Characterization of microbial host receptors

Human intestinal models to study interactions between intestine and microbes

Implementations of suitable in vitro cell culture systems of the human intestine have been essential tools in the study of the interaction among organs, commensal microbiota, pathogens and parasites. Due to the great complexity exhibited by the intestinal tissue, researchers have been developing in vitro/ex vivo systems to diminish the gap between conventional cell culture models and the human intestine. These models are able to reproduce different structures and functional aspects of the tissue. In the present review, information is recapitulated on the most used models, such as cell culture, intestinal organoids, scaffold-based three-dimensional models, and organ-on-a-chip and their use in studying the interaction between human intestine and microbes, and their advantages and limitations are also discussed.

Use of real-time, label-free analysis in revealing low-affinity binding to blood group antigens by Helicobacter pylori

Infectious diseases are often initiated by microbial adherence that is mediated by the binding of attachment molecules, termed adhesins, to cell surface receptors on host cells. We present an experimental system, oblique-incidence reflectivity difference (OI-RD) microscopy, which allows the detection of novel, low-affinity microbial attachment mechanisms that may be essential for infectious processes. OI-RD microscopy was used to analyze direct binding of the oncopathogen, Helicobacter pylori ( H. pylori ) to immobilized glycoconjugates in real time with no need for labeling tags. The results suggest the presence of additional Lewis b blood group antigen (Le(b)) binding adhesins that have not been detected previously. OI-RD microscopy also confirmed the high-affinity binding of H. pylori outer-membrane protein BabA to Le(b). The OI-RD microscopy method is broadly applicable to real-time characterization of intact microbial binding to host receptors and offers new strategies to elucidate the molecular interactions of infectious agents with human host cells.

Functional cell models of the gut and their applications in food microbiology--a review

Animal experimentation has a long tradition for risk assessment of new drugs before they reach the clinic. To reduce expensive animal experimentation, attempts have been made to build inexpensive and convenient intestinal functional cell models to study toxicity and bioavailability of new substances along with providing relevant models to study interactions between the host, pathogens and intestinal microflora. We review the available cell lines and models of the intestine and their potential uses. Tumor derived cell lines such as Caco-2, T84 and HT-29 are widely used despite many drawbacks, which are discussed with respect to complexity of the gut, where various cell types interact with commensal microbiota and gut-associated lymphoid tissue. To address this complexity, 3D models of human and animal gut represent a promising in vitro system to mimic in vivo situation without the use of transformed cell lines.

Helicobacter pylori adhesion to carbohydrates

Adherence of bacterial pathogens to host tissues contributes to colonization and virulence and typically involves specific interactions between bacterial proteins called adhesins and cognate oligosaccharide (glycan) or protein motifs in the host that are used as receptors. A given pathogen may have multiple adhesins, each specific for a different set of receptors and, potentially, with different roles in infection and disease. This chapter provides strategies for identifying and analyzing host glycan receptors and the bacterial adhesins that exploit them as receptors, with particular reference to adherence of the gastric pathogen Helicobacter pylori.

The Escherichia coli AIDA autotransporter adhesin recognizes an integral membrane glycoprotein as receptor

The AIDA-I autotransporter adhesin, as a prototype of the AIDA adhesin family, represents a tripartite antigen consisting of the functional adhesin AIDA-I (alpha-domain), which mediates the specific attachment of bacteria to target cells, and a two-domain translocator (AIDA(c)) organized in the beta(1)- and beta(2)-domains. Cellular receptor moieties for the adhesin AIDA-I have not been identified. Here, it is demonstrated that the purified adhesin binds specifically to a high-affinity class of receptors on HeLa cells. Additionally, the adhesin was found to bind to a variety of mammalian cell types, indicating a broad tissue distribution of the receptor moiety. By using complementary techniques, including co-immunoprecipitation and one- and two-dimensional gel electrophoresis, the AIDA-I binding protein on HeLa cells was identified as a surface glycoprotein of about 119 kDa (gp119). The gp119 AIDA-I cellular receptor protein was characterized biochemically and found to be an integral N-glycosylated membrane protein with a pI of 5.2.

Development of a high throughput Pseudomonas aeruginosa epithelial cell adhesion assay

Pseudomonas aeruginosa colonizes the lungs of cystic fibrosis and mechanically ventilated patients by binding to specific carbohydrate residues on the surface of lung epithelial cells. Studies have shown that blocking this interaction may have therapeutic effects in vivo. To test compounds that may have an effect on the binding of P. aeruginosa to epithelial cells, we have developed a pseudomonal adhesion assay that is compatible with high throughput technology. This assay utilizes a 96-well culture plate assay and P. aeruginosa strains that have been modified to bioluminesce. This method has proven to be a rapid, sensitive and reproducible system for screening agents that inhibit bacterial adhesion.

Corynebacterium diphtheriae surface proteins as adhesins to human erythrocytes

Corynebacterium diphtheriae strains express non-fimbrial surface proteins able to recognize and bind to specific host cells receptors. Protein extracts were obtained from bacterial cells by mechanical process and ammonium sulfate precipitation at 25 and 45% (w/v) saturation. SDS-PAGE analysis of the extracts detected two polypeptide bands of 67 and 72 kDa, named 67-72 p. The 67-72 p, rabbit anti-67-72 p IgG antibodies as well as human gastric mucin, N-acetylneuraminic acid and N-acetyl D-glucosamine molecules were able to inhibit bacterial hemagglutination. Hemagglutination assays using 67-72 p-coated latex beads and Western blot analysis of biotin-labeled 67-72 p and erythrocyte receptors demonstrated the binding of 67-72 p to human erythrocyte membranes. Immunolabeled colloidal gold-A protein transmission electron microscopy using anti-67-72 p revealed a diffuse distribution of non-fimbrial 67-72 p on the surface of C. diphtheriae strains of both sucrose-fermenting and non-fermenting biotypes. Non-fimbrial lectin-like surface 67-72 p may play a role as adhesins in bacterial attachment thereby facilitating the early steps in pathogenesis of both toxigenic and non-toxigenic C. diphtheriae.

Secretory immunoglobulin A heavy chain presents Galbeta1-3GalNAc binding structures for Actinomyces naeslundii genospecies 1

Adherence of Actinomyces naeslundii ATCC 12104 to hydroxyapatite beads coated with protein fractions of parotid saliva, obtained by gel filtration on S-200 HR columns, showed GalNAcbeta1-3Galalpha-O-ethyl-inhibitable binding to high-molecular-weight proteins (Strömberg et al., 1992). The present study investigates the nature of these high-molecular-weight binding proteins and determines their specific ability to mediate adherence to representative strains of Actinomyces species. Strain ATCC 12104 bound specifically in a lactose-inhibitable manner to the heavy chain of secretory immunoglobulin A (S-IgA), contained within a high-molecular-weight parotid protein fraction separated on SDS-PAGE and transferred to a solid membrane support. Lactose-inhibitable binding to the heavy chain of S-IgA from human colostrum was also demonstrated. Peanut agglutinin bound to the heavy chain of parotid and colostrum S-IgAs contained on solid support membranes, confirming the presence of Galbeta1-3GalNAc residues on these molecules. Both salivary and colostrum S-IgA aggregated with strain ATCC 12104 in a GalNAcbeta1-3Galalpha-O-ethyl-inhibitable fashion. Further separation of high-molecular-weight salivary proteins on S-500 HR columns showed GalNAcbeta1-3Galalpha-O-ethyl-inhibitable binding to both mucin- and S-IgA-containing fractions. The presence of S-IgA in salivary pellicles formed in vivo on teeth was demonstrated by Western blot analysis of pellicle extracts with anti-IgA antibodies. Among strains representing A. naeslundii genospecies 1 and 2 and A. odontolyticus, only those of genospecies 1 with a particular adherence profile showed efficient GalNAcbeta1-3Galalpha-O-ethyl-inhibitable binding to S-IgA. Thus, oligosaccharides on S-IgA may promote bacterial aggregation (or adherence) and provide a mechanism by which S-IgA can interact with bacteria without prior immunological challenge.

Helicobacter pylori adhesin binding fucosylated histo-blood group antigens revealed by retagging

The bacterium Helicobacter pylori is the causative agent for peptic ulcer disease. Bacterial adherence to the human gastric epithelial lining is mediated by the fucosylated Lewis b (Leb) histo-blood group antigen. The Leb-binding adhesin, BabA, was purified by receptor activity-directed affinity tagging. The bacterial Leb-binding phenotype was associated with the presence of the cag pathogenicity island among clinical isolates of H. pylori. A vaccine strategy based on the BabA adhesin might serve as a means to target the virulent type I strains of H. pylori.