(VI)Gram Positive Cocci (2)*Staphylococcus aureus

Question 1

Characterize (5) : Staph. aureus

Answer 1

(1) Catalase (+)
(2) Coagulase (+)
(3) β-hemolytic
(4) Ferments mannitol
(5) gram (+) cocci

Question 2

What color does Staph. aureus turn mannitol agar?

Answer 2

Yellow

(Aureus = gold)

Question 3

What is Staph. aureus’ main virulence factor?

Answer 3

Protein A

Question 4

MOA: Staph. aureus’ Protein A

Answer 4

**Binds Fc region of IgG **

(⇒ Inhibition of complement ⇒ Inhibition of phagocytosis and opsonization)

Question 5

Where does Staph. aureus colonize?

Answer 5

Nares (nostrils)

(And many other places)

Question 6

Name 7 common infections caused by Staph. aureus

Answer 6

1. Localized skin infections (often suppurative): folliculitis, carbuncle, furuncle, impetigo, cellulitis, surgical wound infection
2. Deep infections (forms deep abscesses): osteomyelitis, septic arthritis, various other organs (kidney, brain, lung)
3. Endocarditis (acute and rapidly fatal, usually left-sided, right-sided occurs in intravenous drug abusers - IVDA)
4. Pneumonia (secondary to influenza viral infections, following right-sided endocarditis – commonly in IVDA)
5. SSSS (due to epidermolytic toxins)
6. Toxic shock syndrome (due to TSST-1)
7. Food poisoning (due to enterotoxins)

Question 7

How does pneumonia caused by Staph. aureus appear on chest x-ray?

Answer 7

Patchy infiltrate

Question 8

What is the most common predisposing factor to developing pneumonia due to Staph. aureus?

Answer 8

Secondary to influenza viral infections

Question 9

Who most commonly contracts Staph. aureus endocarditis?

Answer 9

IV drug abusers (IVDA)

Question 10

Which valve is usually affected in Staph. aureus endocarditis?

Answer 10

Tricuspid valve

(First valve seeded by IV drug use)

Question 11

Exotoxins (3) : Staph. aureus

Answer 11

(1) Epidermolytic toxin
(2) TSST
(3) Enterotoxin

(TSST = Toxin Shock Syndrome Toxin)

Question 12

Which Staph. aureus exotoxin is a superantigen?

Answer 12

Toxic Shock Syndrome Toxin

Question 13

Describe the food poisoning caused by Staph. aureus’ enterotoxin

Answer 13

(1) Rapid onset
(2) Mostly vomiting

(Rapid onset because it’s due to ingestion of preformed toxins)

Question 14

What type of food is most associated with food poisoning due to Staph. aureus?

Answer 14

Mayonnaise and meats

Question 15

What is the preferred treatment for MRSA?

Answer 15

Vancomycin, linzolid, ceftabiprole, ceftaroline, daptomycin

Question 16

Treatment: Methicillin sensitive Staph. aureus

Answer 16

Cloxacillin

Question 17

Hemolysis: Staph. aureus

Answer 17

β

Question 18

A coagulase negative staph that behaves like staph aureus in endocarditis: […]

Answer 18

A coagulase negative staph that behaves like staph aureus in endocarditis: Staph Lugdenensis

Question 19

Coagulase negative staphs are generally susceptible to what drug?
[…]

Answer 19

Coagulase negative staphs are generally susceptible to what drug?
Vancomycin

Question 20

Coagulase test is used to differentiate […]

Answer 20

Coagulase test is used to differentiate Staphylococcus aureus (positive) from Coagulase Negative Staphylococcus (CONS)
CONs = staph lugdunensis, staph epidermidis, staph saprophyticus

Question 21

Impetigo (say “im-puh-TIE-go”) is a bacterial skin infection. It causes red sores that can break open, ooze fluid, and develop a yellow-brown crust. These sores can occur anywhere on the body

What bacteria can cause impetigo?

[…]

Answer 21

Impetigo (say “im-puh-TIE-go”) is a bacterial skin infection. It causes red sores that can break open, ooze fluid, and develop a yellow-brown crust. These sores can occur anywhere on the body

What bacteria can cause impetigo?

Streps or Staph aureus

Question 22

Name some clinical presentation of Staph Aureus (there are 7 commoner ones) (vvvvvvvv IMPT!!!)

[…]

Answer 22

Name some clinical presentation of Staph Aureus (there are 7 commoner ones) (vvvvvvvv IMPT!!!)

1. Localized skin infections (often suppurative): folliculitis, carbuncle, furuncle, impetigo, cellulitis, surgical wound infection
2. Deep infections (forms deep abscesses): osteomyelitis, septic arthritis, various other organs (kidney, brain, lung)
3. Endocarditis (acute and rapidly fatal, usually left-sided, right-sided occurs in intravenous drug abusers - IVDA)
4. Pneumonia (secondary to influenza viral infections, following right-sided endocarditis – commonly in IVDA)
5. SSSS (due to epidermolytic toxins)
6. Toxic shock syndrome (due to TSST-1)
7. Food poisoning (due to enterotoxins)

SSSS = Staphylococcus Scalded Skin Syndrome

Question 23

Rapid onset of symptoms in contaminated food can be attributed to […]

Answer 23

Rapid onset of symptoms in contaminated food can be attributed to PREFORMED TOXINS (eg. from staph aureus or shiga)

Impt concept.

Question 24

Staph Aureus Bacteremia (presence of bacteria in circulating blood). Where most likely did it come from?

[…]

Answer 24

Staph Aureus Bacteremia (presence of bacteria in circulating blood). Where most likely did it come from?

Bones (ask for sore joints)
heart (listen to heart)

Question 25

Staph Saprophyticus can be found in […]

Clinical Presentation:
[…]

Treatment:
[…]

Answer 25

Staph Saprophyticus can be found in vaginal flora

Clinical Presentation:
UTI in sexually active young women (2nd most common cause of UTI in young women, first alw E.coli)

Treatment:
Co-trimoxazole

Question 26

Staphylococcus Aureus

Biochemical Tests: […]

Histology: […]

Character: […]

Answer 26

Staphylococcus Aureus

Biochemical Tests: Catalase positive + Coagulase positive

Histology: Grape like clusters of gram positive cocci

Character: Usually facultative anaerobes

Question 27

Treatment for Staph Aureus (IMPT!!)

1st line: […]
Penicillin allergy: […]
BL producing strains: […]
MRSA: […]
Topical: […]

Answer 27

Treatment for Staph Aureus (IMPT!!)

1st line: Cloxacillin (generally used for staph aureus)
Penicillin allergy: Erythromycin/clindamycin (macrolides)
BL producing strains: Co-amoxiclav (cuz need the BL inhibitor!)
MRSA: Vancomycin/linezolid/ceftabiprole/ceftaroline/daptomycin
Topical: Mupirocin/chlorhexidine (eradicate nasal carriage)

DRAIN THE PUS (V V IMPT WHERE APPROPRIATE)

Question 28

What are the virulence factors of S. Aureus? (got alot,,, j say 4) (IMPT!!)

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Answer 28

What are the virulence factors of S. Aureus? (got alot,,, j say 4) (IMPT!!)

• Protein A which binds the Fc portion of IgG (inhibits opsonisation)
• leukocidin (destroys phagocytes) degradative enzymes (breaks down host molecules to provide nutrients), some products damage host cell membrane
• Enterotoxins A-E (heat stable, source of food poisoning),
• Toxic shock syndrome toxin-1 (TSST-1, a superantigen, able to activate a broad spectrum of T cells, resulting in massive cytokine release),
• Epidermolytic toxins A & B (Staphylococcal scalded skin syndrome: local effects - pemphigus neonatorum in neonates, bullous impetigo in adults; systemic effects - **Ritter’s disease in neonates, toxic epidermal necrolysis in adults) **

Just memorize
Protein A which binds Fc portion of IgG (relate to Staph** A**ureus)
TSST (relate to Toxic Shock Syndrome)
Epidermolytic toxin A&B (relate to SSSS)