Abstract
Among the intestinal pathogenic Escherichia coli, enteroinvasive E. coli (EIEC) are a group of intracellular pathogens able to enter epithelial cells of colon, multiplicate within them, and move between adjacent cells with a mechanism similar to Shigella, the ethiological agent of bacillary dysentery. Despite EIEC belong to the same pathotype of Shigella, they neither have the full set of traits that define Shigella nor have undergone the extensive gene decay observed in Shigella. Molecular analysis confirms that EIEC are widely distributed among E. coli phylogenetic groups and correspond to bioserotypes found in many E. coli serogroups. Like Shigella, also in EIEC the critical event toward a pathogenic life-style consisted in the acquisition by horizontal gene transfer of a large F-type plasmid (pINV) containing the genes required for invasion, intracellular survival, and spreading through the intestinal mucosa. In Shigella, the ample gain in virulence determinants has been counteracted by a substantial loss of functions that, although important for the survival in the environment, are redundant or deleterious for the life inside the host. The pathoadaptation process that has led Shigella to modify its metabolic profile and increase its pathogenic potential is still in infancy in EIEC, although maintenance of some features typical of E. coli might favor their emerging relevance as intestinal pathogens worldwide, as documented by recent outbreaks in industrialized countries. In this review, we will discuss the evolution of EIEC toward Shigella-like invasive forms going through the epidemiology, including the emergence of new virulent strains, their genome organization, and the complex interactions they establish with the host.
Highlights
Escherichia coli is a harmless commensal of the human and animal intestine and a major cause of morbidity and mortality (Kaper et al, 2004; Wirth et al, 2006)
Genomics approaches in combination with phenotypic analyses have a strong potential toward the formulation of new intriguing hypotheses on the ongoing evolution of enteroinvasive E. coli (EIEC)
Available comparisons between EIEC and Shigella genomes support the need for a taxonomical revision moving the Shigella genus back within the E. coli species (Michelacci et al, 2016; Pettengill et al, 2016)
Summary
Escherichia coli is a harmless commensal of the human and animal intestine and a major cause of morbidity and mortality (Kaper et al, 2004; Wirth et al, 2006). Enteroinvasive E. coli and Shigella spp. share several phenotypic and genotypic characteristics, often making the discrimination between the two genera challenging (Silva et al, 1980; Toledo and Trabulsi, 1983; Bando et al, 1998; Lan and Reeves, 2002; Pavlovic et al, 2011; van den Beld and Reubsaet, 2012), especially in case of shared serogroups This difficulty biases the interpretation of the epidemiological information available, hindering the evaluation of the real burden of EIEC infections. Pheno-genotypic characterization of the strains involved in the three episodes suggests that the EIEC O96:H19 could be emerged as a result of the recent acquisition of the invasion plasmid by an E. coli strain (Michelacci et al, 2016)
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