E. coli as an All-Rounder: The Thin Line Between Commensalism and Pathogenicity

Abstract

Escherichia coli is a paradigm for a versatile bacterial species which comprises harmless commensal as well as different pathogenic variants with the ability to either cause intestinal or extraintestinal diseases in humans and many animal hosts. Because of this broad spectrum of lifestyles and phenotypes, E. coli is a well-suited model organism to study bacterial evolution and adaptation to different growth conditions and niches. The geno- and phenotypic diversity, however, also hampers risk assessment and strain typing. A marked genome plasticity is the key to the great variability seen in this species. Acquisition of genetic information by horizontal gene transfer, gene loss as well as other genomic modifications, like DNA rearrangements and point mutations, can constantly alter the genome content and thus the fitness and competitiveness of individual variants in certain niches. Specific gene subsets and traits have been correlated with an increased potential of E. coli strains to cause intestinal or extraintestinal disease. Intestinal pathogenic E. coli strains can be reliably discriminated from non-pathogenic, commensal, or from extraintestinal E. coli pathogens based on genome content and phenotypic traits. An unambiguous distinction of extraintestinal pathogenic E. coli and commensals is, nevertheless, not so easy, as strains with the ability to cause extraintestinal infection are facultative pathogens and belong to the normal flora of many healthy individuals. Here, we compare insights into phylogeny, geno-, and phenotypic traits of commensal and pathogenic E. coli. We demonstrate that the borderline between extraintestinal virulence and intestinal fitness can be blurred as improved adaptability and competitiveness may promote intestinal colonization as well as extraintestinal infection by E. coli.

Extra-intestinal pathogenic Escherichia coli (ExPEC): Disease, carriage and clones

“…Over the last decade, a number of authors have sought to establish the prevalence of E. coli with ExPEC potential colonising the gut by performing microbiological screening studies on the stool of healthy individuals that delineate resident E. coli strains based on their phylogroup (58)(59)(60)(61)(62)(63). Results of these studies have demonstrated that 11-48% of healthy individuals are colonised with E. coli belonging to phylogroup B2, which is traditionally associated with virulence and ExPEC infections.…”

E. coli Bacteremia Strains - High diversity and Associations with Agerelated Clinical Phenomena

“…There is no direct relationship between E. coli pathotype and phylogenetic lineage, and an unambiguous distinction of ExPEC and commensals is complicated, as strains with ability to cause extraintestinal infection are facultative pathogens and belong to the normal flora of many healthy individuals [37]. Moreover, there is a notion of extensive horizontal gene transfer and the transmission of the genetic source of whole pathotypes in a single step via mobile elements [37].…”

Bacillus subtilis and Escherichia coli essential genes and minimal cell factories after one decade of genome engineering

“…B. subtilis is a commensal bacterium able to form metabolically inactive dehydrated endospores allowing survival in nutrient-free environments (McKenney et al, 2013). In contrast to B. subtilis, E. coli does not form endospores and, depending on the genome configuration, its lifestyle might vary from commensalism to pathogenicity (Clements et al, 2012;Leimbach et al, 2013). Some E. coli strains are important enteric and extra-intestinal pathogens (Leimbach et al, 2013).…”