<i>In Vivo</i> Emergence of Resistance to Novel Cephalosporin–β-Lactamase Inhibitor Combinations through the Duplication of Amino Acid D149 from OXA-2 β-Lactamase (OXA-539) in Sequence Type 235 Pseudomonas aeruginosa

Abstract

Resistance development to novel cephalosporin-β-lactamase inhibitor combinations during ceftazidime treatment of a surgical infection by <i>Pseudomonas aeruginosa</i> was investigated. Both initial (97C2) and final (98G1) isolates belonged to the high-risk clone sequence type (ST) 235 and were resistant to carbapenems (<i>oprD</i>), fluoroquinolones (GyrA-T83I, ParC-S87L), and aminoglycosides (<i>aacA7/aacA8/aadA6</i>). 98G1 also showed resistance to ceftazidime, ceftazidime-avibactam, and ceftolozane-tazobactam. Sequencing identified <i>bla</i>_OXA-2 in 97C2, but 98G1 contained a 3-bp insertion leading to the duplication of the key residue D149 (designated OXA-539). Evaluation of PAO1 transformants producing cloned OXA-2 or OXA-539 confirmed that D149 duplication was the cause of resistance. Active surveillance of the emergence of resistance to these new valuable agents is warranted.