“The Prolongation of Life; Optimistic Studies” By Elie Metchnikoff and Published in 1908. In this work, Elie Metchnikoff exposes the relationships between microbiota and health: MICROBES AS THE CAUSE OF SENILITY
Metchnikoff developed a theory about how aging could be caused by toxic bacteria in the gut and where lactic acid bacteria could prolong life. He theorized that health could be enhanced and senility delayed by manipulating the intestinal microbiome with host-friendly bacteria found in yogurt.
Metchnikoff also predicted the existence of bacterial translocations and anticipated theories linking chronic inflammation with the pathogenesis of atherosclerosis and other disorders of the aged.