OmpK35 and OmpK36 Deficiencies Driving High-level Carbapenem Resistance in ST11 Klebsiella Pneumoniae

BACKGROUND: Factors contributing to the success of carbapenem-resistant Klebsiella pneumoniae (CRKP) of sequence type 11 (ST11) remain poorly understood. METHODS: All GenBank-available K. pneumoniae genome sequences were retrieved. Isolates from mainland China carrying blaKPC and exhibiting high-quality assembly were selected for determining ST, virulence factors, antimicrobial resistance genes, plasmid types, and outer membrane porins (OmpK35 and OmpK36). Cloning experiments were performed for complementing porin deficiencies. In vitro growth assays under carbapenem selection pressure and carbon utilization assays were conducted. The structure alteration of OmpK36 with a two-amino-acid Gly-Asp insertion (OmpK36GD) was modeled. RESULTS: ST11 accounted for 87.22% (8930/10 238) of all blaKPC-carrying CRKP Chinese strains. The majority (96.13%, 8584/8930) of ST11 CRKP strains had a truncated OmpK35 (OmpK35-del), with a 17%-amino-acid remnant, and OmpK36GD. Only 6.42% (84/1308) of non-ST11 CRKP possessed such alterations. The GD insertion obstructs the outermost channel and compromises OmpK36 function. ST11 CRKP with OmpK35-del and OmpK36GD exhibited higher minimum inhibitory concentrations to carbapenems, which was reduced by complementing wild-type of OmpK35 and/or OmpK36. Strains possessing OmpK35-del and OmpK36GD had better growth under low concentration (2 or 4 mg/L) meropenem. Unlike truncations of OmpK36, OmpK36GD does not interfere with utilizing carbon sources. CONCLUSIONS: OmpK35 deficiency and OmpK36 structure alteration, combined with KPC-2 carbapenemase production, contribute to the high-level carbapenem resistance observed in ST11 CRKP strains. OmpK36GD represents an optimal model for OmpK36 deficiencies due to its minimal fitness cost. With the porin deficiencies, ST11 CRKP strains demonstrate enhanced growth and proliferation under carbapenem selection pressure, likely promoting their prevalence.