genomic analysis of fosfomycin resistance in multi-drug resistant uropathogens and comparison of in-vitro susceptibility methods uropathogens

Background and objectives: urinary tract infection is one of the most common bacterial infections causing high morbidity and mortality. the alarming rise of multidrug-resistant uropathogens worldwide forced the clinician to re- think the old drugs like fosfomycin for its therapeutic management. our objective was to compare agar dilution, disc diffusion and e-test method for antimicrobial susceptibility testing of fosfomycin against different drug-resistant uropathogens. materials and methods: consecutive 181 uropathogens were tested for fosfomycin susceptibility using agar dilution, disc diffusion and e-test. results were interpreted using clinical and laboratory standards institute (clsi) and european committee on antimicrobial susceptibility testing (eucast) breakpoints. whole genome sequencing analysis was done on the 4 xdr/pdr fosfomycin resistant klebsiella pneumoniae isolates. results: escherichia coli was found as the most common (62.4%) uropathogen followed by klebsiella pneumoniae (21%). considering agar dilution as the gold standard, 6.1% of isolates were resistant to fosfomycin. following clsi breakpoints, the susceptibility of escherichia coli, klebsiella pneumoniae, 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/ disc diffu- sion for all the organisms were 91.2%/not applicable, 95%/93.9%, 1.8%/4.7%, 9.1%/9.1%, respectively. whole-genome sequencing showed mutation uhpt gene as well as the presence of plasmid-mediated fosa5 or fosa6 genes conferring fos- fomycin resistance. conclusion: this result supports very low resistance of enterobacterales against fosfomycin; hence should be considered a valuable option to treat multidrug-resistant uropathogens. disc diffusion was observed to be a convenient method for fosfo- mycin susceptibility testing compared to agar dilution.