Lecture 27 - Staphylococcus aureus

Etiology
Staphylococcus aureus is a firmicutes. It is a beta hemolytic Gram-positive cocci that tests positive for coagulase tests 90% of the time. It is an opportunist organism as opposed to a primary invader like TB. It colonizes people's skin and nasopharynx but not all people have bodies that are suitable for its growth.

Morbidity
Causes about 20% of nosocomial (hospital-acquried) infection because injured people are more susceptible to being infected.

Diseases
-Toxic Shock Syndrome

Toxic shock syndrome is associated with the menstrual cycle because it was found in the highly absorbent material of the tampons, and also the absorbent padding in nose surgery procedures.

It is caused by the TSST1 exotoxin, which is only produced by a few strains of Staph aureus. Those strains can be part of your body and not cause a problem because Magnesium +2 ions inhibit the expression of the toxin. However, highly absorbent material absorbs the Mg+2 and stimulates toxin production.

TSST1 will cause a fever, diarrhea, vomiting, myalgia (muscle pains), hypotension, and later shock and death if untreated.

-Staph Food Poisoning
Food poisoning can cause either a case food infection of a food toxicity.

Some strains of staph produces enough enterotoxin in 3-8 hours to cause food poisoning, but often those amounts of toxin cannot be detected by taste. The symptoms have a quick onset of 1-6 hours after ingestion and will cause vomiting, nausea, and diarrhea, also called "two bucket syndrome" (because you can't puke and poop in the toilet at the same time). This disease is usually self-limiting, or fought off by the immune system, wiithin 24 hours.

Prevention
Eat it fast and don't store it for too long. If you do, store it in the freezer or your food will go bad after a while. The toxin is not heat labile, you'd have to heat it at 100°C for 30 minutes, which you can't reliably do unless you're deep frying the thing to a crisp. Realistically though, just throw away the food.

-Abscess
Kind of like acne, but bigger. Caused by a staph infection of hair follicles

Furuncles ~1cm

Carbuncles 2cm+

-Osteomyelitis
A bone infection that is mostly (80%) caused by septicemia of staph.

-Meningitis
Infection of the meninges (brain epithelium) can be caused by staph, but it is not one of the main causes.

-Endocarditis
Infection of the heart caused by septicemia of staph, but it is not one of the main causes.

-Pneumonia
Infections of the lungs, caused by staph sticking to the lungs.

-Bullous impertigo
Impertigo specifically cause by staph. It causes sores and scabs around their mouth.

-SSSS
Staph Scalded Skin Syndrome causes a toxin that causes burn-like skin peeling.

Treatment
One can treat MSSA with oxacillin, cloxacillin, caphalosporin, or any penicillin that is resistant to penicillinase.

One can treat MRSA with Vancomycin or Zyvox.