Streptococci

Question 1

What is the difference between alpha haemolytic and beta haemolytic?

Answer 1

Alpha - go green

Beta- lyse

Question 2

How do virulence factors cause damage in host (2)?

Answer 2

Direct

Via host response

Question 3

What is the structure of streptococci?

Answer 3

Strings of cocci

Gram positive

Question 4

How are streptococci classified by haemolysis? Give important examples

Answer 4

alpha haemolysis - goes green on blood agar - strep pneumoniae

beta haemolysis - complete RBC lysis on blood agar - strep pyogenes

gamma non haemolytic

Question 5

What determines whether a bacteria is haemolytic or not?

Answer 5

Antigens on their cell surface

Question 6

What is the lancefield classification of streptococci?

Answer 6

Serological classification of beta-haemolytic streptococci based on cell wall antigens
A-S

Question 7

Name an organisms that is catalase and coagulase negative

Answer 7

Certain streps

Question 8

Name an organisms that is catalase and coagulase negative

Answer 8

Certain streps

Question 9

Name group A strep

Answer 9

strep pyogenes

Question 10

Name two different classification systems for streps

Answer 10

haemolytic

lancefields

Question 11

Why does strep pneumoniae appear green and wet on agar plate?

Answer 11

Capsule

alpha haemolytic

Question 12

What are 8 virulence factors of strep pyogenes (SMASHED_C)

Answer 12

Streptokinase
M protein
Adhesins
Streptolysins O&S
Hyaluronidase
Exotoxin - pyrogenic
DNAses
Capsule - carb and hyaluronate

Question 13

What do each of the virulence factors do?

Answer 13

Streptokinase - breaks clots to allow pyogenes through
M protein - antiphagocytic
Adhesins - helps it adhere to host
Streptolysins O&S - lyse RBCs, neutrophils, platelets
Hyaluronidase - breaks down ECM so bacteria can spread
Exotoxin - pyrogenic
DNAses - breaks DNA of phagocytes
Capsule - carb and hyaluronate - antiphagocytic

Question 14

When is strep pharyngitis most common (Age)?

Answer 14

5-15 years

Question 15

How is strep A pharyngitis spread?

Answer 15

Droplets

Question 16

What happens if you don’t treat with antibiotics?

Answer 16

Develop M protein antibodies

Question 17

Is strep A throat self limiting?

Answer 17

Can be after around 5 days

Question 18

What are clinical features (5)

Answer 18

Abrupt onset sore throat
Lymphoid hyperplasia
Malaise
Temperature
Throat swap - Group A strep

Question 19

What is a complication of strep pharyngitis? What causes it?

Answer 19

Scarlett fever

Caused by pyrogenic exotoxin strain –> very virulent

Question 20

How is scarlet fever spread?

Answer 20

Local or haemotogenous

Question 21

What are the clinical signs/symptoms of scarlett fever?

Answer 21

High fever
Sepsis
Arthritis
Jaundice

Question 22

What are some complications of strep pharyngitis (5 main ones)?

Answer 22

Peritonsillar cellulitis/abcess
(Quincy)
Scarlett Fever 
Acute rheumatic fever
Acute post-streptococcal glomerulonephritis
Strep toxic shock

Retropharyngeal access
Mastoiditis 
Sinusitis
Otitis media
Meningitis
Brain Abscess

Question 23

What is rheumatic fever? What M types?

Answer 23

Inflammation of heart, joints, CNS

Certain M types of strep that are rheumatogenic cause it

Question 24

What are the possible rheumatic fever mechanisms?

Answer 24

Autoimmune 
Serum sickness
Binding of M protein to collagen
ASO ASS induced tissue injury 
(antistreptolysin S and antistreptolysin O)

Question 25

What is serum sickness?

Answer 25

Reaction to antibody antigen complexes

Question 26

What is acute post strep glomerulonephritis?

Answer 26

Acute inflammation of renal glomerulus

M type specific (diff to rheumatic M type)

Question 27

Does acute post strep glomerulonephritis only occur post strep pharyngitis?

Answer 27

No can occur after other strep infections - most commonly with impetigo

Question 28

How long does it take to develop rheumatic fever?

Answer 28

Sometimes weeks

Question 29

What 4 skin infections can you get from strep pyogenes?

Answer 29

Cellulitis
Erysipelas
Impetigo
Necrotising fasciitis

Question 30

What is impetigo?

Answer 30

2-5 years childhood infection
First colonisation on the skin
then intradermal inoculation
Can cause glomerulonephritis

Question 31

What is erysipelas?

Answer 31

Dermis infection
Lymphatic involvement
Face lower limbs
If on face - often preceded by pharyngitis
Lower legs often secondary to invasion of skin via trauma, skin disease or local fungal infection

Question 32

What is cellulitis? What are two important risk factors?

Answer 32

Skin and subcutaneous tissue infection

Risk factors are impaired lymphatic drainage and IVDU

Question 33

What is necrotising fasciitis?

Answer 33

Infection of deeper subcut tissue and facia 
Fulminant course (rapidly progressing)
Severe pain even before clinical signs 
Necrosis
High mortality rate 20-70%
High fever

Question 34

What 4 things happen in strep toxic shock?

Answer 34

Deep tissue infection with strep pyogenes 
and
Bacteraemia
and 
Vascular collapse
and 
Organ failure

Question 35

What is the pathogenesis of strep toxic shock syndrome?

Answer 35

1) Strep invades blood - strep pyrogenic exotoxins (super antigens) stimulate extreme T cell proliferation by binding to MHCII and TCR on T cells
2) M protein is shed from its surface and forms a complex with fibrinogen
3) M protein-fibrinogen complex binds to integrins on surfaces of neutrophils
4) Neutrophils bind to endothelium and degranulate and produce respiratory burst –> endothelial damage
5) Damaged endothelium is leaky and hypercoaguable
6) Cytokine release IL-1 IL-6 TNF-alpha –> shock
7) DIC, Hypotension, Organ damage

Question 36

What is special about a super antigen?

Answer 36

They don’t need processing by APCs they can just bind straight to MHCII on APC and illicit extreme disregulated T cell production –> loads of cytokines –> shock

Question 37

How would you treat strep pyogenes pharyngitis?

Answer 37

Penicillin

Clarythromycin if allergic