ABSTRACT
The
mucosa-associated microflora is increasingly considered to
play a pivotal role in the pathogenesis of inflammatory bowel disease.
This study explored the possibility that an abnormal mucosal flora is
involved in the etiopathogenesis of granulomatous colitis of Boxer dogs
(GCB). Colonic biopsy samples from affected dogs (n =
13) and controls (n = 38) were examined by fluorescent
in situ hybridization (FISH) with a eubacterial 16S rRNA probe.
Culture, 16S ribosomal DNA sequencing, and histochemistry were used to
guide subsequent FISH. GCB-associated Escherichia coli
isolates were evaluated for their ability to invade and persist in
cultured epithelial cells and macrophages as well as for serotype,
phylogenetic group, genome size, overall genotype, and presence of
virulence genes. Intramucosal gram-negative coccobacilli were present
in 100% of GCB samples but not controls. Invasive bacteria hybridized
with FISH probes to E. coli. Three of four GCB-associated
E. coli isolates adhered to, invaded, and replicated within
cultured epithelial cells. Invasion triggered a“
splash”-type response, was decreased by cytochalasin
D, genistein, colchicine, and wortmannin, and paralleled the behavior
of the Crohn's disease-associated strain E. coli LF 82. GCB
E. coli and LF 82 were diverse in serotype and overall
genotype but similar in phylogeny (B2 and D), in virulence gene
profiles (fyuA, irp1, irp2, chuA,
fepC, ibeA, kpsMII, iss), in having
a larger genome size than commensal E. coli, and in the
presence of novel multilocus sequence types. We conclude that GCB is
associated with selective intramucosal colonization by E.
coli. E. coli strains associated with GCB and Crohn's
disease have an adherent and invasive phenotype and novel multilocus
sequence types and resemble E. coli associated with
extraintestinal disease in phylogeny and virulence gene
profile.
Adherent and Invasive Escherichia coli Is Associated with Granulomatous Colitis in Boxer Dogs