In vitro efficacy of vancomycin combined with fosfomycin against Vancomycin-Resistant Enterococci strains

Vancomycin Combined with Fosfomycin

  • Gulseren Aktas Istanbul University, Istanbul Faculty of Medicine, Department of Medical Microbiology
Keywords: Vancomycin, Fosfomycin, Combination, Vancomycin-resistant enterococci


Objective: Enterococci have been isolated frequently worldwide and have difficulties in the treatment. Combination antibiotherapies have a distinct advantage over monotherapies in terms of their synergistic effect. In the study, it was aimed to investigate in vitro activity of vancomycin combined with fosfomycin against VRE strains.

Methods: A total of 30 VRE strains were included in the study. Bacterial identifications of the strains were undertaken using conventional routine methods. The resistance to agents tested was investigated by using the broth microdilution method. Glucose-6-phosphate (25 mcg/mL) for fosfomycin were used in all experiments. The activity of antibiotics in combination was assessed using a broth microcheckerboard. The fractional inhibitory concentration index (FICI) was interpreted as follows: synergism, FICI ≤0.5. Additionally, two strains in 30 VRE were studied to determine the time-kill curves to verify the synergistic results. For each strain, antibiotics were studied alone and in combination at the minimum inhibitory concentration (1xMIC) values.

Results: Susceptibility rate to fosfomycin was found at 26.6 % (8/30). The MIC50, MIC90 and MIC interval values of antimicrobials were 512, 512, and 512 - 1024 mcg/mL for vancomycin, and 128, 160, and 64 - 224 mcg/mL for fosfomycin, respectively. The rate of synergism was found as 100 % by both checkerboard and time-kill methods.

Conclusion: The result shows that the combination of vancomycin with fosfomycin could be an alternative in the treatment of infections caused by VRE.


How to cite this:
Aktas G. In vitro efficacy of vancomycin combined with fosfomycin against Vancomycin-Resistant Enterococci strains. Pak J Med Sci. 2020;36(2):281-285. doi:

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

How to Cite
Aktas, G. (2019). In vitro efficacy of vancomycin combined with fosfomycin against Vancomycin-Resistant Enterococci strains. Pakistan Journal of Medical Sciences, 36(2).
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