Sequence type-258 carbapenem-resistant Klebsiella pneumoniae isolates in which ceftazidime-avibactam resistance emerged are not hypermutators.

Ceftazidime-avibactam resistance among carbapenem-resistant Klebsiella pneumoniae at our hospital has emerged in sequence type (ST)-258, clade II isolates. We investigated hypermutability of ST258, clade II (n = 6) and clade I K. pneumoniae (n = 8) using a standard rifampin assay. Mutational frequencies were ≤10, indicating that isolates were not hypermutators. Mutational frequencies did not differ between clade II and I isolates. Ceftazidime-avibactam resistance among ST258, clade II K. pneumoniae is most likely a reflection of our hospital's ecology.