Streptococci (Gram positive cocci) Lecture 37

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Streptococci (Gram positive cocci)Lecture 37
Faculty Dr. Alvin Fox
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Key Words

• 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
  

• 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

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

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Streptococcus in chains (Gram stain)
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Streptococcus pneumoniae (diplococcus).
Fluorescent stain
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• Identification Lancefield groups
• - carbohydrate antigens

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groupable streptococci

• A, B and D
• frequent
• C, G, F
• less frequent

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Non-groupable

• S. pneumoniae
• pneumonia
• viridans streptococci
• e.g. S. mutans
• dental caries

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hemolysis reaction - sheep blood agar

• a (alpha)
• partial hemolysis
• green color
• ß (beta)
• complete clearing
• ? (gamma)
• - no lysis

White colonies
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Hemolysis

• Groups A an B
• ß
• Group D
• a or ?
• S. pneumoniae and viridans
• a

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Identification hemolysis reaction one
biochemical characteristic
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Group A streptococcus (S. pyogenes)
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Group A streptococcal infections affect all
ages peak incidence at 5-15 years of age
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S. pyogenes -suppurative

• non-invasive
• pharyngitis
• skin infection, impetigo
• invasive bacteremia
• toxic shock-like syndrome
• "flesh eating" bacteria
• pyrogenic toxin

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Pyrogenic toxin

• Superantigen
• Non-specific activation of T cells
• Cross-link antigen presenting cells (MHC) and T
  cell receptor
• Cytokine production

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Scarlet fever

• rash
• erythrogenic toxin

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non-suppurative

• rheumatic fever
• inflammatory disease
• life threatening
• chronic sequalae
• fever
• heart
• joints
• rheumatic NOT rheumatoid arthritis

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Rheumatic fever -etiology

• M protein
• cross-reacts heart myosin
• autoimmunity
• Cell wall antigens
• poorly digested in vivo
• persist indefinitely

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Rheumatic fever

• penicillin
• terminates pharyngitis
• decreases carditis

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Acute glomerulonephritis

• immune complex disease of kidney

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Major pathogenesis factors

• lipoteichoic acid/F protein
• fimbriae
• binds to epithelial cells
• M protein
• anti-phagocytic

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S. pyogenes
lipoteichoic acid F-protein
fibronectin
epithelial cells
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M protein
IMMUNE
Complement
IgG
M protein
NON-IMMUNE
peptidoglycan
fibrinogen
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M protein

• major target
• natural immunity
• strain variation
• antigenicity
• re-infection
• occurs with different strain

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Capsules

• Anti-phagocytic
• mucoid strains

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Isolation and identification

• ß hemolytic colonies
• bacitracin inhibits growth
• ß hemolytic colonies
• group A antigen

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ß hemolysis

• Hemolysin/streptolysin O
• sensitive oxygen
• Hemolysin/streplysin S
• insensitive oxygen

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Modern Rapid Strep Test
Throat swab extract (/- streptococcal antigen)
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Antibody
Liposome
Streptococcal antigen
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Post-infectious diagnosis (serology)

• antibodies to streptolysin O
• important if delayed clinical sequelae occur

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Typing
Traditional serotyping of proteins - M - T - R
Current - Sequencing of M protein gene
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Group B streptococcus

• neonatal meningitis
• septicemia
• transmission
• vaginal flora

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Group B streptococcus - identification

• ß hemolysis
• hippurate hydrolysis
• CAMP reaction
• increases ß hemolysis of S. aureus

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Group D streptococcus

• Growth on bile esculin agar
• black precipitate
• 6.5 saline
• grow
• enterococci
• no growth
• non-enterococci

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Enterococci

• distantly related to other streptococci
• genus Enterococcus
• gut flora
• urinary tract infection
• fecal contamination
• opportunistic infections
• particularly endocarditis
• most common E. (S.) faecalis

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Enterococci

• resistant to many antibiotics
• including vancomycin
• terminal D-ala replaced by D-lactate

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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
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Viridans streptococci

• diverse species
• oral
• dental caries
• a hemolytic and negative for other tests
• non-groupable.
• includes S. mutans
• occassional endocarditis after tooth extraction