Evolution of Imipenem-Relebactam Resistance Following Treatment of Multidrug-Resistant Pseudomonas aeruginosa Pneumonia

We report the emergence of imipenem-relebactam nonsusceptible Pseudomonas aeruginosa in 5 patients treated for nosocomial pneumonia for 10-28 days. Genome sequence analysis identified treatment-emergent mutations in MexAB-OprM and/or MexEF-OprN efflux operons that arose independently in each patient across distinct P. aeruginosa sequence types. Testing with efflux-inhibitor PA beta N restored imipenem-relebactam susceptibility.