Fosfomycin-meropenem synergistic combination against NDM carbapenemase-producing Klebsiella pneumoniae strains.

Carbapenemase-producing Enterobacteriaceae (CPE) are an increasing threat to global public health. Treatment of CPE isolates, like New Delhi metallo-β-lactamase (NDM), is limited and often necessitates combination therapies. The aim of this study was to evaluate the synergistic meropenem/fosfomycin combination against K.pneumoniae-producing NDM isolates. Fosfomycin/meropenem, fosfomycin/colistin and meropenem/colistin were tested alone and in combination, using e-test and time-kill assay against 20 clinical carbapenemase-producing K. pneumonia (CPKp NDM) isolates collected from September 2022 to December 2022. K. pneumoniae strains were resistant to meropenem, ceftazidime/avibactam and ceftolozano/tazobactam, 75% and 80% of isolates were susceptible for cefiderocol and for colistin respectively. Fosfomycin/meropenem combination was synergic in 95% (n=19) strains. Fosfomycin/colistin and colistin/meropenem combination showed only 10% synergistic combination strains. In 16 isolates (80%) indifference action for fosfomycin/colistin and colistin/meropenem was reported. For 0.8% of CpKP NDM isolates colistin/meropenem and fosfomycin/colistin combinations found to be antagonistic. In this study, time kill assay showed combination therapies action versus K.pneumoniae metallo-b-lactamase producing (NDM) strains and confirmed the synergistic action of fosfomycin/meropenem combination. In vitro synergy testing should be routinely performed in multidrug resistance infections and combo therapies can be used as a possible alternative in targeted patients with the goal of reducing overall antibiotic costs.