S. Beeckmans

A General Procedure for the Purification of Fimbrial Lectins from Escherichia Coli

The presence of lectins on the surface of E. coli has been known since Duguid et al. (1955) described in the mid-1950’s the hemagglutinating properties of some E. coli strains (reviewed by Duguid and Old 1980). Especially during the past years, much effort has been devoted to the purification and characterization of surface lectins from several bacterial species (Sharon 1987; Jann and Jann 1990; Bertels et al. 1991; Gilboa-Garber and Avichezer 1993). Without doubt, the E. coli fimbrial lectins are among the most thoroughly investigated. This is not surprising, since although E. coli are advantageous commensals of the large intestine of mammals and birds, some strains are able to colonize other niches as well, and are the causative agents of both intestinal and extra-intestinal diseases in man and his domestic animals. It is now generally recognized that the attachment of bacteria to the host’s mucosae is an initial step in pathogenesis and that attachment or adhesion is mediated by bacterial surface lectins which can be of either fimbrial or nonfimbrial nature. Consequently, inhibition of bacterial adhesion is the way of choice to prevent infection (Beachy 1981).

Chapter 20 Strategies for the prevention of E. coli infection in the young animal1

Publisher Summary This chapter discusses the strategies to prevent colonization of the gut by enterotoxigenic E. coli (ETEC). The chapter describes the attachment of E. coli , by virtue of fimbriae, to the intestinal wall, and the molecules involved both at the bacterial surface and on the intestinal epithelium. ETEC are pathogens that cause diarrhoea in humans and livestock. These bacteria colonize the small intestinal epithelium by of expressing adhesins (lectins) in the form of long proteinaceous appendages that protrude from their surface, and that are called fimbriae. Because of their size, architecture and extracellular expression, fimbriae can easily be obtained in a highly purified state and in appreciable quantities to be used as vaccine components. Purified fimbriae have proven to be strong immunogens, and humoral antibodies are readily generated in rodents, chickens and farm animals. Plant lectins are potential candidates to block intestinal mucosal E. coli lectin receptors, because most plant lectins are rather resistant to proteolytic degradation in the stomach and small intestine, and, can bind to glycoconjugates present in the intestinal mucosa. The beneficial effect of probiotics in protecting the host from intestinal disorders and/or colonization of the intestine is because of one or a combination of the following effects: (1) stimulation of the immune system; (2) competitive inhibition for bacterial adhesion sites on the intestinal surface; (3) degradation of intestinal toxin receptors; and (4) production of inhibitory substances such as bacteriocins, hydrogen peroxide or organic acids.