Transcriptional and mutational profiling of an aminoglycoside resistant Pseudomonas aeruginosa small colony variant
Antimicrobial Agents and Chemotherapy, (2017)Abstract
Pseudomonas aeruginosa is a major causative agent of both acute and chronic infections. Although aminoglycoside antibiotics are very potent drugs to fight such infections, antibiotic failure is steadily increasing mainly due to increasing resistance of the bacteria. Many molecular mechanisms that determine resistance such as acquisition of genes encoding for aminoglycoside-inactivating enzymes or overexpression of efflux pumps have been elucidated. However, there are additional, less-well described mechanisms of aminoglycoside resistance. In this study we have profiled a clinical tobramycin resistant P. aeruginosa strain that exhibited a small colony variant (SCV) phenotype. Both, the resistance and the colony morphology phenotypes were lost upon passaging the isolate under rich medium conditions. Transcriptional and mutational profiling revealed that the SCV harbored activating mutations in the two two-component systems AmgRS and PmrAB. Introduction of these mutations singularly into the type strain PA14 conferred tobramycin and colistin resistance, respectively. However, their combined introduction had an additive effect on the tobramycin resistance phenotype. Activation of the AmgRS system slightly reduced the colony size of the PA14 wild-type, whereas the simultaneous overexpression of gacA, the response regulator of the GacSA two component system, further reduced colony size. In conclusion, we uncovered combinatorial influences of two-component systems on clinically relevant phenotypes, such as resistance and the expression of the SCV phenotype. Our results clearly demonstrate that combined activation of P. aeruginosa two-component systems exhibit pleiotropic effects with unforeseen consequences.