Genomic Characterization of Imipenem- and Imipenem- Relebactam-Resistant Clinical Isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic human pathogen and a major cause of nosocomial infections. The global spread of carbapenem-resistant strains is grow-ing rapidly and has become a major public health challenge. Imipenem-relebactam (I/R) is a novel carbapenem-beta-lactamase inhibitor combination that can overcome carbapenem re-sistance. In this study, we aimed to understand the mechanism underlying resistance to imi-penem and imipenem-relebactam. For this purpose, we performed a genomic comparison of 40 new clinical P. aeruginosa strains with different antibiotic sensitivity patterns as well as the presence/absence of carbapenemases. Results indicated the presence of a reduced flexi-ble genome (15% total) mostly represented by phages and defense mechanisms against them, showing an important role in evolution and pathogenicity. We found a high diversity of antibiotic resistance genes grouped in small clusters mobilized via integrative and conju-gative elements and facilitated by the high homologous recombination detected. Ortholog genes were found in several pathogenic strains from distantly related taxa in different mo-bile elements with a global distribution. The microdiversity found in those strains without carbapenemases did not reveal a clear pattern that could be associated with carbapenem resistance, suggesting multiple mechanisms of resistance in the core genome. Our results provide new insight into the dynamics and high genomic plasticity by which clinical strains of P. aeruginosa acquire resistance. This knowledge can be applied to other multidrug-resist-ant microbes to create predictive frameworks for assessing common molecular mechanisms of antibiotic resistance and integrated into new strategies for their prevention. IMPORTANCE The growing emergence and spread of carbapenem-resistant pathogens worldwide exacerbate the clinical challenge of treating these infections. Given the impor-tance of carbapenems for the treatment of infections caused by Pseudomonas aeruginosa, this study aimed to investigate the underlying genomic properties of the clinical isolates that exhibited resistance to imipenem and imipenem-relebactam. This information will enhance our ability to forecast traits of resistant strains and design reliable treatments against this important threat. Our results provide new insight into the dynamics and high genomic plasticity by which clinical strains of P. aeruginosa acquire resistance as well as offers a methodology that can be applied to many other opportunistic pathogens with broad antibiotic resistance.