Pathogenicity-associated islands in extraintestinal pathogenic Escherichia coli are fitness elements involved in intestinal colonization.
The virulence of many human pathogens does not seem to be an evolutionarily selected trait, but an accidental by-product of the selection that operates in another ecological context. We investigated the possibility that virulence of the extraintestinal pathogenic Escherichia coli (ExPEC) strains, which frequently cause disease in the host in which they asymptomatically colonize the intestine, is the consequence of commensalism. Most of the ExPEC virulence factors are clustered on genomic islands called pathogenicity-associated islands (PAIs). We constructed and characterized several mutants of the ExPEC 536 strain with either (i) deletions of each single PAI or (ii) a complete deletion of all seven PAIs. In vitro phenotypic characterization of 536 mutants showed that the seven PAIs were dispensable for growth in the absence of external stress, as well as under a range of biologically relevant stressors, i.e., serum, bile, and oxidative, nitrosative, hyperosmotic, and acidic stress. However, challenge against the wild-type (WT) strain in a murine model shows that the deletion of all seven PAIs drastically reduces the fitness of 536 during persistent intestinal colonization. This defect seems to be linked to the hypermotility observed for mutants devoid of all seven PAIs. In addition, we show that PAIs diminish fitness of their carrier during growth in urine, suggesting that urinary tract infections are unlikely to provide selective pressure for the maintenance of ExPEC PAIs. Our results are in accordance with the coincidental-evolution hypothesis postulating that extraintestinal E. coli virulence is a by-product of commensalism.
Diard
Médéric
M
INSERM U1001, Faculté de Médecine Paris Descartes, Université Paris Descartes, 156 rue de Vaugirard, 75730 Paris Cedex 15, France.
Garry
Louis
L
Selva
Marjorie
M
Mosser
Thomas
T
Denamur
Erick
E
Matic
Ivan
I
D000818:Animals; D018441:Biofilms / Q000254:growth & development; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity*; D005260:Female; D016680:Genome, Bacterial / Q000235:genetics; D044404:Genomic Islands / Q000235:genetics / Q000502:physiology*; D007422:Intestines / Q000382:microbiology*; D051379:Mice; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014552:Urinary Tract Infections / Q000382:microbiology; D014774:Virulence / Q000235:genetics / Q000502:physiology