Synergistic activity of fosfomycin–meropenem and fosfomycin–colistin against carbapenem resistant Klebsiella pneumoniae: an in vitro evidence

AIM: To evaluate the antibacterial activity of fosfomycin–meropenem and fosfomycin–colistin combinations against carbapenem-resistant Klebsiella pneumoniae (CR-Kp). METHODS: A total of 50 CR-Kp isolates recovered from blood cultures were included in this study. All the CR-Kp isolates were screened for the presence of carbapenem resistant genes bla(IMP). bla(VIM). bla(NDM). bla(OXA-48) like, bla(KPC). bla(GES).#x00A0;and bla(SPM). Combination testing of fosfomycin–meropenem and fosfomycin–colistin were performed using time-kill assay. RESULTS: Fosfomycin–meropenem combination showed synergy in 20% of the tested CR-Kp isolates. While, fosfomycin–colistin exhibited synergy against 16% of the isolates. A total of 68% (n = 34) of CR-Kp isolates were characterised as OXA-48-like producers and 22% (n = 11) as NDM producers. Synergistic activity of these combinations was observed against OXA-48, NDM and NDM + OXA-48 co-producers. CONCLUSION: Considerable synergistic antibacterial activity of fosfomycin–meropenem and fosfomycin–colistin was not observed against CR-Kp isolates. Therefore, these combinations may not be promising for infections associated with CR-Kp.