Streptococcus

Hugh B. Fackrell

Filename:Strept.ppt

Streptococcus Outline

• Streptococcus Characteristics

• Streptococcal Diseases

Streptococcus: characteristics

• Genus definition

• Growth requirements

• Capsule

• Colonial morphology

• Hemolysis
  • Destruction of RBCs

• Hemolysins
  • molecules that destroy RBCs

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

Fastidious

• Most Streptococci are fastidious in their growth requirements

• Grow poorly on nutrient agar

• Grow well on blood agar

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

Colonial Morphology

• GLOSSY: no capsule, colonies small

• MUCOID: capsule, colonies are large, glistening, viscous

• MATT:capsule, older colonies are dried, flatter rougher

Two Forms of Hemolysis

Beta Hemolysis

Clearing

(Gamma hemolysis = no lysis)

Streptococcal Beta Hemolysis

• Two hemolysins

• Both cause clearing

• Both involved in disease

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

Hemolysin O

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

• Antistreptolysin O test

Streptococcus pyogenes Suppurative Diseases

• Pharyngitis

• Scarlet Fever

• Erysipalas ( St. Antony’s fire)

• Cellulitis

• Puerperal Fever

• Sepsis

• Meningitis

• Pneumonia

• Subacute Bacterial Endocardititis

• Otitis Media

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:

Streptococcal Suppuration

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

Post vaccination Streptococcal Infection

Streptococcal Cellulitis

Scarlet Fever

Scarlet Fever Rash

• Peticial hemorrhage
  • Pin point
  • Subcutaneous

• Erythrogenic toxin
  • Scarletina toxin
  • causes rash
  • associated with a temperate phage

Scarlet Fever

Strawberry Tongue

Schultz-Charlton test

• Inject 0.1 ml antitoxin subcutaneously

• Rash fades after 6-8 hours (possible delay 14 h)

• Differentiates from other similar rashes

Erysipalas

• Secondary invasion
  • minor original lesion

• Skin reddened thickened
  • later purple

• Bacteria only in advancing edge

Erysipalas: butterfly rash

• Butterfly rash
  • common near nose
  • spreads after 4-6 days

• Septicemia common complication

• No toxin

• No immunity
  • repeated attacks possible

Rheumatic Fever

• autoimmune

• acute glomerulonephritis

• Acute, non suppurative

• post streptococcal inflammation
  • Joints, heart valves,myocardium,nerves
    • chorea- inflammation of nerves

Scarred heart valves

• reduced cardiac output

• heart failure

• Mitral valve stenosis

• edema, hypertension, hematuria and proteinuria

Rheumatic Endocarditis

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

Aschoff Bodies

• Inflammation of myocardium

• Mononuclear cell infiltration

• Granuloma-like nodules

• Characteristc of rheumatic fever

Streptococcal Antigens

• Lancefield groups

• M antigens

• T antigens

• R antigens

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

Lancfield Groups

• S. pneumoniae N/A

• S.pyogenes -- Lancefield Group A

• S.agalactiae -- Lancefield Group B

• Enterococcus-Lancefield Group D

• Viridans group

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

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

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

Pathogenesis

• capsule -- non-immunogenic

• M Protein -- antiphagocytic, anticomplementary

• Lipoteichoic acid (LTA):
  • mediates adherence to epithelial cells

• LTA binding protein
  • Host cell membrane:
  • Deacylated LTA

Enzymes

• Streptokinase A & B:
  • lyse blood clots

• DNA ase:
  • depolymerase DNA in pus

• Hyaluronidase:
  • hyaluronic acid

• DPN ase

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

S. pneumoniae

Streptococcus pneumoniae

• Gram positive cocci in pairs, singles, short chains

• alpha hemolysis -- aerobic

• beta hemolysis -- anaerobic

• capsule -- immunogenic (84 serotypes)

Diseases:

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

• Sinusitis

• Meningitis

• Bacteremia

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

Mechanisms of Pathogenicity

• aspiration of S. pneumoniae, an endogenous oral organism

• organism colonizes the oropharynx

• epiglottal reflex, coughing is inhibited

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

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

The End