A 24 h artificial colon fermentation was performed to assess the effects of a prebiotic MIX and synthetic consortium (S7) on gut microbiota composition and microbial metabolite production in clinically stratified older adults (healthy and frail). Treatments included supplementation of the donor microbiota with a synthetic microbial consortium (S7), a prebiotic mix (MIX), and a combination of MIX and S7 (MIX+S7). The S7 treatment decreased the alpha diversity of long-stay-dwelling donor (LS, "frail") microbiota and increased the relative abundance of S7 taxa at 16 h. MIX alone caused the enrichment of reportedly beneficial genera such as and in community-dwelling donor (CM, "healthy") microbiota and and in LS microbiota. The MIX+S7 treatment sustained higher overall S7 species richness and consortium taxon abundance at 24 h. Both MIX and MIX+S7 treatments enhanced short-chain acid production compared to control. These findings highlight the differential responses of microbiota from distinct elderly health strata to prebiotic and microbial consortia supplementation.