Streptococci (strep pyogenes) Flashcards
How do we classify streptococci by haemolysis?
Alpha- partial haemolysis
Beta- Complete haemolysis
Gamma- No RBC break down at all
What are lancefield groups?
Antigen groupings for beta haemolytic streptococci based on serology.
List virulence factors for Streptococcus pyogenes
Hyaluronic acid capsule M protein Adhesins Streptolysins O and S DNA-ases Hyaluronidase Streptokinase Streptococcal pyogenic exotoxins
What are potential complications of a streptococcal pharyngitis?
Scarlet fever- strep pyogenes (pyrogenic exotoxin strain)
Rheumatic fever
Acute post-streptococcal glomerulonephritis
Suppurative complications
What shape and gram stain are streptococci?
Gram Positive cocci
Streptococcus pyogenes is what Lancfield and hamolysis type?
Lancefield A and beta haemolysis
Streptococcus pneumoniae shows what type of haemolysis?
Alpha
What are sherman classifications?
4 classes of Strep Pyogenic Viridans Enetrococcal Lactic
Why is a hyaluronic acid capsule a virulence factor?
Inhibits phagocytosis
Poor immunogen, very similar to human CT.
What is M protein?
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.
What VF can help streptococcus adhere and colonise in an infection?
Adhesins
What do streptolysins do?
Lysis of RBC, neutrophils and platelets
Why is DNAses degrading DNA helpful to the Streptoccoci?
Inactivates phagocytes
How do streptococci ensure they can spread in CT?
Degradation of hyaluronic acid by hyalunoidase
Converting plasminogen to plasmin does what?
Plasmin helps fibrinolysis and streptokinase catalyse the activation of plasmin from plasminogen.
Which Strep VF cleaves IgG and is a member of the super antigen family?
Streptococcal pyrogenic toxin.
What age group are most susceptible to strep pharyngitis? What microbe causes it (what strain)?
5-15 year olds
strep pyogenes
How is Strep throat spread?
droplets
What happens to most people with strep pharyngitis if left untreated?
M protein specific antibodies develop and most people recover.
What are the symptoms of a strep throat?
Abrupt onset of sore throat Malaise Fever Headache Lymphoid hyperplasia Tonsillopharyngeal exudates
How do you confirm its strep and why is this not the most useful thing in practice?
Throat swab
Takes a few days to get results by which time people have either got better or deteriorated.
Why do we worry about scarlet fever?
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.
List some suppurative complications of a strep progenies throat infection.
Peritonsillar cellulitis or absces
Retropharyngeal abscess
Mastoiditis, sinusitus or otitis media
Meningitis or brain abcess
What happens in rheumatic fever?
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
Is it the same M protein that causes glomerulonephritis as rheumatic fever?
No
Acute inflammation of the glomerulus after a strep throat is caused by what?
Specific M protein strains where antigen/antibody complexes aggregate in the glomerulus.
Name two types of streptococcal skin infections.
Impetigo
Erysipelas
What is impetigo?
Strep progenies skin infection- tends to be in 2-5 year olds. Skin colonised and then inoculated. Linked to glomerulonephritis.
What is erysipelas?
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.
What is cellulitis?
Skin and subcutaneous infection. Often in patients which have lymphatic problems or are IV drug users.
What is necrotising fasciitis?
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.
What is toxic shock?
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.
