Microbiome

Joshua Lederberg

Term for the totality of all microorganisms (bacteria, viruses, fungi, protozoa) colonizing the human organism. The microbiome colonizes all our contact points with the environment. This concerns mainly the intestine and skin as well as the so-called semi-mucous membranes such as the oral and genital mucosa. The microbiome comprises about 2% of our body weight. The number of microorganisms that humans harbor exceeds the number of human cells by a factor of 10. The species diversity of a habitat is reflected by the alpha diversity. Alpha diversity describes the number of species present in a habitat or biotope.

This term microbiome was coined in reference to the term "genome".

Microbiota (plural of microbiome) refers to individual (organ-related) colonizations. It will be the aim of future research to examine the effects of diseases on the microbiome. Furthermore, the extent to which changes in the intestinal microbiome influence sensitization by food allergens is of interest.

The composition of the microbiome is influenced by the mode of birth (vaginal birth vs. caesarean section), acquires diversity in childhood, stabilizes in adulthood, and decreases again in older age. The microbiome consists mainly of four bacterial strains, the so-called phylogenetic core:

• Firmicutes,
• Bacteroides..,
• Proteobacteria and
• Actinobacteria.

In patients with IBD (inflammatory bowel disease), there is a quantitative and qualitative change in the microbiome:

• Bacterial diversity decreases.
• The composition becomes unstable.
• There is an increase in Enterobacteria and unusual bacterial strains.

The North American"Human Microbiome Project (HMP)" was launched in 2007. In Europe, the program "Metagenomics of the human intestinal tract (MetaHIT)" was initiated in 2008.

In analogy to the term microbiom, the term"mycobiom" was coined to describe the totality of all commensal or pathogenic fungi that colonize humans or other living beings.

1. Kahlerta, C et al.(2014) Microbiom - the discovery of an organ. Switzerland Med Forum 14:342-344
2. ADF/ECARF Award (2016) Communication from ECARF. Allergology 39: 345