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Streptococci (Gram Streptococci (Gram positive cocci)positive cocci)
Lecture 37Lecture 37Faculty: Dr. Alvin Fox
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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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• StreptococciStreptococci – facultative anaerobefacultative anaerobe– Gram-positiveGram-positive– usually chains (sometimes pairs) usually chains (sometimes pairs) – catalase negativecatalase negative
(staphylococci are catalase positive)(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 groupsIdentification : Lancefield groups- carbohydrate antigens- carbohydrate antigens
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groupable streptococci streptococci
• A, B and DA, B and D– frequentfrequent
• C, G, F C, G, F – less frequentless frequent
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Non-groupableNon-groupable
• S. pneumoniaeS. pneumoniae– pneumonia pneumonia
• viridans streptococciviridans streptococci– e.g.e.g. S. mutans S. mutans
*dental cariesdental caries
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hemolysis reaction - sheep blood agarhemolysis reaction - sheep blood agar
• α (alpha) (alpha)– partial hemolysis partial hemolysis – green colorgreen color
• β (beta) (beta) – complete clearingcomplete clearing
• γ (gamma) (gamma)
- - no lysisno lysis
White colonies
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HemolysisHemolysis
• Groups A an B Groups A an B – β
• Group D Group D – α or or γ
• S. pneumoniaeS. pneumoniae and viridans and viridans – α
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Identification: hemolysis reaction + one biochemical characteristic
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Group A streptococcus (Group A streptococcus (S. pyogenesS. pyogenes))
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Group A streptococcal infections affect all agesGroup A streptococcal infections affect all agespeak incidence at 5-15 years of agepeak incidence at 5-15 years of age
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S. pyogenes -suppurative. pyogenes -suppurative
• non-invasive non-invasive – pharyngitis pharyngitis – skin infection, impetigoskin infection, impetigo
• invasive bacteremia invasive bacteremia – toxic shock-like syndrome toxic shock-like syndrome – "flesh eating" bacteria"flesh eating" bacteria– pyrogenic toxinpyrogenic toxin
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Pyrogenic toxin• Superantigen Superantigen
• Non-specific activation of T cellsNon-specific activation of T cells
− Cross-link antigen presenting Cross-link antigen presenting cells (MHC) and T cell receptorcells (MHC) and T cell receptor
− Cytokine productionCytokine production
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Scarlet feverScarlet fever
• rash rash • “ “erythrogenic toxin”erythrogenic toxin”
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non-suppurative• rheumatic fever
– inflammatory diseaseinflammatory disease– life threateninglife threatening– chronic sequalaechronic sequalae
• fever fever • heart heart • jointsjoints
• rheumatic NOT rheumatoid arthritisrheumatic NOT rheumatoid arthritis
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Rheumatic fever -etiologyRheumatic fever -etiology
• M protein M protein – cross-reacts heart myosin cross-reacts heart myosin – autoimmunityautoimmunity
• Cell wall antigens Cell wall antigens – poorly digested poorly digested in vivoin vivo– persist indefinitelypersist indefinitely
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Rheumatic feverRheumatic fever
• penicillinpenicillin- terminates pharyngitisterminates pharyngitis
- decreases carditisdecreases carditis
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Acute glomerulonephritisAcute glomerulonephritis
• immune complex disease of kidneyimmune complex disease of kidney
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Major pathogenesis factorsMajor pathogenesis factors
• lipoteichoic acid/F proteinlipoteichoic acid/F protein– fimbriaefimbriae– binds to epithelial cells binds to epithelial cells
• M protein M protein – anti-phagocyticanti-phagocytic
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S. pyogenesS. pyogenes
fibronectinfibronectin
lipoteichoic acidlipoteichoic acidF-proteinF-protein
epithelial cellsepithelial cells
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M protein M protein
M proteinM protein
fibrinogenfibrinogen
rrr
peptidoglycanpeptidoglycan
rrr
IgGIgG
Complement Complement IMMUNEIMMUNE
NON-IMMUNENON-IMMUNE
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M proteinM protein
• major target major target – natural immunitynatural immunity
• strain variationstrain variation– antigenicityantigenicity
• re-infectionre-infection– occurs with different strainoccurs with different strain
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CapsulesCapsules
• Anti-phagocyticAnti-phagocytic– mucoid strainsmucoid strains
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Isolation and identificationIsolation and identification
• β hemolytic colonies hemolytic colonies – bacitracin inhibits growthbacitracin inhibits growth
• β hemolytic colonies hemolytic colonies– group A antigengroup A antigen
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β hemolysishemolysis
• Hemolysin/streptolysin O Hemolysin/streptolysin O – sensitive oxygensensitive oxygen
• Hemolysin/streplysin SHemolysin/streplysin S– insensitive oxygeninsensitive oxygen
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Modern Rapid “Strep” TestModern Rapid “Strep” TestThroat swab extract Throat swab extract (+/- streptococcal antigen)(+/- streptococcal antigen)
AntibodyAntibody
Liposome
++
-
Streptococcal antigenStreptococcal antigen
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Post-infectious diagnosis Post-infectious diagnosis (serology)(serology)
• antibodies to streptolysin O antibodies to streptolysin O • important if delayed clinical important if delayed clinical
sequelae occursequelae occur
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Traditional serotyping of Traditional serotyping of proteins:proteins:- M - M - T - T - R- R
TypingTyping
Current:Current:- Sequencing of M protein gene- Sequencing of M protein gene
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Group B streptococcusGroup B streptococcus
• neonatal meningitisneonatal meningitis
• septicemiasepticemia
• transmission transmission – vaginal floravaginal flora
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Group B streptococcus Group B streptococcus - identification- identification
• β hemolysishemolysis
• hippurate hydrolysishippurate hydrolysis
• CAMP reactionCAMP reaction
– increases increases β hemolysis of hemolysis of S. aureusS. aureus
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Group D streptococcusGroup D streptococcus• Growth on bile esculin agarGrowth on bile esculin agar
– black precipitate black precipitate
• 6.5% saline6.5% saline• growgrow
– enterococcienterococci• no growth no growth
– non-enterococcinon-enterococci
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EnterococciEnterococci
• distantly related to other streptococcidistantly related to other streptococci• genus genus EnterococcusEnterococcus • gut floragut flora
– urinary tract infection urinary tract infection • fecal contaminationfecal contamination
– opportunistic infectionsopportunistic infections• particularly endocarditisparticularly endocarditis
• most common most common E. (S.) faecalisE. (S.) faecalis
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EnterococciEnterococci
• resistant to many antibiotics resistant to many antibiotics – including vancomycinincluding vancomycin
• terminal D-ala replaced by D-lactate terminal D-ala replaced by D-lactate
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Minute colony streptococciMinute colony streptococciVarious groups/hemolysis (e.g. group A)Various groups/hemolysis (e.g. group A)
– genetically distinct genetically distinct from large colony (e.g. S. pyogenes)from large colony (e.g. S. pyogenes)– no rheumatic feverno rheumatic fever
Large colonyLarge colony Minute colonyMinute colony
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Viridans streptococciViridans streptococci• diverse species diverse species • oral oral • dental cariesdental caries• α hemolytic and negative for other tests hemolytic and negative for other tests • non-groupable.non-groupable.• includes includes S. mutansS. mutans
– occassional endocarditis after tooth extractionoccassional endocarditis after tooth extraction