Hannah Singh, 31, is not only
painfully thin but also frequently in pain due to the
cramping and diarrhea associated with Crohn's disease.
Hannah's disease is incurable and its cause is unknown.
A report in the August issue of Gastroenterology,
however, pointed to an E coli strain in the ileum
of Crohn's disease patients as a foothold to further our
understanding of the possible roots of this mysterious
disease.
The study from the Université
d'Auvergne in Clermont-Ferrand, France builds on research
that links E coli infection with Crohn's disease.
In 1998, lead author Arlett Darfeuille-Michaud, PhD,
and her colleagues published observations that E
coli strains recovered from people with Crohn's
disease were more adherent to intestinal tissue cells
than E coli recovered from people free of the
disease. A year later, they chronicled how the presence
of pili � surface structures that protrude out like
feelers � drives the adhesion of the bacteria to the
intestinal surface. Once attached to the surface, the
bacteria can enzymatically dynamite holes in the surface
and burrow inside the cells. This double whammy led
the researchers to dub such strains adherent-invasive
E coli (AIEC).
In the latest study, the researchers
found an "abnormally high prevalence" of AIEC in mucosal
cells from the ileum in patients with Crohn's disease.
But this prevalence was not seen in ileal cells from
patients without inflammatory bowel disease, in colon
cells from Crohn's patients or patients with ulcerative
colitis, or people who did not have any bowel maladies.
In order to separate the AIEC from
other E coli strains, the researchers treated
tissue cells with gentamicin. E coli that survived
the antibiotic blast were presumed to be residing inside
the cells rather than on the surface, a defining characteristic
of AIEC.
Of the 63 Crohn's patients who
were examined, 21.7% harboured AIEC in ileal cells,
versus only 6.2% of control patients. When cells were
recovered from the transition region where the ileum
ends and the colon begins, AIEC strains were present
in 66.4% of the early stage lesions of Crohn's disease,
a rate that significantly exceeded the incidence of
this strain (22.2%) in the lesions of healthy controls.
The colon was a desert when it came to AIEC. Only 3.7%
of Crohn's patients, none of the ulcerative colitis
patients, and 1.9% of healthy controls harboured AIEC
in this region.
"AIEC strains are associated specifically
with ileal mucosa in [Crohn's disease]," concluded the
researchers. The finding of the strains in some colon
cell samples from healthy people indicated that while
the bacteria may not be specific to Crohn's, there's
something about the disease that makes the ileal mucosal
cells a very attractive place for this bacterial strain.
The nature of this attraction is
still puzzling. An altered ileal mucosal surface is
one possibility. If the surface target for the E
coli adhesion can be found, blocking adhesion could
protect intestinal cells.
|
