Identification of cpxS mutational resistome in Pseudomonas aeruginosa

Pseudomonas aeruginosa easily produces drug-resistant mutants. A large number of mutational resistome genes exist in the genome of P. aeruginosa. In this study, whole genome sequencing analysis of a multidrug-resistant P. aeruginosa strain isolated by in vitro antibiotic treatment showed a mutation in the cpxS gene. Random mutagenesis of cpxS was conducted and introduced into the PA14 Delta cpxS strain. Numerous CpxS mutants, including 14 different single amino acid substitutions, were identified, which led to reduced antibiotic susceptibility. Moreover, some of them were also present in the published genomes of P. aeruginosa isolates. Around cpxS, a gene coding for a putative sensor kinase, the nearest gene coding for a response regulator is cpxR in the genome of P. aeruginosa. Deletion of cpxR restored antibiotic susceptibility in the above cpxS mutant strains. As an extension of our previous work, where the expression of the mexAB-oprM operon is directly activated by CpxR in P. aeruginosa, in this study, we showed that the expression of the mexA promoter was increased in the above cpxS mutant strains in a cpxR-dependent manner, and mexA is prerequisite for the reduced antibiotic susceptibility. Therefore, we propose that the putative sensor kinase CpxS, together with CpxR, comprises a two-component regulatory system regulating the expression of the mexAB-oprM operon in P. aeruginosa. Our work indicates that cpxS, as a novel member of mutational resistome, plays important roles on the development of multidrug resistance in P. aeruginosa.