Streptococcus

Characters, hemolysis, diseases, pathogenesis and cirulence factors, diagnosis, prophylaxis, treatment

1. Streptococcus

2. Streptococci
Characters of Streptococci
Gram positive cocci
Size 1µm
Chains or pairs
Non motile
Non spore forming
Facultative anaerobes
Fastidious
Catalasenegative

3. Classification of Streptococci
According to:
–Oxygen requirement
Anaerobic (Peptostreptococcus)
Aerobic or facultative anaerobic (Streptococcus)
–Hemolysison Blood Agar-α, β, Ƴ
–Lancefield classification-for βhemolytic
streptococci, based on C antigen

4. Hemolysison Blood Agar
Hemolysison BA
–-hemolysis
Partial hemolysis
Small zone
Viridansstreptococci
Green discoloration around colonies
e.g. S. pneumoniae& S. viridans
–-hemolysis
Complete hemolysis
Clear zone of hemolysisaround colonies
2-4mm zone
Hemolytic streptococci
e.g.Lancefield Group A & B (S. pyogenes& S. agalactiae)
–-hemolysis
No hemolysis
e.g. Group D (Enterococcussp.)

5. Hemolysison Blood agar
-hemolysis
-hemolysis
-hemolysis

6. Lancefield Classification-βhemolytic
Classification based on C-carbohydrate antigen of cell wall
20 Lancefield groups from A-H & K-V
One or more species per group
Group A-Further subdivided based on M, T, R protein
(Griffith typing) in to 80 sertypes
Streptococci
Group A
S. pyogenes
Group B
S. agalactiae
Group C
S. equisimitis
Group D
Enterococcus
Lanciefield classification
Other groups
(E-U)

7. A and O
Fibrin lysis
Dnase
RNase
A,B,C
Super antigen
TSS and scarlet fever
Antigens

8. Disease caused by S. pyogenes
(Group A)
Suppurative
Non-Invasive
Pharyngitis(Sore throat) -inflammation of the
pharynx, tonsillitis, otitismedia, mastoiditis, rarely
meningitis
Pyoderma-Impetigo-localisedpus-producing
lesions usually occur on face, arms, or legs
-

9. Suppurative
Invasive
Erysipelas-diffuse infection of skin, involves
superficial lymphatics. well demarcated borders
Cellulitis-infection of skin & subcutaneous tissue,
spreading
3. Necrotizing Fasciitis (Streptococcal Gangrene)—
This is infection of the subcutaneous tissues and fascia.There
is extensive and very rapidly spreading necrosis oftheskin and
subcutaneous tissues
PuerperalFever—Ifthestreptococcientertheuterusafter
delivery,puerperalfeverdevelops,whichisessentiallya
septicemiaoriginatingintheinfectedwound(endometritis)
Bacteremia/Sepsis—Infectionoftraumaticorsurgical
wounds with streptococci results in bacteremia

10. Toxin Mediated Diseases
Scarlet fever-rash begins on chest & spreads across body
Necrotizing fasciitis-Pyrogenicexotoxinproduced by some
trains of S. pyogenes-Can lead to DIC.
Streptococcal Toxic Shock Syndrome
shock, bacteremia, respiratory failure, and multiorgan
failure

11. Scarletfever
PyrotoxinA-C
Skin rashes

12. Non Suppurativecomplications or sequelae
–Rheumatic fever: following pharyngitis
carditis, poly arthritis, damage to heart valves
fever, malaise, a migratory nonsuppurativepolyarthritis,
and evidence of inflammation of all parts of the heart
(endocardium, myocardium, pericardium)
potentially fatal
–Acute Glomerulonephritits-following skin infection
Immune complex mediated disease
inflammation of glomerulidue to Ag-Abcomplex deposit on
basement membrane
Clinically-Hematuria, Proteinuria, Hypertension
Good prognosis

13. Pathogenesis & Virulence Factors
Structural components
–M protein inhibits phagocytosisof bacteria
–Lipoteichoicacid helps in adhesion of bactera
–Capsule-camouflages bacteria
Enzymes
–Streptokinases-fibrinolysin
–Deoxyribonucleases
–Hyaluronidase
Pyrogenic/ Erythrogenicexotoxin
Hemolysins
–StreptolysinO-Oxygen labile, antigenic
–StreptolysinS-serum soluble
Facilitate spread of
streptococci in tissues

15. S.pneumoniae

16. Diagnosis
–Acute infection –culture
–Nonsuppurativecomplication –antibody
–diagnosis
–Presumptive–gram staining (Pus/CSF)
–Sheep blood agar culture –hemolysis (-veto
H.hemolyticus)
–Rheumatic fever, glomerulonephritis –Abto
toxin
–Streptozymetest –passive hemagglutination
test

17. Prophylaxis
Prevention of rheumatic fever
Long term administration of penicillin
Prevents heart damage
Not applicable for glomerulonephritis

18. Treatment
Beta hemolytic group A-Penicillin G
Erythromycin and cephalexin –for allergic

19. Summary
Streptococcus general characters
Lancefield Classification
Toxins / Enzymes of S. pyogenes
Infections / Sequelaecaused
Laboratory Diagnosis