Urbanization-Associated Microbial Diversity Loss and Its Impact on Elderly Health: Integrating Environmental and Host Microbiome Dynamics.

Urbanization is strongly associated with microbial diversity loss in both built environments and elderly gut microbiomes, with significant health consequences. This study across 12 rural-to-urban care facilities in eastern China analysed 320 environmental and 120 faecal samples. Urbanization progressively reduced microbial alpha diversity in air, surfaces, and resident guts. Urban environments showed increased opportunistic pathogens and antibiotic resistance genes (ARGs), alongside decreased beneficial taxa and short-chain fatty acid pathways. Strong environment-host microbiome concordance was observed, with intensified microbial transmission in urban settings. Critically, environmental microbiome features mediated over 50% of urbanization's detrimental effects on resident frailty, inflammation, and cognitive decline. Models combining environmental and gut microbiome data accurately predicted frailty (AUC = 0.89). The findings highlight that urbanization-induced microbial alterations in care facilities are key mediators of elderly health decline, underscoring the need for microbiome-informed design to mitigate these risks.