LAUSR

Despite being fundamentally important and having direct therapeutic implications, the functional genomics of the clinical isolates of multidrug-resistant (MDR) pathogens is often impeded by the lack of genome-editing tools. Here, we report the establishment of a highly efficient, in situ genome-editing technique applicable in clinical and environmental isolates of the prototypic MDR pathogen P. aeruginosa by harnessing the endogenous type I-F CRISPR-Cas systems. Using this approach, we generate various reverse mutations in an epidemic MDR genotype, PA154197, and identify underlying resistance mechanisms that involve the extensive synergy among three different resistance determinants. Screening a series of "ancestor" mutant lines uncovers the remarkable sensitivity of the MDR line PA154197 to a class of small, cationic peptidomimetics, which sensitize PA154197 cells to antibiotics by perturbing outer-membrane permeability. These studies provide a framework for molecular genetics and anti-resistance drug discovery for clinically isolated MDR pathogens.