A Specific Genetic Background Is Required for Acquisition and Expression of Virulence Factors in Escherichia coli

Abstract

In bacteria, the evolution of pathogenicity seems to be the result of the constant arrival of virulence factors (VFs) into the bacterial genome. However, the integration, retention, and/or expression of these factors may be the result of the interaction between the new arriving genes and the bacterial genomic background. To test this hypothesis, a phylogenetic analysis was done on a collection of 98 Escherichia coli/Shigella strains representing the pathogenic and commensal diversity of the species. The distribution of 17 VFs associated to the different E. coli pathovars was superimposed on the phylogenetic tree. Three major types of VFs can be recognized: (1) VFs that arrive and are expressed in different genetic backgrounds (such as VFs associated with the pathovars of mild chronic diarrhea: enteroaggregative, enteropathogenic, and diffusely-adhering E. coli), (2) VFs that arrive in different genetic backgrounds but are preferentially found, associated with a specific pathology, in only one particular background (such as VFs associated with extraintestinal diseases), and (3) VFs that require a particular genetic background for the arrival and expression of their virulence potential (such as VFs associated with pathovars typical of severe acute diarrhea: enterohemorragic, enterotoxigenic, and enteroinvasive E. coli strains). The possibility of a single arrival of VFs by chance, followed by a vertical transmission, was ruled out by comparing the evolutionary histories of some of these VFs to the strain phylogeny. These evidences suggest that important changes in the genome of E. coli have occurred during the diversification of the species, allowing the virulence factors associated with severe acute diarrhea to arrive in the population. Thus, the E. coli genome seems to be formed by an "ancestral" and a "derived" background, each one responsible for the acquisition and expression of different virulence factors.

Genomic analysis of the PAI ICL3 locus in pathogenic LEE-negative Shiga toxin-producing Escherichia coli and Citrobacter rodentium

“…Therefore, the observed link between complete PAI I CL3 genotype and seropathotype C demonstrates a striking phylogenetic link between intact PAI I CL3 and ECOR group B1. Consistent with previous studies that suggest that the arrival and stability of a PAI in a genome require a particular genetic background (Escobar-Paramo et al, 2004;Reid et al, 2000), a B1 genetic background seems to be necessary for the maintenance of a full complement of PAI I CL3 genes. The finding that E. coli strains belonging to phylogenetic groups E (EHEC EDL933 and Sakai), B2 (ExPEC CFT073 and APEC O1) and D (EAEC O42) carry exclusively the deleted versions of PAI I CL3 supports this concept.…”

Detection of virulence genes and the phylogenetic groups of Escherichia coli isolated from dogs in Brazil

“…Moreover, in our study, cnf1 strains were usually classified in phylogroups B2 and D (Table 2). In previous studies, it was shown that ExPEC strains are clustered mostly in groups B2 and D (ESCOBAR- PÁRAMO et al, 2004). Interestingly, E. coli strains isolated from septicemic human patients belonged mainly to groups B2 and D (ČUROVÁ et al, 2014).…”

“…E. coli genomic structure has shown that the strains belonging to different phylogroups are associated with the disease state and source of isolation (CLERMONT et al, 2013). The extraintestinal pathogenic E. coli (ExPEC) strains are clustered mostly in groups B2 and D and intestinal pathogenic E. coli are mostly in phylogroups A, B1, and E (ESCOBAR- PÁRAMO et al, 2004; CLERMONT et al, 2011). Although phylogenetic characterization is an important tool to improve the understanding of E. coli populations and the relationship between strains and disease (CLERMONT et al, 2011;COURA et al, 2015), few studies have determined phylogenetic groups of E. coli isolated from dogs worldwide, and of those that did, the most frequently used method was a triplex PCR method developed by CLERMONT in 2000.…”

tDNA locus polymorphism and ecto-chromosomal DNA insertion hot-spots are related to the phylogenetic group of Escherichia coli strains

“…3). This distinction based on the ECOR group is reminiscent of the hypothesis made by Escobar-Paramo et al (2004), who showed that the genetic background of strains belonging to the B2 ECOR group might be a critical player in the acquisition of ExPEC virulence factors. Since tDNAs are ECDNA insertion hot-spots, the tDNA pattern of one strain is also likely to have an influence on the acquisition/loss of ECDNA regions and could explain the specific properties of B2 strains, including their pathogenic properties (Picard et al, 1999).…”

“…Actually, Escobar et al (2004) identified two subgroups (groups C and E) that are not discriminated by the PCR described by Clermont et al (2000) used in this study. It is therefore possible that the heterogeneity of cluster 3 is linked to the fact that it contains strains from groups C and E.…”