Although the microbiota in adults has been extensively studied, investigation into structural changes and compositional evolution from infants to the elderly has only recently begun. Very little information is available pertaining to possible variations that occur with ageing. In healthy adults, 80% of the identified fecal microbiota can be classified into three dominant phyla: Bacteroidetes, Firmicutes and Actinobacteria [6]. In general terms the Firmicutes

to Bacteroidetes ratio is MK-2206 molecular weight regarded to be of significant relevance in human gut microbiota composition [7]. On a more refined level, however, the fecal microbiota is a highly complex and diverse bacterial ecosystem. Within this ecosystems exists a hierarchy of dominant (> 109 Colony Forming Units (CFU)/g)) anaerobic bacteria, represented by the genera Bacteroides, Eubacterium, Bifidobacterium, Peptostreptococcus, Ruminococcus, Clostridium and Propionibacterium, and sub-dominant (< 109 CFU/g), bacteria of the Enterobacteriaceae family, especially E. coli, and the genera Streptococcus, Enterococcus, Lactobacillus, Fusobacterium, Desulfovibrio and Methanobrevibacter [8]. Establishment of the intestinal microbiota has been shown to be a progressive process [9]. This process of increasing PLX4720 diversity is required for proper development and is important for overall health.

The major functions attributed to the microbiota present in the gut begin to manifest at the end of the second year of life and comprise: i) nutrients absorption and food fermentation [10], ii) stimulation of the host immune system [11] and iii) barrier effects against pathogens [12]. Once climax composition

is achieved near the end of adolescence, 4��8C this ecosystem displays a high stability in healthy adults [13]. Although the intestinal microbiota is relatively stable throughout adult life, recent studies indicated that modifications occur in the composition in elderly individuals. For example, a reduction in the numbers of Bifidobacteria and Bacteroides has been observed, accompanied also by a decrease of Lactobacilli. A commensurate increase in the number of facultative anaerobes also highlights the variation between adults and elderly individuals [14–17]. Such variation was also observed by Ley et al. [7] when a correlation between body weight and gut microbial ecology was analysed. The microbiota in obese subjects shows an elevated proportion of Firmicutes and a reduced population of Bacteroides. Conversely, a decreased Firmicutes/Bacteroidetes ratio has been directly related to weight loss [7]. The work presented here aims to continue to expand our understanding of the intestinal flora including its establishment, composition, and evolution. To that end, we focused on the important ratio between Firmicutes and Bacteroidetes. We used a qPCR-based approach to enumerate changes in bacterial populations in the human intestine.