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P376. Phylogenetic and phenotypic characterisation of Faecalibacterium prausnitzii isolates from the human large intestine

P376. Phylogenetic and phenotypic characterisation of Faecalibacterium prausnitzii isolates from the human large intestine

M. Lopez-Siles1, T.M. Khan2, S.H. Duncan3, H.J.M. Harmsen2, J. Garcia-Gil1, H.J. Flint3

1Grup de Microbiologia Clínica i Malalties Infeccioses, Universitat de Girona, Girona, Spain; 2Department of Medical Microbiology, University of Groningen, Groningen, The Netherlands; 3Microbial Ecology Group, Rowett Institute of Nutrition and Health, Aberdeen, United Kingdom

Faecalibacterium prausnitzii is one of the most abundant commensal bacterial species that inhabits the human gut. A diminished prevalence and abundance of F. prausnitzii has been described in Inflammatory Bowel Disease patients [1–3]. Recent studies suggests phylogenetic diversity within F. prausnitzii and closely relatived groups [4–5]. In a previous study, one particular phylotype (AM075691) that is 98% similar to F. prausnitzii, was significantly less prevalent in Crohn's disease patients than in control subjects [1].

Aim: To describe the diversity within F. prausnitzii by performing phylogenetic and phenotypic characterisation of human faecal isolates.

Material and Methods: Phylogeny based on 16S rRNA gene sequences has been analysed using the ARB-software package [6]. Key characteristics of 8 F. prausnitzii isolates have been studied including substrate utilization of 17 different carbohydrates as described previously [7]. Fermentation products were analysed by capillary gas chromatography following a previously described method [7]. Changes in growth rate due to variation in initial medium pH and bile salt tolerance were assessed as previously reported [8–9].

Results: Phylogenetic analysis showed that few F. prausnitzii phylogroups are responsible for the abundance of this species in the gut. Cultured representatives correspond only to the two most abundant phylogroups. Careful attention must be paid to isolates close to phylotype AM075691 as this group seems to be extremely sensitive to abnormal gut conditions.

All isolates tested were able to ferment a wide range of carbohydrates of different dietary origin and structures, some of which are host derived. Concerning F. prausnitzii physiology, isolates showed better growth rates at pH 6.7 than at slightly acidic pH values. Below pH 5.75 F. prausnitzii growth was inhibited, consistent with the lower colonic pH values reported in ulcerative colitis patients [10]. None of the F. prausnitzii isolates tested was able to grow above 0.5% bile salt concentration and that may be comparable to the bile concentrations present in the diseased colon.

Conclusion: All cultured F. prausnitzii representatives were extremely sensitive to some of the changes in the gut ecologically conditions that may occur in the diseased state which may account for the major reduction in this important commensal under these conditions. Since no major differences were observed concerning diet or environmental factors among isolates or phylogroups, other factors might play a key role in shaping the differential presence of these phylotypes in the gut.

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9. Maxwell F.J PhD thesis, Aberdeen, 1994.

10. Nugent SG, et al. Gut 2001; 48(4): 571–7.