Polymyxin Resistance of Pseudomonas aeruginosa phoQ Mutants Is Dependent on Additional Two-Component Regulatory Systems

Abstract

e Pseudomonas aeruginosa can develop resistance to polymyxin as a consequence of mutations in the PhoPQ regulatory system, mediated by covalent lipid A modification. Transposon mutagenesis of a polymyxin-resistant phoQ mutant defined 41 novel loci required for resistance, including two regulatory systems, ColRS and CprRS. Deletion of the colRS genes, individually or in tandem, abrogated the polymyxin resistance of a ⌬phoQ mutant, as did individual or tandem deletion of cprRS. Individual deletion of colR or colS in a ⌬phoQ mutant also suppressed 4-amino-L-arabinose addition to lipid A, consistent with the known role of this modification in polymyxin resistance. Surprisingly, tandem deletion of colRS or cprRS in the ⌬phoQ mutant or individual deletion of cprR or cprS failed to suppress 4-amino-L-arabinose addition to lipid A, indicating that this modification alone is not sufficient for PhoPQ-mediated polymyxin resistance in P. aeruginosa. Episomal expression of colRS or cprRS in tandem or of cprR individually complemented the Pm resistance phenotype in the ⌬phoQ mutant, while episomal expression of colR, colS, or cprS individually did not. Highly polymyxin-resistant phoQ mutants of P. aeruginosa isolated from polymyxin-treated cystic fibrosis patients harbored mutant alleles of colRS and cprS; when expressed in a ⌬phoQ background, these mutant alleles enhanced polymyxin resistance. These results define ColRS and CprRS as two-component systems regulating polymyxin resistance in P. aeruginosa, indicate that addition of 4-amino-L-arabinose to lipid A is not the only PhoPQ-regulated biochemical mechanism required for resistance, and demonstrate that colRS and cprS mutations can contribute to high-level clinical resistance.

Irreproducible and Uninterpretable Polymyxin B MICs for Enterobacter cloacae and Enterobacter aerogenes

“…A third regulator, ParRS, has also been shown to be involved in adaptive resistance to polymyxins (18). More recently, two additional regulators (ColRS and CprRS) that are essential for PhoPQmediated peptide resistance have been identified (20,25). Adding to the complexity, ColRS and CprRS also appear to regulate polymyxin resistance outside of 4-amino-L-arabinose modification of lipid A.…”

“…Several two-component regulatory systems that control expression of the arn operon have been identified. Under the pressure of low-Mg conditions (19) or exposure to polymyxins (12,18,20,21), PhoPQ has been demonstrated to regulate expression of the arn operon. Similarly, PmrAB can also affect expression of the arn operon under low-cation conditions (22) or following exposure to polymyxins (12,18,22,23).…”

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

“…Mutations in this system cause constitutive expression of the pmrHFIJKLM operon and thus lead to the addition of L-Ara4N to the LPS, leading to colistin resistance. Additionally, mutations in the ColRS and CprRS two-component regulatory systems may also contribute to polymyxin resistance, since the association of mutations in the phoQ gene and mutations in the colS or cprS gene confers a high level of colistin resistance (172). The action of the ColRS and CprRS systems may occur through the activation of the phoQ gene and/or through other genes that have not yet been identified.…”