Klebsiella pneumoniae Outer Membrane Porins OmpK35 and OmpK36 Play Roles in both Antimicrobial Resistance and Virulence

OmpK35 and OmpK36 are the major outer membrane porins of Klebsiella pneumoniae. In this study, a virulent clinical isolate was selected to study the role of these two porins in antimicrobial resistance and virulence. The single deletion of ompK36 (Delta ompK36) resulted in MIC shifts of cefazolin, cephalothin, and cefoxitin from susceptible to resistant, while the single deletion of ompK35 (Delta ompK35) had no significant effect. A double deletion of ompK35 and ompK36 (Delta ompK35/36) further increased these MICs to high-level resistance and led to 8-and 16-fold increases in the MICs of meropenem and cefepime, respectively. In contrast to the routine testing medium, which is of high osmolarity, susceptibility tests using low-osmolarity medium showed that the Delta ompK35 mutation resulted in a significant (>= 4-fold) increase in the MICs of cefazolin and ceftazidime, whereas a Delta ompK36 deletion conferred a significantly (4-fold) lower increase in the MIC of cefazolin. In the virulence assays, a significant (P < 0.05) defect in the growth rate was found only in the Delta ompK35/36 mutant, indicating the effect on metabolic fitness. A significant (P < 0.05) increase in susceptibility to neutrophil phagocytosis was observed in both Delta ompK36 and Delta ompK35/36 mutants. In a mouse peritonitis model, the Delta ompK35 mutant showed no change in virulence, and the Delta ompK36 mutant exhibited significantly (P < 0.01) lower virulence, whereas the Delta ompK35/36 mutant presented the highest 50% lethal dose of these strains. In conclusion, porin deficiency in K. pneumoniae could increase antimicrobial resistance but decrease virulence at the same time.