Medical Microbiology

StreptococcusandEnterococcus 241

Diagnosis.Thelaboratorydiagnosisincludesdetectionofthepathogenin

appropriatetestsamplesbymeansofmicroscopyandculturing.Pneumococ-

cicanbedifferentiatedfromothera-hemolyticstreptococcibasedontheir

greatersensitivitytooptochin(ethylhydrocupreinhydrochloride)inthe

disktestortheirbilesolubility.Bilesaltsincreaseautolysisinpneumococci.

Therapy.Penicillinisstilltheantibioticofchoice.Therehavebeenreportsof

high-frequencyoccurrenceofstrainsresistanttopenicillin(SouthAfrica,

Spain,Hungary,USA).ThesestrainsarestillrelativelyrareinGermany,Swit-

zerland,andAustria(5– 10 %).Macrolideantibioticsareanalternativetopen-

icillins,butresistancetothemisalsopossible.

Penicillinresistanceisnotduetopenicillinase,butrathertomodifiedpen-

icillin-bindingproteins(PBPs)towhichpenicillinshavealowerlevelofaffi-

nity.PBPsarerequiredformureinbiosynthesis.Biochemically,penicillinre-

Streptococcuspneumoniae

Fig.4. 5 aGramstainingofapre-

parationofmiddleearsecretion:

gram-positive,round-oval,encap-

sulated cocci; clinical diagnosis:

otitismedia.

bCultureonbloodagar:graycolo-

niesshowinglittleintrinsiccolor,

oftenmucoid(duetocapsules);

azoneofgreeningisoftenob-

servedaroundthecolonies,caused

bya-hemolysis;theshinyappear-

anceofthecoloniesiscausedby

lightreflectionsfromtheirmucoid

surface.

4

Kayser, Medical Microbiology © 2005 Thieme