Combination of Ceftazidime-Avibactam and Aztreonam Effectively Treated Post-Cardiac Surgery Pneumonia Caused by Hypervirulent KPC- and NDM-Producing Klebsiella pneumoniae: A Case Report

Background: Hypervirulent carbapenem‑resistant Klebsiella pneumoniae (hv-CRKP) co‑producing Klebsiella pneumoniae carbapenemase‑2 (KPC‑2) and New Delhi metallo‑β‑lactamase‑1 (NDM‑1) represents a serious clinical threat due to limited treatment options and high mortality. This study aimed to describe the clinical course, microbiological characteristics, and therapeutic outcome of a severe postoperative pneumonia caused by such a strain, and to evaluate the effectiveness of combination antimicrobial therapy. Case Presentation: A 59‑year‑old woman developed severe pneumonia and acute respiratory distress syndrome following cardiac surgery. Bronchoalveolar lavage fluid culture yielded carbapenem‑resistant K. pneumoniae . Antimicrobial susceptibility testing showed resistance to meropenem (minimum inhibitory concentration [MIC] ≥ 16 μg/mL), ceftazidime‑avibactam (CZA) (MIC ≥ 16/4 μg/mL), and aztreonam (ATM) (MIC ≥ 64 μg/mL). Molecular analysis identified bla KPC and bla NDM carbapenemase genes and hypervirulence‑associated genes including rmpA and iucA. In vitro synergy testing demonstrated a marked reduction in MIC (≤ 1 μg/mL) when CZA was combined with ATM. Based on these findings, combination therapy was initiated, resulting in rapid clinical improvement, a decline in procalcitonin levels from 4.83 ng/mL to 0.5 ng/mL, radiographic resolution of pulmonary infiltrates, and sustained microbiological clearance. Conclusion: This case demonstrates that CZA combined with ATM may be an effective therapeutic option for severe infections caused by hypervirulent KPC‑2‑ and NDM‑1‑producing K. pneumoniae . Early molecular identification and synergy‑guided antimicrobial therapy are essential for optimizing outcomes in critically ill patients.