Streptococcus pyogenes Flashcards
1
Q
What is streptococci?
A
- Gram-positive, coccus shaped, grows in chains
- ”Streptos” – Greek for bent or twisted
- non-motile, non-endospore forming
- Initially classified by their pattern of hemolysis on blood agar
2
Q
What are the different groups of Strptococci?
A
- “alpha”-hemolytic
- “beta”-hemolytic
- “gamma”- hemolytic
3
Q
“alpha”-hemolytic
A
- S. pneumoniae (pneumococcus)
- viridans group including:
- S. viridans - endocarditis
- S. mutans – tooth decay
- S. thermophilus – dairy foods
4
Q
“beta”-hemolytic
A
- S. pyogenes (Group A Streptococcus)
- S. agalactiae (Group B Streptococcus)
- S. equi (Group C Streptococcus)
5
Q
“gamma”-hemolytic
A
- Enterococcus species (Group D Streptococcus)
- Lactococcus lactis (Group N Streptococcus)
6
Q
What is streptococcus pyogenes
A
- a common human specific pathogen
- an extracellular pathogen
- “pyo” means pus
- 5-15% asymptomatic carriage
- historically a major cause of mortality due to scarlet fever, puerperal sepsis, and wound infections in soldiers
- today a common cause of pharyngitis and impetigo
- also causes severe invasive streptococcal disease and the streptococcal toxic shock syndrome (“flesh-eating” disease)
- an important cause of “post infection sequelae” including acute rheumatic fever
- produces an arsenal of virulence factors
- a master at hiding from the immune system
- armed to cause severe damage
7
Q
What is the M protein?
A
- an anti-phagocytic cell surface expressed protein
- binds “C4-binding protein” - a complement regulatory protein complex that protects self cells from complement
- > 100 M protein serotypes
- hypervariable N-terminus – basis for M protein serotypes
- e.g. M1, M3 typically cause pharyngitis and invasive disease
- e.g. M18 typically cause acute rheumatic fever
- however, if you have antibodies to a particular M protein serotype you will opsonize and kill these bacteria
8
Q
What is the hyaluronic acid capsule?
A
- a polysaccharide
- hyaluronic acid is a major component of host tissues – bacteria “look like self”
- can also block opsonization through C3b (typical of other capsules)
9
Q
What are the two hemolysins that S. pyogenes make?
A
Streptolysins (O and S)
- streptolysin S produces β-hemolysis
- streptolysin O is “O2-sensitive”
10
Q
S. pyogene superantigens
A
- secreted exotoxins
- Streptococcal pyrogenic exotoxins (Spe’s)
- function as potent activators of T cells and can result in a cytokine storm disease known as the toxic shock syndrome
- NOT emetic like the staphylococcal enterotoxins (SE’s)
11
Q
What is pharyngitis (strep throat)?
A
- most common in school aged children and teenagers
- fever and severe sore throat
- typically absence of cough
- swollen cervical lymph nodes
- tonsillar exudate (pus)
- skin rash
12
Q
How to diagnosed pharyngitis?
A
- through a rapid strep test
- positive test
- strep throat -> antibiotics
- negative test
- throat culture
13
Q
Treating pharyngitis with antibiotics
A
- β-lactams (no documented resistance!!!!)
- erythromycin (resistant strain exist)
- untreated pharyngitis can lead to a number of complications including acute rheumatic fever
14
Q
What is impetigo?
A
- most common among children
- also caused by S. aureus
- a superficial skin infection
- red sores that forms crusts, normally on the face
- highly contagious through direct contact
15
Q
What is scarlet fever?
A
- rash that develops typically during strep throat
- 5-15 years of age
- high fever, “strawberry tongue”
- rash – small red bumps
- normally on the chest and stomach
- can look like a sunburn
- rough sandpaper
- lasts 2-7 days
- toxin mediated - caused by the “scarlet fever toxins”
- same toxins as streptococcal pyrogenic exotoxins
