Veterinary Immunology and Immunopathology

Escherichia coli was described in 1885 by a German pediatrician, Theodor Escherich, in the faeces of a child suffering diarrhoea. In 1893, a Danish veterinarian postulated that the E. coli species comprises different strains, some being pathogens, others not. Today the E. coli species is subdivided into several pathogenic strains causing different intestinal, urinary tract or internal infections and pathologies, in animal species and in humans. Since this congress topic is the interaction between E. coli and the mucosal immune system, the purpose of this manuscript is to present different classes of adhesins (fimbrial adhesins, afimbrial adhesins and outer membrane proteins), the type 3 secretion system, and some toxins (oligopeptide, AB, and RTX pore-forming toxins) produced by E. coli, that can directly interact with the epithelial cells of the intestinal, respiratory and urinary tracts. © 2012 Elsevier B.V. All rights reserved. 1. Pathogenic Escherichia coli Escherichia coli is a Gram-negative, rod-shaped bacterium belonging to the family Enterobacteriaceae that was described in 1885 by a German pediatrician, Theodor Escherich (1857–1911) in the faeces of a child suffering diarrhoea (Escherich, 1885). While many strains occur as commensal members of the microbiota in the intestinal tract of animals and humans, some strains are, however, important pathogens that cause a wide spectrum of diseases, ranging from self-limiting to life-threatening intestinal and extra-intestinal illnesses (Sussman, 1997; Wray and Woodward, 1997; Kaper et al., 2004; Nataro et al., 2011). This was a puzzling observation at the time, because according to the Koch’s postulates (Koch, 1884), one bacterial species was either pathogen or not. In 1893, a Danish veterinarian postulated that the E. coli species comprises different strains, some being pathogens, others not (Jensen, 1893). Not only his assertion proved true but also E. coli is today subdivided into several pathogenic strains causing different intestinal, urinary tract or internal ∗ Tel.: +32 4 3669522; fax: +32 4 3664261. E-mail address: [email protected] infections and pathologies, in all animal species and in humans. Those pathogenic E. coli serotypes were therefore named by the clinical syndrome they can cause (Table 1 ): diarrhoeagenic E. coli (DEC), uropathogenic E. coli (UPEC), septicaemic E. coli (SePEC), neonatal meningitis-associated E. coli (NMEC), etc.; or sometimes according to the target host: avian pathogenic E. coli (APEC) (Mainil, 2003a). The question soon changed to how identifying in vitro the pathogenic strains of E. coli. The first answer came from the serotyping system developed by Kauffmann in the 1940s, i.e. the identification of somatic (O antigen), capsular (K antigen) and flagellar (H antigen) surface antigens (Kauffmann, 1947). Some serotypes are indeed more frequently than others associated with specific clinical syndromes (Sojka, 1965; Orskov and Orskov, 1992; Lior, 1994). Fortunately from the late 1960s onwards, several specific properties that differentiate the pathogenic strains from each other and from non-pathogenic strains were unravelled. It therefore became possible to name the different classes of pathogenic E. coli on the basis of their specific properties instead of the clinical syndrome they can produce. Focusing on diarrhoeagenic E. coli, three classes were so defined in humans in the 1970s (World Health Organization, 1980) (Table 1): enterotoxigenic E. coli (ETEC) producing (entero)toxins causing 0165-2427/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.vetimm.2012.09.032 Author's personal copy J. Mainil / Veterinary Immunology and Immunopathology 152 (2013) 2– 12 3