Medical Microbiology

230 4 BacteriaasHumanPathogens

Staphylococcusaureus................................

Morphologyandculturing.Fig.4.1ashowstheappearanceofGram-stained

S.aureus.Thisisafacultativeanaerobethatisreadilyculturedonnormal

nutrientmediumsat 378 C.ColoniesasinFig.4.1bdevelopafter 24 hours

ofincubation.Hemolyticzonesarefrequentlyobservedaroundthecolonies.

Finestructure.Thecellwallconsistsofathicklayerofmurein.Linearteichoic

acidsandpolysaccharidesarecovalentlycoupledtothemureinpolysacchar-

ide(Fig.3. 10 ,p. 1 54).Thelipoteichoicacidspermeatingtheentiremurein

layerareanchoredinthecellmembrane.Teichoicandlipoteichoicacids

cantriggeractivationofcomplementbythealternativepathwayandstimu-

latemacrophagestosecretecytokines.Cellwall-associatedproteinsare

boundtothepeptidecomponentsofthemurein.Clumpingfactor,fibronec-

tin-bindingprotein,andcollagen-bindingproteinbindspecificallytofibrino-

gen,fibronectin,andcollagen,respectively,andareinstrumentalinadhesion

totissuesandforeignbodiescoveredwiththeappropriatematrixprotein.

ProteinAbindstotheFcportionofimmunoglobulins(IgG).Itisassumed

that“false”bindingofimmunoglobulinsbyproteinAprevents“correct”

bindingofopsonizingantibodies,thushinderingphagocytosis.

Table4. 1 OverviewoftheStaphylococcusSpeciesThatAffectHumansMost

Frequently

Species Parameter

S.aureus Coagulase-positive;coloniesgoldenyellow.Localpurulent

infections:furuncles,carbuncles,bullousimpetigo,wound

infections,sinusitis,otitismedia,mastitispuerperalis,ostitis,

postinfluenzapneumonia,sepsis.Toxin-causedillnesses:food

poisoning,dermatitisexfoliativa,toxicshocksyndrome

S.epidermidis Coagulase-negative;sensitivetonovobiocin;mostfrequentCNS*

pathogen;opportunist;infectionrequireshostpredisposition;

foreignbodyinfectionswithdiscreteclinicalsymptoms

S.saprophyticus Coagulase-negative;resistanttonovobiocin.Urinarytract

infectionsinyoungwomen(1 0 – 20 %);occasionalnonspecific

urethritisinmen

*CNS:coagulase-negativestaphylococci

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Kayser, Medical Microbiology © 2005 Thieme