Medical Microbiology

214 3 GeneralBacteriology

colorofsinglecolonies.Thespecialproliferationformsobservedinnutrient

brothandnutrientagargiveanexperiencedbacteriologistsufficientinforma-

tionforaninitialclassificationofthepathogensothatidentifyingreactions

canthenbetestedwithsomedegreeofspecificity.

Conditionsrequiredforgrowth.Theoptimumproliferationtemperaturefor

mosthumanpathogenbacteriais 378 C.

Bacteriaaregenerallyculturedunderatmosphericconditions.Itoften

provesnecessarytoincubatetheculturesin 5 %CO 2 .Obligateanaerobes

mustbeculturedinamilieuwithalowredoxpotential.Thiscanbeachieved

byaddingsuitablereductionagentstothenutrientbrothorbyproliferating

theculturesunderagasatmospherefromwhichmostoftheoxygenhasbeen

removedbyphysical,chemical,orbiologicalmeans.

IdentificationofBacteria..................................

Theessentialprincipleofbacterialidentificationistoassignanunknown

culturetoitsplacewithinthetaxonomicclassificationsystembasedonas

fewcharacteristicsaspossibleandasmanyasnecessary(Table3. 8 ).

&Morphologicalcharacteristics,includingstaining,aredeterminedunder

themicroscope.

&Physiologicalcharacteristicsaredeterminedwithindicatormediums.

Commerciallyavailableminiaturizedsystemsarenowfrequentlyusedfor

thispurpose(Fig.3. 36 ).

DeterminationofMetabolicCharacteristicswithIndicatorMediums

Fig.3. 36 IdentificationofEnterobacteriaceaeusingAPI20E,astandardizedmicro-

platemethod.Positiveandnegativereactionsareshownbycolorreactions.

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Kayser, Medical Microbiology © 2005 Thieme