Influence of Urine on Antimicrobial Gradient and Disk Diffusion Susceptibility Testing of Co-trimoxazole, Fosfomycin, Norfloxacin and Nitrofurantoin against Urinary Escherichia coli

Aim: The aim of present study is to examine the influence of urine on zone of inhibition and Minimum inhibitory concentration by antimicrobial gradient strips of Co-trimoxazole, Fosfomycin, Norfloxacin and Nitrofurantoin against urinary E. coli. Study Design: Cross- sectional study. Place and Duration of Study: Department of Medical Microbiology, School of Medical Education, Kottayam, Kerala, India. Between January 2023 and November 2023. Methodology: A total of 75 E. coli isolates collected from various diagnostic microbiology laboratories were included in the study. Identification of isolates and antimicrobial susceptibility testing was done. Direct v/s standard zone of inhibition and MIC was determined. The data was statistically analysed using Cohen’s kappa for interrater reliability and Intraclass correlation coefficient for consistency level. Results: Current study evaluated the effect of urine on zone of inhibition and MIC by disc diffusion and antibiotic gradient testing respectively. The kappa value, a measure of agreement between direct v/s standard zone of inhibition and MIC for Co-trimoxazole, Fosfomycin, Norfloxacin was a perfect 1 (P=.000), indicating complete agreement. While, The kappa value, a measure of agreement between direct and standard MIC determination for Nitrofurantoin, was .67 (P=.000), indicating substantial agreement. Conclusion: The present study suggest that direct antimicrobial susceptibility testing can be employed for Co-trimoxazole, Fosfomycin, Norfloxacin and Nitrofurantoin which are important drugs in the management of UTI, after further standardization.