A copper-activated two-component system interacts with zinc and imipenem resistance in Pseudomonas aeruginosa

Department of Botany and Plant Biology, Sciences III, and Department of Microbiology and Molecular Medicine, Centre Médical Universitaire, University of Geneva, Switzerland

^* To whom correspondence should be addressed. Email: karl.perron{at}medecine.unige.ch.

	Abstract

The effects of copper (Cu) on trace metal and antibiotic resistance of Pseudomonas aeruginosa have been investigated. Cu treatments induced not only resistance to this metal but also, surprisingly, to zinc (Zn). Quantitative RT-PCR (qRT-PCR) revealed that after Cu treatment the transcription of the czcRS two-component system (TCS) operon was enhanced as well as that of the czcCBA operon encoding an efflux pump specific for zinc, cadmium, and cobalt. Cu treatments at the same time caused a decrease in the production of OprD porin resulting in resistance to the carbapenem antibiotic imipenem. The CzcR regulator was known to repress oprD. However Cu was still able to decrease the production of OprD and induce imipenem resistance in a czcRS knock-out mutant. This strongly suggested that another Cu-dependent regulatory system was acting negatively on oprD expression. TCS regulator genes copR-copS have been shown to be involved in Cu tolerance in P. aeruginosa. qRT-PCR showed that overproduction of the CopR or of the CzcR regulators resulted in increased transcription of the czcC gene as well as in a decrease in oprD gene transcription, either in the wild type strain or in the czcRS knock-out mutant. Overproduction experiments suggest that a metal-dependent mechanism operates at the posttranscriptional level to control the production of the CzcCBA efflux pump. This study shows that CopR is a new negative regulator of OprD porin and that it links Zn, Cu, and imipenem resistances by interacting with the CzcRS TCS.