Staphylococci

Question 1

Staphylococci general characteristics (6).

Answer 1

1. Gram positive.
2. Cocci in bunches.
3. Non-motile.
4. Catalase +.
5. Coagulase +/-.
6. Can grow in medium up to 10% NaCl.

Question 2

Staphylococcus aureus (10):

Answer 2

1. Gram positive.
2. Cluster-forming coccus.
3. Nonmotile.
4. Non-spore forming.
5. Facultative anaerobe.
6. Ferments mannitol.
7. Catalase positive.
8. Coagulase positive.
9. Golden yellow colony on agar.
10. Normal flora of nares, skin and mucous membranes.

Question 3

MRSA:

Answer 3

Methicillin Resistant Staph Aureus

• Mutated PCN binding protein.
• MecA gene.

Question 4

Protein A (4):

Answer 4

• Present on the surface of most S. aureus.
• Covalently linked with the peptidoglycan layer.
• Unique affinity to bind the Fc portion of IgG.
• Resists opsonization and phagocytosis.

Question 5

Coagulase:

Answer 5

Converts fibrinogen to fibrin, protects bacteria under fibrin mesh.

Question 6

Staphylococcal toxins (4):

Answer 6

• Cytolytic toxins.
• Exfoliative toxins.
• Enterotoxins.
• Toxic shock syndrome toxin - 1 (TSST-1).

Question 7

Panton-Valentine Leukocidin (6):

Answer 7

• Active against PMNs and macrophages causing cell lysis.
• Makes S. aureus more resistant to phagocytosis.
• Necrotizing pneumonia.
• Airway bleeding.
• Erythroderma.
• Leukopenia.

Question 8

Staphylococcus aureus infections (10):

Answer 8

1. Skin: impetigo, folliculitis, furuncles and carbuncles.
2. Wound infections.
3. Scalded skin syndrome (SSS).
4. Bullous impetigo: localized form of SSS.
5. Food poisoning.
6. Toxic shock syndrome (extended use of tampons).
7. Osteomyelitis (#1).
8. Infective arthritis (#1).
9. Acute endocarditis (#1).
10. Bacteremia and sepsis (#1).

Question 9

Staphylococcal scalded skin syndrome:

Answer 9

• Perioral erythema covers entire body within 2 days.
• Positive Nikolsky’s sign.
• Exfoliative toxin destroys the intracellular connections in the skin.

Question 10

Bullous impetigo:

Answer 10

• Localized staph scalded skin syndrome.
• Culture positive.
• Negative Nikolsky’s sign.
• Highly communicable.

Question 11

Staph. aureus pneumonia:

Answer 11

• Aspiration pneumonia: Patchy infiltrates with consolidation or abscess.
• Hematogenous pneumonia from bacteremia or endocarditis.

Question 12

Staphylococcus epidermidis (6):

Answer 12

1. Gram positive.
2. Cocci in clusters.
3. Coagulase negative.
4. Gloycocalyx.
5. Beta-lactamase
6. Mutant PCN-binding protein.

Question 13

Staph. epidermidis virulence factors:

Answer 13

Glycocalyx: Exopolysaccharide “slime” helps in adhesion, antiphagocytosis and makes it resistant to antibiotics.