?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.relation=http%3A%2F%2Fd-scholarship-dev.library.pitt.edu%2F36337%2F&rft.title=Identification+of+colistin+resistance+mechanisms+in+pmrC-%2C+pmrA-%2C+and+pmrB-deficient+Acinetobacter+baumannii&rft.creator=Mettus%2C+Roberta&rft.description=Acinetobacter+baumannii+is+a+menacing+nosocomial+pathogen+that+readily+develops+resistance+to+antibiotics.+Colistin%2C+a+polymyxin%2C+is+currently+the+last-line+choice+for+treating+infections+caused+by+multidrug-resistant+A.+baumannii.+This+cationic+peptide+is+attracted+to+the+negatively+charged+lipopolysaccharide+(LPS)+on+Gram-negative+bacterial+membranes+and+acts+by+destabilizing+and+permeabilizing+it.+Unfortunately%2C+there+is+a+disturbing+trend+of+strains+developing+resistance+to+colistin+in+recent+years.+A.+baumannii+is+known+to+modify+its+LPS+in+order+to+interrupt+the+initial+charge+interaction+with+colistin.+The+most+common+mechanism+implicated+in+this+resistance+strategy+is+the+upregulation+of+the+pmrAB+genes+encoding+a+two-component+regulatory+system%2C+which+in+turn+upregulates+pmrC+that+encodes+phosphoethanolamine+transferase.+PmrAB+have+also+been+shown+to+be+global+regulators+of+cellular+growth+processes+and+virulence.+Gain-of-function+mutations+in+pmrAB+are+the+most+commonly+reported+colistin+resistance+mechanism.+However%2C+it+is+not+known+if+and+how+A.+baumannii+strains+deficient+in+any+of+the+pmrCAB+genes+develop+colistin+resistance.+We+therefore+aim+to+determine+secondary+mechanisms+of+colistin+resistance+in+pmrCAB-deficient+strains.%0D%0A%09Using+A.+baumannii+strain+AB5075+and+inactivation+mutants+of+pmrC%2C+-A%2C+and+-B%2C+we+generated+genetically+stable+colistin-resistant+mutants+on+agar+containing+increasing+colistin+concentrations.+We+conducted+whole+genome+sequencing+to+identify+genetic+changes+responsible+for+colistin+resistance.+We+also+characterized+their+phenotypes%2C+including+resistance+profiles+to+Gram-positive+antimicrobials%2C+LPS+structure%2C+in+vitro+growth+fitness%2C+and+in+vivo+virulence+using+a+Galleria+mellonella+model.+%0D%0A%09Colistin-resistant+mutants+possessed+mutations+in+lpx+and+mla+genes%2C+which+are+involved+in+lipid+biosynthesis+and+membrane+composition%2C+respectively.+Most+mutants+were+susceptible+to+Gram-positive+antimicrobial+agents%2C+likely+resulting+from+severely+compromised+outer+membranes.+Furthermore%2C+colistin-resistant+mutants+displayed+reduced+fitness+in+vitro+and+decreased+virulence+in+vivo.%0D%0A%09A.+baumannii+is+adept+at+evading+colistin+by+modifying+its+membrane+structure%2C+even+outside+of+the+control+of+pmrCAB.+However%2C+mutations+that+disrupt+membrane+integrity+are+costly+and+unlikely+to+persist+in+clinical+settings.+Therefore%2C+colistin-resistant+mutants+with+such+mutations+seemingly+carry+low+public+health+significance.+Even+if+these+mutants+do+emerge+in+the+clinic%2C+various+Gram-positive+agents+can+be+included+as+treatment+options.&rft.date=2019-06-26&rft.type=University+of+Pittsburgh+ETD&rft.type=PeerReviewed&rft.format=application%2Fpdf&rft.language=en&rft.identifier=http%3A%2F%2Fd-scholarship-dev.library.pitt.edu%2F36337%2F1%2FMettusRoberta_MSThesis_4_2019.pdf&rft.identifier=++Mettus%2C+Roberta++(2019)+Identification+of+colistin+resistance+mechanisms+in+pmrC-%2C+pmrA-%2C+and+pmrB-deficient+Acinetobacter+baumannii.++Master's+Thesis%2C+University+of+Pittsburgh.++++(Unpublished)++