title: PmrB mutations promote polymyxin resistance of Pseudomonas aeruginosa isolated from colistin-treated cystic fibrosis patients.
abstract: Pseudomonas aeruginosa can develop resistance to polymyxin and other cationic antimicrobial peptides. Previous work has shown that mutations in the PmrAB and PhoPQ regulatory systems can confer low to moderate levels of colistin (polymyxin E) resistance in laboratory strains and clinical isolates of this organism (MICs of 8 to 64 mg/liter). To explore the role of PmrAB in high-level clinical polymyxin resistance, P. aeruginosa isolates from chronically colistin-treated cystic fibrosis patients, most with colistin MICs of >512 mg/liter, were analyzed. These cystic fibrosis isolates contained probable gain-of-function pmrB alleles that conferred polymyxin resistance to strains with a wild-type or pmrAB deletion background. Double mutant pmrB alleles that contained mutations in both the periplasmic and dimerization-phosphotransferase domains markedly augmented polymyxin resistance. Expression of mutant pmrB alleles induced transcription from the promoter of the arnB operon and stimulated addition of 4-amino-l-arabinose to lipid A, consistent with the known role of this lipid A modification in polymyxin resistance. For some highly polymyxin-resistant clinical isolates, repeated passage without antibiotic selection pressure resulted in loss of resistance, suggesting that secondary suppressors occur at a relatively high frequency and account for the instability of this phenotype. These results indicate that pmrB gain-of-function mutations can contribute to high-level polymyxin resistance in clinical strains of P. aeruginosa.
authors: Department of Pediatrics, Massachusetts General Hospital, Boston, Massachusetts, USA. smoskowitz@partners.org
authors: Samuel M
authors: SM
authors: Moskowitz
authors: Mark K
authors: MK
authors: Brannon
authors: Nandini
authors: N
authors: Dasgupta
authors: Miyuki
authors: M
authors: Pier
authors: Nicole
authors: N
authors: Sgambati
authors: Amanda K
authors: AK
authors: Miller
authors: Sara E
authors: SE
authors: Selgrade
authors: Samuel I
authors: SI
authors: Miller
authors: Miles
authors: M
authors: Denton
authors: Steven P
authors: SP
authors: Conway
authors: Helle K
authors: HK
authors: Johansen
authors: Niels
authors: N
authors: Høiby
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D003091:Colistin / Q000494:pharmacology / Q000627:therapeutic use; D003550:Cystic Fibrosis / Q000188:drug therapy / Q000382:microbiology*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008826:Microbial Sensitivity Tests; D009154:Mutation; D011113:Polymyxins / Q000494:pharmacology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D014157:Transcription Factors / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C409039:PmrB protein, bacteria; D011113:Polymyxins; D014157:Transcription Factors; D003091:Colistin