Antimicrobial susceptibilities of clinical bacterial isolates from urinary tract infections to fosfomycin and comparator antibiotics determined by agar dilution method and automated micro broth dilution

Uncomplicated bUTIs are often caused by <i>Escherichia coli</i>, <i>Klebsiella pneumoniae</i>, and <i>Enterococcus faecalis</i>. Fosfomycin is one of the recommended firstline antibiotics for the treatment of symptomatic, uncomplicated bUTIs. Fosfomycin susceptibility testing is complicated by the fact that although both CLSI and EUCAST recognize agar dilution (AD) as the reference method albeit being labor-intensive, breakpoints are different, and Etest is only approved by EUCAST. We investigated the susceptibility of bUTI clinical isolates to fosfomycin using AD and compared performance in a subset of isolates to Etest. Fosfomycin susceptibility profiles of bacterial isolates were compared to other firstline antibiotics. We found isolates were susceptible to fosfomycin at similar or higher rates compared to other firstline antibiotics. Importantly, fosfomycin was effective against isolates producing extended-spectrum beta-lactamases and those that were resistant to other firstline treatments. Furthermore, our data showed Etest was a viable option for susceptibility testing with 94% agreement to the AD.