Staphylococcus aureus


General:

Staphylococcus aureus commonly known as a “Staph” infection (1)









Risk:

Staphylococcus aureus is a very common microorganism It exists on skin, throat and nasal passages all the time. (1) Problems arise when bacteria enters body via open wound in skin due to injury or surgery. S. aureus can cause infections anywhere in the body. (1) Most people with healthy immune systems are not susceptible to staph infections; however, those at greatest risk are those with compromised immune systems, whose treatment requires an invasive device such as a cathter and those with chronic illnesses such as:

Summary of Disease:

Infection occurs when skin barrier is broken due to injury or surgery and immune system cannot combat the bacteria. (3)

Methods of nosocomial contraction:

Complications of Staph infection: The bacteria is generally localized to site of infection, characterized by raised temperature at the site, swelling, pus accumulation, and necrosis of the tissue. (2) A fibrin clot may form, walling off the bacteria, forming an abscess or boil Septicemia may occur and is rapidly fatal (2) Bacteremia can fill in other internal abscesses, skin lesions, infections of the lungs, kidney, heart, skeletal muscles or meninges. (2)

Tests:

Swab taken from site; cultured to be identified by biochemical tests.

Treatment:

Antibiotics—some strains have become extremely resistant to antibiotics—especially in hospitals (1)
Resistant to antiseptics, disinfectants(2)

Antibiotic resistance:

Why is S. aureus so virulent?

S. aureus has developed drug resistance in the usual ways: mutations in genome followed by selection of resistant strains and acquisition of virulence genes in the form of plasmids, transducing particles, transposons, or other DNA inserts. (2)

Since the introduction of penicillin in the 1940s, S. aureus has been very quick to adapt to the introduction of new drugs. There are strains that have become resistant to most normal antibiotics, and there is fear that a new drugs are not on the horizon. Therefore, pharmaceutical companies are looking at drugs that would block certain molecular targets (i.e. active sites for enzyme binding) to combat the emerging resistant strains of S. aureus. (2)

A plasmid associated with vancomycin resistance has been found in enterococci that can be transferred to S. aureus in the laboratory, which may occur in the Gastrointestinal tract between S. aureus and normal flora. (2)

What about a Vaccine?

No vaccine is currently available for active immunity, however, when the exact molecular mechanism for the binding of S. aureus to its host is known, a synthetic inhibitor may be made to block the interaction to stop colonization. (2) There are ongoing clinical trials for a vaccine against S. aureus called StaphVAX. StaphVAX is S. aureus type 5 and 8 capsular polysaccharides conjugated to nontoxic recombinant Pseudomonas aeruginosa exotoxin A. This vaccine gives immunity for 40 weeks, and is ideal for a surgery patient setting because the patient doesn’t need immunity for the rest of his life, rather just for his stay in the hospital. (2)

Stats:

During the 1950s and 1960s Staph was the number one nosocomial infection. Gram-negative bacilli have since taken over the top spot for most common nosocomial infection, however, Staph continues to be a problem. (2)

References:

  1. http://www.goaskalice.columbia.edu/2109.html
  2. http://www.bact.wisc.edu/Bact330/lecturestaph
  3. http://www.nabi.com/releases/pdf/Final%20Staph%20Aureus%20Fact%20Sheet.pdf