Prevalence of ESBL-producing Escherichia coli in urinary tract infections and their in-vitro susceptibility to Fosfomycin: a tertiary care experience

Urinary tract infections (UTIs) are among the most common bacterial infections, with Escherichia coli being the predominant uropathogen. The global rise of Extended-Spectrum Beta-Lactamase (ESBL)–producing E. coli has narrowed therapeutic choices, prompting renewed interest in older oral antibiotics such as Fosfomycin. The present study was conducted to determine the prevalence of ESBL-producing E. coli among urinary isolates and to evaluate their in-vitro susceptibility to Fosfomycin and other commonly used antimicrobials. A prospective observational study was conducted over nine months (March 2024 to December 2024) in the Department of Microbiology of a tertiary care centre in Western Gujarat, India. A total of 2,400 non-duplicate, mid-stream urine samples received from various wards, ICUs and out-patient departments were processed by semi-quantitative culture on MacConkey agar and blood agar. Significant bacteriuria was defined as colony counts ≥ 10⁵ CFU/mL. Isolates were identified by standard biochemical reactions. Antimicrobial susceptibility testing was performed by the Kirby–Bauer disc diffusion method on Mueller-Hinton agar and interpreted as per CLSI M100 (2024) guidelines. ESBL screening was carried out using ceftazidime, cefotaxime and ceftriaxone discs, and confirmation was done by the Phenotypic Combined Disc Diffusion Test (PCDDT) using ceftazidime alone and in combination with clavulanic acid. Categorical variables were compared using the chi-square test, with p < 0.05 considered statistically significant. Of 2,400 samples, 659 (27.46%; 95% CI 25.7–29.3%) were culture-positive. E. coli was the predominant uropathogen, accounting for 404/659 (61.30%; 95% CI 57.5–64.9%) isolates. ESBL production was confirmed in 150 of 404 (37.12%; 95% CI 32.6–41.9%) E. coli isolates. ESBL-producing E. coli predominated in females (67.33%) and in the 41–60 year age group (32%); the highest burden was from medicine wards (40.66%), and complicated UTI was the most frequent associated diagnosis (52%). Fosfomycin susceptibility was 85.33% (95% CI 78.8–90.1%) in ESBL-producing and 95.27% (95% CI 91.9–97.3%) in non-ESBL-producing E. coli , a statistically significant difference ( p < 0.001). Among ESBL isolates, the most active agents were ceftazidime-avibactam (99.33%), carbapenems (96.66%), piperacillin-tazobactam (86%), Fosfomycin (85.33%) and nitrofurantoin (77.33%). Resistance was high for ampicillin (100%), third-generation cephalosporins (94%), aztreonam (82%), tetracycline (74.67%) and cotrimoxazole (77.34%). ESBL-producing E. coli accounted for more than one-third of urinary E. coli isolates in this tertiary care setting, with marked resistance to most first-line oral agents. Fosfomycin retained good in-vitro activity against ESBL-producing E. coli , although this activity was significantly lower than in non-ESBL isolates ( p < 0.001). These in-vitro findings suggest Fosfomycin may be a useful oral option for uncomplicated and lower UTIs, pending confirmation by clinical outcome data, which this study did not assess. Continued antimicrobial stewardship and surveillance are recommended to monitor the resistance signal observed in a subset of isolates.