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Original article
Stool consistency is strongly associated with gut microbiota richness and composition, enterotypes and bacterial growth rates
  1. Doris Vandeputte1,2,3,
  2. Gwen Falony1,2,
  3. Sara Vieira-Silva1,2,
  4. Raul Y Tito1,2,3,
  5. Marie Joossens1,2,3,
  6. Jeroen Raes1,2,3
  1. 1Department of Microbiology and Immunology, KU Leuven, Rega Institute, Leuven, Belgium
  2. 2VIB, Center for the Biology of Disease, Leuven, Belgium
  3. 3Faculty of Sciences and Bioengineering Sciences, Microbiology Unit, Vrije Universiteit Brussel, Brussels, Belgium
  1. Correspondence to Jeroen Raes, Department of Microbiology and Immunology, KU Leuven, Rega Institute, Herestraat 49, Leuven B-3000, Belgium; jeroen.raes{at}


Objective The assessment of potentially confounding factors affecting colon microbiota composition is essential to the identification of robust microbiome based disease markers. Here, we investigate the link between gut microbiota variation and stool consistency using Bristol Stool Scale classification, which reflects faecal water content and activity, and is considered a proxy for intestinal colon transit time.

Design Through 16S rDNA Illumina profiling of faecal samples of 53 healthy women, we evaluated associations between microbiome richness, Bacteroidetes:Firmicutes ratio, enterotypes, and genus abundance with self-reported, Bristol Stool Scale-based stool consistency. Each sample’s microbiota growth potential was calculated to test whether transit time acts as a selective force on gut bacterial growth rates.

Results Stool consistency strongly correlates with all known major microbiome markers. It is negatively correlated with species richness, positively associated to the Bacteroidetes:Firmicutes ratio, and linked to Akkermansia and Methanobrevibacter abundance. Enterotypes are distinctly distributed over the BSS-scores. Based on the correlations between microbiota growth potential and stool consistency scores within both enterotypes, we hypothesise that accelerated transit contributes to colon ecosystem differentiation. While shorter transit times can be linked to increased abundance of fast growing species in Ruminococcaceae-Bacteroides samples, hinting to a washout avoidance strategy of faster replication, this trend is absent in Prevotella-enterotyped individuals. Within this enterotype adherence to host tissue therefore appears to be a more likely bacterial strategy to cope with washout.

Conclusions The strength of the associations between stool consistency and species richness, enterotypes and community composition emphasises the crucial importance of stool consistency assessment in gut metagenome-wide association studies.


This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:

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