Résumé
Crohn’s disease (CD) is an inflammatory bowel disease in which
Escherichia coli strains have been suspected of being
involved. We demonstrated previously that ileal lesions of CD are
colonized by E. coli strains able to adhere to intestinal
Caco-2 cells but devoid of the virulence genes so far described in the
pathogenic E. coli strains involved in gastrointestinal
infections. In the present study we compared the invasive ability of
one of these strains isolated from an ileal biopsy of a patient with
CD, strain LF82, with that of reference enteroinvasive (EIEC),
enteropathogenic (EPEC), enterotoxigenic (ETEC), enteraggregative
(EAggEC), enterohemorrhagic (EHEC), and diffusely adhering (DAEC)
E. coli strains. Gentamicin protection assays showed that
E. coli LF82 was able to efficiently invade HEp-2 cells.
Its invasive level was not significantly different from that of EIEC
and EPEC strains (P > 0.5) but significantly higher
than that of ETEC (P < 0.03), EHEC
(P < 0.005), EAggEC (P < 0.004) and
DAEC (P < 0.02) strains. Strain LF82 also
demonstrated efficient ability to invade intestinal epithelial cultured
Caco-2, Intestine-407, and HCT-8 cells. Electron microscopy examination
of infected HEp-2 cells revealed the presence of numerous intracellular
bacteria located in vacuoles or free in the host cell cytoplasm. In
addition, the interaction of strain LF82 with epithelial cells was
associated with the elongation of microvillar extensions that extruded
from the host cell membranes and engulfed the bacteria. This
internalization mechanism strongly resembles Salmonella- or
Shigella-induced macropinocytosis. The use of cytochalasin
D and colchicine showed that the uptake of strain LF82 by HEp-2 cells
was mediated by both an actin microfilament-dependent mechanism and
microtubule involvement. In addition, strain LF82 survived for at least
24 h in HEp-2 and Intestine-407 cells and efficiently replicated
intracellularly in HEp-2 cells. PCR and hybridization experiments did
not reveal the presence of any of the genetic determinants encoding
EIEC, EPEC, or ETEC proteins involved in bacterial invasion. Thus,
these findings show that LF82, which colonized the ileal mucosa of a
patient with CD, is a true invasive E. coli strain and
suggest the existence of a new potentially pathogenic group of E.
coli, which we propose be designated adherent-invasive E.
coli.