Binding of Escherichia coli S fimbriae to cultured human endothelial cells

Antiadhesion as a functional concept for protection against uropathogenic Escherichia coli: in vitro studies with traditionally used plants with antiadhesive activity against uropathognic Escherichia coli

ETHNOPHARMACOLOGICAL RELEVANCE

Investigation of medicinal plant extracts traditionally used against uncomplicated urinary tract infections (UTI) and identification of antiadhesive effects under in vitro conditions against binding of uropathogenic Escherichia coli (UPEC) on bladder cell surface.

MATERIALS AND METHODS

Literature search on traditionally used medicinal plants for UTI was performed by online data bases and standard herbal monographs. For further identification shortlisting was done by intensive evaluation of results by plausibility and phytochemical aspects. Plant material with documented antibacterial effects was not considered for further investigations. Direct cytotoxicity of EtOH-water (1:1; v/v) extracts of the shortlisted plants was investigated against UPEC strain 2980 and bladder cell line T24. Inhibition of UPEC adhesion to T24 cells was monitored either after pretreatment of bacteria or eukaryotic cells by flow cytometry.

RESULTS

Literature search on traditionally used medicinal plants for UTI resulted in 275 plant species, from which 20 were shortlisted by a validated selection process for experimental testing. While direct cytotoxicity of the extracts (1-2000 μg/mL) against UPEC and T24 cells was excluded significant antiadhesive effects were monitored for five plant extracts. Two of them, prepared from the rhizome of Agropyron repens L. and the stigmata of Zea mays L. decreased bacterial adhesion (IC(25) 630 μg/mL, IC(50) 1040 μg/mL, resp.) by interacting with bacterial outer membrane proteins, which was shown by pretreatment of UPEC. Preparations of three plant extracts from the leaves of Betula spp. (according to European pharmacopoeia 7.0), Orthosiphon stamineus BENTH. and Urtica spp. showed antiadhesive effects by interacting with T24 cells (IC(50) 415, 1330 μg/mL, resp. IC(25) 580 μg/mL). Combination of two extracts, one interacting with the bacterial surface (Zea mays L., Agropyron repens L.) and one with the eukaryotic target (Orthosiphon stamineus BENTH.) revealed synergistic effects, as shown by strongly decreased IC(50) values (131 μg/mL, 511 μg/mL, resp.).

CONCLUSIONS

Different plant extracts, traditionally used for UTI, exhibit antiadhesive effects against UPEC under in vitro conditions. Molecular targets can be different, either on the bacterial or on the host cell surface. Combination of these medicinal plants with different targets, as observed often in phytotherapy, results in synergistic effects.

Inhibition of adhesion of uropathogenic Escherichia coli bacteria to uroepithelial cells by extracts from cranberry

Cranberry extract has been reported as a therapeutic agent, mainly in urinary tract infections due to its anti-adhesive capacity. In order to compare the effects of proanthocyanidin (procyanidin) (PAC)-standardized cranberry extracts and commercial PAC A2, we first investigated the presence of genes encoding known adhesins on 13 strains of uropathogenic strains coming from patients with cystisis. After this characterization, the anti-adhesive effects of PAC A2 were assayed on selected uropathogenic Escherichia coli strains before testing cranberry extracts. Before checking inhibitory effect on bacterial adhesion to cells, we showed that neither PAC A2 or three cranberry extracts (A, B, and C) specifically inhibited the growth and did not supply any potential nutrient to E. coli strains, including the unrelated control strain. PAC A2 exhibited an inhibitory effect on the adhesion of two selected uropathogenic strains of E. coli. This work also showed that a preliminary exposure of bacteria to PAC A2 significantly reduced the adhesion. This phenomenon has been also observed with a lesser impact when uroepithelial cells were pretreated with PAC A2. Moreover, the assays were more robust when bacteria were in fast growing conditions (exponential phase): the adhesion to uroepithelial cells was greater. Significant reduction of adhesion to urepithelial cells was observed: around 80% of inhibition of adhesion with the cranberry extracts at equivalent PAC concentration of 50 μg/mL. The effects of the different assayed extracts were not obviously different except for extract B, which inhibited approximately 55% of adhesion at an equivalent PAC concentration of 5 μg/mL.

The major subunit, CfaB, of colonization factor antigen i from enterotoxigenic Escherichia coli is a glycosphingolipid binding protein

Bacterial adherence to mucosal surfaces is an important virulence trait of pathogenic bacteria. Adhesion of enterotoxigenic Escherichia coli (ETEC) to the intestine is mediated by a number of antigenically distinct colonization factors (CFs). One of the most common CFs is CFA/I. This has a fimbrial structure composed of a major repeating subunit, CfaB, and a single tip subunit, CfaE. The potential carbohydrate recognition by CFA/I was investigated by binding CFA/I-fimbriated bacteria and purified CFA/I fimbriae to a large number of variant glycosphingolipids separated on thin-layer chromatograms. For both fimbriated bacteria and purified fimbriae, specific interactions could be identified with a number of nonacid glycosphingolipids. These included glucosylceramide, lactosylceramide with phytosphingosine and/or hydroxy fatty acids, neolactotetraosylceramide, gangliotriaosylceramide, gangliotetraosylceramide, the H5 type 2 pentaglycosylceramide, the Lea-5 glycosphingolipid, the Lex-5 glycosphingolipid, and the Ley-6 glycosphingolipid. These glycosphingolipids were also recognized by recombinant E. coli expressing CFA/I in the absence of tip protein CfaE, as well as by purified fimbriae from the same strain. This demonstrates that the glycosphingolipid-binding capacity of CFA/I resides in the major CfaB subunit.

Enterohemorrhagic Escherichia coli (EHEC)

Enterohaemorrhagic Escherichia coli has since the last 2 decades been known to cause severe and bloody diarrhoea as well as haemorrhagic colitis (HC) and haemorrhagic uraemic syndrome (HUS) especially among children. The importance of screening for EHEC among children and older patients with severe symptoms is apparent. Production of the verocytotoxins VT1 and VT2 are the main features of EHEC, and the VT types and mode of action during human infection is described. There are, however, other features adding to the pathogenicity. In this review we deal with the importance of properties such as fimbriae and adhesins as well as systems to meet the bacterial need for iron during infection. These factors are probably important for the establishment of EHEC in the gut and add to the bacterial virulence. It has now become evident that VT producing E. coli, irrespective of serogroup, might be human pathogens. We conclude that knowledge of the different possible virulence factors adds to the possibility of separating more virulent from less virulent isolates.

Virulence genes in verocytotoxigenic Escherichia coli strains isolated from humans and cattle

Verocytotoxigenic Escherichia coli (VTEC) causing diarrhoea, haemorrhagic colitis and haemolytic-uremic syndrome usually have additional traits such as the adhesin intimin and a large plasmid that seems to increase virulence. There are, however, isolates of VTEC causing serious symptoms that do not harbour these traits. In the present study we have used PCR with primers detecting adhesin genes other than eaeA, namely fimA, papC, sfaD/sfaE and daaE. We have also used PCR to detect the genes hlyA and iutA that besides the plasmid-borne gene E-hly possibly support the bacterial access to iron. The aim of the study was to identify and compare the presence of virulence genes in VTEC isolates of human and cattle origin. The main finding was that the absence of E-hly might be compensated for by the gene iutA coding for aerobactin or hlyA coding for alpha-haemolysin as 94% of the human VTEC isolates had at least one of these genes. Interestingly, only 45% of VTEC isolated from cattle had any of these genes. We propose that this might be the reason for the relatively low incidence of symptomatic VTEC infections among humans in relation to the high number of VTEC among cattle.

Increased frequency of intestinal Escherichia coli carrying genes for S fimbriae and haemolysin in IgA-deficient individuals

Persons with selective IgA deficiency carry an increased risk of coeliac disease, inflammatory bowel disease and perhaps also gastrointestinal malignancies. Inflammatory bowel disease is associated with an increased carriage of adherent and haemolytic Escherichia coli in the intestinal microflora. This study was designed to investigate whether IgA-deficient individuals carry E. coli with virulence-associated properties in their gut flora. The last free-lying colony of E. coli isolates obtained from rectal flora of 25 IgA-deficient and 20 age-matched control individuals was assayed by multiplex PCR for genes for the following adhesins or virulence determinants: P, type 1 and S fimbriae, Dr haemagglutinin, haemolysin, aerobactin and the capsular types K1 and K5. E. coli strains from the intestinal microflora of IgA-deficient individuals more often had the gene for S fimbriae (36% of the strains compared with 0% in control subjects, P=0.003) as well as for haemolysin (40 vs 10% of the strains, P=0.040). IgA-deficient individuals had instead lower frequencies of E. coli carrying genes for type 1 fimbriae in their microflora (68 vs 90%, P=0.14). The results suggest that IgA-deficient individuals carry an increased frequency of E. coli with potentially inflammatogenic properties in their microflora, which may contribute to the development of gastrointestinal disorders such as inflammatory bowel diseases.

S-fimbriae from Escherichia coli bind to soluble glycoproteins from human milk

BACKGROUND

Escherichia coli (E. coli) strains, expressing S-fimbriae, belong to the most common gram-negative pathogens that cause sepsis and meningitis in neonates. The attachment of S-fimbriae to the cell surface is mediated by membrane glycoconjugates, which often carry N-acetylneuraminic acid.

METHODS

Binding studies were performed with glycoproteins from the whey fraction of human milk to investigate whether they exert a potential inhibitory effect on bacterial adhesion. Whey glycoproteins were separated according to their molecular weight by fast protein liquid chromatography gel filtration. After sodium dodecyl sulfate-polyacrylamide gel electrophoresis, proteins were transferred to nitrocellulose membranes and incubated with isolated S-fimbriae from recombinant E. coli strain HB 101 (pANN 801-4).

RESULTS

S-fimbriae recognized four whey proteins with a molecular mass of more than 200 kDa, 170 to 150 kDa, and 80 kDa. Their glycosylation pattern was investigated using the lectins Sambucus nigra, Maackia amurensis, Galanthus nivalis, and Arachis hypogaea. Thus the presence of N- and O-glycans in these proteins was confirmed. The preferential binding to N-acetylneuraminic acid containing glycoproteins was demonstrated by a complete abolishment of these reactions by incubation with acidic lactose-derived oligosaccharides. However, the cleavage of N-acetylneuraminic acid from glycoproteins by mild acid hydrolysis revealed a second binding site for S-fimbriae on milk proteins of a similar molecular weight range. Terminal galactose in human milk glycoconjugates were thought to react with S-fimbriae as well.

CONCLUSION

These data further support the opinion that glycoproteins from human milk are potential receptor analogues for certain bacteria that may prevent microbial adhesion to the epithelial cell surface.

Binding of the type 3 fimbriae of Klebsiella pneumoniae to human endothelial and urinary bladder cells

Binding of the two identified type 3 fimbrial variants of Klebsiella pneumoniae to human endothelial EA-hy926 and bladder T24 cells was assessed. The recombinant Escherichia coli strain LE392(pFK12), expressing plasmid-encoded type 3 fimbriae of K. pneumoniae, adhered to both cell lines, and the fimbriae purified from the strain bound to both cell lines in a dose-dependent manner. Adhesiveness to both cell lines of chromosomally encoded type 3 fimbriae from K. pneumoniae IApc35 was lower. No binding was detected with type 1 fimbriae of K. pneumoniae. Both type 3 fimbrial variants exhibited a significantly lower affinity for the cell lines than did S fimbriae of meningitis-associated E. coli.

Adhesive properties of P-like fimbriae in Klebsiella-species

Clinical isolates of three encapsulated Klebsiella strains with type 1 (mannose-sensitive, MS+MR-), type 3 (mannose-resistant, MS-MR+), type 1.3 (MS+MR+) fimbriae and facultatively coexpressing P-like fimbria were investigated for their ability to adhere to uroepithelial cells (UECs) and tracheal epithelial cells (TECs). Irrespective of the type of epithelial cells, adhesion of the MS+MR+ (type 1.3) fimbriated Klebsiella strain was significantly stronger than adhesion of strains carrying only type 1 (MS+MR-) or type 3 (MS-MR+) fimbriae. The coexpression of P-like fimbriae increased the adhesive properties of Klebsiella strains to UECs but not to TECs. Adhesion of P-like fimbriated Klebsiella strains to UECs was significantly inhibited in the presence of the P+ fimbriae-specific Gal alpha-4-Gal beta (galabiose). Such adhesion was unrelated to the coexpression of type 1, type 3 or type 1.3 fimbriae. However, adhesion to TECs was only moderately inhibited.

S fimbriae of uropathogenic Escherichia coli bind to primary human renal proximal tubular epithelial cells but do not induce expression of intercellular adhesion molecule 1

We have recently reported an increase of expression of the intercellular adhesion molecule 1 by renal carcinoma cells in response to S fimbriae of Escherichia coli. Now we demonstrate that E. coli expressing S and P fimbriae strongly binds to human proximal tubular epithelial cells. However, in primary and simian virus 40-transfected renal tubular epithelial cells S fimbriae do not enhance the expression of intercellular adhesion molecule 1.

Sialyloligosaccharide chains of laminin as an extracellular matrix target for S fimbriae of Escherichia coli

S fimbriae purified from recombinant Escherichia coli HB101(pANN801-13) bound strongly to extracellular matrices of cultured endothelial and epithelial cells; only poor binding was seen with the fimbriae purified from the sfaS mutant strain HB101(pANN801-1321). E. coli HB101(pANN801-13) adhered strongly to laminin immobilized on glass; no adhesion was seen to type I, III, IV, or V collagen. Strain HB101(pANN801-1321) failed to adhere to any of the target proteins. Adhesion to laminin of strain HB101(pANN801-13) was inhibited by sialyl-alpha-2,3-lactose as well as by periodate oxidation and neuraminidase treatment of laminin. In Western blotting, the purified S fimbriae recognized more strongly the A chain than the B chains of laminin.

An investigation of the suitability of three support matrices for the culture of cells derived from the secretory alveoli of the bovine mammary gland

The suitability of three support matrices, (thick collagen gels, aluminium oxide and cellulose ester membranes, the latter two both thinly coated with collagen) for the production of primary cultures of bovine mammary epithelial cells was investigated. Single secretory alveoli were isolated from mammary tissue of animals in early lactation by enzymatic digestion and differential filtration. Cell growth was monitored by light and scanning electron microscopy. The cellulose ester membrane was found to give the best results, allowing growth of monolayers with a morphology closely resembling that of the natural epithelium of the gland. There were low levels of fibroblast contamination, and the membranes could be easily manipulated for further studies.

Differential expression of interleukin-6, intracellular adhesion molecule 1, and major histocompatibility complex class II molecules in renal carcinoma cells stimulated with S fimbriae of uropathogenic Escherichia coli

The production of interleukin-6, intracellular adhesion molecule 1, and major histocompatibility complex class II molecules by a renal carcinoma cell line (ACHN) in response to S fimbriae of uropathogenic Escherichia coli was studied. S fimbriae adhered to ACHN cells and stimulated the production of interleukin-6 and intercellular adhesion molecule 1 but did not affect major histocompatibility complex class II expression by renal carcinoma cells. Our data demonstrate that S fimbriae of E. coli display immunomodulating properties on kidney-derived epithelial cells.

Adherence to and cytotoxicity of Escherichia coli for eucaryotic cell lines quantified by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide)

Adherence of Escherichia coli to human epithelial cells (HEp-2) was studied using MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) which is cleaved by enzymes of eucaryotic or procaryotic cells to formazan. This method allows to quantify adherence of Escherichia coli to HEp-2 cells and offers the advantage of assaying a large number of eucaryotic cells without using specific antisera or radioactive material. Furthermore, toxic effects of isolated hemolysin cloned in Escherichia coli onto a renal tubular cell line (LLC-PK1) was investigated by this method, showing reduced cellular viability of tubular cells after an incubation period of 10 to 20 min. MTT is therefore considered to be useful to assay the adherence of Escherichia coli to eucaryotic cells and to quantify toxic effects in eucaryotic cells induced by bacterial virulence factors.

Protective role of bovine neutrophils in Pasteurella haemolytica-mediated endothelial cell damage

The purpose of this study was to determine if Pasteurella haemolytica can directly injure bovine pulmonary endothelial cells (EC) and if neutrophils have a beneficial or detrimental role in bacterium-EC interaction. Various combinations of live P. haemolytica, heat-killed P. haemolytica, anti-P. haemolytica immune serum, polymyxin B, and bovine neutrophils were added to confluent monolayers of bovine EC. Monitoring included determination of 51Cr release from EC, phase microscopy, and transmission electron microscopy. Although toxic changes were not evident at 5 h postinoculation, both live and heat-killed P. haemolytica produced extensive EC damage by 22 h postinoculation. Damage by live P. haemolytica was prevented only when both neutrophils and immune serum were used. Polymyxin B effectively prevented the toxic effect of heat-killed P. haemolytica, suggesting that lipopolysaccharide was the major toxic factor. Morphological studies showed close apposition of P. haemolytica to EC membranes, neutrophil activation, and adherence to EC but no evidence of neutrophil-associated EC membrane damage. These studies demonstrate that neutrophils and immune serum in combination are effective in preventing EC damage mediated by live P. haemolytica.

Cells within the vascular system capable of mediating trypanocidal activity in vitro

Cure of Trypanosoma musculi infection involves an effector mechanism mediated by immunoglobulin G2a antibody, C3, and an unidentified effector cell. In the present study, experiments were designed to identify the cell(s) within the vascular system that may be responsible for cure of trypanosomiasis. The ability of various cell populations to mediate killing of trypanosomes in the presence of C3 and immune plasma (IP) was tested in vitro. Blood-derived platelets or leukocytes or Bio-Gel-elicited macrophages or neutrophils were incubated at various concentrations with T. musculi, C3, and IP diluted up to 1 in 8. Trypanocidal activity was dependent upon the presence and concentration of IP and on the number of cells in the wells. Macrophages, neutrophils, and platelets were shown to kill with different potencies. With a 2:1 cell-to-parasite ratio, both macrophages and neutrophils reduced parasite numbers by 2 log, while platelets at a 40:1 ratio mediated a 1 log decrease. In addition, even in the absence of C3, the phagocytes were capable of killing trypanosomes while platelet trypanocidal activity was abrogated. The time course of trypanocidal activity was monitored for macrophages and neutrophils. The number of parasites decreased by 0.5 log by 4 h and 1 to 2 log by 8 h and by 20 h was reduced to zero. Cultured monolayers of endothelial cells were also tested for trypanocidal activity and shown to kill the parasites in the presence of IP and C3. The level of trypanocidal activity was dependent on the concentration of IP.

Type 1 fimbriae of Salmonella enteritidis

Salmonella enteritidis was previously shown to produce fimbriae composed of 14,000-molecular-weight (Mr) fimbrin monomers (J. Feutrier, W. W. Kay, and T. J. Trust, J. Bacteriol. 168:221-227, 1986). Another distinct fimbrial structure, comprising 21,000-Mr fimbrin monomers, has now been identified. These fimbriae are simply designated as SEF 14 and SEF 21, respectively (for S. enteritidis fimbriae and the Mr [in thousands] of the fimbrin monomer). A simple method for the purification of both structures was developed by using the different biochemical properties of these fimbriae. SEF 21 remained intact after being boiled in sodium dodecyl sulfate but readily dissociated into subunits of 21,000 Mr at pH 2.2. The overall amino acid composition and the N-terminal amino acid sequence of the SEF 21 fimbrin were distinct from those of SEF 14 but were virtually identical to the predicted sequence for type 1 fimbrin of Salmonella typhimurium. Immunoelectron microscopy of S. enteritidis clearly revealed fimbrial structures that reacted with immune serum specific to the 21,000-Mr fimbrin. Immune sera raised against this subunit were cross-reactive with type 1 fimbrins found in whole-cell lysates of S. typhimurium, Salmonella illinois, and Salmonella cubana. However, there was no cross-reaction with Escherichia coli type 1 fimbriae or with other fimbrins produced by S. enteritidis. Under certain growth conditions, S. enteritidis produced both SEF 14 and SEF 21. However, when S. enteritidis was grown at 30 degrees C or lower, only the 21,000-Mr SEF 21 fimbrin could be detected. There was a direct correlation between mannose-sensitive hemagglutination and the presence of SEF 21.

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.

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.

Type of fimbriation determines adherence of Klebsiella bacteria to human epithelial cells

Clinical isolates of three Klebsiella strains (encapsulated and nonencapsulated mutants) with type 1 (mannose-sensitive, MS+MR-), type 3 (mannose-resistant, MS-MR+) and type 1 and 3 (MS+MR+) fimbriae were investigated for their ability to adhere to epithelial cells. Considerable adhesion to human buccal, tracheal, pulmonary and uroepithelial cells could be demonstrated. Independent of encapsulation and type of epithelial cells, adhesion of MS+MR+ (type 1.3) fimbriated Klebsiella bacteria was significantly stronger than adhesion of microorganisms carrying only type 1 (MS+MR-) or type 3 (MS-MR+) fimbriate, respectively. Adherence of nonencapsulated type 1 and 3 (MS+MR+) fimbriated Klebsiella bacteria to mammalian cells was significantly inhibited in the presence of D-mannose. Certain carbohydrates (D-glucose, D-galactose) did not interfere with this adhesion process.

Genetically engineered S and F1C fimbriae differ in their contribution to adherence of Escherichia coli to cultured renal tubular cells

Escherichia coli K-12 strains producing S-fimbrial adhesins, F1C fimbriae, and mutagenized fimbriae were tested in a binding assay with a renal tubular cell line. S-fimbrial adhesins and F1C fimbriae mediated binding to tubular cells. The SfaA, SfaG, and SfaS subunits of S fimbriae contributed to attachment. Site-specific mutations in the sfaS gene reduced binding. The inhibition profile of F1C fimbriae resembled that of S fimbriae.