Streptococcus Pyogenes Flashcards
What type of bacteria is streptococci?
A gram positive bacteria
It stains purple
It appears as chains on a microscopic slide ( cocci shape )
What is one way we can classify streptococci ?
Classification by haemolysis. This is where we see how well the streptococci break down intact red blood cells on an agar plate. We use blood because it contains a lot of nutrients - for example iron which is an important mineral for growth of bacteria. Those bacteria that can break down iron better on an agar plate are bacteria that can dangerously grow rapidly.
There are three types : beta haemolysis , non-haemolytic ( gamma ) , alpha haemolysis
How does beta haemolysis appear ?
A clear white zone - bacteria have broken down the RBC very well. ( complete haemolysis )
How does alpha haemolysis appear ?
Partial haemolysis ( a in alpha for pArtial)
This appears a green colour on the agar plate because only some of the RBC have been broken down.
What does ‘viridans ‘ streptococcus mean ?
An adjective used to describe streptococci- where ythey only partially break down RBC. THe microscopic slide would appear green.
What does gamma haemolysis mean ?
NO breakdown of RBC ( non-haemolytic)
What is streptococcus pyogenes ?
- gram positive bacteria
- lancefield group A ( pyogenic )
- beta-haemolytic
What are virulence factor’s of streptococcus pyogenes?
- M protein : resistance to phagocytosis by inhibiting activation of alternative complement pathways on bacterial surface.
- Hyaluronic acid capsule : inhibits phagocytosis by neutrophils and macrophages.
- Adhesins : adherence is the first step in colonisation
- Streptolysins O and S : lysis of RBC, neutrophils and platelets
- Dnases A , B , C and D : degradation of DNA.
- Hyaluronidase : degradation of hyaluronate acid in connective tissue
- Streptokinase : dissolution of clots throug conversion of plasminogen into plasmin.
- Streptococcal pyrogenic exotoxins :
What is the cause of streptococcus pharyngitis? ( tonsillitis) And mechanism occurs transmission , peak incidence , symptoms
Streptococcus pyogenes
Peak incidence : 5-15 years of age
Mechanism of transmission : dropper spread
You can get better without treatment , antibiotics will only reduce the day by like 1 day.
However , untreated patients develop M proteins specific antibody.
Symptoms : exudate on the tonsils , abrupt sore throat , malaise , fever , headaches , lymphoid hyperplasia. A throat swab would indicate group A strep.
What are complications of streptococcal pharyngitis?
- scarlet fever : A fever assosiated with rashes too.
- this is due to infection with streptococcal pyrogenic exotoxin strain of S.Pyogenes. - Acute rheumatic fever
Hat other diseases does streptococcus pyogenes cause ?
- Impetigo
- Erysipelas
- Cellulitis
- Necrotising fasciitis
What is impetigo?
Caused by strep.P
Childhood infection (2-5 years)
Appears as red sores on the face especially around the child’s nose and mouth. The sores burst and develop honey coloured crusts.
( looks like cornflakes stuck to skin)
What is erysipelas?
Dermis infection with lymphatic involvement
Affects the face and lower limbs
Facial lesions frequently preceded by pharyngitis
What is necrotising fasciitis ?
Infection of deeper subcutaneous tissues and fascia
Rapid , extensive necrosis
Usually secondary to skin break
Severe pain
High fever
What is streptococcal toxic shock syndrome ?
Deep tissue infection with strep pyogenes , bacteraemia ( bacteria in blood) , vascular collapse , organ failure.
