LAUSR

Serine β-lactamases are dominant causes of β-lactam resistance in Klebsiella pneumoniae isolates. Recently, this has driven clinical deployment of the β-lactam–β-lactamase inhibitor pairs ceftazidime/avibactam and meropenem/vaborbactam. We show that four steps, i.e., ompK36 and ramR mutation plus carriage of OXA-232 and KPC-3-D178Y variant β-lactamases, confer ceftazidime/avibactam and meropenem/vaborbactam resistance when both pairs are used together. ABSTRACT Serine β-lactamases are dominant causes of β-lactam resistance in Klebsiella pneumoniae isolates. Recently, this has driven clinical deployment of the β-lactam–β-lactamase inhibitor pairs ceftazidime/avibactam and meropenem/vaborbactam. We show that four steps, i.e., ompK36 and ramR mutation plus carriage of OXA-232 and KPC-3-D178Y variant β-lactamases, confer ceftazidime/avibactam and meropenem/vaborbactam resistance when both pairs are used together. These findings have implications for decision making about sequential and combinatorial use of these β-lactam–β-lactamase inhibitor pairs to treat K. pneumoniae infections.