Enteropathogenic Escherichia coli strain RDEC-1 produces a novel electrogenic factor active on rabbit ileum in vitro

Rabbit-specific fimbriae, Ral, alter the patterns of in vitro adherence and intestinal colonisation of rabbits by human-specific enteropathogenic E. coli

Enteropathogenic Escherichia coli (EPEC) poses a significant threat to human health, causing diarrhoea in children worldwide, and is a leading cause of infant mortality in developing countries. The pathogenic effects of EPEC and other attaching-effacing (A/E) bacteria result from adhesion to the intestinal mucosa by a variety of mechanisms, including fimbrial adhesins, which are believed to contribute to the host and tissue specificity of EPEC by their interaction with specific receptors on cell surfaces. In this study we investigated the contribution of a fimbrial adhesin, Ral, of rabbit-specific EPEC (REPEC) to host specificity by introducing Ral into derivatives of human-specific EPEC (hEPEC) strain, E2348/69, in which expression of the fimbrial adhesin, Bfp, had been interrupted. Although unable to cause diarrhoeal disease in rabbits, Ral-bearing hEPEC strains colonised rabbit intestine more efficiently and showed altered intestinal localisation when compared to an isogenic Ral-negative strain. These findings suggest that Ral enhances the initial interaction between a DeltabfpA mutant of hEPEC and rabbit intestine and may influence tissue specificity, but is not sufficient on its own to transform hEPEC into a rabbit pathogen. This study affords new insights into the complex mechanisms which determine the host range of bacterial pathogens.

Attaching-effacing bacteria in animals

Enteric bacteria with a demonstrable or potential ability to form attaching-effacing lesions, so-called attaching-effacing (AE) bacteria, have been found in the intestinal tracts of a wide variety of warm-blooded animal species, including man. In some host species, for example cattle, pigs, rabbits and human beings, attaching-effacing Escherichia coli (AEEC) have an established role as enteropathogens. In other host species, AE bacteria are of less certain significance. With continuing advances in the detection and typing of AE strains, the importance of these bacteria for many hosts is likely to become clearer. The pathogenic effects of AE bacteria result from adhesion to the intestinal mucosa by a variety of mechanisms, culminating in the formation of the characteristic intimate adhesion of the AE lesion. The ability to induce AE lesions is mediated by the co-ordinated expression of some 40 bacterial genes organized within a so-called pathogenicity island, known as the "Locus for Enterocyte Effacement". It is also believed that the production of bacterial toxins, principally Vero toxins, is a significant virulence factor for some AEEC strains. Recent areas of research into AE bacteria include: the use of Citrobacter rodentium to model human AEEC disease; quorum-sensing mechanisms used by AEEC to modulate virulence gene expression; and the potential role of adhesion in the persistent colonization of the intestine by AE bacteria. This review of AE bacteria covers their molecular biology, their occurrence in various animal species, and the diagnosis, pathology and clinical aspects of animal diseases with which they are associated. Reference is made to human pathogens where appropriate. The focus is mainly on natural colonization and disease, but complementary experimental data are also included.