In Vitro Selection of Meropenem Resistance among Ceftazidime-Avibactam-Resistant, Meropenem-Susceptible Klebsiella pneumoniae Isolates with Variant KPC-3 Carbapenemases

Ceftazidime-avibactam resistance is mediated by bla(KPC-3) mutations, which restore carbapenem susceptibility. We subjected Klebsiella pneumoniae isolates with different bla(KPC-3) mutations (n=5) or wild-type bla(KPC-3) (n=2) to serial passages with meropenem. The meropenem MIC against each isolate increased. Mutations in the ompK36 porin gene evolved in 5 isolates. Among isolates with D179Y substitutions in KPC-3, bla(KPC-3) mutations reverted to wild type, were replaced by new mutations, or were retained. Carbapenem treatment of ceftazidime-avibactam-resistant K. pneumoniae infections may select for carbapenem resistance.