Impact of porin deletions on cefepime-taniborbactam activity against Klebsiella pneumoniae.

We determined the frequency of resistance to cefepime-taniborbactam in NDM-1-producing Klebsiella pneumoniae at <10-10. Isolated mutants that were less susceptible to cefepime-taniborbactam had an increased copy number of the blaNDM-1 gene or disruption of major porins OmpK36 and OmpK35. Antibacterial susceptibility testing using K. pneumoniae isogenic strains indicated that while cefepime penetrates into the periplasm mainly through the major porins, taniborbactam does not have a strong dependence on OmpK35 or OmpK36 for periplasmic accumulation.