Ceftazidime/avibactam resistance associated with L169P mutation in the omega loop of KPC-2

Objectives: Ceftazidime/avibactam resistance due to mutation in the omega loop of KPC-2 has been documented in vitro and in vivo. This study evaluated the mechanism of ceftazidime/avibactam resistance in a KPC-2-expressing Klebsiella pneumoniae isolated from a patient following ceftazidime/avibactam combination therapy with gentamicin for the treatment of ventilator-associated pneumonia. Methods: Ceftazidime/avibactam-susceptible and -resistant isolates of K. pneumoniae were evaluated by broth microdilution and WGS. The KPC-2 gene was cloned from the ceftazidime/avibactam-resistant isolate and evaluated for susceptibility to ceftazidime/avibactam, in an Escherichia coli background. Results: A single L169P mutation was identified in the KPC-2 gene between the ceftazidime/avibactam-resistant and -susceptible isolates. The novel KPC-2 allele, designated KPC-35, was shown to confer reduced susceptibility to ceftazidime/avibactam and increased susceptibility to carbapenems, as compared with KPC-2. Conclusions: A novel L169P mutation was identified in KPC-2 and was shown through cloning experiments to confer reduced susceptibility to ceftazidime/avibactam.