Streptococci Flashcards
Streptococci gram stain
Gram +ve cocci
How are streptococci classified?
By haemolysis
Serologically (Lancefield - for beta haemolytic)
Pyogenic (Sherman pus or not)
16S ribosomal RNA sequencing
Types of streptococci haemolysis
alpha haemolysis: partial haemolysis, viridans streptococci (green stain)
beta haemolysis: complete haemolysis, gain iron, grow abundantly
non haemolytic (gamma) haemolysis
alpha, beta haemolytic and non haemolytic examples
alpha: streptococcus pneumoniae
beta: streptococcus pyogenes
Non haemolytic: Enterococcus faecalis
Sherman classification
Pyogenic or not
All beta haemolysis strep are pyogenic
All alpha haemolysis are viridans
Streptococcus pyogenes classification
Lancefield Group A
Beta haemolytic streptococcus
Streptococcus causing abscesses
Streptococcus anginosus spp
Mouth commensal streptococcus
Streptococcus mutans
Streptococcus salivarius
(can cause endocarditis)
Virulence factors for streptococcus pyogenes
Hyaluronic capsule M protein Adhesins (lipoteichoic acid, M protein, fibronectin binding proteins) Streptolysins O and S DNAses ABCD Hyaluronidase Streptokinase Streptococcal pyrogenic exotoxins
Hyaluronic acid capsule function
Inhibits phagocytosis by neutrophils and macrophages
similar to human connective tissue hyaluronate
M protein function
Resistance to phagocytosis by inhibiting activation of complement pathway
Different serotypes from emm gene
Adhesins function
First step in colonisation/infection
Streptolysins O and S function
Lysis of erythrocytes, neutrophils and platelets
DNAases ABCD
Degrade DNA
Hyaluronidase function
Degrade hyaluronic acid in connective tissue
Streptokinase function
Dissolution of blood clots - converts plasminogen to plasmin (inactive to active)
Streptococcal pyrogenic exotoxins function
Cleaves IgG bound to group A strep
Superantigenic Spe family (can cause clonal T cell proliferation - toxic shock)
M proteins appearance microscope
Fuzzy peach appearance of microbe
‘fur’ = M proteins
Streptococcal pharyngitis cause
Streptococcus pyogenes
How does streptococcal pharyngitis spread?
Droplet spread
Associated with overcrowding (poor living conditions and schools)
When is streptococcal pharyngitis likely to occur?
5-15 years old
What do untreated streptococcal pharyngitis patients develop?
M protein specific antibody
Clinical features streptococcal pharyngitis
Abrupt onset sore throat
Malaise, fever, headache
Lymphoid hyperplasia
TONSILLOPHARYNGEAL EXUDATE
Throat swab = group A strep
Complications of streptococcal pharyngitis and cause (main)
Scarlet fever - if infected with streptococcal pyrogenic exotoxin strain
Spread of scarlett fever through body
Local or haematogenous
Complications/signs associated with scarlett fever
High fever
Sepsis
Arthritis (joint swelling)
Jaundice
Complications associated with pus and streptococcal pharyngitis (suppurative)
Peritonsillar cellulitis/abscess
Retropharyngeal abscess
Mastoiditis, Sinusitis, Otitis media
Meningitis, Brain abscess
How does streptococcal pharyngitis spread from origin?
Through lateral pharyngeal space - could go to mediastinum or back up to head
Acute complications of streptococcal pharyngitis
Acute rheumatic fever
Acute post-streptococcal glomerulonephritis
What is acute rheumatic fever?
Inflammation of heart, joints and CNS (could cause endocarditis, pericarditis or epicarditis)
From Rheumatogenic M types following pharyngitis
Mechanisms of acute rheumatic fever?
Autoimmune response to M proteins
Serum sickness
Binding of M protein to collagen
ASO (antistreptolysin O titier) or ASS induced tissue injury
What is acute post-streptoccocal glomerulonephritis
Acute inflammation of renal glomerulus
M type specific
Antigen-antibody complex in glomerulus - blood sticks here
When does RF occur after streptococcal pharyngitis
Delayed onset.
Patient seems to be getting better and then gets worse
Streptococcus pyogenes skin infection
Impetigo
Erysipelas
Impetigo
Childhood infection (2-5 years old) Skin colonisation and then intradermal inoculation
No acute rheumatic fever but COMMON cause of glomerulonephritis
Erysipelas
Dermis infection with lymphatic involvement
Face/lower limbs
Facial lesions = usually following pharyngitis
Leg lesions = usually from skin invasion via trauma, skin disease or local fungal infection
Impetigo vs erysipelas appearance
Impetigo: Crusty around mouth in particular
Erysipelas: Redness with pronounced margins
Streptococcus pyogenes skin infections
Cellulitis
Necrotising fasciitis
Cellulitis + risk factors
Skin and subcutaneous tissue infection
RISK FACTORS:
Impaired lymphatic drainage
Injecting drug use
Necrotising fasciitis
Infection deeper of subcutaneous tissue causing rapid and extensive necrosis Severe pain (even before gross clinical changes)
Risk factor necrotising fasciitis
Secondary to skin break
Necrotising fasciitis problems
High fever
Severe/sudden onset
High mortality rate
Testing for necrotising fasciitis
Sweep test
See if can sweep finger under subcutaneous tissue
If you can, shows necrosis is present and +ve for NF
Streptococcal toxic shock syndrome cause (steps)
Deep tissue infection with streptococcus pyogenes \+ Bacteraemia \+ Vascular collapse \+ Organ failure
What occurs in streptococcal toxic shock syndrome?
Group A strep enters deeper tissues and blood
Streptococcal pyrogenic exotoxins stimulate T cells by binding to MHC class 2 on APC cells and V beta region of T cells
Induces monocyte cytokines and lymphokines
M protein fibrinogen complex formation
Cytokines and lymphokines released during strep A infection
Cytokines - TNF-alpha, IL1B, IL6
Lymphokines - TNF beta, IL2, IFN-gamma
What does M protein fibrinogen complex cause
Bind to integrins on neutrophils
Activates them and they adhere to endothelium and degranulate
Release hydrolytic enzymes and respiratory burst
What does respiratory burst to endothelium?
hypercoagulable state –> disseminated intravascular coagulation
tissue damage –> vascular leakage –> hypotension
Lack of organ perfusion = organ failure
