Andy Goren1, Maja Kovacevic2, John McCoy3, Mirna Situm2, Zeljana Bolanca2, Andrija Stanimirovic4, Rachita Dhurat5, Jill Chitalia5, Aseem Sharma5, and Torello Lotti6
1 Department of Dermatology and Venereology, Università degli Studi Guglielmo Marconi, Rome, Italy
2 Department of Dermatology and Venereology, University Hospital Center Sestre Milosrdnice, Zagreb, Croatia
3 Applied Biology, Inc., Irvine, CA, USA
4 Department of Clinical Medicine, University of Applied Health Sciences, Zagreb, Croatia
5 Department of Dermatology, LTM Medical College and Hospital Sion, Mumbai, India
6 Centro Studi per la Ricerca Multidisciplinare e Rigenerativa, Università degli Studi Guglielmo Marconi, Rome, Italy
The human microbiota was defined by Joshua Lederberg as “the ecological community of commensal, symbiotic, and pathogenic microorganisms that literally share our body space .
Ancient texts dating back to the first century BCE elude to the existence of unseen miniaturized life forms. In his codex Res Rusticae from 36 BCE, Marco Terentius Varro wrote: “Precautions must also be taken in the neighborhood of swamps, both for the reasons given, and because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there cause serious diseases” . However, the first documented observation of micro‐organisms is generally attributed to the Dutch scientist Antonie Philips van Leeuwenhoek. Through the development of specially crafted microscopes he was able to observe what he termed animalcules (“tiny animals” in Latin) . Among his notable discoveries were bacteria in 1683 and spermatozoa in 1677. At the time, the link between microbial organisms and disease was not widely accepted. The prevailing theory of disease transmission was called miasma (“pollution” in Greek) or foul air . According to the theory, foul or toxic air is the cause of disease. Over the next 200 years, armed with progressively refined scientific methods and equipment, scientists gradually linked micro‐organisms to disease in what is known as the germ theory of disease .
The culmination of human knowledge marking this period was a series of formal scientific experiments in the 1800s conducted by Louis Pasteur and Robert Koch. Pasteur and Koch demonstrated that micro‐organisms can cause disease . Louis Pasteur demonstrated that micro‐organisms caused food to spoil, in contrast to the prevailing theory at that time, spontaneous generation. Spontaneous generation explained how nonliving objects turn into living objects, such as when maggots arise from rotten meat . Robert Koch demonstrated that isolating the anthrax bacteria (Bacillus anthracis) from a sick animal’s blood and injecting into a healthy one induced the development of anthrax . Koch developed four criteria, known as Koch’s postulates, that when met demonstrate a micro‐organism is the cause for a specific disease. On the heels of these new discoveries, ushering a revolutionary era in medicine, the race to develop antibiotics began. Among the most important dates in human history is September 28, 1928: the date the Scottish scientist Alexander Fleming discovered penicillin . The discovery of penicillin had such a pronounced effect on human history that for the next century the vast majority of medical research focused on the elimination of micro‐organisms as they had been deemed disease‐causing parasites residing on or around us.
With the advent of inexpensive large‐scale genetic sequencing, scientists have begun to understand the enormous variety of microbial life . The Human Microbiome Project launched in 2008 was the first attempt to categorize the human microbiome . It is now recognized that the human body is an ecosystem that hosts a variety of bacterial, viral, and fungal species. In fact, the human body hosts as many as 10:1 bacterial to human cells . This ecosystem is essential for our survival; from the gut bacterial flora’s ability to extract energy and synthesis nutrients, to the skin bacterial flora’s ability to regulate and supplemental our immune system . In recent years, understanding the interplay between our genetics and our bacterial ecosystem in health and disease has become the subject of intensive scientific inquiry. We hope that in the coming years, recognizing bacteria as our allies, rather than as pathogens that need to be eliminated, will bear new therapies in dermatological disorders and beyond .
Microbiome Research in Dermatology
The skin is the largest organ in the human body. Being completely exposed to the outside world, our skin cultures and develops a symbiotic relationship with an array of microbes. In fact, each one of us carries a unique bacterial signature partially maintained by our own immune system.
Traditionally, culture‐based methods were used in order to investigate diversity of skin microbial populations. Due to variety in cultivation properties, some species have been underestimated. In order to avoid misinterpretation of the diversity of microbial populations in skin, sequencing methods have been introduced . The main advantage of sequencing methods is the ability to identify members of many microbial populations using conserved taxonomic markers in conserved genes as a molecular fingerprint. For identifying bacterial species, investigators use the 16S ribosomal RNA (rRNA) gene. Similarly, for fungus the internal transcribed spacer 1 (ITS1) region of the eukaryotic ribosomal gene is used.
The composition of microbial populations depends on physiological features of the skin, for example, whether it is moist, dry, or sebaceous. The Propionibacterium genus, due to its lipophylic properties, is most commonly isolated from sebaceous areas of skin. The Staphylococcus and Corynebacterium genus are present in moist areas, including the bends of the elbows and the feet. Among fungal populations, the Malassezia genus is predominately present at trunk and arm sites, whereas foot sites were colonized by more diverse combinations of Malassezia spp., Aspergillus spp., Cryptococcus spp., Rhodotorula spp., Epicoccum spp., etc.