Nitrofurantoin-Aminoglycoside Synergy Against Common Uropathogens Evaluated by Disc Diffusion: A Pilot Study

The emergence of multidrug-resistant uropathogens requires the development of novel therapeutic strategies. This pilot study assessed the in vitro synergy between nitrofurantoin and aminoglycosides (amikacin, gentamicin, and tobramycin) against three major uropathogens: Escherichia coli, Klebsiella pneumoniae, and Enterococcus faecalis. Ninety clinical isolates were tested using the disk diffusion and double-disk synergy methods. Statistical analysis included Kruskal-Wallis and Mann-Whitney U tests, as well as logistic regression models to assess associations between inhibition zone diameters and synergy occurrence. While synergy was observed in all bacterial species, it was neither universally present nor species-specific. Significant associations were identified between nitrofurantoin inhibition zone size and synergy with amikacin and tobramycin in E. coli, and with amikacin in K. pneumoniae. In E. faecalis, synergy was more likely with larger aminoglycoside inhibition zones, particularly tobramycin. These findings underscore the potential of nitrofurantoin-aminoglycoside combinations in treatment of multidrug-resistant urinary tract infections, while emphasizing the need for further studies incorporating quantitative synergy assays and clinical validation.