Comparison of Compositions and Metabolic Activities of Fecal Microbiotas in Young Adults and in Antibiotic-Treated and Non-Antibiotic-Treated Elderly Subjects

Abstract

The colonic microbiota mediates many cellular and molecular events in the host that are important to health. These processes can be affected in the elderly, because in some individuals, the composition and metabolic activities of the microbiota change with age. Detailed characterizations of the major groups of fecal bacteria in healthy young adults, in healthy elderly people, and in hospitalized elderly patients receiving antibiotics were made in this study, together with measurements of their metabolic activities, by analysis of fecal organic acid and ammonia concentrations. The results showed that total anaerobe numbers remained relatively constant in old people; however, individual bacterial genera changed markedly with age. Reductions in numbers of bacteroides and bifidobacteria in both elderly groups were accompanied by reduced species diversity. Bifidobacterial populations in particular showed marked variations in the dominant species, with Bifidobacterium angulatum and Bifidobacterium adolescentis being frequently isolated from the elderly and Bifidobacterium longum, Bifidobacterium catenulatum, Bifidobacterium boum, and Bifidobacterium infantis being detected only from the healthy young volunteers. Reductions in amylolytic activities of bacterial isolates in healthy elderly subjects and reduced short-chain fatty acid concentrations supported these findings, since bifidobacteria and bacteroides are important saccharolytic groups in the colon. Conversely, higher numbers of proteolytic bacteria were observed with feces samples from the antibiotic-treated elderly group, which were also associated with increased proteolytic species diversity (fusobacteria, clostridia, and propionibacteria). Other differences in the intestinal ecosystem in elderly subjects were observed, with alterations in the dominant clostridial species in combination with greater numbers of facultative anaerobes.Bacterial succession in the infant large bowel has been well documented both by culture (6, 52) and, more recently, by using molecular methods (10,16,54), but there have been relatively few studies dealing with changes in the colonic microbiota during the aging process. We therefore know little about the composition of bacterial populations or their metabolic activities in elderly people. Advances in medical science and improved living standards have led to an increased life expectancy in western societies, where people over 60 currently constitute one-fifth of the population, and this number is estimated to rise to one-third by the year 2030 (36).Good nutrition is important in maintaining gastrointestinal function. Malnutrition is one of the main factors responsible for reduced immune responses in old people (28), and the development of preventative nutritional strategies to promote healthy aging is desirable. Increased thresholds for taste and smell (8, 55), resulting in preferences for bland foods, coupled with swallowing difficulties (5) and masticatory dysfunction caused by loss of teeth and muscle bulk (25, 43) can result in ...

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