ABSTRACT
Instead of living as one individual organism, different species coexist in complex ecological niches constantly infl uencing each other. Humans are no exception from the symbiotic way of living since every healthy human individual coexists with an enormous number of microorganisms. The mutually dependent “life together” of two or more species is called symbiosis (Black 1996). Symbiotic relations of humans and microbial species always have positive outcomes for at least one member and this includes the relationships of mutualism and commensalism. Mutualism is a “winwin” situation in which both members benefi t from the relationship (Black 1996). In commensalism the situation is “win-zero” since one member of the relationship benefi ts without helping or harming the other one (Black 1996). When considering the interactions between microbial communities,
1Department of Internal Medicine I, University Hospital Ulm, Ulm, Germany. E-mail: katarina.radulovic@uni-ulm.de 2Department of Visceral Surgery and Medicine, Inselspital, Bern, Switzerland. *Corresponding author: niess108@yahoo.com
some authors also include the relations with the negative outcome to one member into the symbiosis (Faust and Raes 2012). Such relations include parasitism (“win-lose” situation) amensalism (“zero-loose” situation) and competition (“loose-loose” situation) between the microbes (Faust et al. 2012; Faust and Raes 2012).
