Analysis of P fimbriae on Escherichia coli O2, O4, and O6 strains by immunoprecipitation

Local immune response to upper urinary tract infections in children

Vaccines are needed against urinary tract infections (UTIs) in children, as episodes of pyelonephritis (PN) may cause renal scarring. Local immune mechanisms are regarded to confer protection, yet they have been poorly characterized for children. This study explores the local immune response in children by looking for newly activated pathogen-specific antibody-secreting cells (ASC), expected to appear transiently in the circulation as a response to UTI. Urinary tract-originating ASC specific to each patient's own pathogen or P fimbria were studied in 37 children with PN. The children were examined for recidivism and renal scarring in a 6-month follow-up study. Pathogen-specific ASC were found in 33/37 children, with the magnitude increasing with age. In contrast to the case for adults, with immunoglobulin A (IgA) dominance, in 18/33 cases IgM dominated the response, and this occurred more frequently in infants (63%) than in older children (30%). The most vigorous response was found to whole Escherichia coli bacteria (geometric mean, 63 +/- 2,135 ASC/10(6) peripheral blood mononuclear cells [PBMC]), yet responses were found to P fimbriae (13 +/- 33 ASC/10(6) PBMC), too. The response peaked at 1 to 2 weeks and was low/negligible 3 to 7 weeks after the beginning of symptoms. Recidivism was seen in seven patients, and renal scarring was seen in nine patients. In conclusion, a response of circulating ASC was found in children with UTIs, with the magnitude increasing with age. Since IgM is not present in urine, the IgM dominance of the response suggests that systemic immune mechanisms are more important in the immune defense in children than in adults. In 81% of patients, no recidivism was seen, suggesting a successful immune defense.

Analysis of the F antigen-specific papA alleles of extraintestinal pathogenic Escherichia coli using a novel multiplex PCR-based assay

Polymorphisms in PapA, the major structural subunit and antigenic determinant of P fimbriae of extraintestinal pathogenic Escherichia coli, are of considerable epidemiological, phylogenetic, and immunotherapeutic importance. However, to date, no method other than DNA sequencing has been generally available for their detection. In the present study, we developed and rigorously validated a novel PCR-based assay for the 11 recognized variants of papA and then used the new assay to assess the prevalence, phylogenetic distribution, and bacteriological associations of the papA alleles among 75 E. coli isolates from patients with urosepsis. In comparison with conventional F serotyping, the assay was extremely sensitive and specific, evidence that papA sequences are highly conserved within each of the traditionally recognized F serotypes despite the diversity observed among F types. In certain strains, the assay detected serologically occult copies of papA, of which some were shown to represent false-negative serological results and others were shown to represent the presence of nonfunctional pap fragments. Among the urosepsis isolates, the assay revealed considerable segregation of papA alleles according to O:K:H serotype, consistent with vertical transmission within clones, but with exceptions which strongly suggested horizontal transfer of papA alleles between lineages. Sequencing of papA from two strains that were papA positive by probe and PCR but F negative in the new PCR assay led to the discovery of two novel papA variants, one of which was actually more prevalent among the urosepsis isolates than were several of the known papA alleles. These findings provide novel insights into the papA alleles of extraintestinal pathogenic E. coli and indicate that the F PCR assay represents a versatile new molecular tool for epidemiological and phylogenetic investigations which should make rapid, specific detection of papA alleles available to any laboratory with PCR capability.

Sub-MIC ciprofloxacin effect on fimbrial production by uropathogenic Escherichia coli strains

The urine from 210 patients with acute urinary tract infection (UTI) was examined to study the in vitro effect of ciprofloxacin on fimbriae production by uropathogenic Escherichia coli isolates. Forty-nine bacterial samples of density 10(5) CFU/ml were not considered. From the resulting 161 samples, E. coli was the major strain found, present in 54 samples. Other microoganisms found were: Enterococcus sp. (34 samples), Staphylococcus epidermis (22), yeasts (11), Proteus sp. (11), Pseudomonas sp. (11), Klebsiella sp. (8), Enterobacter sp. (6), Citrobacter sp. (3), and Acinetobacter sp. (1). The uropathogenic E. coli strains found were P-fimbriated, as demonstrated by hemoagglutination activity against human erythrocytes with and without mannose, SDS-PAGE of fimbrial proteins and transmission electron microscopy (TEM). All E. coli strains found were exposed in vitro to sub-inhibitory concentrations of ciprofloxacin (1/8 MIC). Our results showed that: 1) P-fimbriated E. coli is the most prevalent microorganism in acute UTI (34%); 2) exposure to sub-MICs of ciprofloxacin inhibits fimbrial production in 79% of E. coli strains; 3) the pattern of SDS-PAGE fimbrial proteins is modified after exposure; in particular, the most affected synthesis involves the protein at 18 kD known as P-fimbriae.

The GafD protein of the G (F17) fimbrial complex confers adhesiveness of Escherichia coli to laminin

Escherichia coli IHE11088(pRR-5) expressing the G (F17) fimbria adhered to immobilized laminin as well as to reconstituted basement membranes. No adhesion was seen with the plasmidless strain IHE11088 or with the deletion derivative IHE11088(pHUB110), which expresses the G-fimbrial filament with a defective GafD lectin and lacks N-acetyl-D-glucosamine-specific binding. Adhesion of IHE11088(pRR-5) to laminin and to reconstituted basement membranes was specifically inhibited by N-acetyl-D-glucosamine, and adhesion was abolished after N-glycosidase F treatment of laminin. The results show that the GafD lectin binds to laminin carbohydrate and suggest a novel function for the F17 fimbria in binding to mammalian basement membranes.

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.

K-antigen identification, hemolysin production, and hemagglutination types of Escherichia coli O6 strains isolated from patients with urinary tract infections

Serotyping of 1918 Escherichia coli strains isolated in significant cell numbers from the urine of patients with urinary tract infections (UTI) revealed the presence of 117 O6 strains. The K antigens were identified by means of K-specific phages and serological methods. The phages used included a K1 phage pool (phi 1, A-E) and the separate phages phi 2, phi 5, phi 7, phi 12 and phi 13. The presence of H antigens, type 1 fimbriae formation, hemolysin production and mannose-resistant hemagglutination (MRHA) ability with human A, sheep, calf and pig erythrocytes were also analyzed. Six different MRHA types were defined and discussed in relation to the O6:K:H serotype. Remarkably, E. coli O6 strains were found to possess a whole arsenal of virulence factors (K antigens, MRHA, hemolysin). The most common serotypes - O6:K2:H1/H- (26), O6:K5:H1/H- (35) and O6:K13:H1/H- (20) - differed from each other in some cases in both MRHA type and hemolysin production.

Tissue-binding affinity of Proteus mirabilis fimbriae in the human urinary tract

Binding characteristics of the two major fimbrial hemagglutinin types of uropathogenic Proteus mirabilis were determined in frozen sections of human kidney and in exfoliated uroepithelial cells. P. mirabilis 3087, which expresses the MR/P fimbriae, adhered avidly to the tubular epithelial cells of the kidney and also to the epithelial cells of urinary sediment. No adhesion to glomerular or peritubular elements of the kidney was detected. Indirect immunogold silver staining also showed that the purified MR/P fimbriae recognized the same kidney domains. Adhesion of strain 3087 to uroepithelial cells was completely inhibited by Fab fragments of antibodies against the purified MR/P fimbriae. A completely different tissue-binding pattern was exhibited by the MR/K fimbriae of P. mirabilis 2456. In the kidney, the MR/K fimbriae bound strongly to the Bowman's capsule of the glomeruli and to the tubular basement membranes. A weak binding to glomerular mesangium and tubular epithelial cells was also seen. Strain 2456 did not adhere to epithelial cells of urinary sediment. Analysis of normal human urine showed that it contains low-molecular-weight molecules capable of inhibiting the binding of the MR/P fimbriae; no urinary inhibitors could be detected for the MR/K fimbriae. Poor in vivo binding capacity to intact human uroepithelial cells may be an important factor in explaining the relatively low pathogenicity of P. mirabilis in healthy hosts.

Two kinds of P-fimbrial variants of uropathogenic Escherichia coli recognizing forssman glycosphingolipid

Various types of fimbriae on pathogenic Escherichia coli strains have been classified by their antigenicities and recognition specificities for receptors. However, the antigenicity of fimbrial proteins does not always correlate with the fimbrial recognition specificity. In this communication, the exact carbohydrate structures recognized by the fimbriae of two human uropathogenic E. coli strains, KS71 (O4) and IH11024 (O6), that have P-fimbrial antigen, were examined. Strain KS71 showed mannose-resistant (MR) hemagglutination (HA) of human blood group OP1 phenotype erythrocytes, and its HA was inhibited by blood group Pk antigen, Gal(alpha,1-4)Gal(beta,1-4)Glc-ceramide and P antigen, GalNAc(beta,1-3)Gal (alpha,1-4)Gal(beta,1-4)Glc-ceramide but not by Forssman antigen, GalNAc(alpha,1-3)GalNAc(beta,1-3)Gal(alpha,1-4)Gal (beta,1-4)Glc-ceramide, as previously described in many papers. The cells also showed MR HA of sheep erythrocytes, which was potently inhibited by Forssman, and weakly by P and Pk antigens. These phenomena could not be explained by the above P adhesin specificity. This adhesin was called Forssman-like adhesin. Strain IH11024 also caused MR HA of sheep erythrocytes but not of human erythrocytes. The HA was inhibited specifically by Forssman but neither by Pk nor P antigen. This adhesin was completely different from P adhesin and Forssman-like adhesin in recognition of the carbohydrate epitope. This adhesin, until now called a pseudotype of P fimbriae, was renamed Forssman adhesin.

Surface antigens from Escherichia coli O2 and O78 strains of avian origin

Fimbriae from O2 and O78 virulent strains of avian Escherichia coli were compared with type 1A fimbriae with regard to the apparent molecular weights of their subunits and their antigenic relationships. Under static broth culture conditions, most O78 strains expressed fimbriae closely related to those of type 1A. Under the same culture conditions, another type of fimbriae, sharing some common properties with type 1A fimbriae, was observed only on O2 strains; however, these fimbriae differed from type 1A fimbriae in the apparent molecular weights of their subunits and in the expression of specific epitopes. They were called type 1-like fimbriae. Homologies in lipopolysaccharide and outer membrane protein profiles were also demonstrated among the strains expressing type 1-like fimbriae, which suggests the existence of a clonal relationship among O2:K1 avian E. coli strains. The O78 strains studied did not appear to be clonally related.

The Dr hemagglutinin, afimbrial adhesins AFA-I and AFA-III, and F1845 fimbriae of uropathogenic and diarrhea-associated Escherichia coli belong to a family of hemagglutinins with Dr receptor recognition

The receptor specificities of four Escherichia coli cloned hemagglutinins, AFA-I, AFA-III, F1845 fimbriae, and the Dr hemagglutinin were studied. Evidence is provided that all four hemagglutinins recognize as their receptor the Dr blood group antigen. However, results of experiments using enzyme-treated erythrocytes and monoclonal antibodies indicate that the four adhesins recognize different epitopes on the Dr antigen and thus constitute a family of Dr receptor-recognizing bacterial adhesins. Furthermore, the same results suggest that the Dr antigen itself may be divided into subcomponents on the basis of bacterial adhesins.

Purified P fimbriae from two cloned gene clusters of a single pyelonephritogenic strain adhere to unique structures in the human kidney

We have completed immunofluorescence binding studies of purified fimbriae from two clones which express Pap or Pap-2 fimbriae. Although the two fimbrial types exhibited common binding to the uroepithelia of the bladder and renal pelvis and to occasional cells located within the glomeruli which we have termed glomerular elements, only Pap-2 fimbriae adhered to Bowman's capsule. Previous studies have demonstrated that the Gal alpha 1----4Gal disaccharide moiety is capable of inhibiting Pap hemagglutination and adherence to uroepithelial cells. Results of our experiments demonstrate that this disaccharide is not sufficient for blocking binding of Pap-2 fimbriae to Bowman's capsule but that GalNAc beta 1----3Gal completely blocks Pap-2 adherence to Bowman's capsule. These results indicate that the different hemagglutination capacities of the two clones reflect different receptor specificities and differential tissue tropisms in the urinary tract. These unique receptor specificities may provide uropathogenic strains of Escherichia coli carrying multiple chromosomal copies of pap-like gene clusters with the advantage of increased numbers of binding sites within the urinary tract. This, in turn, might improve the chances of colonization and the establishment of infection.

Type 3 fimbriae among enterobacteria and the ability of spermidine to inhibit MR/K hemagglutination

The distribution of the gene cluster encoding type 3 fimbriae among various isolates of the family Enterobacteriaceae was investigated by using 112 clinical and nonclinical isolates. Closely related DNA sequences were detected in all Klebsiella strains, in most Enterobacter isolates, in a smaller number of Escherichia coli and Salmonella spp., and in a single isolate each of Yersinia enterocolitica and Serratia liquefaciens but not in isolates of Morganella or Providencia species or Serratia marcescens. Except for E. coli and Salmonella strains, the presence of gene sequences was correlated with the phenotypic expression of either the MR/K hemagglutinin or fimbriae that reacted with specific antibodies. In one isolate of Y. enterocolitica the expression of type 3 fimbriae was plasmid determined. The polyamine spermidine was identified as an inhibitor of MR/K hemagglutinating activity, exhibiting an MIC of 1.2 mM. Spermidine inhibited the hemagglutination of 37 MR/K-positive clinical isolates from various genera. However, one clinical isolate of Enterobacter cloacae and most (four of five) nonclinical Klebsiella isolates were not completely inhibited.

Binding characteristics of Escherichia coli adhesins in human urinary bladder

We studied domains in the human bladder that acted as receptors for Escherichia coli P, S, type 1, type 1C, and O75X fimbriae or adhesin and domains in the human kidneys that were receptors for E. coli type 1C fimbriae. Binding sites in frozen tissue sections were localized by direct staining with fluorochrome-labeled recombinant strains and by indirect immunofluorescence with the purified adhesins. In the bladder, the P and S fimbriae showed closely similar binding to the epithelial and muscular layers, and the S fimbriae also bound to the connective tissue elements. Type 1 fimbriae bound to vascular walls and to muscle cells, whereas the O75X adhesin bound avidly to connective tissue elements and to some extent to epithelial and muscle cells of the bladder. The type 1C fimbriae bound to distal tubules and collecting ducts of the kidney and to vascular endothelial cells in both the kidney and bladder. The binding of all adhesin types was inhibited by specific receptor analogs or Fab fragments. The results reveal a possible mechanism by which the type 1C fimbriae may help invasion of E. coli in the kidneys but do not support a pathogenetic role for type 1 fimbriae. Similar tissue specificity of P and S fimbriae in the human urinary tract indicates that the presence of binding sites on uroepithelia does not fully explain the virulence properties of P fimbriae in human urinary tract infections.

Detection of pilus subunits (pilins) and filaments by using anti-P pilin antisera

P pilus filaments are important in binding to globoside through an adhesin located at the tip of the pilus. There is considerable antigenic variation among P pili, and the immunologic response is usually serotype specific. We purified denatured pilin subunits and used them as immunogens to prepare more broadly cross-reactive antisera. Although antifilament antisera (AFA) detected predominantly the homologous strain, antisubunit antisera (ASA) prepared from two different strains detected P pili in 16 of 16 and 14 of 16 P-piliated strains by Western blotting (immunoblotting). The binding of ASA to the homologous pilus filament was inhibited by only 3 of 17 strains. ASA agglutinated only two of nine heterologous strains and immunoprecipitated pili from one of three heterologous strains. By immunoelectron microscopy ASA was seen to bind to pilus filaments but not as strongly as AFA. Antiserum raised to the denatured pilin subunit was not substantially more reactive with pilus filaments derived from heterologous strains than was AFA. ASA was, however, a very useful probe for detecting most P pilins.

Characterization of P fimbriae on O1, O7, O75, rough, and nontypable strains of Escherichia coli

P fimbriae of 37 uropathogenic Escherichia coli O1:K1, O7:K1, O22, O75, rough:K1, and nontypable strains were characterized by immunoprecipitation with 14 fimbria-specific rabbit antisera. The fimbrial composition of these strains, as reflected by the apparent molecular weights of the fimbrial peptides, was correlated with the O serogroup of the strains, but serological cross-reactivity of P fimbriae of different E. coli serogroups was frequently observed. The genetic clonal relationships of the strains were analyzed by determining the electrophoretic types, based on 18 chromosomally encoded enzymes. Among the O1:K1 strains, the same P-fimbrial variants occurred on strains that were either closely related or very distinct in their electrophoretic types, indicating that the P fimbriae have evolved in association with the O and K antigens. In contrast, certain O7:K1 and R:K1 strains as well as some O22 and O75 strains were genotypically identical and shared similar P-fimbrial variants, which differed serologically from those of other E. coli serogroups. Our results show that, despite the structural variability seen in electrophoretic analysis of P fimbriae of different serogroups, many P-fimbrial variants share common antigenic determinants that are recognized by rabbit antisera. Based on immunoprecipitation analyses, three anti-P-fimbria sera have now been identified that react with P fimbriae of 82 of 84 uropathogenic E. coli strains characterized in Finland.

Total and specific immunoglobulin response to acute and chronic urinary tract infections in a rat model

Total and specific levels of immunoglobulins IgG, A and M were determined by an enzyme-linked immunosorbent assay (ELISA) in a rat model of urinary tract infections (cystitis) during the early and late phases of infection. The early response was characterized by rapid rise in IgM in serum and urine. This response decreased rapidly and was undetectable in urine after eight weeks. Correlation between total serum and urine levels of IgM was not found although a chronological relationship was observed. Total and specific serum and urine IgA responses were erratic. Concentrations of IgA were low and this antibody class was undetectable in urine until the infection had been established for six weeks. In contrast, total serum and urine IgG increased in concentration at five days post infection and reached total maximum by weeks four to eight, then declined, but remained detectable over 24 weeks. Specific IgG titers remained elevated in serum but declined in urine between four and 10 weeks. A correlation between total serum and total urine IgG was found. Also, bacteria generated a concomitant nonspecific response, a part of which was detected against a common antigen expressed on E. coli J5 strain that cross-reacts with a number of gram negative genera. The results show that IgM chronologically is the first antibody to appear in increased amounts in the serum and urine, followed by IgG. The data also suggests a relationship exists between total serum IgG and total urine IgG which may affect the host's ability to eliminate urinary infection.

Localization of binding sites for purified Escherichia coli P fimbriae in the human kidney

Binding sites in the human kidney for purified P fimbriae of pyelonephritogenic Escherichia coli were determined. The purified KS71A (F7(1)) fimbriae bound only to epithelial elements of the kidney, i.e., to the apical aspect of proximal and distal tubular cells, as well as to the apical and cytoplasmic sites of collecting ducts. In addition, binding was seen at the vascular endothelium throughout the kidney and at the parietal epithelium of the glomeruli. The binding was specifically inhibited by the receptor analog of E. coli P fimbriae, globotriose. The binding sites identified suggested a possible pathogenetic mechanism for the invasion of P-fimbriated bacteria into the renal parenchyma, as well as for their subsequent spread into the circulatory system.