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.

New Amphiphilic Neamine Derivatives Active against Resistant Pseudomonas aeruginosa and Their Interactions with Lipopolysaccharides

“…Its expression is regulated by at least four two-component regulatory systems (PmrAB, PhoPQ, ParRS, and CprRS) (45,46). Since mutations in the genes phoQ, pmrB, parS, parR, colS, cprS, and cprR were previously identified to contribute to polymyxin resistance in P. aeruginosa clinical strains, we amplified and sequenced them in the four CF clinical strains selected (45)(46)(47). Sequences analysis (Table 2) revealed that all the strains harbored the amino acid substitution Tyr345His in the PmrB protein, which was also identified in many susceptible strains, such as strains PA14, PACS2 2192, and C3719.…”

Polymyxins: Antibacterial Activity, Susceptibility Testing, and Resistance Mechanisms Encoded by Plasmids or Chromosomes

“…The colistin resistance in P. aeruginosa is mediated by five two-component systems that regulate LPS modifications. As for the Enterobacteriaceae, alterations in the PmrAB (74,118,(166)(167)(168)(169) and PhoPQ (118,166,168,170) twocomponent systems have been shown to be responsible for acquired resistance to colistin. Mutations in these two-component systems cause constitutive alterations and consequently activate transcription of the pmrHFIJKLM operon and the subsequent addition of L-Ara4N to the LPS, finally leading to colistin resistance.…”

From Pigs to Patients: Transmissible, Single Gene-mediated Resistance to Colistin

“…Of interest, this experiment shows that in the absence of colistin, the mcr-1+ strain has a slight fitness defect [3]. Whether this is due to the mcr-1 gene itself or other genetic elements on pHNSHP45 is unknown, but it has been well documented that regulatory changes associated with colistin resistance often reduce the fitness of the organism containing those mutations in the absence of selection [6,7,16,17]. This suggests that removing the use of colistin may have the added benefit of selecting against the long-term survival of resistant isolates because of their reduced fitness relative to sensitive strains.…”

“…These additions reduce the negative charge and limit antimicrobial peptide binding and membrane disruption [4,5]. The emergence of clinical resistance to colistin is due to point mutations in regulatory proteins that control the genes responsible for these additions, PhoPQ and/or PmrAB (and MgrB in K. pneumoniae) and were transmitted only vertically [6][7][8][9]. These data suggest that contrary to a common argument put forward by those developing novel antimicrobial peptides, resistance to this antibiotic class is common and now transmissable as single gene determinants.…”