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Pathogenic > Streptococcus Pyogenes > Flashcards

Streptococcus Pyogenes Flashcards

1
Q

Streptococcus Pyogeneous

Overview

A
  • G +
  • Cocci, pairs or chains
  • Facultative Anaerobe
  • Catalase -
  • Ferment glucose —> lactic acid
  • complex growth requirements
  • Lance Field Group A
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2
Q

S.pyogenes

Encounter

A
  • Normal flora of skin
  • Normal flora also the nasopharynx (5-15% humans)
  • disease is caused by recently acquired strains.
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3
Q

S.pyogenes

Entry

A
  • Wound infection of skin
  • Inhalation for nasopharynx infection
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4
Q

S.pyogenes

Spread

A
  • Person to person thorugh respiratory droplets
  • Skin to skin contact
  • Contact with fomite
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5
Q

S.pyogenes

Multiplication

A
  • Xtrcl growth on mucous membranes
  • Skin
  • Deep tissue
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6
Q

S.pyogenes

Damage

A
  • Pharyngitis
  • Pyoderma
  • Scarlet Fever
  • Prysipelas
  • Cellulits
  • Necrotizing fasciitis
  • Glumulonephritis
  • Rheumatic fever
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7
Q

S.pyogenes

Diagnosis

A
  • Throat or skin culture on blood agar
  • β hemolysis
  • Immunodetection assays
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8
Q

S.pyogenes

Treatment

A
  • Remain sensitive penicillins/cephalosporins
  • Treatment prevent local infection from becoming invasive rheumatic fever and Person to Person spread
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9
Q

S.pyogenous Virulence Factor (Structural)

Cell Wall

A
  • Cell wall contains specific Ags.
  • Group specific carbohydrate (Lancefield Group A Ag)
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10
Q

S.pyogenous Virulence Factor (Structural)

M Protein

A
  • Extends through cell wall and capsule.
  • Contributes to adhesion, by binding fibrinogen
  • Prevents C3b binding, preventing complement activation and opsonization
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11
Q

S.pyogenous Virulence Factor (Structural)

Pili

A
  • allow attachment to host tissues
  • in S. pyogenes they are encoded by the FCT
  • pathogenicity island
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12
Q

S.pyogenous Virulence Factor (Structural)

F Protein

A
  • binds fibronectin allowing adherence to respiratory cells
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13
Q

S.pyogenous Virulence Factor (Structural)

Capsule

A
  • Composed of hyaluronic acid
  • Hyaluronic acid is commonly found in connective tissue and recognized as “self” by the immune system.
  • Thus capsule allows S. pyogenes to mask itself as a normal component and avoid destruction by the immune system
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14
Q

S.pyogenous Virulence Factor (Structural)

C5a Peptidase

A
  • Protease that inactivates C5a preventing C5a from attracting phagocytic cells to the site of infection
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15
Q

S.pyogenous Virulence Factor (Cytotoxin)

Streptolysin S (SLS)

A
  • disrupts membranes by an unknown mechanism
  • Peptide encoded by sagA that is extensively modified prior to secretion
  • Active against WBCs, RBCs, and platelets
  • Oxygen stable
  • non immunogenic
  • Responsible for Beta hemolysis observed on blood agar plates
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16
Q

S.pyogenous Virulence Factor (Cytotoxin)

Streptolysin O

A
  • Pore forming cytotoxin, binds to cholestrol
  • Oxygen labile
  • Very immunogenic —> Antistreptolysin O antibodies (ASO)
  • Free cholesterol in skin inhibits toxin binding to membranes —>Cutaneous infections do not develop ASO.
17
Q

S.pyogenous Virulence Factor

Pyrogenic Exotoxins (SPE)

A
  • Four toxins (SpeA-D)
  • All act as superantigens
  • SpeA and SpeC are encoded by a lysogenic bacteriophage.
  • Play a role in specific diseases
  • Not all strains posses pyrogenic toxins
18
Q

S.pyogenous Virulence Factor (enzymes)

Streptokinase A & B

A
  • Enzyme that cleaves human plasminogen releasing activated plasmin
  • Plasmin goes on to cleave fibrin and fibrinogen.
  • Action is to break blood clots facilitate rapid spread of the S. pyogenes from the site of the infection.
19
Q

S.pyogenous Virulence Factor (enzymes)

Streptodornases A-D

A
  • Deoxyribonuclease enzymes that can break down free DNA in the environment (Dnases)
  • B and D can also break down RNA.
  • Thought to facilitate spread by breaking down nucleic acids present in pusand decreasing the viscosity of the pus.
  • Immunogenic
  • AB to Dnase B are one test for cutaneous infection.
20
Q

S.pyogenous Virulence Factor (enzymes)

Hyaluronidase

A
  • cleaves hyaluronic acid in host connective tissue.
  • Thought to play a role in the spread of the organism from the original site of infection.
  • Also cleaves the S. pyogenes capsule!
21
Q

S.pyogenes Diseases

A
  • S. pyogenes disease breaks down into two categories:
  1. Suppurative disease or pus producing diseases
  2. Non supparative disease, non pus producing
  • usually a complication of an infection causing supparative disease
    Example: Rheumatic fever
22
Q

S.pyogenes **Suppurative **Diseases:

Pharyngitis

A
  • Most common
  • Spread by saliva or nasal secretions from infected person.
  • Organism is inhaled and adheres to and colonizes the nasopharynx
  • Incubation 2-4 days
  • S/Sx: Sore throat, fever, malaise, and headache.
  • Characteristic erythematous rash on back of throat (red rash caused by dilated and congested capillaries)
  • Left untreated it can lead to abscess in pharynx and tonsils and disseminated disease.
23
Q

S.pyogenes Suppurative Diseases:

Scarlet Fever

A
  • Scarlet Fever is a complication of Strep. pharyngitis
  • Occurs when the infecting S. pyogenes contains a gene w/ a Spe toxin.
  • The resulting inflammation produces a characteristic erythematous rash on the upper chest and extremities 1-2 days after symptoms of pharyngitis
  • Also produces a rash on the tongue called “strawberry tongue
  • Rash clears in 5-7 days.
24
Q

S.pyogenes Suppurative Diseases:

Necrotizing Fascciitis

A
  • Rare, and seen primarily in immuno-compromised individuals.
  • Most often associated with S. pyogenes
  • Characterized by massive deep tissue destruction (deep tissue, below dermis) which spreads along the fascia (the connective tissue that surrounds muscle, blood vessels, and nerves).
  • S. pyogenes is introduced through a wound in the skin and disseminates to the deep tissues.
  • SpeB protease activity is not very specific, it degrades complement components, antibody, extracellular matrix proteins, destroying tissues.
  • Spe(A-D) superantigen action causes a massive inflammation response contributing to edema (swelling) and tissue destruction.
  • Disease will progress quickly leading to septic shock and multiple organ failure.
  • Aggressive treatment required including both antibacterial treatment and surgical removal of infected tissues.
25
Q

S.pyogenes Non-Suppurative Diseases:

Rheumatic Fever

A
  • Complication of Strept. Pharyngitis
  • Chronic inflammation of the heart, joints, skin and possibly brain.
  • Believed to be caused cross reactivity of anti-streptococcal AB to host proteins.
  • Antibody to M protein may cross react with myosin of heart muscle fibers.
  • This leads to immune system attack of heart valves and reduced heart function.

Pathogenic (8 decks)

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