Streptococci Flashcards by RG Cattermole

What is the difference between alpha haemolytic and beta haemolytic?

Alpha - go green

Beta- lyse

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

Direct

Via host response

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What is the structure of streptococci?

Strings of cocci

Gram positive

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How are streptococci classified by haemolysis? Give important examples

alpha haemolysis - goes green on blood agar - strep pneumoniae

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

gamma non haemolytic

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What determines whether a bacteria is haemolytic or not?

Antigens on their cell surface

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What is the lancefield classification of streptococci?

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

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Name an organisms that is catalase and coagulase negative

Certain streps

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Name an organisms that is catalase and coagulase negative

Certain streps

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Name group A strep

strep pyogenes

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Name two different classification systems for streps

haemolytic

lancefields

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

Capsule

alpha haemolytic

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What are 8 virulence factors of strep pyogenes (SMASHED_C)

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

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What do each of the virulence factors do?

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

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When is strep pharyngitis most common (Age)?

5-15 years

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How is strep A pharyngitis spread?

Droplets

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What happens if you don’t treat with antibiotics?

Develop M protein antibodies

Is strep A throat self limiting?

Can be after around 5 days

What are clinical features (5)

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

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

Scarlett fever

Caused by pyrogenic exotoxin strain –> very virulent

How is scarlet fever spread?

Local or haemotogenous

What are the clinical signs/symptoms of scarlett fever?

High fever
Sepsis
Arthritis
Jaundice

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

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

What is rheumatic fever? What M types?

Inflammation of heart, joints, CNS

Certain M types of strep that are rheumatogenic cause it

What are the possible rheumatic fever mechanisms?

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

What is serum sickness?

Reaction to antibody antigen complexes

What is acute post strep glomerulonephritis?

Acute inflammation of renal glomerulus | M type specific (diff to rheumatic M type)

Does acute post strep glomerulonephritis only occur post strep pharyngitis?

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

How long does it take to develop rheumatic fever?

Sometimes weeks

What 4 skin infections can you get from strep pyogenes?

Cellulitis Erysipelas Impetigo Necrotising fasciitis

What is impetigo?

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

What is erysipelas?

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

What is cellulitis? What are two important risk factors?

Skin and subcutaneous tissue infection Risk factors are impaired lymphatic drainage and IVDU

What is necrotising fasciitis?

``` 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 ```

What 4 things happen in strep toxic shock?

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

What is the pathogenesis of strep toxic shock syndrome?

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

What is special about a super antigen?

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

How would you treat strep pyogenes pharyngitis?

Penicillin Clarythromycin if allergic