Usefulness of Probiotics for Neonates

In humans there are a multitude of site-specific communities of bacteria localized on the skin, mucosal surfaces, and in the intestinal tract [1,2]. The total number of prokaryotic cells is estimated to be around 1014, ten times more than the number of eukaryotic cells. These microbial communities interact extensively with the host, a process which is crucial for host development and homeostasis. Most of the microbiota is located in the gastrointestinal (GI) tract, and progressively increase in number from the jejunum to the colon. In the colon, the levels of bacteria are as high as 1011 microorganisms per gram of luminal content with a very wide diversity. The composition of gut microbial communities was originally known through culture-based studies, which estimated that 400 to 500 different species are present in the adult human intestinal tract [3]. Through the most recent culture-independent analyses, gut microbiota is thought to comprise up to 1000 bacterial species per individual and over 5000 species in total [4]. The gut microbiota is dominated by only four phyla, i.e. Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria, although there are more than 50 bacterial phyla on Earth [1].