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Staphylococcus aureus and S. epidermis


Gram stain:  positive
Cell shape:  coccus
Arrangement:  staphylo
Oxygen requirements:  
Other:  S. epidermis produces a white pigmented colony; S. aureus produces a yellow pigment.

Habitat:  soil, skin, mucous membranes.
S. aureus is found in especially large numbers in the nasal passages (its presence on the skin is usually the result of transport from these passages).
S. epidermis may represent up to 90% of the normal microbiota of the skin

Pathogenicity:  S. epidermis are normally non-pathogenic unless the skin barrier is broken or through contamination with medical procedures.

S. aureus is the most pathogenic of all the staphylococci. It produces an enzyme called coagulase that causes the fibrin in blood to clot. These clots protect the bacteria from phagocytosis and other host defenses. They also produce many toxins and are associated with many opportunistic and nocosomial infections, including: folliculitis, stys, boils, impetigo, scalded skin syndrome, toxic shock syndrome, acute bacterial endocarditis, and staphylococcal food poisoning. This organism is the causative agent of the most common form of food poisoning. Intoxication causes a rapid response of GI disturbance, usually within 1 to 6 hours after eating. Unfortunately, the toxin is very heat resistant and reheating foods will not destroy it, although the bacteria may be destroyed.

Treatment:  Penicillin used to be the drug of choice, but now only 10% of all S. aureus strains are sensitive, then methicillin or vancomycin must be used. Unfortunately, there are many MRSA organisms also and some have even developed a resistance to vancomycin.



LINKS

CDC: Staphylococcus aureus with decreased susceptibility to vancomycin
Doctors' Answers to "Frequently Asked Questions" - Cellulitis
FDA/CFSAN Bad Bug Book - Staphylococcus aureus
Methicillin-Resistant Staphylococcus aureus (MRSA)
Staphylococcus spp.
Staphylococci - The Emerging Threat
Toxic Shock Syndrome