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* = Presenting author

P375. Microbiota in Crohn's perianal fistulae

P. Tozer1,2, N. Rayment3, H.O. Al-Hassi4, A.U. Murugananthan1, N. Daulatzai1, S.C. Knight4, R.K.S. Phillips1,2, K. Whelan3, A.L. Hart1,2

1St Mark's Hospital, London, United Kingdom; 2Imperial College, London, United Kingdom; 3Kings College, London, United Kingdom; 4APRG, Imperial College, London, United Kingdom

Aims: The aetiology of Crohn's disease remains obscure but genetic, microbiological and immunological factors are thought to play a role. Faecal diversion prevents recurrence of luminal inflammation after resection and leads to improvement in some anal fistulae in Crohn's disease. Partial efficacy of antimicrobial agents in treating Crohn's perianal fistulae also suggests the importance of gut bacteria. Microbial diversity is reduced in active Crohn's disease with reduced clostridia and Faecalibacterium prausnitzii and increased enterobacteria such as E. Coli.

The relationship between rectal microbiota and the presence of anal fistulae in Crohn's disease or idiopathic fistulae has not been well documented.

Our aim was to characterise the fistula tract and rectal bacteria in patients with Crohn's perianal fistulae and idiopathic fistulae using fluorescent in situ hybridisation (FISH).

Methods: Fistula and rectal biopsies were taken from patients with Crohn's or idiopathic anal fistulae and rectal samples from patients with isolated luminal Crohn's disease. Samples were taken using a standardised technique, washed in sterile phosphate buffered saline and snap frozen in liquid nitrogen. Frozen sections were hybridised with 16S RNA probes and mucosa associated bacteria were identified and quantified. Gram staining and electron microscopy were also used to confirm the fistula tract findings.

Results: Thirty-six patients with anal fistulae (18 Crohn's disease [CPD], 18 idiopathic [IPD]) had rectal and fistula tract biopsies taken. As a control group, 12 patients with luminal Crohn's disease (and no perianal disease [CD]) had rectal samples taken.

 NAgeFemaleDuration of perianal diseaseDuration of luminal diseaseLocation of luminal diseaseStomaImmunomodulatorsSmoker
IPD1846.563.4 yearsNANA0NA6
CPD1831.5105.9 years12 years3× L1p
6× L2p
6× L3p
3× p
23× oral steroids
7× thiopurines
CD12328NA115× L1
1× L2
6× L3
33× thiopurines
1× methotrexate

None of the fistula tract biopsies from either the Crohn's disease patients or the patients with idiopathic fistulae contained any mucosa-associated bacteria, with the exception of one sample (idiopathic). This finding was identified using FISH, Gram staining and electron microscopy. When comparing rectal microbiota, Bifidobacteria were present in higher numbers in patients with idiopathic anal fistulae than Crohn's fistulae and Crohn's luminal disease (P = 0.02). Rectal microbiota were otherwise similar across the three groups. In all patients with Crohn's disease, a longer duration of disease was associated with a higher number of Bacteroides (p = 0.02).

Conclusions: Our findings suggest that there is altered rectal microbiota (decreased Bifidobacteria) in patients with Crohn's anal fistulae, but that the fistula tracts themselves are lacking in mucosa-associated microbiota.