Beta-Hemolytic Streptococci-Pumerantz

Question 1

What are the 7 basic characteristics of Streptococci?

Answer 1

1. Genus: Streptococcus.
2. Gram-positive cocci
3. Non-sporulating
4. Non-motile
5. Pairs/chains of varying lengths due to division in one plane
6. Catalase-negative
7. Diseases: Scarlett fever, pharyngeal tonsillitis, harisyphillis cellulitis, preceptal cellulitis, necrotizing fasciitis.

Question 2

What are the Lancefield antigens?

Answer 2

oC carbohydrate-extracted from streptococcal cell walls react with different group-specific antisera
o20 serogroups-A, B, C, D, and G are most common human pathogens

Question 3

What are the 6 characteristics of Group A Strep? Give and example.

Answer 3

1. Strongly β-hemolytic
2. Small translucent colonies (compared to S. aureus)
3. Facultative anaerobes
4. Sensitive to bacitracin.
5. Nutritionally fastidious
6. Inhibited by low concentrations of bacitracin
   Example: S. pyogenes

Question 4

Where does S. pyogenes colonize? Who does it effect? What are the 2 associated poststreptococcal diseases?

Answer 4

Colonization of skin, then nasopharynx after 2 to 3 wks
-School-aged children more common than adults
-Rates vary with geography and season (late winter, early spring in temperate climates)
-Pharyngitis is very common in children
-Pyoderma (skin infection) risks:
•Children aged 2 to 5 years
•Low socioeconomic conditions
•Poor hygiene
•Close person-person contact
•Insect bites
•Tropical/subtropical climates, peaking in late summer and early fall (higher humidity)
-Nonsuppurative (poststreptococcal) diseases: Acute Rheumatic Fever (ARF), Acute Glomerulonephritis (AGN)

Question 5

What are the virulence factors of S. pyogenes? What are their functions?

Answer 5

1. Hyaluronic acid capsule
•Mimics connective tissue
•Anti-phagocytic
•Poorly immunogenic
•Colonies appear mucoid
2. Carbohydrate antigen layer
•Rhamnose and N-acetyl glucosamine (2:1 ratio)
3. Peptidoglycan cell wall
•Thick, densely cross-linked
•“Gram-positive”
4. Streptolysin O and S: pore forming cytolysins.

Question 6

What are the 4 characteristics of Group B Strep? Give and example.

Answer 6

1. Weakly β-hemolytic
2. Resistant to bacitracin
3. Hydrolyze sodium hippurate
4. ~100% strains produce CAMP factor-Synergistic hemolysis with S. aureus β-hemolysin after 24-h incubation on SBA @ 37°C
   Example: S. agalactiae

Question 7

What is the reservoir of S. agalactiae?

Answer 7

Reservoir is lower GI tract
oResident flora of GU and lower GI tract of ~20 to 40% of pregnant and non-pregnant women
oRisk of neonatal transmission is ~50% in pregnant women vaginally colonized at term
oDiabetes mellitus is independently associated with higher rates of colonization during pregnancy
oMore common among black women

Question 8

Where does S. agalactiae colonize? What are the other risk factors?

Answer 8

Oropharyngeal colonization ~5% (~20% in MSM)
Other risk factors:
osexual activity
omultiple partners by altering vaginal microenvironment

Question 9

What obstetric and neonatal diseases are associated with S. agalactiae?

Answer 9

Obstetrical Disease
1. Endometritis
2. Premature rupture of membranes 
3. UTI
4. Maternal case-fatality rate ~3%
Neonatal Disease
1. Early-onset (<7 d; mean,12 h)
•Bacteremia and sepsis (60%)
•Pneumonia (30%)
•Meningitis (10%)
2. Late-onset (7 to 89 d; mean, 24 d)
•Occult bacteremia
•Meningitis

Question 10

What are the 3 virulence factors of S. agalactiae?

Answer 10

1. Capsular polysaccharide-anti-phagocytic
2. C5a peptidase-deters recruitment of phagocytes
3. Sialic acid-inhibits alternate complement pathway
4. No cytotoxic enzymes or exotoxins
5. No immunologically induced disease

Question 11

What are the 2 adhesins and what do they do?

Answer 11

1. Fibronectin-binding proteins and lipoteichoic acid (LTA) bind fibronectin to facilitate adherence to oral epithelial cell membranes (E)
2. M-protein (anti-phagocytic, somatic virulence factor):
   •>50 serotypes
   •inhibits alternate complement pathway
   •M-1 and M-3 can bind fibronectin
   •Causes suppurative and nonsuppurative diseases

Question 12

What are the 2 nonsupportive (post-streptococcal_ disease? Describe them. What role does penicillin play in preventing/treating each?

Answer 12

1. Acute Glomerulonephritis (AGN)
   •“Nephritogenic” strains: M-12 (pharyngitis or tonsillitis); M-49 (pyoderma)
   •Immune complex deposition in glomerular basement membrane
   •Recurrences are rare
   •Penicillin does NOT prevent GN but can eradicate nephritogenic strains from patients and their colonized family contacts
2. Acute Rheumatic Fever (ARF)
   •“Rheumatogenic” strains: Antibodies to M protein cross-react with heart tissue sarcolemma, fix complement and cause damage
   •>1/3 follow pharyngitis
   •High risk of recurrence (RRF) following repeated streptococcal infections (recurrent rheumatic fever)
   •Penicillin prevents ARF/RRF
   •Jones criteria for diagnosis

Question 13

What are the 5 spreading factors and which groups use them?

Answer 13

1. Hyaluronidase
   •Most common spreading factor for Group A Strep.
   •degrades connective tissue and Group A capsule
2. DNase (streptodornases A-D)
   •liquefy pus
3. Streptokinase
   •dissolves clots by activating plasminogen
4. C5a peptidase
   •cleaves chemotaxin C5a at the PMN binding site to deter recruitment of phagocytes
5. Streptococcal pyrogenic exotoxin B (SpeB)
   •Least common spreading factor for Group A Strep.
   •potent protease and superantigen