Medical Microbiology

246 4 BacteriaasHumanPathogens

Clostridium........................................................

&Clostridiaare 3 – 8 lmlong,thick,Gram-positive,sporingrodbacteriathat

canonlybeculturedanaerobically.Theirnaturalhabitatisthesoil.Thepatho-

genicityofthedisease-causingspeciesinthisgenusisduetoproductionof

exotoxinsand/orexoenzymes.Themostfrequentcausativeorganismin

anaerobiccellulitisandgasgangrene(clostridialmyonecrosis)isC.perfrin-

gens.TetanusiscausedbyC.tetani.Thispathogenproducestheexotoxinte-

tanospasmin,whichblockstransmissionofinhibitoryCNSimpulsestomotor

neurons.BotulismisatypeoffoodpoisoningcausedbytheneurotoxinsofC.

botulinum.Thesesubstancesinhibitstimulustransmissiontothemotorend

plates.PseudomembranouscolitisiscausedbyC.difficile,whichproduces

anenterotoxin(A)andacytotoxin(B).Diagnosisofclostridialinfectionsre-

quiresidentificationofthepathogen(gasgangrene)and/orthetoxins(teta-

nus,botulism,colitis).AllclostridiaarereadilysensitivetopenicillinG.Anti-

toxinsareusedintherapyoftetanusandbotulismandhyperbaricO 2 isused

totreatgasgangrene.Themostimportantpreventivemeasureagainstteta-

nusisactivevaccinationwithtetanustoxoid. &

Occurrence.Clostridiaaresporingbacteriathatnaturallyinhabitthesoiland

theintestinaltractsofhumansandanimals.Manyspeciesareapathogenic

saprophytes.Undercertainconditions,severalspeciescausegasgangrene,

tetanus,botulism,andpseudomembranouscolitis.

Morphologyandculturing.Allclostridiaarelarge,Gram-positiverodbacte-

riaabout 1 lmthickand 3 – 8 lminlength(Fig.4. 7 ).Manycellsinoldercul-

turesshowaGram-negativereaction.WiththeexceptionofC.perfringens,

clostridiaareflagellated.Clostridiasporulate.Theyarebestculturedinan

anaerobicatmosphereat 378 C.C.perfringenscoloniesareconvex,smooth,

andsurroundedbyahemolyticzone.Coloniesofmotileclostridiahavean

irregular,raggededge.

ThePathogensThatCauseGasGangrene

(ClostridialMyonecrosis)andAnaerobicCellulitis

Pathogenspectrum.Thepathogensthatcausetheseclinicalpicturesinclude

Clostridiumperfringens,C.novyi,C.septicum,andC.histolyticum.Speciesob-

servedlessfrequentlyincludeC.sporogenes,C.sordellii,andC.bifermentans.

ThemostfrequentcausativepathogeningasgangreneisC.perfringens.

Toxins,enzymes.Thetoxinsproducedbyinvasiveclostridiashownecro-

tizing,hemolytic,and/orlethalactivity.Theyalsoproducecollagenases,

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Kayser, Medical Microbiology © 2005 Thieme