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Involvement of AmgRS in the induction of Pseudomonas aeruginosa MexAB-OprM pump by cinnamon essential oil
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International audience. Background. Cinnamaldehyde (CNA) is a phytoaldehyde able to kill Pseudomonas aeruginosa. At subinhibitory doses, this electrophilic molecule triggers a complex stress response which in part results in the overproduction of efflux system MexAB-OprM and transient multidrug resistance. Induction of the pump activity is dependent on ArmR, the anti-repressor of operon mexAB-oprM. However, recent transcriptomic analyses of strain PA14 exposed to CNA revealed that genes regulated by the two-component system (TCS) AmgRS are also overexpressed. Since AmgRS is known to increase the activity of MexAB-OprM and membrane-bound proteases following cell envelope alterations, we investigated its protective role in the survival of P. aeruginosa to CNA. Methods. Relative expression of target genes was determined by RT-qPCR. Genes amgRS and/or armR were inactivated in strain PA14 by allelic exchange. Time-kill and MIC experiments were performed to assess the susceptibility of the mutants to CNA and antibiotics.Results. As expected, induction of mexAB-oprM expression (6-fold) by CNA was abolished in mutant PA14∆armR, consistent with the loss of transient antibiotic resistance. Under the same conditions, PA14∆amgRS overexpressed mexAB-oprM 2-fold, suggesting that along with ArmR, AmgRS also contributes to the regulation of the pump in CNA treated bacteria. However, this low induction was not sufficient to confer a multidrug resistance phenotype. Conversely, the deletion of amgRS had a higher impact on the susceptibility of PA14 to CNA than that of armR.Conclusion. Beyond its role in the modulation of MexAB-OprM activity, AmgRS protects P. aeruginosa from electrophilic stressors by other mechanisms that likely prevent protein aggregation.
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