative bacteria as well as to yeast, Saccharomyces cerevisiae, whereas it does not bind to formaldehyde-fixed Gram-positive bacteria. The intact masquerade (mas)-like protein is present in crayfish hemocytes as a heterodimer composed of two subunits with molecular masses of 134 and 129 kDa. Under reducing conditions the molecular masses of the intact proteins are not changed. After binding to bacteria or yeast cell walls, the mas-like protein is processed by a proteolytic enzyme. The 134 kDa of the processed protein yields four subunits of 65, 47, 33, and 29 kDa, and the 129-kDa protein results in four subunits of 63, 47, 33, and 29 kDa in 10% SDS-PAGE under reducing conditions. The 33-kDa protein could be purified by immunoaffinity chromatography using an Ab to the C-terminal part of the mas-like protein. This subunit of the mas-like protein has cell adhesion activity, whereas the two intact proteins, 134 and 129 kDa, have binding activity to LPSs, glucans, Gram-negative bacteria, and yeast. E. coli coated with the mas-like protein were more rapidly cleared in crayfish than only E. coli, suggesting this protein is an opsonin. Therefore, the cell adhesion and opsonic activities of the mas-like protein suggest that it plays a role as an innate immune protein.     

Curli fibers are required for development of biofilm architecture in Escherichia coli K-12 and enhance bacterial adherence to human uroepithelial cells

Sessile bacteria show phenotypical, biochemical, and morphological differences from their planktonic counterparts. Curli, extracellular structures important for biofilm formation, are only produced at temperatures below 30 C in Escherichia coli K-12 strains. In this report, we show that E. coli K-12 can produce curli at 37 C when grown as a biofilm community. The curli-expressing strain formed more biofilms on polyurethane sheets than the curli-deficient strain under growth temperatures of both 25 C and 37 C. Curli are required for the formation of a three-dimensional mature biofilm, with characteristic water channels and pillars of bacteria. Observations by electron microscopy revealed the presence at the surfaces of the curli-deficient mutant in biofilm of flagella and type I pili. A wild-type curli-expressing E. coli strain significantly adhered to several lines of human uroepithelial cells, more so than an isogenic curlideficient strain. The finding that curli are expressed at 37 C in biofilm and enhance bacterial adherence to mammalian host cells suggests an important role for curli in pathogenesis.     

Fimbriae and adherence of Stenotrophomonas maltophilia to epithelial cells and to abiotic surfaces

Stenotrophomonas maltophilia is an emerging nosocomial bacterial pathogen associated with several infectious diseases and opportunistic infections, especially in immunocompromised patients. These bacteria adhere avidly to medical implants and catheters forming a biofilm that confers natural protection against host immune defences and different antimicrobial agents. The nature of the bacterial surface factors involved in biofilm formation on inert surfaces and in adherence of S. maltophilia to epithelial cells is largely unknown. In this study, we identified and characterized fimbrial structures produced by S. maltophilia grown at 37 degrees C. The S. maltophilia fimbriae 1 (SMF-1) are composed of a 17 kDa fimbrin subunit which shares significant similarities with the N-terminal amino acid sequences of several fimbrial adhesins (G, F17, K99 and 20K) found in Escherichia coli pathogenic strains and the CupA fimbriae of Pseudomonas aeruginosa. All of the clinical S. maltophilia isolates tested produced the 17 kDa fimbrin. Antibodies raised against SMF-1 fimbriae inhibited the agglutination of animal erythrocytes, adherence to HEp-2 cells and biofilm formation by S. maltophilia. High resolution electron microscopy provided evidence of the presence of fimbriae acting as bridges between bacteria adhering to inert surfaces or to cultured epithelial cells. This is the first characterization of fimbriae in this genus. We provide compelling data suggesting that the SMF-1 fimbriae are involved in haemagglutination, biofilm formation and adherence to cultured mammalian cells.