Staphylococcus aureus Diseases PATHOGEN:

Staphylococcus aureus is a Gram-positive non-spore-forming coccus that is often part of the normal microflora of the human skin, nose, throat and mouth.

S. aureus is a facultative anaerobe, is a facultative halophile, and produces enterotoxins.

RESERVOIR(S):

Humans are the significant reservoir host with respect to human disease. Animals may carry S. aureus, but most human infections are acquired from other humans.

TRANSMISSION: Staphylococcal food intoxication

S. aureus produces an exotoxin (which is an enterotoxin) that affects the digestive tract. Ingestion of the toxin results in the disease.

Food is most often contaminated with S. aureus through contact with open wounds infected with the bacterium or respiratory secretions from healthy, asymptomatic people who carry the bacterium in the back of their noses (the nares).

Foods most often associated with transmission of the disease include high-protein foods that are not cooked immediately prior to consumption, such as custards and cream pies, but foods that are contaminated after cooking, and are not immediately refrigerated and allowed to cool gradually, also serve as a source of transmission. Salty foods, such as cured hams, have been associated with transmission of the disease because the bacterium is not inhibited by fairly high concentrations of salt.

Staphylococcal food intoxication is not transmissible from one person to another, because it is the toxin, not the bacteria, which must be ingested.

Staphylococcal skin and wound infections

The bacteria enter through a break in the skin. Wounds may be contaminated with the host’s own normal flora, direct contact with an infected lesion of another person, or through contact with contaminated fomites. Nosocomial infections due to S. aureus are of great concern.

DISEASE: Staphylococcal food intoxication

Ingestion of the bacterial toxin causes the disease, which is characterized by a very short incubation period (1/2-8 hours), vomiting, abdominal cramps, nausea, and, in some cases, diarrhea. Full recovery usually occurs within 24-48 hours.

The disease is rarely fatal in healthy people, but the disease can be serious in the elderly and immunocompromised.

Staphylococcal skin and wound infections

S. aureus infections are characterized by pus producing wounds. These usually remain localized, but the bacteria may enter the bloodstream and become systemic, resulting in a variety of serious diseases ranging from meningitis to arthritis.

CONTROL:

Staphylococcal food Intoxication

Wash one’s hands before preparing food!

Cooking will kill the bacteria, preventing toxin production, but reheating food is often not effective in inactivating toxin that is already present in the food. The toxin is extremely heat stable and can withstand 30 minutes of heating at 100

0C (221

0F).

The principle method of prevention is to inhibit bacterial growth and subsequent toxin production in foods. Refrigeration of foods at or below 41

0 F slows the growth of the

staphylococci bacteria, which helps reduces toxin production, and holding food at or above 140

0 F kills the bacteria.

When outbreaks of staphylococcal food intoxication occur, health inspectors usually test for the presence of the toxin or the bacteria in food that is suspected to be the source of the disease.

Staphylococcal skin and wound infections

Good hygienic practices and protecting oneself from exposure to the bacterium is the only method of preventing infection.

TREATMENT: Staphylococcal food Intoxication

Treatment is usually not necessary. The bacterium is susceptible to antibiotics, but is often not ingested. The toxin, which causes symptoms of the disease, is not affected by antibiotics.

Staphylococcal skin and wound infections

Although many S. aureus bacteria can be effectively treated with standard antibiotic therapy, methicillin resistant S. aureus (MRSA) is resistant to all beta-lactam drugs and presents challenges for effective treatment.

VACCINE:

There is no vaccine for diseases caused by S. aureus.