In vitro activity of fosfomycin trometamol and other oral antibiotics against multidrug-resistant uropathogens

- Fosfomycin inhibited all of the ESBL E. coli, P. mirabilis and MR S. saprophyticus strains.
- Fosfomycin was slightly less active against KPC-producing Klebsiella pneumoniae isolates.
- The in vitro activity of fosfomycin found using the three methods showed good agreement against Enterobacteriaceae.

Clinical midstream and urinary catheter isolates (n = 106) of extended-spectrum β-lactamase (ESBL)-positive Escherichia coli, Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae, Proteus mirabilis and meticillin-resistant Staphylococcus saprophyticus were tested against fosfomycin using the agar dilution method, the broth microdilution method and the gradient test described by the Clinical and Laboratory Standards Institute. Nitrofurantoin, co-trimoxazole, amoxicillin/clavulanic acid, cefuroxime, levofloxacin and ciprofloxacin were tested using the gradient test alone. Breakpoints from the European Committee on Antimicrobial Susceptibility Testing 2015 guidelines were used. Fosfomycin inhibited all of the ESBL-positive E. coli, P. mirabilis and meticillin-resistant S. saprophyticus strains isolated from urine, as well as 82% of KPC-producing K. pneumoniae isolates. Substantial agreement for fosfomycin activity was found for the three test methods, particularly for Enterobacteriaceae. This study confirmed that fosfomycin has good in vitro activity against more common multidrug-resistant uropathogens. Fosfomycin could be a reliable empirical therapeutic option for uncomplicated urinary tract infections caused by these organisms, and a valid option for sparing parenteral antibiotics, such as carbapenems.