Purification and characterization of the Dr hemagglutinins expressed by two uropathogenic Escherichia coli strains

Adhesive threads of extraintestinal pathogenic Escherichia coli

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

Probiotic agents to protect the urogenital tract against infection

The urogenital microflora of a healthy woman comprises approximately 50 species of organisms, which differ in composition according to reproductive stages and exposure to several factors, including antibiotics and spermicides. Infections are very common with > 300 million cases of urinary tract infections, bacterial vaginosis, and yeast vaginitis worldwide per annum. At the time of infection in the bladder and vagina, the urogenital flora is often dominated by the infecting pathogens, in contrast with healthy phases when indigenous organisms dominate. Premenopausal women have a flora of mostly lactobacilli, and certain properties of these strains, including adhesive ability and production of acids, bacteriocins, hydrogen peroxide, and biosurfactants, appear important in conferring protection to the host. Efforts to artificially restore an unbalanced flora with the use of probiotics have met with mixed results but research aimed at selecting scientifically based strains could well provide a reliable alternative treatment and preventive regimen to antibiotics in the future.

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.

Extracellular localization of a nonfimbrial hemagglutinin of Yersinia pseudotuberculosis

A nonfimbrial hemagglutinin (HA) of Yersinia pseudotuberculosis was observed by immunoelectron microscopy using monospecific HA antiserum and protein A-gold conjugate. The HA, an amorphous but morphologically identifiable entity, was located in a region distal to or detached from the outer edge of bacteria.

Molecular structure of the Dr adhesin: nucleotide sequence and mapping of receptor-binding domain by use of fusion constructs

The Dr hemagglutinin of uropathogenic Escherichia coli mediates adherence to the upper urinary tract. E. coli strains which express this adhesin bind to the Dr blood group antigen and mediate mannose-resistant hemagglutination (MRHA). Chloramphenicol inhibits MRHA produced by the Dr hemagglutinin and may act as an analog for the tissue receptor at the adhesin-binding site. The nucleotide sequence of the Dr hemagglutinin fimbrial subunit was determined and found to have significant homology with that of F1845, a fimbrial adhesin associated with diarrhea, and with the afimbrial adhesin AFA-I of uropathogenic E. coli. Chimeric adhesin determinants consisting of the Dr structural subunit and F1845 accessory genes or of the F1845 structural subunit and Dr accessory genes were constructed. The Dr and F1845 determinants were shown to have a close structural relationship, with functional differences concentrated in the fimbrial subunit. Oligonucleotide-directed site-specific mutagenesis was used to facilitate construction of a hybrid adhesin subunit gene containing the amino terminus of F1845 fused to the carboxy terminus of the Dr structural gene. The resulting construct confers chloramphenicol-resistant hemagglutination when introduced into an E. coli strain expressing the cloned Dr hemagglutinin. The chloramphenicol sensitivity or resistant phenotype of MRHA produced by this family of adhesins is determined solely by the fimbrial subunit gene. Domains responsible for the chloramphenicol sensitivity of Dr-mediated MRHA reside within the amino-terminal portion of the fimbrial subunit.