Medical Microbiology

TheMorphologyandFineStructureofBacteria 157

unstablewhensubjectedtoosmoticinfluences.Theyaretotallyresistantto

betalactams,whichblockthebiosynthesisofmurein.Theclinicalsignificance

oftheL-formsisnotclear.Theymayreverttothenormalbacterialformwhen

betalactamtherapyisdiscontinued,resultinginarelapse.

Capsule................................................

Manypathogenicbacteriamakeuseofextracellularenzymestosynthesizea

polymerthatformsalayeraroundthecell:thecapsule.Thecapsuleprotects

bacterialcellsfromphagocytosis.Thecapsuleofmostbacteriaconsistsofa

polysaccharide.Thebacteriaofasinglespeciescanbeclassifiedindifferent

capsularserovars(orserotypes)basedonthefinechemicalstructureofthis

polysaccharide.

Flagella.................................................

Flagellagivebacteriatheabilitytomoveaboutactively.Theflagella(singular

flagellum)aremadeupofaclassoflinearproteinscalledflagellins.Flagel-

Bacterialflagella

Fig.3. 13 aFlagellatedbacterialcell(SEM, 13000 !).bHelicalstructureofbac-

terialflagella(SEM, 77000 !).

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Kayser, Medical Microbiology © 2005 Thieme