8. Microbiology
        8.1. Gram-positive cocci
            8.1.1. Staphylococcus
8.1.1.1. Staphylococcus aureus

Staphylococcus Aureus

Characteristics

 

Pathogenesis

Cell wall virulence factors:

 

Cytolytic exotoxin (hemolysins)

(Type alpha, beta, gamma, delta)

Destorys mammalian cells and red blood cells.

 

Superantigen exotoxin

Stimulates up to 20% of the available T cells (thus causing toxin shock via IL-2, IFN-gamma, TNF-alpha)

 

Clinical significance

1. Localised skin infection

2. Deep localised infections

3. Acute endocarditis

Associated with IV drug use

4. Septicaemia

5. Pneumonia

Severe and necrotising

6. Nosocomial infection

7. Toxinoses

Diseases caused by toxins

7.1. Toxic shock syndrome

Most cases are caused by the use of certain types of tampons in women with vaginal colonisation -> growth of S. aureus -> release of TSST.

7.2 Staphylococcal gastroenteritis
7.3 Scalded skin syndrome

Superficial bullae.

May be infected locally or caused by toxin produced elsewhere.

 

Laboratory identification

Colony morphology - yellow and hemolytic

Coagulase positive (distinguishes from other staph)

Mannitol positive (distinguishes from most other staph)

 

Treatment

Almost all s. aureus are resistent to penicillin G.

Methicillin-resistant s. aureus (MRSA) - modified penicillin-binding protein -> low affinity to penicillin

First line: oxacillin, nafcillin

Second line: vancomycin

Prevention/Immunity

Barrier precaution, handwashing etc.

No vaccine,

No lasting immunity


Things to revise/add later:

Bibliography: LWW microbiology


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Created20040322
Updated20040329


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