Streptococci (strep pyogenes)

Question 1

How do we classify streptococci by haemolysis?

Answer 1

Alpha- partial haemolysis
Beta- Complete haemolysis
Gamma- No RBC break down at all

Question 2

What are lancefield groups?

Answer 2

Antigen groupings for beta haemolytic streptococci based on serology.

Question 3

List virulence factors for Streptococcus pyogenes

Answer 3

Hyaluronic acid capsule 
M protein 
Adhesins
Streptolysins O and S
DNA-ases
Hyaluronidase
Streptokinase
Streptococcal pyogenic exotoxins

Question 4

What are potential complications of a streptococcal pharyngitis?

Answer 4

Scarlet fever- strep pyogenes (pyrogenic exotoxin strain)
Rheumatic fever
Acute post-streptococcal glomerulonephritis
Suppurative complications

Question 5

What shape and gram stain are streptococci?

Answer 5

Gram Positive cocci

Question 6

Streptococcus pyogenes is what Lancfield and hamolysis type?

Answer 6

Lancefield A and beta haemolysis

Question 7

Streptococcus pneumoniae shows what type of haemolysis?

Answer 7

Alpha

Question 8

What are sherman classifications?

Answer 8

4 classes of Strep
Pyogenic 
Viridans
Enetrococcal
Lactic

Question 9

Why is a hyaluronic acid capsule a virulence factor?

Answer 9

Inhibits phagocytosis

Poor immunogen, very similar to human CT.

Question 10

What is M protein?

Answer 10

M protein is an important virulence factor for streptococci it is resistant to phagocytosis because it inhibits the complement cascade. Lots of variants for M protein antigenically. M protein is important in adhesion as well.

Question 11

What VF can help streptococcus adhere and colonise in an infection?

Answer 11

Adhesins

Question 12

What do streptolysins do?

Answer 12

Lysis of RBC, neutrophils and platelets

Question 13

Why is DNAses degrading DNA helpful to the Streptoccoci?

Answer 13

Inactivates phagocytes

Question 14

How do streptococci ensure they can spread in CT?

Answer 14

Degradation of hyaluronic acid by hyalunoidase

Question 15

Converting plasminogen to plasmin does what?

Answer 15

Plasmin helps fibrinolysis and streptokinase catalyse the activation of plasmin from plasminogen.

Question 16

Which Strep VF cleaves IgG and is a member of the super antigen family?

Answer 16

Streptococcal pyrogenic toxin.

Question 17

What age group are most susceptible to strep pharyngitis? What microbe causes it (what strain)?

Answer 17

5-15 year olds

strep pyogenes

Question 18

How is Strep throat spread?

Answer 18

droplets

Question 19

What happens to most people with strep pharyngitis if left untreated?

Answer 19

M protein specific antibodies develop and most people recover.

Question 20

What are the symptoms of a strep throat?

Answer 20

Abrupt onset of sore throat
Malaise
Fever
Headache
Lymphoid hyperplasia 
Tonsillopharyngeal exudates

Question 21

How do you confirm its strep and why is this not the most useful thing in practice?

Answer 21

Throat swab

Takes a few days to get results by which time people have either got better or deteriorated.

Question 22

Why do we worry about scarlet fever?

Answer 22

Strep pyogenes has spread locally or in the blood from the initial pharyngitis. It is the pyrogenic exotoxin strain of strep progenies that gives the red each on the trunk and arms.
High fever, sepsis, arthritic and jaundice are all potential complications.

Question 23

List some suppurative complications of a strep progenies throat infection.

Answer 23

Peritonsillar cellulitis or absces
Retropharyngeal abscess
Mastoiditis, sinusitus or otitis media
Meningitis or brain abcess

Question 24

What happens in rheumatic fever?

Answer 24

Inflammation of heart, joints and CNS.
Rheumatogenic M type Strep throat proceeds by 10-14 days.

Mechanism is not confirmed, theories include:

• autoimmune
• serum sickness
• Binding of M protein to collagen
• ASO, ASS induced injury

Question 25

Is it the same M protein that causes glomerulonephritis as rheumatic fever?

Answer 25

No

Question 26

Acute inflammation of the glomerulus after a strep throat is caused by what?

Answer 26

Specific M protein strains where antigen/antibody complexes aggregate in the glomerulus.

Question 27

Name two types of streptococcal skin infections.

Answer 27

Impetigo

Erysipelas

Question 28

What is impetigo?

Answer 28

Strep progenies skin infection- tends to be in 2-5 year olds. Skin colonised and then inoculated. Linked to glomerulonephritis.

Question 29

What is erysipelas?

Answer 29

Dermis infection with lymphatic involvemnt tending to affect the face and lower limb often following a throat infection. Lower limb tend to be associated with skin breaches.

Question 30

What is cellulitis?

Answer 30

Skin and subcutaneous infection. Often in patients which have lymphatic problems or are IV drug users.

Question 31

What is necrotising fasciitis?

Answer 31

A deeper infection that cellulitis where there is rapid and extensive necrosis. Initially the pain will far outweigh the appearance. Patients have a high fever and this has a high mortality.

Question 32

What is toxic shock?

Answer 32

Deep tissue infection+ Bacteraemia+ Vascular collapse+ organ failure
All caused by a group A strep in deep tissues and blood stream. Streptococcal progenies exotoxins stimulate T cells by binding MHC class 2 APCs. M protein causes fibrinogen complexes by aggregation it to the surface of neutrophils.
Dead in hours.