Streptococcus pyogenes

Question 1

What is streptococci?

Answer 1

• 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

Question 2

What are the different groups of Strptococci?

Answer 2

• “alpha”-hemolytic
• “beta”-hemolytic
• “gamma”- hemolytic

Question 3

“alpha”-hemolytic

Answer 3

• S. pneumoniae (pneumococcus)
• viridans group including:
• S. viridans - endocarditis
• S. mutans – tooth decay
• S. thermophilus – dairy foods

Question 4

“beta”-hemolytic

Answer 4

• S. pyogenes (Group A Streptococcus)
• S. agalactiae (Group B Streptococcus)
• S. equi (Group C Streptococcus)

Question 5

“gamma”-hemolytic

Answer 5

• Enterococcus species (Group D Streptococcus)

- Lactococcus lactis (Group N Streptococcus)

Question 6

What is streptococcus pyogenes

Answer 6

• 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

Question 7

What is the M protein?

Answer 7

• 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

Question 8

What is the hyaluronic acid capsule?

Answer 8

• 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)

Question 9

What are the two hemolysins that S. pyogenes make?

Answer 9

Streptolysins (O and S)

• streptolysin S produces β-hemolysis
• streptolysin O is “O2-sensitive”

Question 10

S. pyogene superantigens

Answer 10

• 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)

Question 11

What is pharyngitis (strep throat)?

Answer 11

• 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

Question 12

How to diagnosed pharyngitis?

Answer 12

• through a rapid strep test
• positive test
• strep throat -> antibiotics
• negative test
• throat culture

Question 13

Treating pharyngitis with antibiotics

Answer 13

• β-lactams (no documented resistance!!!!)
• erythromycin (resistant strain exist)
• untreated pharyngitis can lead to a number of complications including acute rheumatic fever

Question 14

What is impetigo?

Answer 14

• 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

Question 15

What is scarlet fever?

Answer 15

• 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

Question 16

What is rheumatic fever

Answer 16

• a “post infection” sequelae
• occurs 2-3 weeks after infection (e.g. strep throat or scarlet fever)
• typically occurs in children 5-15 years of age
• a form of autoimmunity caused by antibody cross-reactivity with the M protein

Question 17

What is acute rheumatic fever?

Answer 17

The initial inflammation can cause painful swollen joints

Question 18

What is rheumatic heart disease?

Answer 18

• damaged heart valevs
• can lead to congestive heart failure
• patients are at increased risk for infective endocarditis by other pathogens
• rare in developed countries but endemic in many developing countries

Question 19

What is invasive strptococal disease

Answer 19

• rare in developed countries but very serious
• “invasive streptococcal disease” is defined as isolation of S. pyogenes from a normally sterile site
• blood isolation -> bacteremia
• if soft tissue involved -> necrotizing fasciitis
• if muscle involved -> necrotizing myositis
• streptococcal toxic shock syndrome

Question 20

What are the risk factors for invasive streptococcal disease?

Answer 20

• Tissue injury (penetrating and nonpenetrating)
• Prior use of nonsteroidal antiinflammatory agents
• Chicken pox in children (58-fold increased risk)
• Postpartum
• Lack of immunity to superantigens and M protein
• MHC class II haplotypes (ie. superantigen receptors)

Question 21

What are the treatment for invasive streptococcal disease?

Answer 21

• Antibiotics
• Supportive therapy
• Debridement/amputation
• Intravenous immunoglobulin (IVIG)
• neutralize superantigen activity
• opsonization of S. pyogenes