OmpK35/36 absence does not confer carbapenem-resistance alone nor ceftazidime-avibactam resistance with one bla _KPC-2

Investigate the genetic background of porin OmpK35/36 in Klebsiella pneumoniae and their influence on antimicrobial susceptibility, particularly carbapenems and ceftazidime-avibactam (CZA).

1407 K. pneumoniae genomes in GenBank were selected for analyzing outer membrane protein-related genes through BLAST method, including ompK35, ompK36, ompK26, ompK37, ompA, ompR, and carbapenemase genes, including bla _KPC, bla _VIM, bla _IMP, bla _NDM, bla _OXA-48. Using MEGA 11.0, OmpK35/36 and ompK35/36 phylogenetic trees were built among serotypes K1 and K2 strains. Further, serotype K1 NTUH-K2044 and bla _KPC-2 were used to construct mutants to elucidate impacts of OmpK35/36 on drug-resistance.

The rates of ompK35, ompK36, ompK26, ompK37, ompA, and ompR in K. pneumoniae strains were 97.5%, 99.3%, 99.5%, 99.4%, 99.9%, and 100.0% respectively. The sequence similarities of OmpK35/36 and ompK35/36 were both over 90.0%. K. pneumoniae strains with abnormal ompK35/36 presented higher rates of carbapenemase genes than those with normal ompK35/36. As to ΔompK36, the minimum inhibitory concentrations (MICs) of piperacillin, cefoxitin, cefazolin, cefuroxime, and imipenem increased to 4, 4, 4, 8, and 4 times respectively compared with those against NTUH-K2044; the MICs of piperacillin, cefoxitin, cefazolin, cefuroxime, imipenem, and meropenem increased to 8, 32, 32, 16, 8, and 8 times in ΔompK35/36 respectively. The deletions of ompK35/36, especially the double deletion, would greatly help NTUH-K2044+bla _KPC-2 induce resistance to certain β-lactams. Further, the absence of ompK35/36 elevated the MIC of CZA against NTUH-K2044+bla _KPC-2.

Highly conserved ompK35/36 are widely present in K. pneumoniae strains. The loss of OmpK35/36 confers increased resistance to certain β-lactams, with OmpK36 being dominant. Moreover, OmpK35/36 loss is a contributor but not a determinant in the formation of carbapenem-resistance under the absence of bla _KPC-2, as well as in the formation of CZA-resistance with one bla _KPC-2.