STREPTOCOCCI - medsyllabus.org · 2 Key Words • Lancefield groups • Hemolysis (alpha, beta,...
Transcript of STREPTOCOCCI - medsyllabus.org · 2 Key Words • Lancefield groups • Hemolysis (alpha, beta,...
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STREPTOCOCCI
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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
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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
• α (alpha)– partial hemolysis – green color
• β (beta) – complete clearing
• γ (gamma) - no lysis
White colonies
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Hemolysis
• Groups A an B –β
• Group D – α or γ
• S. pneumoniae and viridans –α
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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 agespeak 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• T cell mitogen • activates immune system
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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
fibronectin
lipoteichoic acidF-protein
epithelial cells
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M protein
M protein
fibrinogen
rrr
peptidoglycan
rrr
IgG
Complement IMMUNE
NON-IMMUNE
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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
• β hemolytic colonies – bacitracin inhibits growth
• β hemolytic colonies– group A antigen
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β hemolysis
• hemolysin O – sensitive oxygen
• hemolysin S– insensitive oxygen
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Modern Rapid “Strep” TestThroat swab extract (+/- streptococcal antigen)
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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Traditional serotyping of proteins:- M - T - R
Typing
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
• β hemolysis• hippurate hydrolysis• CAMP reaction
– increases β 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 streptococciVarious 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• α hemolytic and negative for other tests • non-groupable.• includes S. mutans
– occassional endocarditis after tooth extraction