Hope Against Resistance: In Vitro Activity of the Ceftazidime-Avibactam and Aztreonam Combination Against Colistin-Resistant Klebsiella pneumoniae

Background Carbapenem-resistant Klebsiella pneumoniae (CRKP) represents a major global health threat. Rising colistin resistance in CRKP further restricts therapeutic options. With no newer antibiotics in the pipeline, the combination of ceftazidime-avibactam (CZA) and aztreonam (ATM) has emerged as a rational strategy to overcome complex β-lactamase-mediated resistance. Aim The aim of this study was to determine the in vitro susceptibility and synergy rates of CZA + ATM among colistin-resistant CRKP isolates. Methods A prospective laboratory study including 17 colistin-resistant CRKP isolates was conducted. Synergy testing was performed using the disk elution method in cation-adjusted Mueller-Hinton broth (CA-MHB), as per the latest CLSI guidelines. Results Notably, 12 of 17 (70.6%) isolates demonstrated synergistic susceptibility to CZA + ATM. Three isolates (17.6%) were susceptible to CZA alone, and the remaining two (11.8%) were susceptible to ATM alone. Conclusion CZA + ATM demonstrates remarkable in vitro efficacy against colistin-resistant CRKP and is a notable carbapenem- and colistin-sparing treatment alternative.