Microbial Flora of Skin
Background information about that stuff called skin
And what can grow on it...
The average human adult has 2m2 of skin surface. The chemical composition and
moisture of skin varies and dictates what type of bacteria will grow on it and how much. The
surface of skin (epidermis) is not a favorable place for microbial growth because it is often dry,
salty, and has low pH. Most microorganisms are associated with sweat glands and hair follicles
because of the moist and nutritious environment. Urea, amino acids, salts, lactic acids, and
lipids are secreted through the skin and provide microorganisms with what they need to grow.
Some of the most commonly found microorganisms on the skin are Corneybacterium
diptheriae, Staphylococcus aureus, Micrococcus luteus, Staphylococcus epidermis, and
Pityrosporum ovale. Most bacteria are beneficial to the skin because they prevent colonization
of the skin by pathogens and they control the other organisms on the skin. But if a cut is
present, these bacteria can enter the body and cause damage. Below are brief descriptions of
these common microorganisms and the diseases they can cause.
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Corneybacterium diptheria
Above is a picture of this bacteria. Some characteristics are that it is gram positive, aerobic,
non-motile, tests positive for catalase, belongs to the Mycobacteriacae family, and is rodshaped. It is implicated in causing acne. More seriously, this bacteria causes diptheria.The
clinical symptoms of this disease include muscle weakness, edema, and pseudomembranous
material in the upper respiratory tract. There is a vaccine for diptheria and treatments involve
administration of penicillin, erythromycin or gentamicin.
Staphylococcus aureus
Staphylococcus aureus is gram positive, forms clusters, non-motile, non spore-forming, and is a
faculitive anaerobe. This bacteria tests positive for coagulase, catalase, and forms yellow
colonies on agar. It is found mainly in the nose and on skin. Ailments that are caused by the
bacteria include food poisoning, toxic shock syndrome, skin
lesions (boils, styes, and furuncles), pnuemonia, and other
diseases.
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Micrococcus luteus is a strict anaerobe that produces yellow to cream-white water insoluble
pigment on agar (as shown above). This bacteria is nitrogen reductase negative and oxidase
positive. It can cause septic shock, pnuemonia, and urinary tract infections in an immunedeficient person.
Staphylococcus epidermis is non-motile, gram-positive cocci, arranged in irregular clusters,
and unlike Staphylococcus aureus, it is coagulase-negative. This bacteria is an opportunistic
pathogen that does not cause problems unless it enters the bloodstream via cuts, catheters, or
needles, for example. Below is a picture of a man who had a small scrape in which bacteria
entered into his left hand. The effect from the bacteria is an infection and a swollen hand that
can progress into other systemic effects.
Pityrosporum ovale is a yeast that gets into hair follicles and sebaceous glands and causes acne
(shown above) and dandruff. This sungus causes the disease Pityriasis vesicolor. It appears as
dandruff or multi-colored scaley patches on the skin. UV light is used in detection of this
disease, the color given off by the skin is analyzed. Treatment is itraconazole capsules or
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selenium shampoo.
If this page has made you feel like you want to scrub your skin off, then the
link below is a good website to check out. It assures you that bacteria are necessary and can be
good for you. You can access this site by clicking on the icon on the left.
Hygiene of the Skin: When is Clean Too Clean
http://www.cdc.gov/ncidod/eid/vol7no2/larson.htm
*Fun Trivia*
Why do you stink when you sweat?
Answer: Body odor results from bacterial activity. Your actual apocrine (sweat) gland
secretions are odorless, but these glands (especially those associted with hair follicles)
harbor bacteria which are smelly microorganisms!
References:
-Kerr and McHale. 2003. Applications in General Microbiology, A laboratory Manual. p.327.
-Brocks Biology of Microorganisms, Tenth Edition, by Michael T. Madigan, John M. Martinko,
and Jack Parker. p.730
-http://www.cehs.siu.edu/fix/medmicro/coryn.htm
-http://www.sciencenet.com.au/frames/profiles/positive/families/micrococ/profile.htm
-http://www.netdoctor.co.uk/diseases/facts/pityriasisversicolor.htm
Home A Wonderful
World of Bacteria
Page 1 Aseptic
Technique
Page 2
History
Page 3 Skin
Bacteria
Page 4 Nasal and
Throat Bacteria
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