Resistance to Ceftazidime/Avibactam Plus Meropenem/Vaborbactam When Both are Used Together Achieved in Four Steps From Metallo-β-Lactamase Negative Klebsiella pneumoniae.

Serine cephalosporinases and carbapenemases are dominant causes of critically important {beta}-lactam resistance in Klebsiella pneumoniae. This has led to the recent clinical deployment of new serine {beta}-lactamase inhibitors used in combination with {beta}-lactams. Starting with clinical K. pneumoniae isolates and adding plasmids carrying the OXA-48-like class D carbapenemase, OXA-232, the class A carbapenemase KPC-3, the class A cephalosporinase CTX-M-14 and mutant derivatives of these enzymes, we set out to identify the steps required to give resistance to the recently approved {beta}-lactam/{beta}-lactamase inhibitor pairs ceftazidime/avibactam and meropenem/vaborbactam when both are used together. We show that four steps: ompK36 and ramR loss-of-function plus carriage of OXA-232 and KPC-3-D178Y, all of which have been observed in clinical isolates, allow K. pneumoniae to resist the combined use of both {beta}-lactam/{beta}-lactamase inhibitor pairs. These findings have implications for decision making about sequential and combinatorial use of {beta}-lactam/{beta}-lactamase inhibitor pairs to treat K. pneumoniae infections, and suggest simple surveillance activities that might identify intermediate stages in resistance acquisition and therefore guide therapy to reduce the emergence of dual resistant strains.