Rapid detection of fosfomycin resistance in Escherichia coli and Klebsiella spp. strains isolated from urinary tract infections

This study evaluates whether the rapid fosfomycin resistance (fosfomycin NP) method can be used for detecting fosfomycin resistance in routine laboratory work. Results from the disk diffusion and rapid fosfomycin NP methods were compared with the reference agar dilution method for Escherichia coli and Klebsiella spp. strains isolated from urinary tract infections. The study included 57 E. coli and 48 Klebsiella spp. isolates from urinary tract infections. The reference agar dilution and disk diffusion methods were performed in accordance with EUCAST recommendations, and the results were evaluated according to EUCAST V.10.0. The method developed by Nordmann et al. was used for rapid detection of fosfomycin resistance (Nordmann, P., Poirel, L., Mueller, L., 2019. Rapid Detection of Fosfomycin Resistance in Escherichia coli. J Clin Microbiol. 57(1), e01531-18. doi:https://doi.org/10.1128/JCM.01 531-18). The acceptable categorical agreement (CA >= 90%) and the rates of major error (ME <3%) and very major error (VME < 3%) of the two methods were compared with the reference method according to the criteria of ISO 20776-1. Fosfomycin resistance was detected in 15.8% of E. coli and 75% of Klebsiella spp. isolates using the reference method. Disk diffusion method showed CA 89.5%, ME 12.5% in E. coli isolates, and CA 75%, ME 100% in Klebsiella spp. isolates. No VME was detected in both methods. The rapid fosfomycin NP method resulted in CA 96.4%, ME 0.0%, VME 22.2% in E. coli isolates, and CA 77.3%, ME 81.8%, and VME 3% in Klebsiella spp. isolates. We believe the results from both of disk diffusion assay and rapid fosfomycin NP for the E. coli and Klebsiella spp. isolates are incompatible with the reference method and should not be used as an alternative to the agar dilution method.