Staph Aureus

Question 1

Where does it Colonize

Answer 1

Nasopharynx (also skin, GI)
(not part of normal microbiota, but often carried asymptomatically = colonization)

Question 2

Asymptomatic Carriage?

Answer 2

10 - 30% among general population

Question 3

Gram

Answer 3

Gram Positive

Question 4

Morphology

Answer 4

• Golden colonies
• Grape-like clusters
• Ferments Mannitol (mannitol salt agar turns yellow)
• Resistant to environmental conditions, easy to culture

Question 5

Hemolysis?

Answer 5

B-Hemolytic

Question 6

Biochem properties

Answer 6

• Catalase +
• Coagulase +

Question 7

Virulence factors main groups

Answer 7

• Cellular virulence factors
• Enzymes
• Exotoxins

Question 8

Cellular virulence factors

Answer 8

• Protein A (cell wall)
• Capsule
• Biofilm formation
• Specific adhesin proteins (fibrinogen, fibronectin, fibrin, collagen)

Question 9

Protein A

Answer 9

Binds Fc region of antibodies to prevent them from binding and opsonization so no phagocytosis

Question 10

Enzymes

Answer 10

• Coagulase
• Fibrinolysin = Staphylokinase (spread)
• Hyaluronidase
• Phosphatase
• DNase
• Lipase
  = Lysis of human tissue, necrosis

Question 11

Exotoxins

Answer 11

• TSST-1
• Exfoliative Toxin A/B
• Heat stable Enterotoxins
  (Superantigens)
• Leukocidins (panton-valentine)
• Hemolysins

Question 12

Diseases by Toxin

Answer 12

• TSS
• Scalded Skin S (Ritter)
• Food Poisoning

Question 13

Toxic Shock Syndrome & what can cause it

Answer 13

• From TSST superantigen
• Develops from prolonged tampon, unchanged gauze
• Initially flu-like then dermal rash & shock, MOF

Question 14

Scalded Skin Syndrome

Answer 14

• Exfoliative Toxins
• Cleave Desmogelin 1 which holds skin layers together
• No inflammation
• Positive Nikolsky sign where top layers slip off lower when rubbed

Question 15

Food Poisoning

Answer 15

• Enterotoxin B
• Heat stable so even killing bacteria still causes symptoms
• Rapid onset within hours

Question 16

Systemic Diseases

Answer 16

• Osteomyelitis
• Pneumonia (post-viral) & patchy X-ray infiltrate
• Endocarditis (tricuspid)
• Septic arthritis

Question 17

Skin & Soft tissue Infections

Answer 17

• Folliculitis, Furuncle, Carbuncle
• Impetigo
• Wound infections
• Cellulitis
• Bullous Impetigo

Question 18

Microbiological Diagnosis

Answer 18

• Catalase test (staph vs strep)
• Coagulase (aureus): Tube or Clumping test

Question 19

Treatment MSSA

Answer 19

B-lactams
- Penicillins (nafcillin, methicillin, oxacillin)
- Flucloxacillin or floxacillin
- Cephalosporins, fluoroquinolones

Question 20

Treatment MRSA

Answer 20

Resistant to all B-lactams by PBP modification
- IV Vancomycin
- Daptomycin
- Linezolid
- 5th Gen Cephalosporins (ceftaroline)

Question 21

Special about Staph Aureus

Answer 21

Only Staph that is Coagulase Positive