Introduction: Nowadays, antibiotic resistance is a major problem for the Iranian society. The aim of this research was to investigate the effects of silver and titanium dioxide nanoparticles on gram-negative bacteria causing urinary infections resistant to multiple antibiotics.
 
Materials & Methods: This study was conducted on gram-negative bacilli from multitude of speciesstrains, including Acinetobacter baumannii, Escherichia coli, Klebsiella pneumonia, Enterobacter aerogenes, Proteus vulgaris, Pseudomonas aeruginosa, and Citrobacter freundii. A total of 140 samples (i.e., 20 samples from each) were selected through a variety of biochemical tests to isolate and identify the bacteria. The samples were all the primarily cause of urinary tract infections and resistant to multiple antibiotics. The sensitivity of silver and titanium dioxide nanoparticles with the size of 10 nm were assessed through in vitro methods, such as disk diffusion, agar-well diffusion, and broth microdilution.
 
Finding: The results of agar-well diffusion and agar disk diffusion methods on silver nanoparticles with the concentration of 1000 ppm indicated that the largest and lowest values for the diameter of growth were in Pseudomonas aeruginosa and Klebsiella pneumonia, respectively. Moreover, macro dilution analysis of silver nanoparticles revealed that the minimum inhibitory concentration and minimum bactericidal concentration were at their lowest levels in the Pseudomonas aeruginosa. However, titanium dioxide nanoparticles, similar in size and shape to silver nanoparticles, had no effect on bacteria.
 
Discussion & Conclusions: Regarding two metal types of nanoparticles, the obtained results of in vitro revealed that silver nanoparticles could significantly affect the investigated types of bacteria, whereas, titanium dioxide nanoparticles had no effect on them.