CpxR-CpxS two-component system exacerbates development of antibiotic resistance in Pseudomonas aeruginosa

Pseudomonas aeruginosa, as a member of the ESKAPE pathogens, is well known for its ability to develop multidrug resistance following antibiotic therapy. Overexpression of the efflux pumps, often caused by dysfunction of related transcriptional factors, is well known as a common mechanism underpins multidrug resistance. Previous work showed direct regulatory link of CpxR-CpxS, an OmpR-EnvZ family two-component system, with the expression of the predominant MexAB-OprM efflux pump in P. aeruginosa. However, the contribution of this regulatory link to the development of antibiotic resistance has not been fully elucidated. In this work, it has been shown that deletion of cpxR, but not cpxS, reduces the emergence of multidrug resistant colonies almost 1000 times lower compared to the parental wild type P. aeruginosa PA14 following sub-lethal antibiotic exposure, suggesting that apart from CpxS, other sensory component(s) or pathway(s) can also mediate CpxR activity in the development of antibiotic resistance in P. aeruginosa. We further demonstrate that when glucose is used as the sole carbon source, it leads to increased expression levels of mexA and reduced antibiotics susceptibilities in the PA14ΔcpxS strain in a cpxR dependent manner. GtrS, another EnvZ family sensor kinase, but not the well-known AckA-Pta pathway, mediates this glucose effects. Both in vivo and in vitro evidences support that GtrS can activate CpxR in a cross-talk manner in the absence of CpxS. Besides gtrS, at least four other sensor kinase genes (envZ, tctE, phoR and colS) can exert activation effect upon CpxR in the PA14ΔcpxS strain. Having the risk of multiple way to antibiotic resistance development, cpxS null mutations can be emerged in P. aeruginosa clinical isolates. Since many OmpR-EnvZ family two-component system have been shown to be engaged in antibiotic resistance, its potential risk of exacerbating antibiotic resistance in ESKAPE pathogens has been discussed.