S6) Beta-Haemolytic Streptococci Flashcards Preview

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Classify the Streptococci by haemolysis

- Alpha haemolysis e.g. Streptococcus pneumonia 

- Beta haemolysis e.g. Streptococcus pyogenes

- Non-haemolytic gamma e.g. Enterococcus faecalis


Identify and describe 3 virulence factors of Streptococcus pyogenes

- Hyaluronic acid capsule: inhibits phagocytosis by neutrophils and macrophages 

- M protein: resistance to phagocytosis by inhibiting activation of alternative complement pathway on bacterial cell surface

- Hyaluronidase: degradation of hyaluronic acid in connective tissue 


What is Streptococcal pharyngitis?

- Streptococcal pharyngitis is a form of pharyngitis caused by Strep pyogenes, spread through respiratory droplets and associated with over-crowding

- It presents with malaise, fever, headache, lymphoid hyperplasia, tonsillopharyngeal exudates and an abrupt onset sore throat


One complication of streptococcal pharyngitis is Scarlet Fever. 

What is Scarlet Fever?

- Scarlet fever is a condition arising due to an infection with streptococcal pyrogens (exotoxins strain of S.pyogenes)

- It is transmitted through local/haematogenous spread and presents with high fever, sepsis, arthritis, jaundice



One complication of streptococcal pharyngitis is Acute Rheumatic Fever.

What is Acute Rheumatic Fever?

- Acute Rheumatic Fever is the inflammation of the heart, joints and CNS which follows on from pharyngitis

- It might arise due to auto-immunity, serum sickness or M proteins binding to collagen


One complication of streptococcal pharyngitis is Acute post-streptococcal glomerulonephritis.

What is Acute glomerulonephritis?

Acute glomerulonephritis is the acute inflammation of renal glomerulus due to antigen-antibody complexes forming in the glomerulus


Identify 4 suppurative complications of streptococcal pharyngitis

- Peritonsillar cellulitis/abscess

- Retropharyngeal abscess

- Mastoiditis, sinusitis, otitis media

- Meningitis, brain abscess


What is Impetigo?

- Impetigo is a streptococcus pyogenes skin infection, often occurring in children of 2-5 years and commonly caused by glomerulonephritis

- It involves an initial skin colonisation, followed by intradermal inoculation


What is Erysipelas?

- Erysipelas is a streptococcus pyogenes skin infection wherein the dermis of the face and/or lower limbs is infected with lymphatic involvement

- Facial lesions are preceded by pharyngitis and lower limb lesions are secondary to invasion of skin via trauma, skin disease or local fungal infection


What is Cellulitis? 

- Cellulitis is a streptococcus pyogenes skin infection wherein the skin and subcutaneous tissue are infected

- Impaired lymphatic drainage and illicit injecting drug use are important risk factors


What is necrotising fasciitis?

- Necrotising fasciitis is an infection of deeper subcutaneous tissues and fascia, caused by streptococcus pyogenes

- It usually occurs secondary to skin break and involves rapid, extensive necrosis, presenting with severe pain initially and high fever (mortality 20-70%)


What is Streptococcal toxic shock syndrome?

- Streptococcal toxic shock syndrome is a deep tissue infection with caused by Strep pyogenes

- It presents with bacteraemia, vascular collapse and organ failure and patients go from health to death in hours


In four steps, describe the pathogenesis of Streptococcal Toxic Shock Syndrome

⇒ Group A strep enter into deeper tissues and bloodstream

⇒ Streptococcal pyrogenic exotoxins stimulate T-cells through binding to MHC class II antigen-presenting cells

⇒ Monocyte cytokines (TNF-α, IL-1β, IL-6) and lymphokines (TNF-β, IL-2, IFN-γ) are induced

⇒ M-protein fibrinogen complex formation


In four steps, explain the link between a patient's oral health and heart disease

⇒ Poor dental hygiene can lead to chronic inflammation (periodontal disease)

⇒ The mouth is a harbour of a significant range of bacteria (aerobes, anaerobes, Gpos & Gneg)

⇒ This creates portal system for bacteria to enter the venous system

Local/systemic infection results 


What is a Bicuspid aortic valve?

Bicuspid aortic valve (BAV) is congenital heart defect wherein the two leaflets of the aortic valve fuse resulting in a bicuspid valve instead of a tricuspid valve

- This may become calcified, leading to various degrees of aortic stenosis and aortic regurgitation, predisposing one to heart disease


Explain the findings highlighted by the arrows in the picture

- The vegetation is the growth of bacteria on the valve leaflet (biofilm formation)

- There are calcium deposits (BAV may become calcified)

- The leaflet perforation is an effect of the infection


Describe the use of the coagulase test

- Coagulase is an enzyme that causes a clot to form when bacteria are incubated with plasma

- The test is used to differentiate Staphylococcus aureus from coagulase-negative staphylococci