In vitro Assessment of Fosfomycin: A Beacon of Hope in Drug Resistant Organisms Causing Urinary Tract Infections

Introduction: Urinary tract infections (UTI) are the most common bacterial infections affecting humans.. Fosfomycin has been approved for use in uncomplicated UTI caused by E. coli and Enterococcus. However, data regarding sensitivity of organisms causing hospital acquired or complicated UTI is scarce worldwide. We aimed to determine the in vitro sensitivity of drug resistant organisms causing hospital acquired and complicated UTI towards fosfomycin.

Materials and Methods: Over a 6 month period, urine samples were processed as per standard microbiological protocols. Bacterial isolates were identified by routine microbiological methods followed by automated methods. Antibiotic sensitivity tests were done for different antibiotics. Fosfomycin sensitivity was tested by disc diffusion assay and minimum inhibitory concentration (MIC) was determined by E test method.

Results: A total of 248` organisms causing hospital acquired and/or complicated UTI were isolated of which E. coli 88(35.48%) was most common followed by K. pneumoniae 78(31.45%) and P. aeruginosa 64(25.80%). Of 248, 92.74% (230/248) isolates were sensitive to fosfomycin. All the E. coli isolates were sensitive to fosfomycin with a low MIC (range 0.064-16 mg/L) while 97.43% (76/78) of the K. pneumoniae and 71.87% (46/64) P. aeruginosa of isolates were sensitive with a higher MIC (range 0.5-32 mg/L and 6-64mg/L respectively). Fosfomycin MIC geometric mean among E. coli, K. pneumoniae and P. aeruginosa was; 1.05, 7.19 and 19.61 mg/L respectively. K. pneumoniae and P. aeruginosa showed a significantly higher geometric mean MIC compare to E. coli (P <0.0001).

Conclusions: This study suggests that fosfomycin has the potential to replace the parenteral antibiotics for treating complicated or hospital acquired lower UTI especially in case of Enterobacteriaceae.