Emergence of Ceftazidime-Avibactam-Induced KPC Variants (KPC-25/127) in Intracranial Infection and Implications for Clinical Management.

The emergence of novel Klebsiella pneumoniae carbapenemase (KPC) variants contributing to clinical treatment failure poses a substantial threat to public health. To inform the clinical management of infections caused by KPC-variant-harboring K. pneumoniae, this study reports the complex evolutionary trajectory of ceftazidime-avibactam (CAZ-AVI)-resistant KPC-variant-harboring K. pneumoniae in a single patient during CAZ-AVI treatment. Three KPC-producing K. pneumoniae (KPC-KP) isolates were obtained from a patient with K. pneumoniae infection who received sequential treatment with imipenem followed by CAZ-AVI. Isolate K2, harboring blaKPC-2, exhibited carbapenem resistance. After 12 days of CAZ-AVI administration, isolate K25 (carrying blaKPC-25) showed CAZ-AVI resistance but remained susceptible to imipenem. In contrast, isolate K127 (harboring blaKPC-127 firstly identified by our group), recovered after combined CAZ-AVI and imipenem therapy, displayed dual resistance to both CAZ-AVI and carbapenems; this carbapenem resistance was attributed to outer membrane protein mutations combined with blaKPC-127 overexpression. Analysis of the genetic regions revealed that all subtypes were located within a conserved genetic background: IS26-ISKpn8-blaKPC-ΔISKpn6-ΔtnpR-Tn1721. Cloning and heterologous expression of the KPC variants, followed by enzymatic kinetic analyses and minimum inhibitory concentration (MIC) determinations, confirmed that the variants altered the MICs of CAZ-AVI and carbapenems. Compared with the KPC-2 protein, both variant proteins exhibited reduced hydrolytic activity against ceftazidime. Additionally, the half-maximal inhibitory concentration (IC50) of avibactam against the KPC variants was significantly higher than that of the wild-type KPC-2 protein. These results indicate that the KPC variant proteins have low affinity for avibactam, thereby reducing susceptibility to this inhibitor.