Streptococcus

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Streptococcus

• Hugh B. Fackrell
• FilenameStrept.ppt

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Streptococcus Outline

• Streptococcus Characteristics
• Streptococcal Diseases

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Streptococcus characteristics

• Genus definition
• Growth requirements
• Capsule
• Colonial morphology
• Hemolysis
• Destruction of RBCs
• Hemolysins
• molecules that destroy RBCs

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StreptococcusGenus Definition

• Gram ve cocci, chains or pairs
• Catalase -ve facultative anaerobes
• some strictly anaerobic
• some capnophilic (CO2)
• Ferment sugars to mixed acids and ethanol
• Lancefield group D is motile

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Fastidious

• Most Streptococci are fastidious in their growth
  requirements
• Grow poorly on nutrient agar
• Grow well on blood agar

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Capsule

• Made of hyaluronic acid
• polymer of glucuronic acid N-acetylglucosamine
• Non immunogenic
• hyaluronic acid intercellular cement
• detected only in young(2-4 h) broth cultures
• bacteria produce hyaluronidase

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Colonial Morphology

• GLOSSY no capsule, colonies small
• MUCOID capsule, colonies are large, glistening,
  viscous
• MATTcapsule, older colonies are dried, flatter
  rougher

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Two Forms of Hemolysis
Beta Hemolysis Clearing
(Gamma hemolysis no lysis)
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Streptococcal Beta Hemolysis

• Two hemolysins
• Both cause clearing
• Both involved in disease

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Hemolysin S (stable in air)

• Beta hemolysis on blood agar
• Do not develop antibodies
• Induces arthritis
• Two parts
• Carrier
• hemolysin polypeptide
• cell bound hemolysin
• lyses leukocytes and platelets
• stimulates release of lysosomal contents

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Hemolysin O

• Oxidized in air
• oxygen labile (reversible)
• Protein
• Cardiotoxic
• patients develop antibodies
• ASOT
• cholesterol labile (irreversible)
• Antistreptolysin O test

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Streptococcus pyogenes Suppurative Diseases

• Pharyngitis
• Scarlet Fever
• Erysipalas ( St. Antonys fire)
• Cellulitis
• Puerperal Fever
• Sepsis
• Meningitis
• Pneumonia

• Subacute Bacterial Endocardititis
• Otitis Media

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Diseases of S. pyogenes

• Pharyngitis
• incubation period of 2 to 4 days
• sore throat, fever, malaise, headache
• Erythema of the pharynx
• cervical lymphadenopathy
• diagnosis -- differential -- viral pharyngitis

• Scarlet fever
• all of the above plus red rash and red tongue
• Pyoderma
• Non-suppurative, inflammatory

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Streptococcal Suppuration
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Puerperal Fever

• Childbirth Fever
• Semmelweis
• Membranes of genital tract ruptured
• fulminating septicemia
• fatal 24-48 hr
• S. pyogenes 60-75 of cases
• Anaerobic streptococci 20-25

• S. pyogenes Not isolated from vagina of healthy
  females before birth
• 50-60 from physician
• rest from own nose throat

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Post vaccination Streptococcal Infection
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Streptococcal Cellulitis
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Scarlet Fever
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Scarlet Fever Rash

• Peticial hemorrhage
• Pin point
• Subcutaneous
• Erythrogenic toxin
• Scarletina toxin
• causes rash
• associated with a temperate phage

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Scarlet Fever
Strawberry Tongue
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Schultz-Charlton test

• Inject 0.1 ml antitoxin subcutaneously
• Rash fades after 6-8 hours (possible delay 14 h)
• Differentiates from other similar rashes

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Erysipalas

• Secondary invasion
• minor original lesion
• Skin reddened thickened
• later purple
• Bacteria only in advancing edge

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Erysipalas butterfly rash

• Butterfly rash
• common near nose
• spreads after 4-6 days
• Septicemia common complication
• No toxin
• No immunity
• repeated attacks possible

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Rheumatic Fever

• autoimmune
• acute glomerulonephritis
• Acute, non suppurative
• post streptococcal inflammation
• Joints, heart valves,myocardium,nerves
• chorea- inflammation of nerves

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Scarred heart valves

• reduced cardiac output
• heart failure
• Mitral valve stenosis
• edema, hypertension, hematuria and proteinuria

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Rheumatic Endocarditis
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Rheumatic fever latent period

• Latent period 2-4 weeks
• same after repeated infections
• not immunological
• Antibiotics taken during first week of pharyngeal
  infection
• Drop Steptococcal count
• Block rheumatic fever

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Aschoff Bodies

• Inflammation of myocardium
• Mononuclear cell infiltration
• Granuloma-like nodules
• Characteristc of rheumatic fever

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Streptococcal Antigens

• Lancefield groups
• M antigens
• T antigens
• R antigens

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StreptococcusLancefield Groups

• Rebecca Lancefield
• Grouped by presence of distinctive cell wall
  antigens
• Polysacchardies or glycero teichoic acids
• Antigens labelled A-T
• exclude I J
• Group A Streptococci Clinically Important

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Lancfield Groups

• S. pneumoniae N/A
• S.pyogenes -- Lancefield Group A
• S.agalactiae -- Lancefield Group B
• Enterococcus-Lancefield Group D
• Viridans group

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Group A Streptococci

• S. pyogenes Group A
• clinically important
• Lancefield grouping time consuming
• Group A correlated with sensitivity to bacitracin

Bacitracin sensitive Beta hemolytic Strept
reported as Group A Strept
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Group D Streptococci

• glycerol teichoic acid -- associated with the
  cytoplasmic membrane
• Streptococcus bovis, Enterococcus faecalis,
  Enterococcus faecium
• resist bile and high concentrations of sodium
  chloride

• Disease
• urinary tract infection
• intra-abdominal abcesses
• wound infection
• Endocarditis

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M antigens

• proteins of the pilus
• sensitive to Pepsin Trypsin
• soluble at pH 2
• 50 types
• Involved in rheumatic fever
• 5-8 types
• Antibodies neutralize streptococcal infections

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Pathogenesis

• capsule -- non-immunogenic
• M Protein -- antiphagocytic, anticomplementary
• Lipoteichoic acid (LTA)
• mediates adherence to epithelial cells
• LTA binding protein
• Host cell membrane
• Deacylated LTA

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Enzymes

• Streptokinase A B
• lyse blood clots
• DNA ase
• depolymerase DNA in pus
• Hyaluronidase
• hyaluronic acid
• DPN ase

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Lab diagnosis

• Gram stain -- good in cases of pyoderma
• fluorescent antibody
• detection of antibodies to Streptolysin O ASO
• 3-4 weeks after exposure
• Culture
• swab the lesion directly
• blood agar plates - hemolysis
• Eliza

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S. pneumoniae
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Streptococcus pneumoniae

• Gram positive cocci in pairs, singles, short
  chains
• alpha hemolysis -- aerobic
• beta hemolysis -- anaerobic
• capsule -- immunogenic (84 serotypes)

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Diseases

• Pneumonia -- inflammation of the lungs with
  exudation and consolidation (solidification)
• Sinusitis
• Meningitis
• Bacteremia

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Pathogenesis

• virulence factor, capsule -- prevents
  phagocytosis
• Pneumolysin is a temperate and oxygen labile
  hemolysin
• Purpura-producing principal is released during
  cell autolysis
• Neuraminidase -- glycoproteins and glycolipids
• Autolysins, amidases -- autolyse peptidoglycan
  layer

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Mechanisms of Pathogenicity

• aspiration of S. pneumoniae, an endogenous oral
  organism
• organism colonizes the oropharynx
• epiglottal reflex, coughing is inhibited

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Lobar Pneumoniae

• multiplication in the alveolar spaces
• viral infection frequently precedes bacterial
  infection
• highly invasive due to capsule
• bacteremia common
• Meningitis -- most often in children
• Treatment
• Penicillin, Erythromycin

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Laboratory Diagnosis

• sputum -- gram cocci, lancet shaped,capsule, may
  appear over-decolourized
• alpha-hemolytic, optochin sensitive
• Quellung reaction -- specific antiserum to
  capsular polysaccharide
• capsular antigen can be detected by very
  sensitive immunologic tests

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The End