Medical Microbiology

160 3 GeneralBacteriology

ilizationproceduresrequireveryhightemperaturestokillthemeffectively.

Potentialcontributingfactorstosporeheatresistanceincludetheirthickwall

structures,thedehydrationofthespore,andcrosslinkingoftheproteinsby

thecalciumsaltofpyridine-2,6-dicarboxylicacid,bothofwhichrenderpro-

teindenaturingdifficult.Whenaspore’smilieuonceagainprovidesfavorable

conditions(nutrientmedium,temperature,osmoticpressure,etc.)itreturns

tothevegetativestateinwhichspore-formingbacteriacanreproduce.

ThePhysiologyofMetabolismandGrowthinBacteria............

&Humanpathogenic bacteria are chemosyntheticand organotrophic

(chemo-organotrophic).Theyderiveenergyfromthebreakdownoforganic

nutrientsandusethischemicalenergybothforresynthesisandsecondary

activities.Bacteriaoxidizenutrientsubstratesbymeansofeitherrespiration

orfermentation.Inrespiration,O 2 istheelectronandprotonacceptor,infer-

mentationanorganicmoleculeperformsthisfunction.Humanpathogenic

bacteriaareclassifiedintermsoftheirO 2 requirementsandtoleranceasfa-

cultativeanaerobes,obligateaerobes,obligateanaerobes,oraerotolerant

anaerobes.Nutrientbrothoragarisusedtocultivatebacteria.Nutrient

agarcontainstheinertsubstrateagarose,whichliquefiesat 1008 Cand

gelsat 458 C.Selectiveandindicatormediumsareusedfrequentlyindiagnos-

ticbacteriology.

Bacteriareproducebymeansofsimpletransversebinaryfission.Thetime

requiredforcompletecelldivisioniscalledgenerationtime.Thein-vitrogen-

erationtimeofrapidlyproliferatingspeciesis 15 – 30 minutes.Thistimeis

muchlongerinvivo.Thegrowthcurveforproliferationinnutrientbroth

isnormallycharacterizedbythephaseslag,log(orexponential)growth,sta-

tionarygrowth,anddeath. &

BacterialMetabolism......................................

TypesofMetabolism..................................

Metabolismisthetotalityofchemicalreactionsoccurringinbacterialcells.

Theycanbesubdividedintoanabolic(synthetic)reactionsthatconsumeen-

ergyandcatabolicreactionsthatsupplyenergy.Intheanabolic,endergonic

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Kayser, Medical Microbiology © 2005 Thieme