In vitro Optimization of Ceftazidime/Avibactam for KPC-Producing Klebsiella pneumoniae.

Tiffany Wu,Omar Perez,Michael J Satlin,Barry N Kreiswirth,Liang Chen,Yanqin Huang,Zackery P Bulman,Amisha P Rana

doi:10.3389/fmicb.2021.618087

Abstract

Ceftazidime/avibactam is an important treatment option for infections caused by Klebsiella pneumoniae carbapenemase-producing K. pneumoniae (KPC-Kp), however, resistance can emerge during treatment. The objective of the study was to define the ceftazidime/avibactam concentrations required to suppress bacterial regrowth in ceftazidime/avibactam susceptible isolates and identify active therapies against ceftazidime/avibactam-resistant KPC-Kp. Time-kill assays were performed against twelve ST258 KPC-Kp isolates that harbored blaKPC–2 or blaKPC–3. Nine KPC-Kp isolates (KPC-Kp 5A, 6A, 7A, 8A, 9A, 24A, 25A, 26A, and 27A) were susceptible to ceftazidime/avibactam, two (KPC-Kp 6B and 7B) were ceftazidime/avibactam resistant and meropenem susceptible, and one (KPC-Kp 1244) was resistant to both ceftazidime/avibactam and meropenem. Sequencing of the blaKPC genes revealed mutations in KPC-Kp 6B (D179Y substitution) and 7B (novel 21 base pair deletion) that both affected the Ω-loop encoding portion of the gene. Time-kill assays showed that against ceftazidime/avibactam-susceptible KPC-Kp, ceftazidime/avibactam concentrations ≥40/7.5 mg/L caused mean 5.42 log10CFU/mL killing and suppressed regrowth. However, regrowth occurred for some KPC-Kp isolates with a ceftazidime/avibactam concentration of 20/3.75 mg/L. Against ceftazidime/avibactam-resistant and meropenem-susceptible KPC-Kp 6B and 7B, bactericidal activity and synergy was observed for ceftazidime/avibactam in combination with meropenem ≤3.125 mg/L, while meropenem concentrations ≥50 mg/L were bactericidal as monotherapy. In contrast, clinically achievable concentrations of ceftazidime/avibactam were bactericidal against KPC-Kp 1244, which was ceftazidime/avibactam-resistant and meropenem-resistant due to outer membrane porin mutations and elevated blaKPC expression. Achieving high ceftazidime/avibactam concentrations may help to suppress bacterial regrowth in the presence of ceftazidime/avibactam. The optimal treatment approach for ceftazidime/avibactam-resistant KPC-Kp likely depends on the mechanism of resistance. Additional studies are warranted to confirm these findings.

Highlights

Carbapenem-resistant Enterobacterales (CRE) is associated with high mortality rates in patients with serious infections and remain a public health concern worldwide
Carbapenem resistance in Enterobacterales is most commonly conferred by carbapenemases, of which the K. pneumoniae carbapenemase (KPC) is the most common in the United States. β-Lactam/β-lactamase inhibitors with activity against KPCKp, such as ceftazidime-avibactam (CAZ/AVI), have been shown to improve clinical outcomes for patients with complicated urinary tract infections and intra-abdominal infections caused by Klebsiella pneumoniae carbapenemase-producing K. pneumoniae (KPC-Kp) compared to older treatment options such as the polymyxins
The nine CAZ/AVI-susceptible KPC-Kp isolates had CAZ MICs ≥32 mg/L,CAZ/AVI MICs ranging from 0.125/4 to 1/4 mg/L, MERO MICs ≥16 mg/L, and imipenem MICs ≥8 mg/L (Table 1)

Summary

Introduction

Carbapenem-resistant Enterobacterales (CRE) is associated with high mortality rates in patients with serious infections and remain a public health concern worldwide. CAZ/AVI resistance can be caused by non-synonymous mutations in the blaKPC gene that lead to amino acid substitutions within the KPC. The KPC -loop encompasses amino acid positions 164 through 179 and some amino acid substitutions within this region enhance the KPC enzyme affinity for ceftazidime, which may prevent the binding of avibactam (Barnes et al, 2017). Some of these mutations in the blaKPC -loop that cause CAZ/AVI resistance restore carbapenem susceptibility (Shields et al, 2017a). The objective of this study was to identify active antimicrobial therapies and optimize their concentrations to maximize bacterial killing and minimize bacterial regrowth of CAZ/AVI-susceptible and resistant KPC-Kp isolates

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