Medical Microbiology

TheMorphologyandFineStructureofBacteria 159

ExamplesofMedicallyImportantBiofilms

&Followingimplantationofendoprostheses,catheters, cardiacpacemakers,

shuntvalves,etc.theseforeignbodiesarecoveredbymatrixproteinsofthemacro-

organismsuchasfibrinogen,fibronectin,vitronectin,orlaminin.Staphylococci

haveproteinsontheirsurfaceswithwhichtheycanbindspecificallytothecorre-

spondingproteins,forexampletheclumpingfactorthatbindstofibrinogenandthe

fibronectin-bindingprotein.Theadheringbacteriathenproliferateandsecretean

exopolysaccharideglycocalyx:thebiofilmmatrixontheforeignbody.Suchbiofilms

representforeignbody-associatedinfectionfoci.

&Certainoralstreptococci(S.mutans)bindtotheproteinscoveringtoothenamel,

thenproceedtobuildaglucanmatrixoutofsucrose.Otherbacteriathenadhereto

thematrixtoformplaque(Fig.3. 14 ),thepreconditionfordestructionoftheenamel

andformationofcaries(seep. 2 43f.).

&Oralstreptococciandotherbacteriaattachtothesurfaceofthecardiacvalvesto

formabiofilm.Professionalphagocytesareattractedtothesiteandattempt,un-

successfully,tophagocytizethebacteria.Thefrustratedphagocytesthenrelease

thetissue-damagingcontentoftheirlysosomes(seep.23),resultinginaninflam-

matoryreactionandtheclinicalpictureofendocarditis.

BacterialSpores........................................

Bacterialspores(endospores)arepurelydormantlifeforms.Theirdevelop-

mentfrombacterialcellsina“vegetative”statedoesnotinvolveassimilation

ofadditionalexternalnutrients.Theyaresphericaltoovalinshapeandare

characterizedbyathicksporewallandahighlevelofresistancetochemical

andphysicalnoxae.Amonghumanpathogenbacteria,onlythegeneraClos-

tridiumandBacillusproducespores.Theheatresistanceofthesesporesis

theirmostimportantqualityfromamedicalpointofview,sinceheatster-

DentalPlaque

Fig.3. 14 Dentalplaquecan

berenderedvisiblewithan

erythrosinstain.

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Kayser, Medical Microbiology © 2005 Thieme