Irritable bowel syndrome (IBS) was not associated with the microbiome composition of either stool or mucosa from individuals in a random Swedish population sample, according to study results published in Gut.
The study researchers characterized the mucosa-associated microbiome (MAM) and fecal microbiome compositions while testing for their association with health correlates (IBS and IBS symptom burden, self-rated health, tobacco use, depression and anxiety, body mass index, [BMI] stool consistency, and use of antibiotics and probiotics) in an urban cohort of individuals with or without IBS who had otherwise healthy guts. IBS was defined by Rome IV criteria. Microbiomes were assessed by 16S rRNA gene sequencing.
The sample of 3556 adults from Stockholm, Sweden, was part of the PopCol study. Approximately 21% of the study population (745/3556) agreed to undergo a colonoscopy with biopsy. Ultimately, microbiome rRNA gene sequencing was conducted on sigmoid biopsy samples (for the MAM) from 63 and 313 individuals with and without IBS, respectively, and on fecal samples from 32 and 153 individuals with and without IBS, respectively. Both sample types were available for a subset of individuals (IBS, n=29; control, n=149).
Differences were identified among sample types. The mucosa and fecal samples had higher relative abundance of Lachnospiraceae and Ruminococcaceae, respectively. In an analysis for potential biomarkers, no clades were associated with diagnosis of IBS, IBS type, or IBS symptoms burden score.
For paired samples from the same individual, microbial richness (R2=0.255; P <3´10-11) and diversity (R2=0.06; P =.0022) in the mucosa and feces were linearly correlated.
When assessing the relationship between within sample diversity and health correlates, poorer self-rated health (r=−0.15; P =.007) was correlated with decreasing MAM diversity, and stool consistency was correlated with fecal microbiome diversity (r=−0.16; P=.043).
Specific taxonomic groups in the mucosa were correlated with age (Bifidobacterium, r=-0.001; P =7.8´10-6), depression (Coprococcus catus, r=−0.003; P =1.7´10-4), and self-reported health (Coprococcus_2, r=-0.002; P =7.80´10-5). BMI also affected MAM composition; individuals considered underweight and obese according to BMI presented greater spread in their microbiome compositions than individuals with normal BMI (r=0.093; P =.002). No significant correlations were found between taxonomic groups in the feces and health correlates.
An analysis of between-sample diversity revealed that individuals without IBS have more similar MAM composition, while those individuals with IBS showed higher degrees of heterogeneity (r=0.131; P =.003).
Study limitations included that for their analysis of the fecal microbiome, the samples were transported at room temperature without preservatives. Furthermore, the metadata available were not as comprehensive and thus some important factors cannot be accounted for in the study, as evidenced by the lack of observed effect of probiotics and antibiotics.
The researchers concluded this is the first study to investigate the mucosa-associated gut microbiome of an adult population-based cohort and that no distinct microbial signature was observed in IBS.
Hugerth LW, Andreasson A, Talley NJ, et al. No distinct microbiome signature of irritable bowel syndrome found in a Swedish random population [published online October 10, 2019]. Gut. doi:10.1136/gutjnl-2019-318717