Staphylococcus aureus is a Gram-positive
facultative anaerobe. This means it can create manitol2.jpg
ATP in the presence of oxygen, but may also use
fermentation as a means of energy production.
Staphylococcus aureus is found most commonly on
the skin and within the nasal passage, oral cavity,
and intestines of humans. When cultured in the
lab, Staphylococcus aureus forms a yellow/gold
colony on the agar surface, it is catalase positive
and the optimum growth temperature range is
thought to lye within 15 to 45 degrees celsius.

Infection:

Staphylococcus aureus microorganisms may be
commensal within the skin environment, within
the nose and occasionally the throat. They may Impetigo.jpg
survive from hours to weeks on dry surfaces.
This bacterium may alsohost bacteriophages.
Staphylococcus aureus may infect the surrounding
tissues of the mucous membranes causing the
formation of furuncles. In young children S. aureus
may cause a more dangerous condition known as staphylococcal scalded skin syndrome.
These infections may be transmitted through
contact with the pus of an infected wound, contact
with infected skin, or contact with objects such as materials which have been touched by the infected person. Certain strains of Staphylococcus aureus also produce an exotoxin which leads to toxic shock syndrome. Toxic shock syndrome is an acute illness which can be deadly. An enterotoxin also produced by this species causes gastroenteritis.

Diagnosis:
An infection with Staphylococcus aureus is usually diagnosed through a series of steps. The first step is a Gram stain, which if positive will show Gram-positive cocci bacteria in clustered colonies. A pure specimen is then isolated from the source and is cultured on a mannitol salt agar plate. The growth of S. aureus on this medium decreases the pH and the mannitol is fermented.
Differentiation can also be carried out at the species level in the form of catalase tests, lipase tests and coagulase tests.

Treatments:
Penicillin is the most commonly used medication for the treatment of infections by Staphylococcus aureus, however this is a problem due to the developing resistance exhibited. For this reason penicillinase resistant beta lactam antibiotics such as flucloxacillin are being used. Gentamicin may be used as part of a combination therapy for the treatment of infections such as endocarditis however it risks kidney damage.
Methicillin-Resistant Staphylococcus aureus:

MRSA progresses within the rapid onset of a day – two days of symptoms. Within seventy two hours it grasps tissues and may develop resistance to treatment. The initial symptoms are red bumps followed by fever and rashes.
MRSA is commonly contracted while staying in hospital or while visiting a healthcare facility, it is also more common in patients being treated by quinolones.
Fluids such as blood, urine, or sputum may be used for the culturing of MRSA for diagnosis. The identification techniques following sample collection include real time PCR along with quantitative PCR.
MRSA is treated with the antibiotic vancomycin, this is a last resort antibiotic due to the unpleasant side effects, and it must also be administered intravenously in order to create control over the infection. Drugs like linezolid and daptomycin are also effective against MRSA.

References:


Kenneth Todar, (2008), Staphylococcus aureus and Staphylococcal disease, Available from: http://www.textbookofbacteriology.net/staph.html, [Accessed 20.03.2011].