Table 2.

Summary of studies exploring the association of fecal microbiota composition with frailty or disability in older individuals.

First Author, Journal, Year [Ref.]	Country	Study Design	Sample Size	Setting/Health Status	Method of Measuring Frailty or Disability	Mean Age (Years)	Main Findings
Claesson MJ, Nature, 2012 [52]	Ireland	Cross-sectional	178	83 community dwelling; 20 outpatient clinic; 15 short-term rehabilitation; 60 nursing homes	Barthel Index	78	Decreased species richness with increased functional dependence measured by the Barthel Index Nursing home residents had a recognizable microbiome cluster Increased abundance of Bacteroides and decreased abundance of Oscillibacter, Ruminococcus, and Prevotella with increasing frailty
Jeffery IB, ISME J, 2016 [56]	Ireland	Prospective	384	Community; outpatient clinic; short-term rehabilitation; nursing homes	Barthel Index	78	The presence of frailty (measured by the Barthel Index) was correlated with reduced species richness and a composition of gut microbiota that is similar to that detected in nursing home residents
Jackson MA, Genome Med, 2016 [67]	United Kingdom	Cross-sectional	728	Community-dwelling twins	Rockwood Frailty Index	63	Frailty was negatively associated with gut microbiota biodiversity The relative abundance of 22 taxa of gut microbiota was associated with frailty (negative association: Faecalibacterium prausnitzii; positive association: Eubacterium dolichum, Eggerthella lenta)
Maffei VJ, J Gerontol A Biol Sci Med Sci, 2017 [68]	United States	Cross-sectional	85	Community-dwelling volunteers	Frailty Index questionnaire validated by authors	63	Inverse correlation between frailty index and gut microbiome biodiversity Frailty is associated with an increased interindividual variability of gut microbiota Frailty is associated with an increased abundance of Coprobacillus and Dialister, and a reduced abundance of Rikenellaceae, Paraprevotella, and Sutterella Frailty is associated with a lower bacterial metabolic activity
Ticinesi A, Sci Rep 2017 [58]	Italy	Cross-sectional	76	Inpatients hospitalized for extraintestinal acute disease	Rockwood Clinical Frailty Scale	83	Frailty is not associated with gut microbiome biodiversity Frailty is associated with the increased representation of seven gut microbiome taxa, including Fonticella, Oscillospira, Peptococcus, Porphyromonas, and Prevotella