Medical Microbiology

StreptococcusandEnterococcus 235

knownamongpneumococci,andisincreasing.Laboratorydiagnosisinvolves

pathogendetectionintheappropriatematerial.Personsathighriskcanbe

protectedfrompneumococcalinfectionswithanactiveprophylacticvaccine

containingpurifiedcapsularpolysaccharides.Certainoralstreptococciarere-

sponsiblefordentalcaries.Oralstreptococcialsocausehalfofallcasesofen-

docarditis.

Althoughenterococcishowonlylowlevelsofpathogenicity,theyfre-

quently cause nosocomial infections in immunocompromised patients

(usuallyaselementsofamixedflora). &

Streptococciareroundtooval,Gram-positive,nonmotile,nonsporingbacter-

iathatformwindingchains(streptos[greek]=twisted)ordiplococci.Theydo

notproducecatalase.Mostarecomponentsofthenormalfloraofthemucosa.

Somecancauseinfectionsinhumansandanimals.

Classification.ThegeneraStreptococcusandEnterococcuscomprisealarge

numberofspecies.Table4. 2 liststhemostimportant.

&a-,b-,c-hemolysis.

a-hemolysis.Coloniesonbloodagararesurroundedbyagreenzone.This

“greening”iscausedbyH 2 O 2 ,whichconvertshemoglobinintomethemoglo-

bin.

b-hemolysis.Coloniesonbloodagararesurroundedbyalarge,yellowish

hemolyticzoneinwhichnomoreintacterythrocytesarepresentandthe

hemoglobinisdecomposed.

c-hemolysis.This(illogical)termindicatestheabsenceofmacroscopically

visiblehemolyticzones.

&Lancefieldgroups.Manystreptococciandenterococcihaveapolymeric

carbohydrate(Csubstance)intheircellwallscalledtheLancefieldantigen.

TheyareclassifiedinLancefieldgroupsA-Vbasedonvariationsintheanti-

genicityofthisantigen.

Specificcharacteristicsofenterococcithatdifferentiatethemfromstrepto-

cocciincludetheirabilitytoproliferateinthepresenceof6.5%NaCl,at

458 CandatapHlevelof9.6.

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Kayser, Medical Microbiology © 2005 Thieme