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Streptococci (Gram positive cocci) Lecture 45. Faculty: Dr. Alvin Fox. Lancefield groups Hemolysis (alpha, beta, gamma) Group A streptococcus (S. pyogenes ) - Bacitracin susceptibility test - M, T, R proteins - Streptolysins O and S - F protein/lipoteichoic acid

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key words
Lancefield groups

Hemolysis (alpha, beta, gamma)

Group A streptococcus (S. pyogenes)

- Bacitracin susceptibility test

- M, T, R proteins

- Streptolysins O and S

- F protein/lipoteichoic acid

- Rheumatic fever/carditis/arthritis

- Glomerulonephritis

- Scarlet fever

- Toxic shock-like syndrome

- Bacteremia

- Flesh-eating bacteria

- Pyrogenic toxin

- Erythrogenic toxin

Group B streptococcus (S.agalactiae)

- Neonatal septicemia/meningitis

- CAMP test

- Hippurate hydrolysis test

Group D streptococcus

- Urinary tract infection

- Endocarditis

- Bile-esculin test

- Enterococci

- Non-enterococci

Large colony

Minute colony

Viridans streptococci

Dental caries/endocarditis

Key Words
slide3

Streptococci

    • facultative anaerobe
    • Gram-positive
    • usually chains (sometimes pairs)
    • catalase negative
  • (staphylococci are catalase positive)
slide6

Identification : Lancefield groups

      • - carbohydrate antigens
groupable streptococci
groupablestreptococci
  • A, B and D
    • frequent
  • C, G, F
    • less frequent
non groupable
Non-groupable
  • S. pneumoniae
    • pneumonia
  • viridans streptococci
    • e.g. S. mutans
      • dental caries
hemolysis reaction sheep blood agar
hemolysis reaction - sheep blood agar
  • α (alpha)
    • partial hemolysis
    • green color
  • β (beta)
    • complete clearing
  • γ (gamma)

- no lysis

White colonies

hemolysis
Hemolysis
  • Groups A an B
    • β
  • Group D
    • α or γ
  • S. pneumoniae and viridans
    • α
slide11

Identification:

hemolysis reaction

+one biochemical characteristic

slide13

Group A streptococcal infections affect all ages

peak incidence at 5-15 years of age

s pyogenes suppurative
S. pyogenes -suppurative
  • non-invasive
    • pharyngitis
    • skin infection, impetigo
  • invasive bacteremia
    • toxic shock-like syndrome
    • "flesh eating" bacteria
    • pyrogenic toxin
pyrogenic toxin
Pyrogenic toxin
  • Superantigen
  • Non-specific activation of T cells
  • Cross-link antigen presenting cells (MHC) and T cell receptor
  • Cytokine production
scarlet fever
Scarlet fever
  • rash
  • “erythrogenic toxin”
non suppurative
non-suppurative
  • rheumatic fever
    • inflammatory disease
    • life threatening
    • chronic sequalae
      • fever
      • heart
      • joints
        • rheumatic NOT rheumatoid arthritis
rheumatic fever etiology
Rheumatic fever -etiology
  • M protein
    • cross-reacts heart myosin
    • autoimmunity
  • Cell wall antigens
    • poorly digested in vivo
    • persist indefinitely
rheumatic fever
Rheumatic fever
  • penicillin
  • terminates pharyngitis
  • decreases carditis
acute glomerulonephritis
Acute glomerulonephritis
  • immune complex disease of kidney
major pathogenesis factors
Major pathogenesis factors
  • lipoteichoic acid/F protein
    • fimbriae
    • binds to epithelial cells
  • M protein
    • anti-phagocytic
s pyogenes
S. pyogenes

lipoteichoic acid

F-protein

fibronectin

epithelial cells

m protein

r

r

r

r

r

r

M protein

IMMUNE

Complement

IgG

M protein

NON-IMMUNE

peptidoglycan

fibrinogen

m protein24
M protein
  • major target
    • natural immunity
  • strain variation
    • antigenicity
  • re-infection
    • occurs with different strain
capsules
Capsules
  • Anti-phagocytic
    • mucoid strains
isolation and identification
Isolation and identification
  • βhemolytic colonies
    • bacitracin inhibits growth
  • β hemolytic colonies
    • group A antigen
hemolysis27
βhemolysis
  • hemolysin O
    • sensitive oxygen
  • hemolysin S
    • insensitive oxygen
modern rapid strep test
Modern Rapid “Strep” Test

Throat swab extract

(+/- streptococcal antigen)

-

+

Antibody

Liposome

Streptococcal antigen

post infectious diagnosis serology
Post-infectious diagnosis (serology)
  • antibodies to streptolysin O
  • important if delayed clinical sequelae occur
slide30

Typing

Traditional serotyping of proteins:

- M

- T

- R

Current:

- Sequencing of M protein gene

group b streptococcus
Group B streptococcus
  • neonatal meningitis
  • septicemia
  • transmission
    • vaginal flora
group b streptococcus identification
Group B streptococcus - identification
  • β hemolysis
  • hippurate hydrolysis
  • CAMP reaction
    • increases β hemolysis of S. aureus
group d streptococcus
Group D streptococcus
  • Growth on bile esculin agar
    • black precipitate
  • 6.5% saline
  • grow
    • enterococci
  • no growth
    • non-enterococci
enterococci
Enterococci
  • distantly related to other streptococci
  • genus Enterococcus
  • gut flora
    • urinary tract infection
      • fecal contamination
    • opportunistic infections
      • particularly endocarditis
  • most common E. (S.) faecalis
enterococci35
Enterococci
  • resistant to many antibiotics
    • including vancomycin
      • terminal D-ala replaced by D-lactate
minute colony streptococci
Minute colony streptococci
  • Various groups/hemolysis (e.g. group A)
    • genetically distinct
    • from large colony (e.g. S. pyogenes)
    • no rheumatic fever

Large colony

Minute colony

viridans streptococci
Viridans streptococci
  • diverse species
  • oral
  • dental caries
  • α hemolytic and negative for other tests
  • non-groupable.
  • includes S. mutans
    • occassionalendocarditis after tooth extraction