Reduced Susceptibility to Cefepime-Taniborbactam in Carbapenem-Resistant Klebsiella pneumoniae Attributed to Penicillin-Binding Protein 3 Modifications.

Abstract

The recent emergence of a carbapenem-resistant Klebsiella pneumoniae (CRKP) strain from a clinical specimen resistant to cefepime-taniboractam (FEP-TAN) raises serious concerns, necessitating further investigation of its resistance mechanisms. Three CRKP clinical isolates were investigated: 1 FEP-TAN-resistant colonizing strain (CRKP068) from a throat swab of a patient with lung infection and 2 FEP-TAN-sensitive controls (CRKP288 and CRKP170141). Whole-genome sequencing and clustered regularly interspaced short palindromic repeats and CRISPR-associated protein 9-mediated mutagenesis of the ftsI gene, encoding penicillin-binding protein 3 (PBP3), in the FEP-TAN-sensitive CRKP288 were used to generate isogenic mutants and confirm that PBP3 alterations were responsible for the resistance. The concurrent Asp76Val/Ala498Val substitutions in PBP3 conferred FEP-TAN resistance in the mutants while inducing filamentous morphology and membrane permeability defects. These mutations also reduced bacterial fitness, evidenced by decreased growth rates (k) under nutrient limitation, suggesting a tradeoff between resistance and proliferative capacity. Although PBP3-mediated FEP-TAN resistance entails measurable fitness costs, especially under nutrient-limited conditions, PBP3 polymorphism surveillance should be incorporated into resistance monitoring.