Medical Microbiology

StreptococcusandEnterococcus 237

Streptococcuspyogenes(AStreptococci).............

Morphologyandculturing.Gram-positivecocciwithadiameterof 1 lm

thatformchains(Fig.4.3a).Coloniesonbloodagar(Fig.4.3b)showb-hemo-

lysiscausedbystreptolysins(seebelow).

Finestructure.Themureinlayerofthecellwallisfollowedbythesero-

groupAcarbohydratelayer,whichconsistsofCsubstanceandiscovalently

boundtothemurein.Long,twistedproteinthreadsthatextendoutwardare

anchoredinthecellwallmurein:theMprotein.Astreptococciareclassified

inserovarswithcharacteristicMproteinchemistry.Likethehyaluronicacid

capsulesseeninsomestrains,theMproteinhasanantiphagocyticeffect.

StreptococcusPyogenes

Fig.4. 3 aGramstainingofpleural

puncture biopsy material:gram-

positivecocciintwistedchains.

bCultureonbloodagar:small,

whitish-gray colonies surrounded

bylargeb-hemolysiszones;a 5 %

CO 2 atmosphereprovidesoptimum

conditionsforb-hemolysis.

4

Kayser, Medical Microbiology © 2005 Thieme