Fosfomycin Susceptibility among ESBL-Producing Gram-Negative Bacilli Causing Urinary Tract Infections

Background: Urinary tract infections (UTIs) caused by extended-spectrum -lactamase (ESBL)-producing gram-negative bacilli pose significant therapeutic challenges due to multidrug resistance.Fosfomycin, an older antibiotic, has re-emerged as a potential treatment option.Methods: A prospective study was conducted on 350 urine samples from patients with confirmed UTIs.ESBL production was confirmed using the double-disk synergy test, and fosfomycin susceptibility was assessed via agar dilution per CLSI guidelines.Bacterial identification was performed using standard biochemical tests and the Vitek 2 system.ESBL production was confirmed via the double-disk synergy test, following CLSI guidelines.Fosfomycin susceptibility was determined using the agar dilution method on Mueller-Hinton agar supplemented with 25 g/mL glucose-6-phosphate, with a minimum inhibitory concentration (MIC) breakpoint of 32 mg/L indicating susceptibility.Results: Of 350 isolates, 220 (62.9%) were ESBL producers, predominantly Escherichia coli (68.2%) and Klebsiella pneumoniae (22.7%).Fosfomycin susceptibility was observed in 78.6% of ESBL isolates, with E. coli showing higher susceptibility (85.3%) than K. pneumoniae (67.4%).Resistance was associated with prior antibiotic exposure.Fosfomycin resistance was observed in 47 (21.4%) isolates, with K. pneumoniae contributing the largest share (17/47, 36.2%).Resistance was more frequent in isolates with higher MICs (64-128 mg/L), suggesting the potential for reduced clinical efficacy at standard doses.Compares susceptibility across antibiotics, showing fosfomycin's superior activity (78.6%) compared to ciprofloxacin (15.5%) and trimethoprim-sulfamethoxazole (22.7%) among ESBL producers.Conclusion: Fosfomycin remains effective against most ESBL-producing gram-negative bacilli causing UTIs, supporting its use as an oral treatment option.