Medical Microbiology

164 3 GeneralBacteriology

MetabolicRegulation..................................

Bacteriaarehighlyefficientmetabolicregulators,coordinatingeachindivid-

ualreactionwithothercellactivitiesandwiththeavailablenutrientsaseco-

nomicallyandrationallyaspossible.Oneformsuchcontrolactivitytakesis

regulationoftheactivitiesofexistingenzymes.Manyenzymesareallosteric

proteinsthatcanbeinhibitedoractivatedbythefinalproductsofmetabolic

pathways.Onehighlyeconomicaltypeofregulationcontrolsthesynthesisof

enzymesatthegenetictranscriptionortranslationlevel(seethesectionon

themolecularbasisofbacterialgenetics(p. 1 69ff.).

GrowthandCulturingofBacteria........................

Nutrients...............................................

Thetermbacterialculturereferstoproliferationofbacteriawithasuitable

nutrientsubstrate.Anutrientmedium(Table3. 2 )inwhichchemoorgano-

trophsaretobecultivatedmusthaveorganicenergysources(H 2 donors)

andH 2 acceptors.Othernecessitiesincludesourcesofcarbonandnitrogen

forsynthesisofspecificbacterialcompoundsaswellasmineralssuchassul-

fur,phosphorus,calcium,magnesium,andtraceelementsasenzymeactiva-

tors.Somebacteriaalsorequire“growthfactors,”i.e.,organiccompounds

theyareunabletosynthesizethemselves.Dependingonthebacterialspecies

involved,thenutrientmediummustcontaincertainamountsofO 2 andCO 2

andhavecertainpHandosmoticpressurelevels.

Table3. 2 NutrientMediumsforCulturingBacteria

Nutrientmedium Description

Nutrientbroth Complexliquidnutrientmedium.

Nutrientagar Complexnutrientmediumcontainingthepolysaccharide

agarose(1.5– 2 %).Nutrientagarliquefieswhenheatedto

1008 Canddoesnotreturntothegelstateuntilcooledto

458 C.Agaroseisnotbrokendownbybacteria.

Selectivemediums Containinhibitorsubstancesthatallowonlycertainbacteria

toproliferate.

Indicatormediums Indicatecertainmetabolicprocesses.

Syntheticmediums Mediumsthatarepreciselychemicallydefined.

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Kayser, Medical Microbiology © 2005 Thieme