Staph Aureus

Question 1

General Features and habitat

Answer 1

Gram +
Cocci in clusters (“staph” = grape)
Habitat- normal flora of nose, throat and skin (20-30% of population are carriers)

Question 2

Biochemical Properties

Answer 2

Catalase + (2H2O2 → 2H2O + O2)
Coagulase + (Fibrinogen → Fibrin) used for masking under a fibrin coat
Enzymes for invasion: Hyaluronidase, Staphylokinase (=Fibrolysin), protein A, Lipase, Nuclease

Question 3

Transmittance

Answer 3

Transmitted by contaminated food (survive high salt content),
respiratory droplets (sneezing),
hand touch
Other pre-disposing factors: surgery, wounds, foreign bodies (i.e. tampons)

Question 4

Protein A

Answer 4

Binds to Fc component of IgG, which inhibits opsonization and phagocytosis

Question 5

Pathogenesis

Answer 5

TSST-1
Exfoliative Toxin (A and B)
Enterotoxins (A-R)
Cytotoxins

Question 6

Clinical features of: Toxic Shock Syndrome

Answer 6

− Characteristic rash (sunburn-like)
− Wound infections
− Fever with cellulitis and/or abscess
− Multi-organ Failure (MOF

Question 7

clinical features of exfoliative Toxin (A and B)- Superantigen

Answer 7

Staphylococcal scalded skin syndrome (SSSS or Ritter’s disease), mainly in children (doesn’t cause inflammation, serious skin condition in which it looks like it got scalded and is peeling)

Question 8

Clinical features of Enterotoxins (A-R)- Superantigen

Answer 8

Rapid onset gastroenteritis (food poisoning)-

Nausea, vomiting and diarrhea

Question 9

Clinical features of Cytotoxins:

Answer 9

1) Osteomyelitis (most common cause)- bone infection
2) Septic arthritis
3) Pneumonia- showing patchy infiltration on X-ray and post-viral
infection (also other respiratory infections- e.g. pharyngitis)
4) Folliculitis, Furuncle, Carbuncle, Impetigo-
Skin infection with redness, swelling and pus
5) Rapid onset of acute endocarditis (mostly Tricuspid)-
IV drug users are at high risk (also other vascular inflammations)
6) Meningitis (in 1-9% of bacterial meningitis cases)
7) Other infections- ear (otitis), urogenital (cystitis) and sepsis

Question 10

Hemolysins

Answer 10

Destroy RBC, platelets,
neutrophils and macrophages
(Hemolysin is a misnomer, act also on WBC)

Question 11

Panton-Valentine Leukocidin

Answer 11

Destroy WBC (cause of necrotic lesions and necrotic hemorrhagic pneumonia)
− Does not destroy RBC (none-hemolytic)
− Associated with CA-MRSA

Question 12

Diagnosis

Answer 12

Hemolysis on Blood agar
Golden colonies on Simple agar
Ferments mannitol on Mannitol Salt agar

Question 13

Treatment

Answer 13

MRSA – alters Penicillin Binding Protein (PBP), disc diffusion (antibiogram) or PCR is essential
Vancomycin to treat MRSA
Others: Quinupristin/Dalfopristin (Synercid) for VRSA, TMP-SMX, Linezolid, Aminoglycosides Rifampin can be combined to eliminate nasal carriage.

In case of gastroenteritis- self-limiting