ABSTRACT
Of the microbial populations associated with the human body, the largest and most complex is that present in the gastrointestinal tract. The human digestive tract is inhabited by more than 100 trillion bacteria and Archaea, which together make up the gut microbiota (Box 1). Microbial communities, predominantly anaerobes, are distributed all along our digestive tract and progressively increase in number from the jejunum to the colon to reach a maximum density in the distal colon with over 1011 bacteria per gram of fecal content and are of great diversity (Suau et al. 1999). Thus, our gut resident bacteria outnumber our own human cells by a factor of 10 (Ley et al. 2006). All higher organisms such as other mammals, insects and fi sh, have their specifi c microbiota. These microbial communities interact extensively with the host and participate in its development and homeostasis. We can therefore be seen as a ‘super-organism’ consisting of a combination of microbial and eukaryotic cells. The intestinal microbiota can be considered a real organ as its impact on our lives (O’Hara and Shanahan 2006). Indeed, it makes a major contribution to the physiological processes of the host with (i) metabolic and nutritional functions as digestion of certain components of our food and vitamin synthesis (Tremaroli and Bäckhed 2012), (ii) structural functions as intestine wall development and (iii) protective functions as immune system maturation and protection against bacterial pathogens (Hooper et al. 2012), also, we could not live without each other. Therefore, any imbalance in the
gut bacterial communities, i.e., dysbiosis, may be associated with alterations of gut functions and lead to diseases. Recently, several diseases such as obesity, diabetes and infl ammatory bowel diseases (IBD) have been linked to gut ecosystem imbalance (Tremaroli and Bäckhed 2012). Consequently, high hopes are placed in therapy to modulate the gut microbiota balance and its functions, for example by the use of probiotics.
