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Gut 49:47-55 doi:10.1136/gut.49.1.47
  • Gastrointestinal infection

Escherichia coli strains colonising the gastrointestinal tract protect germfree mice againstSalmonella typhimuriuminfection

  1. S Hudault,
  2. J Guignot,
  3. A L Servin
  1. Institut National de la Santé et de la Recherche Médicale, Unité 510, Faculté de Pharmacie Paris XI, 92296 Châtenay-Malabry, France
  1. S Hudault. sylvie.hudault{at}cep.u-psud.fr
  • Accepted 19 December 2000

Abstract

BACKGROUND Escherichia coli is part of the normal gastrointestinal microflora which exerts a barrier effect against enteropathogens. SeveralE coli strains develop a protective effect against other Enterobacteriaceae.

AIMS TwoE coli strains, EM0, a human faecal strain, and JM105 K-12 were tested for their ability to prevent in vivo and in vitro infection by Salmonella typhimurium C5.

METHODS Inhibition of C5 cell invasion by E coli was investigated in vitro using Caco-2/TC7 cells. The protective effect ofE coli was examined in vivo in germfree or conventional C3H/He/Oujco mice orally infected by the lethal strain C5.

RESULTS EMO expresses haemolysin and cytotoxic necrotising factor in vitro. In vitro, the two strains did not prevent the growth of C5 by secreted microcins or modified cell invasion of C5. In vivo, establishment of EM0 or JM105 in the gut of germfree mice resulted in a significant increase in the number of surviving mice: 11/12 and 9/12, respectively, at 58 days after infection (2×106/mouse) versus 0/12 in control germfree group at 13 days after infection. Colonisation level and translocation rate of C5 were significantly reduced during the three days after infection. In contrast, no reduction in faecal C5 excretion was observed in C5 infected conventional mice (1×108/mouse) receiving the EM0 or JM105 cultures daily.

CONCLUSIONS Establishment of E coli strains, which do not display antimicrobial activity, protects germfree mice against infection and delays the establishment of C5 in the gut. Possible mechanisms of defence are discussed.

Footnotes

  • Abbreviations used in this paper:
    LB broth
    Luria-Bertoni broth
    hlyA
    α-haemolysin
    cdt
    cytolethal distending toxin
    PBS
    phosphate buffered saline
    TSA
    tryptic soy agar
    SS agar, Shigella and Salmonella agar
    PCR, polymerase chain reaction
    LDH
    lactate dehydrogenase
    CNF
    cytotoxic necrotising factor
    MLN
    mesenteric lymph nodes
    IL
    interleukin
    TNF-α
    tumour necrosis factor α