Khadijeh Ramezani Ali Akbari - Department of Microbiology, Faculty of Biological Sciences, Alzahra University, Tehran, Iran
Ahya Abdi Ali - Department of Microbiology, Faculty of Biological Sciences, Alzahra University, Tehran, Iran

Objective(s): Pseudomonas aeruginosa is a nosocomial pathogen resistant to most antimicrobial treatments. Furthermore, it persists in adverse environments thereby forming biofilms on various surfaces. Researchers have therefore focused on antibiofilm strategies using nanoparticles due to their unique physicochemical properties. Superparamagnetic iron oxide nanoparticles (SIONPs) have recently shown to possess antimicrobial and anti-biofilm characteristics. In this study, the effects of SIONPs and some antibiotics were tested against strong biofilmproducing P. aeruginosa isolates.Materials and Methods: 60 isolates of P.aeruginosa were screened for biofilm formation on microtiter plates using 0.1%w/v crystal violet (CV) staining. Twenty isolates producing strong biofilms were selected for further study on the effects of antimicrobial agents. Microdilution method was used to assay twenty isolates susceptible to antibiotics. The effects of antibiotics and SIONPs on biofilm formation were determined by the microdilution method and 0.1% CV staining. The checkerboard dilution technique was used to determine the combined effects of SIONPs and imipenem.      Results: In twenty isolates, the rate of resistance to ciprofloxacin, levofloxacin, amikacin, azithromycin was 65, 75, 45 and 95% respectively. SIONPs at 30 µg/ml reduced biofilm biomass in 11 isolates; however it stimulated biofilm formation in 9 isolates. The effects of SIONPs in combination with imipenem in the 10 isolates were different exhibiting synergistic or antagonistic relationships.Conclusion: P. aeruginosa has increasingly developed resistance to many antimicrobial agents but the resistance to nanoparticles is less frequently been reported. However, iron oxide nanoparticles could enhance biofilm production in isolate- dependent manner because they may possibly utilize this nanoparticle as an iron source, an important element in biofilm production. The exact mechanism of these effects however, remains to be elucidated.

Antibiotics, Biofilm, Iron oxide nanoparticles, Pseudomonas aeruginosa, Resistance