Phylogenetic Analysis of Enteroaggregative and Diffusely Adherent Escherichia coli

Abstract

The phylogenetics of the various pathotypes of diarrheagenicEscherichia coli are not completely understood. In this study, we identified several plasmid and chromosomal genes in the pathogenic enteroaggregative E. coli (EAEC) prototype strain 042 and determined the prevalence of these loci among EAEC and diffusely adherent E. coli strains. The distribution of these genes is analyzed within an evolutionary framework provided by the characterization of allelic variation in housekeeping genes via multilocus enzyme electrophoresis. Our data reveal that EAEC strains are heterogeneous with respect to chromosomal and plasmid-borne genes but that the majority harbor a member of a conserved family of virulence plasmids. Comparison of plasmid and chromosomal relatedness of strains suggests clonality of chromosomal markers and a limited transfer model of plasmid distribution.

Pathogenesis of Afa/Dr Diffusely AdheringEscherichia coli

“…Only the human adhesins AfaE-I, AfaE-III, Dr, Dr-II, and F1845 have been fully explored with regard to their genetic organization, receptor recognition, and involvement in Afa/Dr DAEC pathogenicity. In addition, it was noted that the EAEC adhesins AAF-I, AAF-II (90), and AAF-III (37) are probably more distantly related members of the Afa/Dr family of adhesins (91). In particular, despite similar genetic organizations of the gene clusters involved in the biogenesis of these three adhesins and Afa/Dr adhesins, it remains important to explore whether or not EAEC adhesins recognized the Afa/Dr receptors, type IV collagen, DAF (CD55), and/or carcinoembryonic antigen-related cellular adhesion molecules (CEACAMs), which play a pivotal role in Afa/Dr DAEC pathogenesis.…”

“…DAEC strains have been identified from their diffuse adherence (DA) pattern on cultured epithelial HEp-2 as well as HeLa cells (307,308,365), and they appear to form a heterogeneous group (91,308). The first class of DAEC strains includes E. coli strains that harbor Afa/Dr adhesins (Afa/Dr DAEC) (322).…”

“…Finally, no genes encoding factors known to subvert host cell proteins, such as the type III secretion system or effector proteins expressed by EPEC (including intimin [Eae] and its receptor [Tir]) (155,443), have been found in strain C1845. The phylogenic analysis of EAEC and DAEC strains has revealed five large clusters of strains (91). Strain C1845 and some other DAEC strains were present in the cluster DAEC1 and appear to be phylogenetically close to the EAEC strains.…”

Pathogenesis of Human Diffusely Adhering Escherichia coli Expressing Afa/Dr Adhesins (Afa/Dr DAEC): Current Insights and Future Challenges

“…Moreover, despite a similar genetic organization with the gene clusters triggering the biogenesis of Afa/Dr adhesins, the EAEC adhesins AAF-I (77), AAF-II (76), AAF-III (75), and Hda (78) are distant pathogenic factors of the Afa/Dr family of adhesins ( Table 1). The four major characteristics of EAEC pathogenesis (79-81) are as follows: (i) adherence to the intestinal mucosa via adhesins (18,(75)(76)(77)(78), (ii) the formation of typical "stacked-brick" microcolonies as each bacterium interacts with others, (iii) production of enterotoxins and cytotoxins, and (iv) the development of a severe mucosal inflammation. Boisen et al (78), analyzing this superfamily of adhesins, have proposed a pertinent phylogram composed of three distinct clusters.…”

“…Five phylogenetic groups, including the main phylogenetic groups A, B1, B2, and D, have been identified in Gram-negative species using multilocus enzyme electrophoresis and sequence typing methods. Afa/Dr DAEC strains belong to the phylogenetic B2 group (18,19). In commensal E. coli from humans (in Europe, the United States, Australia, and Japan), B2 group E. coli strains are predominant (20), and it is noteworthy that these E. coli strains displayed a high capacity to colonize epithelia (21)(22)(23).…”