Streptococci

Question 1

Streotococci comes from which greek word?

Answer 1

Streptos - meaning bent or twisted

Question 2

Describe the bacteria streptococci

Answer 2

• gram positive
• coccus shaped
• grows in chains
• non-motile
• non-endospore

Question 3

How are stretococci initially classified?

Answer 3

by their pattern of hemolysis on blood agar

Question 4

α-hemolytic

Answer 4

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

• green colour du to oxidation of hemoglobin

Question 5

β-hemolytic

Answer 5

• S. pyogenes (Group A Streptococcus)
• S. agalactiae (Group B Streptococcus)
• S. equi (Group C Streptococcus)
• “glowing” complete colouring

Question 6

γ-hemolytic

Answer 6

• Enterococcus species (Group D Streptococcus)
• Lactococcus lactis (Group N Streptococcus)
• you dont have hemolysis

Question 7

Streptococcus pyogenes

Answer 7

• an extracellular pathogen
• pyo = pus
• 5-15% asymptomatic carriage

Question 8

what was Streptococcus pyogenes historically a major cause of?

Answer 8

mortaility due to scarlet fever, puerperal sepsis, wound infection in solidiers

Question 9

What is Streptococcus pyogenes a common cause of, today?

Answer 9

pharyngitis and impetigo

• also causes invasive streptococcal disease and the streptococcal toxic shock syndrome (“flesh-eating” disease)
• an important cause of “post infection sequelae” including acute rheumatic fever

Question 10

What is an asymptomatic carrier?

Answer 10

• has the bacteria, but displays no symptoms

- can still transmitt the disease

Question 11

M - Protein

Answer 11

• an anti-phagocytic cell surface expressed protein
• binds “C4-binding protein” of the complement system
• C4-binding protein is a complement regulatory protein 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 12

Hyaluronic Acid Capsule

Answer 12

• 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 13

S. pyogenes makes 2 hemolysins

Answer 13

Streptolysins (O and S)

Question 14

Streptolysin S

Answer 14

produces B-hemolyssis

Question 15

Streptolysin O

Answer 15

O2 sensitive

Question 16

Superantigens

Answer 16

• 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 17

Pharyngitis (Strep Throat)

Answer 17

• 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 18

Diagnosis - Is it Strep or viral?

Answer 18

• diagnosis by rapid strep test
  positive test = strep throat, therefore treat with antibiotics
  negative test, get throat culture

Question 19

What type of antibiotics are used to treat strep?

Answer 19

• B-lactams (no documented resistance)

- erythromycin (resistant strains exist)

Question 20

What can untreated pharyngitis lead to?

Answer 20

acute rheumatic fever

Question 21

Impetigo

Answer 21

• 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 22

Scarlet Fever

Answer 22

• 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 23

Rheumatic Fever

Answer 23

• “post infection” sequele
• 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
• rare in developed counties since 1960s but endemic in many developing countries

Question 24

Acute Rheumatic Fever

Answer 24

the initital inflammation can cause swollen joints

Question 25

Rheumatic heart disease

Answer 25

• damaged heart valves
• can lead to congestive heart failure
• patients are at increased risk for infective endocarditis by other pathogens

Question 26

Invasive Streptococcal Disease

Answer 26

• rare in developed countries but very serious
• defined as isolation of S. pyogenes from a normally sterile site
• blood isolation –> bacteremia

FLESH EATING DISEASE:
- if soft tissue involved, leads to necrotizing fasciitis
if muscle involved, leads to necrotizing myositis
- streptococcal toxic shock syndrome (TSS)

Question 27

Risk Factors for invasive streptococcal disease

Answer 27

• 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 28

Treatment for invasive streptococcal disease

Answer 28

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

Question 29

Global Burden of Disease

Answer 29

• major burden of disease occurs in developing countries

-

Question 30

Superantigen-mediated T cell activation

Answer 30

• leads to more T cells being activated (20% vs 0.01%)

Question 31

Lancefield Classification

Answer 31

• classified on the basis of surface carbohydrate antigens