Skin
DESCRIPTION OF THE NICHE
Location and Significance
The skin is one of the largest organs of the body composed of the inner dermis and outer epithelium located on the surface the body.
Skin epithelium functions to keep microbes off the rest if the body by:
- Acting as a physical barrier against microbe penetration to tissues underneath
- Secreting a mucus layer so that microbes can not permanently attach to the epithelial cells beneath
- Shedding or keratinization of the outermost skin cells so microbes are removed from the body
- Secreting antimicrobial peptides and proteins to kill off microbes or at least prevent their growth
Physical Conditions
What are the conditions in your niche? Temperature, pressure, pH, moisture, etc.
Skin temperature of the skin varies depending on the location on the body. Toes and fingers tend to have the lowest temperatures, while the axillae and the groin tend to have the highest[1]. The temperatures are usually 25-35 degrees Celcius, which is ideal for mesophiles rather than thermophiles or psychrophiles [1]. The temperature only varies slightly so it there is not a dramatic selection for microbes colonizing certain areas, but does affect the growth rate of the microbes present [1].
The moisture content on the skin is generally low, which limits the survival and growth of microbes. However, the eccrine glands can produce sweat, which increases the moisture on the surface of the skin; especially in areas where evaporation does not occur easily, such as the toes and axillae [1]. Microbes tend to have greater populations in those occluded areas since there is an accumulation of secretions[1].
The skin generally has a high oxygen concentration, so it acts primarily as an aerobic environment for anaerobes to grow [1]. However, the hair follicles inside the skin provide a microaerophillic and/or anaerobic environment that have lower levels of oxygen, so that microaerophiles and obligate anaerobes can also grow [1]. The pH of the skin is usually acidic, but the exact pH may vary depending on the specific location. The skin’s acidity results from lactic acid from the host cells and the microbes, the amino acids from sweat, the fatty acids from sebum, and acids produced during keratinization [1]. Although the skin is acidic, it is only suitable for neutrophile growth and not acidophiles or alkaliphiles[1].
Influence by Adjacent Communities (if any)
Is your niche close to another niche or influenced by another community of organisms?
Conditions Causing Environment Changes
Do any of the physical conditions change? Are there chemicals, other organisms, nutrients, etc. that might change the community of your niche.
Physiochemical determinants that can affect the growth of the indigenous microbes on the skin include: temperature, pH, light, osmolarity, oxygen concentration, nutrient availability, microbe-microbe interactions, host defense systems, and moisture content[1].
Even host characteristics such as age, gender, host’s nutrition, stress, emotional state, disability, hospitalization, personal hygiene, lifestyle, occupation, living conditions, and so on can affect the indigenous microbiota as well [1].
Clothing, air-conditioning, or housing, for example, can be considered forms of protection against extreme environments. However, the conjunctiva and exposed regions of the skin have greater fluctuations in temp, humidity, and so forth, in comparison to other bodily systems [1].
WHO LIVES THERE?
The Microbes Present
You may refer to organisms by genus or by genus and species, depending upon how detailed the your information might be. If there is already a microbewiki page describing that organism, make a link to it.
Microbial Interactions
Microbe-microbe interactions on the skin tend to either be beneficial or antagonistic.
- Beneficial
For example, commensalism is show when Malassezia spp. metabolizes lauric acid which is toxic to propionibacterim acnes, so that the propionibacterim acnes can survive where lauric acid is plentiful [1].
- Antagonistic substances may be produced by cutaneous microbes for competition.
- CO2 is produced by many bacteria against dermophyte growth [1]
- Lysozymes are produced by staphylococci which kills micrococci, Brevibacterium spp., and Corynebacterium spp. [1].
- Proteases are produced by P. acnes to kill off other Propionibacterium spp. and staphylococci[1].
- Propionic acid is produced by propionibacteria, which inhibits other species from growing at low pH’s on the skin [1].
- Acetic acid is produced by propionibacteria and Dermabacter hominis to inhibit the growth of other species [1].
- Lactic acid is produced by staphylococci and D. hominis to inhibit the growth of other species [1].
- Bacteriocins are produced by staphylococci, Coryebacterium spp., Propionibacterium spp., Micrococcus spp., and Brevibacterium spp. to inhibit the growth of or kill cutaneous organisms [1].
- Antagonistic substances may be produced by cutaneous microbes for competition.
Do the microbes change their environment?
Do they alter pH, attach to surfaces, secrete anything, etc. etc.
Do the microbes carry out any metabolism that affects their environment?
Do they ferment sugars to produce acid, break down large molecules, fix nitrogen, etc. etc.
- Mal. globosa produces proteases that can break down skin proteins, so that amino acids become available[1].
- Corynebacterium spp., staphylococci, and Brevibacterium spp. produce ureases which can break down urea into ammonium ions as a nitrogen source[1].
Current Research
Enter summaries of the most recent research. You may find it more appropriate to include this as a subsection under several of your other sections rather than separately here at the end. You should include at least FOUR topics of research and summarize each in terms of the question being asked, the results so far, and the topics for future study. (more will be expected from larger groups than from smaller groups)
References
1. Wilson, Michael. Bacteriology of Humans: an Ecological Perspective. Blackwell Publishing, 2008.
2. Wilson Michael. Microbial inhabitants of Humans: Their Ecology and Role in Health and Disease. Cambridge University Press, 2005.
Edited by Patrick A. McGhee, Susan Lin, ____________________________________, students of Rachel Larsen
