Staphylococcus aureus
Srijana Shrestha

Ever feel food poisoning effects like nausea, prostration, abdominal cramping, or headache after eating a heavy meal? Or had a visit by an unsightly, waxy, red sty on your eye lid? You have just encountered the infamous Staphylococcus aureus. Although seemingly innocent in small numbers, once numbers exceed 100,000 per gram toxin level is reached. Unfortunately these are not the only problem it causes; it causes other pus-forming infections and toxinoses in humans.

S. aureus is a Gram-positive, cluster-forming coccus, nonmotile, nonsporeforming facultative anaerobe (preferably aerobic), catalase-positive enzyme, coagulase-positive, grows in temperature range between 15 to 45 degrees, and in NaCl concentrations up to 15 percent. The name Staphylococcus aureus gives clues to its phenotype: Staphyle = bunch of grapes Coccus = berry aureus = yellow. Once grown on agar the colonies are golden yellow, and looking thru a microscope you will see that it grows in round grape-like clusters. These bacteria can be found nasal passages, skin and mucous membranes.

Unsurprisingly it is considered a potential pathogen. There are three major types of infections it causes: superficial, serious, and then deep-seated infections:

Superficial skin lesions
• boils
• sty's
• furuncles

Serious infections
• Pneumonia
• mastitis
• phlebitis
• meningitis
• urinary tract infections

Deep-seated infections,
• osteomyelitis
• endocarditis.

The release of pyrogenic exotoxins into the blood stream results in toxic shock syndrome. The aforementioned food poisoning is cause by the release of enterotoxins. S. aureus is also responsible for infections associated with of surgical wounds and medical devices.

S. aureus expresses many potential virulence factors:

Here are some examples found from Kenneth Todar's website from the University of Wisconsin-Madison:"
(1) surface proteins that promote colonization of host tissues; (2) invasins that promote bacterial spread in tissues (leukocidin, kinases, hyaluronidase); (3) surface factors that inhibit phagocytic engulfment (capsule, Protein A); (4) biochemical properties that enhance their survival in phagocytes (carotenoids, catalase production); (5) inherent and acquired resistance to antimicrobial agents "

Overall the majority of the adverse effects caused by S. aureus can be avoided but we must be prepared for the future when they acquire the ability to become resistant to our most powerful antibiotics.

Sources:
Todar,Kenneth University of Wisconsin-Madison Department of Bacteriology; http://www.bact.wisc.edu/Bact330/lecturestaph
CDC; FDA/CFSAN Bad Bug Book - Staphylococcus aureus
<vm.cfsan.fda.gov/~mow/chap3.html >
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.

 

Return to Missouri S&T Microbiology HomePage Go to DJW's HomePage