• Heather Davis, Ryan Brown, Deborah Ashcraft, and George Pankey.
• Infectious Disease Translational Research Laboratory, Ochsner Clinic Foundation, New Orleans, LA, USA.
• J Glob Antimicrob Resist. 2020 Sep 1; 22: 78-83.

ObjectiveLinezolid and vancomycin-resistant Enterococcus faecium (LRVREF) is globally emerging as a urinary nosocomial pathogen. A decrease in the amount of successful treatment options has created a necessity for the development of novel antimicrobial therapies. Combination therapy may provide an effective alternative for treatment. Fosfomycin and doxycyclin are currently used individually for the treatment of urinary tract infections. Fosfomycin has recently seen increased use because of its persistent activity against a large spectrum of multidrug-resistant organisms. The purpose of this study was to investigate the interaction of fosfomycin plus doxycyclin against LRVREF isolates.MethodsMICs for fosfomycin and doxycyclin were determined for 24 unique clinical LRVREF isolates (4%, fosfomycin-susceptible; 92%, doxycyclin-susceptible). In vitro synergy testing with the combination of fosfomycin and doxycyclin was performed using an Etest method and time-kill assay.ResultsThe combination of fosfomycin and doxycyclin demonstrated synergy with the Etest method in 11/24 (46%) isolates and in 10/24 (42%) isolates by the time-kill assay. Results from the Etest method and time-kill assay were in agreement for 7/24 (29.2%) of isolates. No antagonism was found.ConclusionsThe combination of fosfomycin and doxycyclin should be evaluated further with additional LRVREF isolates. In vivo studies should also be performed before use in clinical situations.Copyright © 2020 The Author(s). Published by Elsevier Ltd.. All rights reserved.

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