streptococcus-160915064756 (1).pdf

Bsc nursing Microbiology

1. STREPTOCOCCUS
Mrs.JincyEalias
M.Sc. (N)
Asst. Professor
Mr. BinuBabu
MBA, M.Sc. (N)
Asst. Professor

2. StreptococciisGram-positivespherical/ovoid
cocciarrangedinlongchains;commonlyinpairs.
•Classificationofstreptococciincludes;
Classificationsystemisbasedonhemolysis
reactions.
•β-hemolytic–A,B,C,DandG(S.
pyogenes)
•α-hemolytic–S.pneumoniaeandviridans
•γ–hemolytic–S.faecalis
Lancefieldclassificationofb-hemolytic
streptococcibasedonpresenceof
carbohydrateantigenincellwall–17groups
(A,B,C,….)

4. Human Streptococcal Pathogens
•S. Pyogenes
•S. Viridans
•S. Pneumoniae
•S. Faecalis

5. General Characteristics of Streptococci
•Gram-positivespherical/ovoidcocciarranged
inlongchains;commonlyinpairs.
•Non-spore-forming,nonmotile.
•Canformcapsules
•Facultativeanaerobes
•Mostparasiticformsarefastidiousandrequire
enrichedmedia.
•Small,nonpigmentedcolonies.
•Sensitivetodrying,heat,anddisinfectants.

6. S. Pyogenes
•Mostseriousstreptococcalpathogen.Itaparasite
andinhabitsthroat,nasopharynx,occasionally
skin.
Morphology
•Gram-positive
•Spherical/ovoidcocciarrangedinlongchains.
•Nonmotile.
•Canformcapsules.

7. Culturalcharacteristics
•Facultativeanaerobes.
•BestgrowthachievedatpH7.4-7.6and
temperature37⁰C.
•Requiredenrichedmediaforgrowth.
•Coloniesarearound1mmindiameter,
surroundedbyazoneofclearhemolysis,semi
transparentandvaryinappearance.

8. Biochemicalproperties
•Producesmanyvirulencefactors.i.eproduction
ofenzymesandtoxins.

9. VirulencefactorsofS.Pyogenes
Enzymes:
•Streptokinase–digestsfibrinclots
•Hyaluronidase–breaksdownconnectivetissue
•DNase–hydrolyzesDNA
Toxins:
•Streptolysins(hemolysins):-streptolysinO(SLO)
andstreptolysinS(SLS)–bothcausecellandtissue
injury.
•Erythrogenictoxin(pyrogenic):-Inducesfeverand
typicalredrash.
•Superantigens:-Strongmonocyteandlymphocyte
stimulants;causethereleaseoftissuenecrotic
factor.

10. Pathogenesis
•Humansaretheonlyreservoir.
•Inapparentcarriers.(visiblecarriersoftoxinsand
enzyme)
•Transmissionisthroughcontact,droplets,food,
fomites
•Portalofentryisgenerallythroughskinor
pharynx.
•Childrenarepredominantgroupaffectedfor
cutaneousandthroatinfections
•Systemicinfectionsandprogressivediseasesmay
occurifuntreated.

11. S.pyogenesdiseases
•Impetigo(pyoderma)-Itisaskininfection
withsuperficiallesionsthatbreakandform
highlycontagiouscrust.
•Throatinfections
•Rheumaticfever–Ithassubclinical
pharyngitisinchildren;carditiswith
extensiveheartvalvedamagepossible,
arthritis,chorea,fever.
•Acuteglomerulonephritis–Itisthe
inflammationofthenephrons.

12. Impetigo
Pharngitis

13. Laboratory diagnosis
•S.pyogenesisfrequentlyisolatedfrom
samplessuchasskin,throat,sputum,urine,
andblood.
•Differentmethodsforlaboratorydiagnosis
ofS.pyogenesare:
Gramstaining
Culture
Catalasetest

14. Gramstaining
Thediagnosisissuggestedbythefinding
ofgrampositivebacteriacocciinchainsinthe
sample.
Culture
Theorganismisculturedonblood
agarwithanaddedbacitracinantibioticdisk
toshowbeta-hemolyticcoloniesand
sensitivity(zoneofinhibitionaroundthedisk)
fortheantibiotic.

15. Catalasetest
Transferasmallamountofbacterialcolonyto
asurfaceofclean,dryglassslideusingaloopor
sterilewoodenstick.Placeadropof3%H
2O
2onto
theslideandmix.
Apositiveresultistherapidevolutionof
oxygen(within5-10sec.)asevidencedbybubbling.
Anegativeresultisnobubblesoronlyafew
scatteredbubbles.S.Pyogenesarecatalasenegative.

16. Treatment
•S. Pyogenesinfections are treated with
penicillin
•Erythromycin is recommended for
patients who are allergic to penicillin.

17. Prevention
•Long-termpenicillinprophylaxisforpeople
withahistoryofrheumaticfeveror
recurrentstrepthroat.
•S.Pyogenesinfectionsarebestprevented
througheffectivehandhygiene.

18. STREPTOCOCCUS PNEUMONIAE
Thesearecommonlyseeninnasopharynxof
healthypersons.Itwillnotcauseanyillnessitself
unlessaviralinfectionorotherfactorsprovokes.
Morphology
•Theyaregrampositivecocci.
•Measures0.5–1.25µm
•Nonmotileandnonsporing
•Capsulated
•Small,oval-shapedcellsarrangedinpairsand
shortchains.

19. Cultural characteristics
•Culture requires blood or chocolate agar.
•Growth improved by 5-10% CO
2.
•Facultative anaerobes.
•Bestgrowthachievedtemperature25-40⁰C.
•Colonies are surrounded by greenish hemolysis
under aerobic conditions and clear under
anaerobic conditions.

20. Biochemical properties
•No significant toxin is produced in
pneumococci.
•Presence of some of the extra cellular products
–Haemolysin
–ImmunoglobilinA1 protease
–Neuraminidase
–Hyaluronidase
•Lack catalase and peroxidases.
•Ferment glucose, lactose and sucrose with
production of acid.

21. Pathogenesis
•5-50%ofallpeoplecarryitasnormalflorainthe
nasopharynx.
•Youngchildren,elderly,immunecompromised,
thosewithotherlungdiseasesorviralinfections,
areatrisk.
•Pneumococcimultiplyandinducean
inflammatoryresponse.
•Gainsaccesstomiddleearbywayofeustachian
tube.

22. Pneumococcidiseases
•Pneumonia:infectionoflungparenchyma.
•Otitismedia:infectionofmiddleear

23. Laboratory diagnosis
•S.Pneumococciisfrequentlyisolated
fromsamplessuchassputum,blood,
wound,CSF.
•Differentmethodsforlaboratory
diagnosisofS.Pneumococciare:
Gramstaining
Quellungtest
Culture
Catalasetest

24. Gram staining
The diagnosis is suggested by the finding of gram
positive bacteria cocciarranged in pairs and short chains
in the sample.
Quellungtest
The characteristic capsule can be best detected
using the Quellungtest. In this test, application of
antiserum followed by staining with India ink causes the
capsule to appear like a halo around the organism. The
capsule is also visible in smears stained with methylene
blue.

25. Culture
Theorganismisculturedonbloodagaror
chocolateagarwithincubationinanenvironmentof
carbondioxide.
Theorganismisculturedonbloodagarwith
anadded optochindisktoshowalpha-
hemolyticcolonies.
Catalasetest
S.pneumococciiscatalasenegative.

26. TreatmentandPrevention
•TraditionallytreatedwithpenicillinG
orV.
•Broadspectrumantibioticsare
recommendedforpatientswhoare
allergictopenicillin.
•Twovaccinesavailableforhighrisk
individuals:
–Capsularantigenvaccineforolderadultsand
otherhighriskindividuals–effective5years.
–Conjugatevaccineforchildren2to23months.

27. S. Viridans
•Itisalphahaemolyticstreptococci.
•Itisovalinshapeandfoundinshortchains.
•Ithassixspeciesgroups(viridansgroup);
S.mutans,S.oralis,S.salivarus,
S.sanguis,S.milleri,S.mitis
•Foundingumsandteeth,oralcavity,andalsoin
nasopharynx,genitaltract,skin.
•Notveryinvasive;dentalorsurgicalprocedures
facilitateentrance.
•Itcausesdentalcaries,sepsisandendocarditis.
•Personswithpreexistingheartconditionsshould
receiveprophylacticantibioticsbeforesurgeryor
dentalprocedures.

28. S. Faecalis
•Itisalsoknownasenterococci.
•ItisaGram-positive
•Ovalcocciinpairsorshortchains.
•IdentifiedinMaConkeyagar.Coloniesaremagentain
colorandpinpoint.
•Itcangrowintherangeof10to45°Candsurviveat
temperaturesof60°Cfor30min.
•Itisnon-motile,facultativeanaerobicmicrobe.
•Itfermentsglucoseanddoesnotproduceacatalase.
•Itisassociatedwithurinarytractinfections,biliarytract
infections,septicemia,endocarditisandintraabdominal
abscess.
•Aminogycosidesaredrugofchoice.