Staphylococcus aureus

Question 1

Staphylococcus aureus labs

Answer 1

Gram ⊕, 
β-hemolytic, 
catalase ⊕, 
coagulase ⊕ 
cocci in clusters

Question 2

Staphylococcus aureus can

be differentiated from the other beta-hemolytic cocci by

Answer 2

their elaboration of a golden pigment when cultured on sheep blood agar.

Question 3

Of the 3 pathogenic staphylococcal species, which is coagulase positive

Answer 3

Staphylo­ coccus aureus

Question 4

when a gram-positive coccus in clusters is isolated in culture, the microbiology laboratory will do a coagulase test.

If they report coagulase negative gram- positive cocci in clusters, think of

Answer 4

Staphylococcus epidermidis or Staphylococcus saprophyticus.

Question 5

Staphylococcus aureus: Proteins That Disable Our Immune Defenses

Answer 5

1) Protein A:
2) Coagulase:
3) Hemolysins (4 types):
4) Leukocidins:
5) Penicillinase:
6) Novel penicillin binding protein:

Question 6

Community acquired methicillin resistant Staphylococcus aureus (CA-MRSA) produces a particu­ lar leukocidin called

Answer 6

Panton-Valentine Leukocidin (PVL), which is associated with a propensity to form ab­scesses

Question 7

Action of Protein A

Answer 7

binds Fc-IgG, inhibiting complement activation and phagocytosis.

This may protect the organism from opsonization and phagocytosis.

Question 8

Action of Coagulase

Answer 8

Thisenzymecanleadtofibrinformation around the bacteria, protecting it from phagocytosis.

Question 9

Action of Hemolysins

Answer 9

Hemolysins (4 types): Alpha, beta, gamma, and delta.

They destroy red blood cells, neutrophils, macrophages, and platelets.

Question 10

Action of Leukocidin

Answer 10

They destroy leukocytes (white blood cells).

Question 11

Action of Penicillinase

Answer 11

This is a secreted form of beta­ lactamase.

It disrupts the beta-lactam portion of the penicillin molecule, thereby inactivating the antibiotics.

Question 12

Function of Novel penicillin binding protein

Answer 12

This pro­tein, also called transpeptidase,

is necessary for cell wall peptidoglycan formation and is inhibited by penicillin.

Question 13

Staphylococcus aureus: Proteins to Tunnel Through Tissue (tissue destroying proteins)

Answer 13

1) Hyaluronidase
2) Staphylokinase
3) Lipase
4) Protease

Question 14

Action of Hyaluronidase

Answer 14

(“SpreadingFactor”) - This protein breaks down proteoglycans in connective tissue.

Question 15

Action of Staphylokinase

Answer 15

Thisproteinlysesformedfibrin clots (like streptokinase).

Question 16

Action of Lipase

Answer 16

This enzyme degrades fats and oils, which often accumulate on the surface ofour body.

This degradation facilitates Staphylococcus aureus’ coloniza­tion of sebaceous glands.

Question 17

Staphylococcus aureus: Exotoxins

Answer 17

1) Exfoliatin:
2) Enterotoxins
3) Toxic Shock Syndrome toxin (TSST-1)

Question 18

Exfoliatin causes -

Answer 18

A diffusible exotoxin that causes the skin to slough off (scalded skin syndrome).

Question 19

A heatstable - Exotoxins (of Staph. aureus) which cause food poisoning, resulting in vomiting and diarrhea

Answer 19

Enterotoxins (heatstable) Ž

Not destroyed by cooking

Question 20

Toxic Shock Syndrome toxin (TSST-1): this exotoxin is analogous to the

Answer 20

Analogous to the pyrogenic toxin produced by Lancefield group A beta-hemolytic streptococci, but is far more deadly.

Question 21

TSST-1 is a superantigen that binds to

Answer 21

MHC II and T-cell receptor

resulting in polyclonal T-cell activation and cytokine release tu­mor necrosis factor (TNF) and interleukin-1

Question 22

Disease caused by exotoxin release: by staphylococcus aureus

Answer 22

1) Gastroenteritis (rapid-onset food poisoning)
2) Toxic shock syndrome (TSST-1)
3) Scalded skin syndrome (exfoliative toxin)

Question 23

Disease resulting from direct organ invasion by the bacteria: staphylococcus aureus

Answer 23

1) Pneumonia
2) Meningitis
3) Osteomyelitis
4) Acute bacterial endocarditis
5) Septic arthritis
6) Skin infections
7) Bacteremia/sepsis
8) Urinary tract infection

Question 24

S aureus food poisoning due to

Answer 24

ingestion of preformed toxin

rapid-onset food poisoning (enterotoxins)

short incubation period (2–6 hr) followed by non bloody diarrhea and emesis

Enterotoxin is heat stableŽ not destroyed by cooking.

Question 25

Cause of Toxic shock syndrome

Answer 25

Associated with prolonged use of vaginal tampons or nasal packing.

Other causes
1. Infected sutures in surgical wounds,

2. cuta­neous and subcutaneous infections, and
3. infections following childbirth or abortion

Question 26

Staphylococcal toxic shock syndrome (TSS) — features;

Answer 26

fever, vomiting, rash, desquamation, shock, end-organ failure.

TSS results in

increased AST,
increased ALT, 
increased bilirubin

symptoms that you can think of as a hybrid between food poisoning (enterotoxins) and the streptococcal pyrogenic toxin that produces scarlet fever.

Question 27

Toxic shock syndrome involves (clinical features with time interval)

Answer 27

1. Sudden onset of high fever, nausea, vomiting, and watery diarrhea (enterotoxin-like syndrome)

followed in a few days
2. by a Diffuse erythematous (red) rash (like scarlet fever)

3. Palms and soles undergo desquama­tion (fine peeling of the skin)
4. blood pressure may decrease (frank shock)
   -the patient may suf­fer severe organ system damage
   (such as acute respira­tory distress syndrome or acute renal failure)

Question 28

Treatment for Staphylococcal toxic shock syndrome (TSS)—

Answer 28

1. Cleaning the infected foci
2. Removal of the tampon or drainage of an infected wound along with supportive care.

Antibiotics can help by killing the bacteria and preventing more exotoxin from being produced.

However, antibiotics are not curative because it is the exotoxin, not the bacteria, which causes the clinical manifestations.

Question 29

Staphylococcus aureus Commonly colonizes

Answer 29

colonizes the nares, ears, axilla, and groin.