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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