Sketchy Micro: Strep Pyogenes (Group A Strep)

Question 1

Streptococcus tend to grow in _____________.

Answer 1

long chains (unlike Staphylococcus which grows in clusters)

Question 2

S. pyogenes are covered with _____________.

Answer 2

a hyaluronic acid encapsulation (like the Hot Apple pie that is encapsulated by the glass cover)

Question 3

Why is the hyaluronic acid advantageous for S. pyogenes?

Answer 3

Because we have hyaluronic acid in our system and thus do not recognize hyaluronic acid as a foreign molecule

Question 4

True or false: S. pyogenes is beta hemolytic.

Answer 4

True! (Think of the beta-hemolytic lightbulb above the PIE.)

Question 5

How can you distinguish between impetigo from S. aureus and S. pyogenes?

Answer 5

Impetigo from S. pyogenes typically resembles a “honey crust” (like the baker with the honey-crusted pie).

Question 6

Other than impetigo, what infections does S. pyogenes cause?

Answer 6

Pharyngitis (think of the red handkerchief around the baker’s neck) and cellulitis and erysipelas (like the red oven mitts he’s wearing)

Question 7

What three conditions can be caused by Streptococcal pyrogenic exotoxin?

Answer 7

• Scarlet fever: rash that spares the face, strawberry tongue, and pharyngitis (like the gingerbread man with red frosting everywhere but his face, the baker eating the strawberry with his tongue sticking out, and the red handkerchief around the baker’s neck)
• Toxic-shock-like syndrome (TSLS): SPE behaves as a superantigen (think of the baker’s lightning bolt cape)
• Necrotizing fasciitis: the toxin destroys the skin (like the burned gingerbread man with his leg falling off); note, this is caused by SPE-B, which you can remember because the gingerbread man is burnt!

Question 8

What protein causes rheumatic heart disease?

Answer 8

M protein

Question 9

How does M protein work?

Answer 9

It is an anti-phagocytic protein (just like the Master baker preventing his worker from eating the cupcakes) that prevents opsonization.

Question 10

What does M protein mimic that causes rheumatic heart disease?

Answer 10

Myosin (think M!)

Question 11

Review the JONES criteria.

Answer 11

J: joint pain
O: O looks like a heart, signifying heart problems
N: nodules in the skin
E: erythema marginatum
S: sydenham chorea

Question 12

Differentiate the causes of rheumatic fever and PSGN.

Answer 12

RF is only caused by pharyngitis with S. pyogenes, while PSGN can be caused by pharyngitis or impetigo with S. pyogenes.

(Think of the RF bake wearing the red handkerchief and the PSGN baker – on the telephone with the cord that looks like a glomerulus –wearing a red handkerchief and having the honey crumbs on his face.)

Question 13

PSGN occurs __________ after S. pyogenes infection.

Answer 13

two weeks (think of the calendar with the date circled two weeks later)

Question 14

What two symptoms should raise your suspicion for PSGN?

Answer 14

Edema and cola-colored urine

Think of the PSGN baker with puffy cheeks and the coke bottle by his feet.

Question 15

What is ASO?

Answer 15

It is antistreptolysin O antibody. Streptolysin O is a virulence factor that lyses RBCs (just like the baker breaking open those jelly doughnuts).

Question 16

How can you differentiate between group A Strep. and group B Strep.?

Answer 16

Group A Strep. (depicted in this sketch) is bacitracin-sensitive, which you can remember because the basset hound is liking all the pastries.