Other: Molecular Basis of Bacterial Virulence

Question 1

Which toxinoses of S. aureus is associated with staphylococcal food poisoning?

Answer 1

Enterotoxin SeA SeB and SeC

Question 2

What is the function of M protein in the capsule of GAS?

Answer 2

Allows it to bind to multiple body surfaces and interferes with immune response

Question 3

How do adhesions act as a virulence factor for staphylococci?

Answer 3

Fibrinogen-binding (CIfA CIfB) and fibronectin-binding (FnbpA FNbpB) proteins are an important part of colonisation

Question 4

What is Lancefield grouping?

Answer 4

System of classification that classifies streptococci based on the carbohydrate composition of bacterial antigens found on their cell walls (Groups A-G)

Question 5

How does coagulase help S. aureus to evade host defences?

Answer 5

Protein enzyme tightly bound to the surface of S. aureus which can coat its surface with fibrin upon contact with blood → protects against phagocytosis

Question 6

What is Panton-Valentine Leukocidin?

Answer 6

Specific secreted proteins that form one functional complex that attacks white blood cells

Associated with severe skin infections and necrotising pneumonia

Question 7

Define ⍺-haemolysis

Answer 7

Partial haemolysis - green tinge to colony

Question 8

Name the superantigen which is the most common cause of toxic shock and the bacterium it is associated with

Answer 8

TSST-1 S. aureus

Question 9

How does the capsule help S. aureus to evade host defences?

Answer 9

Protects it against phagocytosis

Question 10

Which genus of gram-positive bacteria is classified using haemolysis?

Answer 10

Streptococci

Question 11

Define 𝛾-haemolysis

Answer 11

No haemolysis

Question 12

How does protein A help S. aureus to evade host defences?

Answer 12

Impairs phagocytosis by binding to the Fc portion of antibodies, rendering them inaccessible to the opsonins

Question 13

Name a coagulase-positive staphylococci that colonises the skin and mucous membranes (20-60%)

Answer 13

Staph. aureus

Question 14

Which streptococci are ⍺-haemolytic?

Answer 14

Step. pneumonae, viridans streptococci, most oral streptococci

Question 15

What is streptolysin?

Answer 15

Streptococcal haemolytic exotoxin - causes tissue damage and ulcers

Types include SLO and SLS - SLS is responsible for β-haemolysis

Question 16

Define β-haemolysis

Answer 16

Complete haemolysis

Question 17

Which bacteria is the major cause of infections associated with prosthetic devices and catheters?

Answer 17

Staph. epidermis

Question 18

How do iGAS cause necrotising fasciitis?

Answer 18

iGAS strains penetrate mucous membrane and develop in lesion

Severe infection with rapid destruction of connective tissue develops

Leads to toxic shock (with or without TSLS superantigen)

Question 19

Define Group A Streptococci (GAS)

Answer 19

Strep. pyrogenes (mostly) - β-haemolytic streptococci

Associated with throat infections (strep throat) and skin infections (impetigo, cellulitis, necrotising fasciitis)

Question 20

Define necrotising pneumonia

Answer 20

Severe complication of quite mild infections due to disruption of immune cells

S. aureus necrotising pneumonia is due to the actions of PVL

Question 21

Which streptococci are β-haemolytic?

Answer 21

S. pyogenes and angionosus group of oral streptococci

Question 22

Define virulence factor

Answer 22

The molecular/genetic basis of pathogenesis that characterises species, subspecies and strains

Question 23

Outline how TSST-1 causes toxic shock syndrome

Answer 23

Antigen binds directly to MHCII complex causing the activation of 1 in 5 T cells

This results in a massive release of cytokines and inappropriate immune response

Question 24

Name a coagulase-negative staphlococci that colonises the skin and mucous membranes (100%)

Answer 24

Staph. epidermis

Question 25

Which streptococci are 𝛾-haemolytic?

Answer 25

Enterococci (Lancefield Group D)

Question 26

Define toxinoses

Answer 26

Discrete disease associated with single protein component, a toxin or exotoxin (not the endotoxin)

Question 27

How are Group A streptococci further classified?

Answer 27

Divided according to M protein antigens (coded by emm gene)

Question 28

Which M protein antigens are associated with severe invasive disease (iGAS)?

Answer 28

M3 and M18

Question 29

Which emm gene is associated with GAS epidemics?

Answer 29

emm89