Serial Pseudomonas aeruginosa isolates from acute infection

Ceftazidime-avibactam (CZA) belongs to a new class of broad-spectrum beta lactam/beta lactamase inhibitor combinations designed to treat infections caused by multidrug resistant bacteria. Understanding the emergence of resistance to this important new drug class is of critical importance. Elevated mutational rates may facilitate the acquisition of antimicrobial resistance in Pseudomonas aeruginosa strains in the context of chronic infection. Whether P. aeruginosa hypermutation can also play a role in acute infection remains unclear. In this work, we demonstrate that evolved mismatch repair deficiency in P. aeruginosa, an important pathogen responsible for significant morbidity and mortality among hospitalized patients, may facilitate rapid acquisition of resistance to CZA in the context of acute infection.Whole genome sequencing was performed on 9 serially-cultured blood and respiratory isolates from a patient in whom ceftazidime-avibactam (CZA) resistance emerged in vivo over the course of days. The CZA-resistant clone was differentiated by 14 mutations, including a gain-of-function G183D substitution in the PDC-5 chromosomal AmpC cephalosporinase conferring CZA resistance. This lineage also contained a substitution (R656H) at a conserved position in the ATPase domain of the MutS protein, and elevated mutational rates were confirmed by mutational accumulation experiments. In addition, adaptive evolution experiments demonstrated rapid acquisition of CZA-resistance in MMR-deficient strain compared with the isogenic wild type strain. Our results suggest a possibly underappreciated role for evolved MMR deficiency in facilitating rapid adaptive evolution of P. aeruginosa in the context of acute infection. These findings are relevant for both diagnosis and treatment of antimicrobial resistance emerging in acute infection in the hypermutator background, and additionally may have implications for the emergence of more virulent phenotypes.