The Article Adaptive and mutational responses to peptide dendrimer antimicrobials in Pseudomonas aeruginosa was published in Antimicrobial Agents and Chemotherapy.

Colistin (polymyxin E) is a last resort antibiotic against multidrug-resistant isolates of Pseudomonas aeruginosa. However, the nephro-toxicity of colistin limits its use, spurring the interest in novel antimicrobial peptides (AMP). Here we show that the synthetic dendrimer AMPs G3KL (MW 4531.38, 15 positive charges, MIC = 8 mg/L) showed faster killing than polymyxin B (Pmx-B) and no detectable resistance selection in P. aeruginosa strain PA14. Spontaneous mutants selected on Pmx-B, harboring loss of function mutations in the PhoQ sensor kinase gene, showed increased Pmx-B MICs and arnB operon expression (4-amino-L-arabinose addition to lipid A), but remained susceptible to dendrimers. Two mutants carrying a missense mutation in the periplasmic loop of the PmrB sensor kinase showed increased MICs for Pmx-B (8-fold) and G3KL (4-fold) but not for the dendrimer T7 (MW 4885.64, 16 positive charges, MIC = 8 mg/L). The pmrB mutants showed increased expression of the arnB as well as of the speD2-speE2-PA4775 operon, located upstream of pmrAB, and involved in polyamine biosynthesis. Exogenous supplementation with the polyamines spermine and norspermine increased G3KL and T7 MICs in a phoQ mutant background but not in the PA14 wild-type. This suggests that both addition of 4-amino-L-arabinose and secretion of polyamines are required to reduce susceptibility to dendrimers, probably neutralizing the negative charges present on the lipid A and the KDO sugars of the LPS, respectively. We further show by transcriptome analysis that the dendrimers G3KL and T7 induce adaptive responses through the CprRS two-component system in PA14.

Author(s): Fatma Ben Jeddou, Léna Falconnet, Alexandre Luscher, Thissa Siriwardena, Jean-Louis Reymond, Christian van Delden, Thilo Köhler