Adhesion of Diarrheagenic Escherichia coli and Inhibition by Glycocompounds Engaged in the Mucosal Innate Immunity

Abstract

Escherichia coli colonizes the human intestine shortly after birth, with most strains engaging in a commensal relationship. However, some E. coli strains have evolved toward acquiring genetic traits associated with virulence. Currently, five categories of enteroadherent E. coli strains are well-recognized, and are classified in regard to expressed adhesins and the strategy used during the colonization. The high morbidity associated with diarrhea has motivated investigations focusing on E. coli adhesins, as well on factors that inhibit bacterial adherence. Breastfeeding has proved to be the most effective strategy for preventing diarrhea in children. Aside from the immunoglobulin content, glycocompounds and oligosaccharides in breast milk play a critical role in the innate immunity against diarrheagenic E. coli strains. This review summarizes the colonization factors and virulence strategies exploited by diarrheagenic E. coli strains, addressing the inhibitory effects that oligosaccharides and glycocompounds, such as lactoferrin and free secretory components, exert on the adherence and virulence of these strains. This review thus provides an overview of experimental data indicating that human milk glycocompounds are responsible for the universal protective effect of breastfeeding against diarrheagenic E. coli pathotypes.

Figure 1

Distinctive adhesion patterns displayed by E. coli strains on HeLa cells when in the presence of D-mannose. (A) Localized adherence (LA) developed by a prototype EPEC strain. Note the formation of microcolonies (black arrow) on the host cell surface formed by tight clusters of bacterial cells. (B) Aggregative adherence (AA) formed by the prototype EAEC strain 042. AA phenotype is characterized by the autoagglutination of the bacterial cells into a conformation that resembles stacked bricks. The AA pattern develops on the edge of the host cell and extends forward on the abiotic surface (black arrowhead). (C) Diffusely adherent E. coli strain showing bacterial cells scattered on the surface of host cell as well as on the abiotic surface. (D) Non-adherent E. coli strain.