In Vivo Emergence of Resistance to Novel Cephalosporin-{beta}-lactamase Inhibitor Combinations Through the Duplication of the Amino Acid D149 from OXA-2 {beta}-lactamase (OXA-539) in ST235 Pseudomonas aeruginosa [PublishAheadOfPrint]

Resistance development to novel cephalosporin-β-lactamase inhibitor combinations during ceftazidime treatment of a surgical infection by Pseudomonas aeruginosa was investigated. Both, initial (97C2) and final (98G1) isolates, belonged to the high-risk clone ST235 and were resistant to carbapenems (oprD-), fluoroquinolones (GyrA-T83I, ParC-S87L) and aminoglycosides (aacA7/aacA8/aadA6). 98G1 additionally showed resistance to ceftazidime, ceftazidime-avibactam and ceftolozane-tazobactam. Sequencing identified bla_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.

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