1. Field of the Invention
This invention relates generally to pathogenic, diarrheagenic E. coli and specifically to the diagnosis and treatment of enteropathogenic E. coli (EPEC).
2. Description of Related Art
The Escherichia coli comprise a heterogenous group of microorganisms with wide ranging potential for interacting with their hosts. There are three broad categories into which the E. coli can be subdivided: 1) non-pathogenic E. coli which comprise the normal flora of the host; 2) opportunistic pathogen (e.g., uropathogenic E. coli; and 3) true pathogens. The diarrheagenic E. coli are true pathogens and are further subdivided into at least five or six groups based on defined clinical symptoms and virulence mechanisms. These groups include enteroinvasive (EIEC), enterotoxigenic (ETEC), enterohemmorhagic (EHEC), enteroaggregative (EaggEC), and enteropathogenic (EPEC) and diffuse adhering (DAEC).
The ability of pathogenic bacteria to adhere to host epithelial cells is regarded as a prerequisite for the initial colonization of host tissue (Svanborg-Eden, et al., Lancet, ii:490, 1976; Beachey, E., J. Infect. Dis. 143:325, 1981; Gaastra and deGraaf, Microbiol. Rev. 46:129, 1982). In many cases, the adhesion of E. coli and other gram negative bacteria takes place through the binding of bacterial pili to specific receptors on the host cell surface, some of which have been identified as glycolipids and glycoproteins (Anderson, et al., Infect. Immun. 29:897, 1980; Sharon and Lis, Science 246:227, 1989). The specificity of the bacterial adhesions, on the one hand, and the range of receptor structures expressed by particular epithelial cells, on the otherhand, have been suggested to be important determinants of the host range and tissue tropism of each pathogen.
Enteropathogenic E. coli are diarrheagenic serotypes which do not produce heat labile or heat stable enterotoxins. The virulence determinants of enteropathogenic E. coli strains have not been defined, but the typical mode of attachment to intestinal cells has implicated that the adherence property is a major virulence (Clausen, et al., J. Pediatr. 100:358, 1982). This type of adherence does not appear to be solely mediated by fimbriae (Scotland, et al., FEMS Microbiol. Lett. 20:191, 1983). These strains cause characteristic ultrastructural intestinal lesions and electron microscopic examinations of the affected segments show a marked effacement of the microvilli and disorganization of the underlying cytoskeletal elements.
Enteropathogenic E. coli strains adhere in vitro to epithelial cells such as HeLa or Hep-2 in characteristic patterns that are classified as localized, diffused and aggregative patterns (Cravioto, et al., Curr. Microbiol. 3:95, 1989; Scaletsky, et al., Infect. Immun. 45:534, 1984). The strains showing localized adherence (LA) have been more frequently encountered in persistent diarrhea, and their diarrheagenic potential experimentally proven by human volunteer studies (Levine, et al., J. Infect. Dis. 152:550, 1985). Localized adherent enteropathogenic E. coli strains harbor plasmids of 50-80 MDa called EPEC adhesive factor (EAF) plasmids that have been shown to be involved in the ability to adhere to HeLa or Hep-2 cells (Levine, et al., supra). The epithelial cell surface for interaction with a variety of pathogenic bacteria has been shown to have glycosphingolipids which are a prerequisite for successful colonization. This relationship is best exemplified by the uropathogenic E. coli which bind to Gal.alpha.1-4.beta.Gal structures in glycosphingolipids and Neisseria gonorrheae which recognize the lactosyl portion of the glycolipids.
Although studies of various cell surface interactions between eukaryotic cells and pathogenic bacteria have attempted to identify the ligand/receptor relationships, there is still a need for further identification and characterization of the structures which are specifically bound by enteropathogenic E. coli (Jagannatha, H. M., et al., Microbial Path., 11:259-268, 1991 and Rafiee, et al., J. Cell Biol., 115:1021-1029, 1991). This latter understanding is essential to developing effective therapeutic treatment and methods of diagnosis for enteropathogenic E. coli mediated diseases. The present invention identifies the nature of the interaction between the enteropathogenic E. coli and the epithelial cell and, thereby, provides the basis for a method of ameliorating and diagnosing enteropathogenic E. coli enteric infections.