18. Strep/Entero/Staph

Question 1

What are strep and entero classified based on?

Answer 1

Lysis of RBCs (alpha/beta/gamma-hemolytic)

Question 2

2 rare but sensational diseases caused by S. pyogenes?

Answer 2

• Necrotizing fasciitis

- Streptococcal toxic shock syndrome

Question 3

Hemolysis classification of S.pyogenes?

Answer 3

Beta-hemolytic

Question 4

3 S.pyogenes secreted extracellular substances?

Answer 4

• Streptolysins
• Hyaluronidase
• NADase

Question 5

What are streptolysins?

Answer 5

Cholesterol-dependent pore-forming proteins (like LLO) => responsible for beta-hemolytic phenotype

Question 6

S.pyogenes pili are anchored to what?

Answer 6

Peptidoglycan cell wall (LPXTG motif)

Question 7

Function of sortase?

Answer 7

Link pilin subunits to each other and to PG

Question 8

2 enzymatic activities of sortase?

Answer 8

Protease and transpeptidase

Question 9

S.pyogenes M protein is an example of an ________

Answer 9

MSCRAMM (microbial surface component recognizing adhesive matrix molecules)

Question 10

2 ways S.pyogenes evades immune response

Answer 10

Capsule made of hyaluronic acid => resembles human connective tissue

Fimbrial antigen M protein => hypervariable, resist phagocytosis

Question 11

How does Staph aureus evade immune response (2)?

Answer 11

Has MSCRAMM

Protein A - camoflague to prevent recognition

Clumping factor - inactivates complement protein C3b

Question 12

What is an isopeptide bond?

Answer 12

AMIDE BOND between side chains that is not present on the main chain of a protein

Question 13

Difference between inter and intramolecular isopeptide bonds?

Answer 13

Intermolecular - between subunits

Intramolecular - between side chains W/O a subunit

Question 14

Superantigens bind directly to and crosslinks what 2 things?

Answer 14

THC receptors and MHC class II molecules = activation of T cell

Question 15

What 2 things do S.aureus Protein A do?

Answer 15

• Bind to Fc portion of IgG to prevent opsonin-mediated phagocytosis
• Camouflages bacteria

Question 16

What does MSCRAMM stand for?

Answer 16

Microbial surface component recognizing adhesive matrix molecules

Question 17

G+ pili are isopeptide bonds between C-term of ______ of one pilin and a _____ side chain in adjacent

Answer 17

Thr, Lys

Question 18

Active site of sortase contains what aa?

Answer 18

Cys

Question 19

What would happen if a mutation in housekeeping gene of sortase prevented transpeptidase activity?

Answer 19

Polymerized pilus doesn’t get attached to lipid II = no anchoring to PG

Question 20

What would happen if there was a mutation that encodes Thr311Val in pilin subunit?

Answer 20

Sortase unable to recognition recognition site EVPT^G = no release of pre-pilin from IM = pilus doesn’t assemble