Evaluation of In vitro Effectiveness of Intravenous Phosphomycin in Commonly Drug-Resistant Pseudomonas aeruginosa Strains

Introduction: In recent years, the increasing number of drug-resistant P. aeruginosa strains has led clinicians to seek new treatment alternatives. Discovered in the 1960s, intravenous fosfomycin came to the point of being abandoned in a short time due to the different treatment options and the difficulties of sensitivity testing. However, in recent years, it has come to the fore again due to its in vitro and in vivo activity in common drug-resistant gram-negative bacteria. For determination of minimal inhibitory concentration in fosfomycin in vitro efficacy studies, EUCAST recommends agar dilution supplemented with glucose-6-phosphate (G6P). In our study, we investigated the in vitro susceptibility of fosfomycin in common drug resistant P. aeruginosa strains by agar dilution method. At the same time, we aimed to examine the efficacy of G6P in sensitivity results. Materials and Methods: 28 common drug resistant P. aeruginosa isolates selected from the culture collection in our laboratory were included in the study. Intravenous (IV) fosfomycin sensitivity in line with EUCAST recommendations; agar with 25 mg/L G6P was added by dilution method. In our study, in order to see the effect of glucose 6-phosphate on sensitivity results, the agar dilution method was repeated using Muller-Hinton Agar medium without G6P. Results: When the susceptibility of the strains to fosfomycin was evaluated; all strains were found to be lower than 128 mg/L, which is the epidemiological cut-off value determined by EUCAST. When the sensitivity test was repeated without using G6P, it was observed that there was no change in the MIC results. Conclusion: Our study has shown the usefulness of routine determination of susceptibility to fosfomycin to support intravenous use, as treatment options against P. aeruginosa are decreasing. In addition, our study showed that when determining the MICs of fosfomycin P. it not be to with G6P.