The aim of this study was to determine the in-vitro activity of fosfomycin against Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae) isolates and the frequency of OXA-48, NDM, KPC, VIM, IMP types of carbapenemases in the carbapenem-resistant (CR) groups. A total of 346 isolates (126 E. coli and 220 K. pneumoniae) from nosocomial bloodstream infections were included. Carbapenem and fosfomycin susceptibility were tested by Etest (bioMerieux, France) and agar dilution methods, respectively and evaluated in accordance with EUCAST criteria. The presence of OXA-48, NDM, KPC, VIM, IMP types of carbapenemases were conducted by using PCR method. Of the total 346 isolates, 185 (41 E. coli, 144 K. pneumoniae) were CR. Fosfomycin susceptibility of E. coli was higher than 95% and was not statistically significant between the CR and carbapenem-susceptible (CS) groups. Fosfomycin susceptibility of CS and CR K. pneumoniae was 90.7% and 69.4%, respectively, and statistically significantly lower in CR group. Of the total 185 CR isolates, 163 (32 E. coli, 131 K. pneumoniae) were producing carbapenemases. OXA-48 was the prominent carbapenemase type produced by E. coli (96.8%) and K. pneumoniae (70.9%). The frequency of NDM and KPC types produced by K. pneumoniae was 20.6% and 15.2%, respectively. Fosfomycin has substantial in-vitro activity against nosocomial CS and CR E. coli and CS K. pneumoniae bloodstream isolates. However, due to the risk of emerging resistance with fosfomycin monotherapy, combination therapy should be considered to obtain the possible additive or synergistic activity. Emerging fosfomycin resistance of CR K. pneumoniae isolates is alarming and OXA-48 is still the prominent carbapenemase type in Turkey.

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