Pseudomonas aeruginosa High-Level Resistance to Polymyxins and Other Antimicrobial Peptides RequirescprA, a Gene That Is Disrupted in the PAO1 Strain

Abstract

ABSTRACTThearnlocus, found in many Gram-negative bacterial pathogens, mediates resistance to polymyxins and other cationic antimicrobial peptides through 4-amino-l-arabinose modification of the lipid A moiety of lipopolysaccharide. InPseudomonas aeruginosa, several two-component regulatory systems (TCSs) control thearnlocus, which is necessary but not sufficient for these resistance phenotypes. A previous transposon mutagenesis screen to identify additional polymyxin resistance genes that these systems regulate implicated an open reading frame designated PA1559 in the genome of theP. aeruginosaPAO1 strain. Resequencing of this chromosomal region and bioinformatics analysis for a variety ofP. aeruginosastrains revealed that in the sequenced PAO1 strain, a guanine deletion at the end of PA1559 results in a frameshift and truncation of a full-length open reading frame that also encompasses PA1560 in non-PAO1 strains, such asP. aeruginosaPAK. Deletion analysis in the PAK strain showed that this full-length open reading frame, designatedcprA, is necessary for polymyxin resistance conferred by activating mutations in the PhoPQ, PmrAB, and CprRS TCSs. ThecprAgene was also required for PmrAB-mediated resistance to other cationic antimicrobial peptides in the PAK strain. Repair of the mutatedcprAallele in the PAO1 strain restored polymyxin resistance conferred by an activating TCS mutation. The deletion ofcprAdid not affect thearn-mediated lipid A modification, indicating that the CprA protein is necessary for a different aspect of polymyxin resistance. This protein has a domain structure with a strong similarity to the extended short-chain dehydrogenase/reductase family that comprises isomerases, lyases, and oxidoreductases. These results suggest a new avenue through which to pursue targeted inhibition of polymyxin resistance.