Streptococcus pyogenes Flashcards
Pathogenesis of Streptococcus pyogenes
- adherence: F-protein & M-protein
- invasion: facilitated by production of enzymes such as streptolysins, streptokinases, DNases
- evasion: hyaluronic acid capsule interferes with phagocytosis
: M-protein interferes with C3b binding
: C5a peptidase
- produce specific toxins and enzymes: exotoxins
Epidemiology & Transmission of S. pyogenes
- colonises the pharynx and nares (nostrils)
- transmitted via respiratory droplets; sneezing, coughing
- asymptomatic colonisation if treansient; dependent on persons immune response to M-protein
Clinical manifestations of S. pyogenes (suppurative & non-suppurative)
suppurative: pus formation
- pharyngitis
- scarlet fever
- fasciitis
- streptococcal toxic shock syndrome (STSS)
non-suppurative: no pus formation
- rheumatic fever
Clinical manifestations of S. pyogenes- pharyngitis
- erythematous pharynx with exudate
- cervical lymphadenopathy
Clinical manifestations of S. pyogenes- scarlet fever
- diffuse erythematous rash beginning on the chest and spreading to the extremities
- complication of streptococcal pharynegitis
Clinical manifestations of S. pyogenes- necrotizing fasciitis
- deep infection of skin that involves destruction of muscle and fat layers
Clinical manifestations of S. pyogenes- streptococcal toxic shock syndrome (STSS)
- multi-organ systemic infection resembling staphylococcal toxic shock syndrome
- most patients are bacteremic with evidence of fasciitis
Clinical manifestations of S. pyogenes- rheumatic fever
- characterised by inflammation of heart (paricarditis), joints (arthralgias to arthritis), blood vessels, and subcutaneous tissues
What ages in pharyngitis prevalent in?
- most common in children, especially ages 5-15
Mechanism of pathogenesis for pharyngitis?
- S. pyogenes adheres to host cells using F-protein and lipoteichoic acid
- possibly internalise into oropharyngeal epithelial cells
- causes inflammatory response (cytokine storm)
Lab diagnostics for pharyngitis?
culture
- Sheep blood agar (beta-hemolysis)
rapid test
- streptococcus (Group A)
- group antigen can be detected by the RAPID test
- specimen collection is important
Treatment of pharyngitis?
- S. pyogenes is sensitive to penicillin
What is Pharyngitis and what bacteria causes it?
- Inflammation of the pharynx
- Streptococcus pyrogenes
What are the virulence factors of Streptococcus pyrogenes?
- lipoteichoic acid & F-proteins for adherence (F-proteins bind to fibronectin on host cell surface)
- hyaluronic capsule interferes with phagocytosis
- C5a peptidase: destroy C5 (involved in immune response)
- M-protein: major virulence factor
: type-specific protein associated with virulence strains
: extends through cell wall from cell membrane
: prevents opsonisation
What invasion techniques does Streptococcus pyrogenes use?
Enzymes
- Streptokinases: lyses (breaks apart) clots and fibrin deposits to facilitate spread from the initial site of infection
- Hemolysins: lyses erythrocytes
Streptolysin O: elicits specific anitbodies; inhibited by cholesterol in skin lipids
Streptolysin S: produced in presence of serum, responsible for hemolytic pattern
-hyaluronidases
Toxins
- pyrogenic exotoxins: Spe (A, B, C, F)
- superantigens
What evasion technique does Streptococcus pyrogenes use?
- Capsule
: interferes with phagocytosis
- other factors that interfere with the immune system
What is the incubation period for Pharyngitis?
1 - 2 days
What are the symptoms for pharyngitis?
- abrupt sore throat
- fever
- headache
- malaise
- erythematous pharynx with exudate
- cervical lymphadenopathy
What are other clinical syndromes that Streptococcus pyrogenes can cause?
Streptococcal Toxic Shock Syndrome (STSS)
What is Streptococcus Toxic Shock Syndrome (STSS)?
- caused by Streptococcus pyrogenes
- mediated by production of pyrogenic exotoxins (pyrogenic: causes fever)
: Spe A & Spe C
- can act as superantigens that activate T-cells and induces a Cytokine Storm
(Cytokine storm = overwhelming proinflammatory cytokine response)
- What is this?
- How is it caused?
- Incubation period?
- Symptoms?
- Pharyngitis
- Streptococcus pyrogenes infection
- 1-2 days
- fever, headache, abrupt sore throat, malaise, erythematous pharynx with exudate, cervical lymphadenopathy
