NCBISkiptomaincontentSkiptonavigationResourcesHowToAboutNCBIAccesskeysMyNCBISignintoNCBISignOutTryoutPMCLabsandtelluswhatyouthink.LearnMore.JournalListClinMicrobiolRevv.22(1);2009JanPMC2620637ClinMicrobiolRev.2009Jan;22(1):161–182.doi: 10.1128/CMR.00036-08PMCID:PMC2620637PMID:19136439AmpCβ-LactamasesGeorgeA.Jacoby*GeorgeA.JacobyLaheyClinic,Burlington,MassachusettsFindarticlesbyGeorgeA.JacobyAuthorinformationCopyrightandLicenseinformationDisclaimerLaheyClinic,Burlington,Massachusetts*Mailingaddress:LaheyClinic,41MallRoad,Burlington,MA01805.Phone:(781)744-2928.Fax:(781)744-5486.E-mail:[email protected]©2009,AmericanSocietyforMicrobiologyThisarticlehasbeencitedbyotherarticlesinPMC.Summary:AmpCβ-lactamasesareclinicallyimportantcephalosporinasesencodedonthechromosomesofmanyoftheEnterobacteriaceaeandafewotherorganisms,wheretheymediateresistancetocephalothin,cefazolin,cefoxitin,mostpenicillins,andβ-lactamaseinhibitor-β-lactamcombinations.Inmanybacteria,AmpCenzymesareinducibleandcanbeexpressedathighlevelsbymutation.Overexpressionconfersresistancetobroad-spectrumcephalosporinsincludingcefotaxime,ceftazidime,andceftriaxoneandisaproblemespeciallyininfectionsduetoEnterobacteraerogenesandEnterobactercloacae,whereanisolateinitiallysusceptibletotheseagentsmaybecomeresistantupontherapy.TransmissibleplasmidshaveacquiredgenesforAmpCenzymes,whichconsequentlycannowappearinbacterialackingorpoorlyexpressingachromosomalblaAmpCgene,suchasEscherichiacoli,Klebsiellapneumoniae,andProteusmirabilis.Resistanceduetoplasmid-mediatedAmpCenzymesislesscommonthanextended-spectrumβ-lactamaseproductioninmostpartsoftheworldbutmaybebothhardertodetectandbroaderinspectrum.AmpCenzymesencodedbybothchromosomalandplasmidgenesarealsoevolvingtohydrolyzebroad-spectrumcephalosporinsmoreefficiently.TechniquestoidentifyAmpCβ-lactamase-producingisolatesareavailablebutarestillevolvingandarenotyetoptimizedfortheclinicallaboratory,whichprobablynowunderestimatesthisresistancemechanism.Carbapenemscanusuall