"Evaluating the susceptibility of MBL carbapenemase-producing Enterobacteriaceae and Pseudomonas spp. to ceftazidime/avibactam plus aztreonam and Cefiderocol: A synergy study and susceptibility profile"

Abstract

This study assessed the in vitro susceptibility of aztreonam/avibactam (ATM/AVI) and the synergy analyses against 38 clinical carbapenemase-producing strains (31 Enterobacterales and 7 Pseudomonas spp.) collected over two years. Susceptibility testing were performed followed EUCAST guidelines and synergy was studied using the gradient strip stacking method and FICI analysis. Synergy between aztreonam (AZT) and Ceftazidime/Avibactam (CZA) was observed in 58,1 % of enterobacterales strains overall, with stronger synergy (100 %) in aztreonam-resistant group compared to aztreonam-susceptible ones (18.8 %). ATM/AVI Showed 100 % susceptibility among Enterobacterales with the epsilon test diffusion method. Cefiderocol (FDC) demonstrated high activity, with 93.5 % susceptibility in Enterobacterales and 100 % in Pseudomonas spp. The findings support ATM/AVI as a promising option for MBL-producing Enterobacterales, while the role of aztreonam/avibactam in the clinical treatment of Pseudomonas spp. MBL-type carbapenemases producers is still uncertain. Cefiderocol remains highly effective against MBL-producing Enterobacterales and Pseudomonas spp.

Keywords: Aztreonam/avibactam; Carbapenemase; Cefiderocol; Synergy.