The interaction between a non-pathogenic and a pathogenic strain synergistically enhances extra-intestinal virulence in Escherichia coli.
Finding two or more genotypes of a single species within an infected sample is a not infrequent event. In this work, three Escherichia coli strains of decreasing extra-intestinal virulence (pathogenic B2S and B1S strains, and the avirulent K-12 MG1655 strain) were tested in septicaemia and urinary tract infection (UTI) mouse models, either separately or in pairs. Survival was monitored and bacteria were counted in various organs. Serum interleukin (IL)-6, tumour necrosis factor alpha (TNFα) and IL-10 were measured. We show that a mix of high amounts of B1S or of MG1655 with low amounts of B2S killed more rapidly (B1S), or killed more mice (MG1655), than either high amounts of B1S, high amounts of MG1655 or low amounts of B2S separately in the mouse septicaemia model. This bacterial synergy persisted when high amounts of dead or abnormal-LPS K-12 cells were injected together with a low amount of B2S. In both septicaemia and UTI models, significantly more bacteria were recovered from the organs of mice injected with the MG1655/B2S mix than from those of mice injected with the inocula separately. Consistently, in the septicaemia model, more IL-6 was secreted before death by the mice that were injected with the mix of bacteria than by the mice that were injected with the inocula separately. The synergistically enhanced mortality in the case of co-infection in the septicaemia model persisted in RFcγ(-/-), Myd88(-/-) and IL-6(-/-) knockout mice. This synergistically increased virulence resulting from the interaction between an avirulent and a pathogenic strain of the same bacterial species raises questions about the role of avirulent bacteria in the development of some extra-intestinal infections.
INSERM U722, and Université Paris 7 Denis Diderot, Site Xavier Bichat, 75018 Paris, France.
Jérôme
J
Tourret
INSERM U699, and Université Paris 7 Denis Diderot, Site Xavier Bichat, 75018 Paris, France.
Meryem
M
Aloulou
INSERM U722, and Université Paris 7 Denis Diderot, Site Xavier Bichat, 75018 Paris, France.
Louis
L
Garry
INSERM U722, and Université Paris 7 Denis Diderot, Site Xavier Bichat, 75018 Paris, France.
Olivier
O
Tenaillon
INSERM U722, and Université Paris 7 Denis Diderot, Site Xavier Bichat, 75018 Paris, France.
Sara
S
Dion
CNRS UMR6218, and Université d'Orléans and Molecular Immunology and Embryology, IEM2815, 45071 Orléans, France.
Bernard
B
Ryffel
INSERM U699, and Université Paris 7 Denis Diderot, Site Xavier Bichat, 75018 Paris, France.
Renato C
RC
Monteiro
INSERM U722, and Université Paris 7 Denis Diderot, Site Xavier Bichat, 75018 Paris, France.
Erick
E
Denamur
D000818:Animals; D016470:Bacteremia / Q000382:microbiology / Q000401:mortality* / Q000473:pathology; D004195:Disease Models, Animal; D004926:Escherichia coli / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000472:pathogenicity*; D004927:Escherichia coli Infections / Q000382:microbiology / Q000401:mortality* / Q000473:pathology; D048168:Escherichia coli K12 / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D005260:Female; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009928:Organ Specificity; D014552:Urinary Tract Infections / Q000382:microbiology / Q000401:mortality* / Q000473:pathology; D014774:Virulence