The skin microbiome: Elucidating the structure and function of bacterial communities in health and disease

In this thesis, 20 healthy individuals were swabbed on 14 different body parts and analysed for their bacterial community, whereby the active, as well as the present community was examined. It could be shown that analysis of the 16S rRNA and thus active community should be preferred over the standard protocol of analysing the 16S rDNA gene, not only because the skin is an open environment, but also because only the active community will play a role in the manifestation of a disease. Following this approach, the knowledge of the healthy bacterial community on human skin and on different skin microhabitats could be further extended. The role of Corynebacterium spp. is less pronounced than was assumed over the last years. It could be shown that Staphylococcus spp. are key species that are active all over the skin of humans. The 10 volunteers who were Staphylococcus aureus carriers (as defined by its presence in its the natural habitat, the anterior nares) showed generally elevated levels of S. aureus on the skin, but the dominant regions were the hands and the facial area. This leads to the conclusion that S. aureus is mainly transferred there by hands that touched the nose before. This knowledge can be useful in preventing self-infections during hospital stays. To evaluate the potential role of Staphylococcus hominis which was present on every tested skin site on every volunteer, a strain was isolated from one volunteer. The skin isolate of S. hominis was living in a bacterial community in which its contribution to the active bacterial community was > 63 %. The further analyses showed that it is a versatile organism that grows aerobically as well as anaerobically and is able to produce all amino acids except for asparagine and histidine. Its genome encodes some virulence factors like poly-γ-glutamic acid (PGA) and PSMb. The transcriptomic analysis revealed that both were upregulated under in vivo conditions on the skin. Transporters for the uptake of phosphate, the transport and the synthesis of the osmoprotectant glycine betaine, as well as the synthesis and salvation of the cofactor thiamine pyrophosphate were also upregulated. Patients with the skin disease "Acne Inversa" (AI) are suffering life-long from pain, rash and fistula formation. It is believed that bacteria play a role in this disease; however, no factor has yet been identified that determines the development of this disease. Swab samples were taken from 15 patients and analysed for their active bacterial content to evaluate the theory that not one pathogen causes this disorder but that dysbiosis of the community and therefore the potential absence of important key species result in disease. It could be shown here that contrary to previous assumptions, S. aureus is not responsible for the onset of the disease. AI skin showed a change in the bacterial community composition of the skin, irrespective of being lesional or non-lesional.