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Immunology Pt. 2 > Streptococcus > Flashcards

Streptococcus Flashcards

1
Q

Characteristics of Streptococci

A

Gram-positive cocci arranged in pairs or chains
Most species are facultatively anaerobic
Ferment carbohydrates resulting in lactic acid production
Catalase negative (as opposed to staphylococci)

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2
Q

Classification of Streptococci

A

1) Cell wall carbohydrate antigens recognized by specific antibodies
2) Hemolytic pattern on agar containing blood cells
3) Biochemical properties

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3
Q

Hemolytic Pattern on agar containing blood cells

A

Alpha - partial hemolysis or “greening”
Beta - Complete clearing
Gamma - no change in red blood cells

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4
Q

Lancefield typing can recognize…

A

Group A Streptococci = S. pyogenes
Group B Streptococci = S. agalactiae
Group C = S. Dysgalactiae
Group F = S. Anginosus

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5
Q

S. Pyogenes pathology

A

Pharyngitis
Skin and soft tissue infections
Rheumatic fever
Glomerulonephritis

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6
Q

S. Agalactiae pathology

A

Neonatal disease

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7
Q

S. Dysgalactiae pathology

A

Pharyngitis

Acute glomerulonephritis

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8
Q

S. Pneumoniae pathology

A

Otitis media
Pneumonia
Sepsis, meningitis

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9
Q

Surface Proteins for S. pyogenes
Group specific:
Type specific:
Others:

A

Group specific: Lancefield Group A carbohydrate
Type specific: M proteins encoded by emm genes - epidemiologic markers
Others:
- M-like proteins
- hyaluronic acid capsule
- C5a peptidase

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10
Q

Proteins that mediate adherence to fibronectin

A

Lipoteichoic acid

F Protein

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11
Q

Avoidance of opsonization and phagocytosis

A
  • Hyaluronic acid capsule
  • M proteins block C3b binding
  • M like proteins bind the Fc fragment of antibodies which reduces bound C3b
  • C5a peptidase degrades C5a
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12
Q

Invasion of host cells

A

M protein and F protein

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13
Q

Toxins and Enzymes

A 
Streptococcal pyogenic exotoxins SpeA, B, C and F - phage encoded, act as superantigens
- Mediate cytokine storm
Streptolysin S
Streptolysin O
Streptokinase
Dnases
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14
Q

Spe toxins mediate what manifestations of S. pyogenes infections?

A
  1. Cytokine release may be key to the severity of necrotizing fascitis and toxic shock syndrome
  2. Responsible for rash in patients with scarlet fever
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15
Q

Streptolysin S

A

Oxygen and serum stable cell-bound hemolysin, responsible for complete lysis of red blood cells - kills macrophages and neutrophils

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16
Q

Sterptolysin O

A

Oxygen labile hemolysin

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17
Q

Streptokinase

A

Mediates cleavage of plasminogen, the release of plasmin and subsequent cleavage of fibrin and fibrinogen

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18
Q

Dnases

A

Depolymerize released DNA from lysed cells aiding spread of streptococci through infected tissues

19
Q

Streptococcus Pyogenes: Patients with antibodies to ___ _______ are protected

A

M proteins

20
Q

Streptococcus Epidemiology

A
  • Transient colonizer of the oropharynx of healthy children and adults
  • Spread by droplet transmission
  • Pharyngitis affects children between 5 and 15 y
  • Soft tissue infections by organisms introduced into superficial or deep tissues through a wound
21
Q

Streptococcal pharyngitis

A

redness and edema of the mucous membranes, fever, pus, tonsilitis

22
Q

Scarlet fever

A

Streptococcal pharyngitis and an erythematous punctiform rash due to the Spe toxins

23
Q

Impetigo or pyoderma

A

Infection of the superficial layers of the skin in children - vesicles develop into pustules rupture and crust over

24
Q

Erysipelas

A

Infection of the skin and subcutaneous tissues edema, induration with an distinct advancing border

25
Q

Streptococcal toxic shock

A

Focal infection, bacteremia, shock hypotension, in conjugation with 2 or more of either ARDS, renal impariment, liver abnormality, coagulopathy, rash

26
Q

Endocarditis

A

Streptococcal bacteremia allows access to normal, injured or congenitally deformed heart tissue

27
Q

Necrotizing fasciitis

A

Infection of deeper subcutaneous tissues and fascia, extensive necrosis and gangrene

28
Q

Rheumatic fever (Group A - late sequelae)

A

Follows respiratory infections, hypersensitivity response to streptococcal antigens

29
Q

Glomerulonephritis (Group A - late sequelae)

A

Deposition of antigen-antibody complexes in the glomerular basement membrane

30
Q

Streptococcus Pyogenes - Laboratory Diagnosis

A 
Gram stain
Antigen detection
Nucleic acid amplification
Culture (gram positive cocci in chains, catalase negative...)
Antibodies to streptolysin O
31
Q 
Streptococcus, Prevention and control
Pharyngitis:
Penicillin allergic patients:
Severe:
Soft tissue:
A

Pharyngitis: Penicillin, penicillin V amoxicillin
Penicillin allergic patients: cephalosporin or macrolide
Severe: Penicillin IV + a protein synthesis inhibitor antibiotic
Soft Tissue: Surgical debridement and antibiotics

32
Q

S. agalactiae - Group B
Physiology and structure:
Pathogenisis and immunity:
Epidemiology:

A

Physiology and structure: Expresses group B carbohydrate antigen
Pathogenisis and immunity: avoids phagocytosis by expressing a capsule
Epidemiology: Asymptomatic colonizatio of the lower gastrointestinal tract and genitourinary tract

33
Q

S. agalactiae: Laboratory diagnosis

Treatment, Prevention and control

A

Gram stain of CSF for meningitis, pneumonia and wound infections
Treatment: drug of choice penicillin G for serious infections penicillin

34
Q

Physiology and structure of S. pneumonia

A

Encapsulated Gram-positive, elongated or oval coccus arranged in pairs of chains
α-hemolytic colonies on blood agar

35
Q

_______ ______ are the basis for the classification of S. Pneumonia strains

A

Capsular polysaccharides

36
Q

S. Pneumonia - unique cell wall composition of phophorylcholine + species specific teichoic acids (2 types)

A

C polysaccharide - binds to serum
- C-reactive protein a marker for acute inflammation
F antigen - cross reacts with Forssman surface antigens on mammalian cells

37
Q

S. Pneumonia pathogenseis
Colonization:
Resistance:
Inflammatory Response:

A

Colonization: Bacterial colonization is mediated by surface protein adhesins
Resistance: S. Pneumonia produces a secretory IgA protease that cleaves the Fc portion of IgA and prevents the association with host mucins
Inflammatory Response: Teichoic acids, peptidoglycan - activate complement pathways

38
Q

S. Pneumonia - epidemiology

A

Transiently colonizes normal healthy individuals
Can occur when endogenous oral organisms are aspirated in to the lower airways
Disease = breakdown of natural defense mechanisms
In children - common cause of otitis media

39
Q

Pneumococcal pneumonia

A

Replication of bacteria in the alveolar spaces

Abrupt onset, severe chill, sustained fever

40
Q

Sinusitis and Otitis media

A

Infection of the paranasal sinuses and ear

41
Q

______ occurs in 25-30% of patients with pneumonia and 80% of patients with meningitis

A

Bacteremia

42
Q

S. Pneumonia laboratory diagnosis

A

Gram stain
Quellung reaction - detection of capsule with antibodies
ELISA
Culture
Isolate tested for bile solubility, should exhibit α-hemolysis on blood agar

43
Q

S. Pneumonia treatment, prevention and control
Resistance:
Serious Infections:

A
  • Many strains are now resistant to penicillin
  • Resistance is documented for macrolides and cephalosporins
  • Serious infections: Vancomycin + ceftriazone followed by monotherapy
44
Q

Immunization: S. pneumonia
Adults and Children > 2 yrs:
Children < 2 yrs:

A

Adults and Children > 2 yrs: Immunize with vaccine containing 23 different capsular polysaccharides
Children < 2 yrs: Immunize with 13-valent conjugated vaccine

Immunology Pt. 2 (11 decks)

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