Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 18 1 2026 02 14 67 73 Arun Sachu Department of Microbiology, Believers Church Medical College, Thiruvalla, Kerala, India Alice David Department of Biostatistics, Believers Church Medical College, Thiruvalla, Kerala, India 2025 11 15 2025 12 16 Background and Objectives: Urinary Tract Infections (UTIs) are most frequently caused by uropathogenic Escherichia coli, which accounts for approximately 80% of the cases. Other causative agents include Klebsiella spp., Proteus spp., Enterobacter spp., Enterococcus spp., and Staphylococcus saprophyticus. The main objectives of the study were to estimate the in vitro antimicrobial activity of fosfomycin against multidrug-resistant uropathogens (MDR) isolated from patients with suspected UTI using CLSI and EUCAST criteria and to describe the antimicrobial susceptibility pattern of uropathogens isolated during the study. Materials and Methods: This was a descriptive study in which a total of 900 urine samples were collected from patients presenting with physician-assessed signs and symptoms suggestive of a UTI. Only samples exhibiting significant bacteriuria that were also multidrug-resistant (MDR) were included. Although fosfomycin disk diffusion criteria, according to CLSI and EUCAST, are only validated for E. coli, susceptibility among other Gram-negative bacteria was also interpreted using the same criteria. This represents a major limitation of the study. Results: In the study, 251 samples grew multi drug resistant organisms. Only 57% of the Gram-negative isolates were sensitive according to EUCAST guidelines, while 87.6% of all isolates were sensitive by CLSI criteria. Among the 161 carbapenem-resistant isolates, 135 (83.9%) were fosfomycin-susceptible and 18 (11.2%) were resistant according to CLSI. In contrast, by EUCAST criteria, only 40 (24.9%) isolates were fosfomycin-susceptible, and the remaining 121 (75.1%) were resistant. Conclusion: Our study showed that using fosfomycin disc diffusion criteria of E. coli for other organisms is not ideal; therefore, performing an alternative form of susceptibility testing for non-E. coli isolates is recommended. Continuous monitoring of fosfomycin susceptibility is warranted to detect any emerging resistance and to guide its clinical application. https://ijm.tums.ac.ir/index.php/ijm/article/view/5931 https://ijm.tums.ac.ir/index.php/ijm/article/download/5931/1863