Lately, microbes that colonise the gut and skin in humans have attracted enormous attention. Diverse physiological roles are being attributed to the human microbiota; one of the most studied is the contribution to the immune response (Lopes et al. 2016). For obvious reason these studies are targeted at human beings, but we can infer that in other animals the importance of commensal microbes should be relevant as well. Changing or eliminating some members of microbial communities may lead to undesirable systemic effects in the host organism. One practical example of such imbalance occurs with the action of antibiotics (Raymond et al. 2016). In general, intensive use of antibiotics has a devastating impact on the composition of the human microbiota, and might negatively influence long-term health (Jernberg et al. 2010). These facts demonstrate the complexity and non-linearity of the phenomenon of life.
All living beings appear to be trapped in a delicate web of interactions and survival relationships. An interesting fact of this interactive web of life is that the diversity of microbial communities are not stable and are highly susceptible to environmental factors. A succession of species can be tracked as the changes proceed. For example, dietary habits might select for a particular set of bacterial species, and these changes might be driven by simple modifications such as more or less fiber in the composition of the diet (Voreades et al. 2014).
The action of external or environmental effects are completely unpredictable from a host perspective. We cannot know in advance when an external element will start an interaction with a particular node of the web of life. It simply happens, and if we have sufficient knowledge, we can at least take some control of the effects of this interaction. This is the case of parasitism. Once the infection is established, in most cases, the host is able to limit the effects of this parasite relationship. Even if the parasitic infection cannot be fully controlled, we now have the tools to analyse it from a different perspective: its contribution to the alteration of microbial communities in the host. For certain protozoa parasites, e. g. Leishmania braziliensis, the success in infecting a human being also means remarkable alterations of the microbial community of the skin. In the April issue of the Memórias do Instituto Oswaldo Cruz [2016; 111(4)], the article “The microbiological signature of human cutaneous leishmaniasis lesions exhibits restricted bacterial diversity compared to healthy skin”, by Salgado et al. (2016), describes the succession of bacterial species as the Leishmania infection progresses.
With greater or less bacterial diversity, it is clear that this protozoan parasite is contributing to alter the intricacy of this node, which is only another in the big web of life. The essential point is to determine when this interactive web leads to beneficial or harmful events, and how to restore the system when a disequilibrium arises. Here, balance is the key word.
Jernberg C, Löfmark S, Edlund C, Jansson JK. Long-term impacts of antibiotic exposure on the human intestinal microbiota. Microbiology. 2010; 156(Pt 11): 3216-23.
Lopes ME, Carneiro MB, dos Santos LM, Vieira LQ. Indigenous microbiota and Leishmaniasis. Parasite Immunol. 2016; 38(1): 37-44.
Raymond F, Ouameur AA, Déraspe M, Iqbal N, Gingras H, Dridi B, et al. The initial state of the human gut microbiome determines its reshaping by antibiotics. ISME J. 2016; 10: 707-20.
Salgado VR, de Queiroz ATL, Sanabani SS, de Oliveira CI, Carvalho EM, Costa JML, et al. The microbiological signature of human cutaneous leishmaniasis lesions exhibits restricted bacterial diversity compared to healthy skin. Mem Inst Oswaldo Cruz. 2016; 111(4): 241-51.
Voreades N, Kozil A, Weir TL. Diet and the development of the human intestinal microbiome. Front Microbiol. 2014; 5: 494.