Medical Microbiology

198 3 GeneralBacteriology

Table3. 5 MechanismsofActionoftheMostImportantAnti-InfectiveAgents

Substancegroup Mechanism,activitysite

Sulfonamides Competitionwithp-aminobenzoicacidasasubstratefor

dihydroptericacidsynthetase,thustoolittletetrahydrofolic

acid

Trimethoprim Inhibitionofdihydrofolicacidreductase,thustoolittle

tetrahydrofolicacid

Betalactamantibiotics Disturbanceofmureinbiosynthesis:

—IrreversibleinhibitionofDD-transpeptidase,which

catalyzesthepeptidecrosslinkageinmurein

—Releaseofaninhibitorofautolyticmureinenzymes

—Enzymaticdestructionofmureinarchitecturewith

autolysins:“wrongplaceatthewrongtime”

—Lysisduetohighinternalosmoticpressure

Vancomycin

Teicoplanin

Fosfomycin

Bacitracin

Disturbanceofmureinbiosynthesisatvariousdifferent

molecularstages

Rifamycin Transcription:

BlockageofDNA-dependentRNApolymerase

Aminoglycosides Translation:

—Geneticcodeisnotreadcorrectly(miscoding)

—Blockageofe-type(elongationribosome)A-position

occupancybyAA-tRNA

Tetracyclines Translation:

—Blockageofe-type(elongationribosome)and

i-type(initiationribosome)A-positionoccupancy

byAA-tRNA

Chloramphenicol Translation:

Inhibitionofpeptidyltransferaseactivity

Macrolides,ketolides Translation:

Inhibitionofelongationofthepolypeptidechain

4-Quinolones InhibitionoftheDNAgyraseandtopoisomeraseIV

resultingintheinhibitionofDNAreplication

Polymyxins Cytoplasmicmembrane:Structuraldisruption

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Kayser, Medical Microbiology © 2005 Thieme