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: <i>Escherichia coli</i>, <i>Klebsiella pneumoniae</i>, and <i>Enterococcus faecalis</i>. 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 <i>E. coli</i>, and with amikacin in <i>K. pneumoniae</i>. In <i>E. faecalis</i>, 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.