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