Medical Microbiology

4 BacteriaasHumanPathogens

F.H.Kayser

Staphylococcus

&StaphylococciareGram-positivecoccioccurringinclusters.Theycanbe

culturedonnormalnutrientmediumsbothaerobicallyandanaerobically.

Themostimportantspeciesfromtheviewpointofhumanmedicineis

S.aureus.Anumberofextracellularenzymesandexotoxinssuchascoa-

gulase,alphatoxin,leukocidin,exfoliatins,enterotoxins,andtoxicshocktoxin

areresponsiblefortheclinicalsymptomsofinfectionsbythispathogen,

whichareobservedinthethreetypesinvasiveinfections,puretoxicoses,

andmixedforms.Theantibioticsofchoicefortherapyoftheseinfections

arepenicillinase-resistantpenicillins.Laboratorydiagnosisinvolvesidentifi-

cationofthepathogenbymeansofmicroscopyandculturing.S.aureusis

afrequentpathogeninnosocomialinfectionsandlimitedoutbreaksinhos-

pitals.Handwashingbymedicalstaffisthemostimportantprophylactic

measureinhospitals.

Coagulase-negativestaphylococciareclassicopportunists.S.epidermidis

andotherspeciesarefrequentagentsinforeignbodyinfectionsduetotheir

abilitytoformbiofilmsonthesurfacesofinertobjects.S.saprophyticusis

responsibleforbetween 10 and 20 %ofacuteurinarytractinfectionsinyoung

women. &

Staphylococciaresmallsphericalcells(1lm)foundingrapelikeclusters.

Staphylococciarenonmotile,catalase-producingbacteria.ThegenusStaphy-

lococcusincludesover 30 speciesandsubspecies.Table4. 1 brieflysum-

marizesthecharacteristicsofthosemostimportantinthemedicalcontext.

S.aureus(andE.coli)areamongthemostfrequentcausalorganismsin

humanbacterialinfections.

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Kayser, Medical Microbiology © 2005 Thieme