Comparison of in-vitro susceptibility of Fosfomycin against drug resistant uropathogens by various susceptibility testing methods.

Abstract Urinary tract infections are one of the most common bacterial infections causing high morbidity and mortality. Alarming rise of multidrug resistant uropathogens worldwide, forced the clinician to rethink about the old drugs like Fosfomycin for its therapeutic management. Our objective was to compare agar dilution (AD), disc diffusion (DD) and E test method for antimicrobial susceptibility testing (AST) of Fosfomycin against different drug resistant uropathogens. Consecutive 181 uropathogens were tested for Fosphomycin AST using AD, DD and E test. Results were interpreted using Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints. Escherichia coli was found as the most common (62.4%) uropathogen followed by Klebsiella spp. (21%). Considering agar dilution as gold standard, 6.1% of isolates were resistant to Fosfomycin. Following CLSI breakpoints, the susceptibility of E.coli, Klebsiella spp., other Enterobacterales and Pseudomonas aeruginosa were 92.9%, 92.1%, 100 %, 100%; whereas using EUCAST breakpoints the susceptibility rates were 85.7%, 86.9%, 92.9%, and 100%, respectively. The essential agreement, categorical agreement, major error, and very major error for E-test/ DD for all the organisms were 91.2%/Not Applicable, 95%/93.9%, 1.8%/4.7%, 9.1%/9.1%, respectively. This result supports very low resistance of Enterobacterales against Fosfomycin; hence should be considered as a valuable option to treat multidrug resistant uropathogens. DD observed to be a convenient method for Fosphomycin AST comparing AD.