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.

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 rod-shaped.  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.

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 immune-deficient 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.
 
 
 
 

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