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Aim: In order to find new therapeutic alternatives for difficult-to-treat infections produced by Pseudomonas aeruginosa we evaluated the effect of silver nanoparticles (AgNPs) on growth and biofilm production. Method: We selected 30 clinical strains of multidrug resistant Pseudomonas aeruginosa isolated from infected wounds with a prolonged evolution, and control strain Pseudomonas aeruginosa ATCC 27853. We synthetized 4 different types of functionalized silver nanoparticles (Ag@PEG, Ag@EG, AG@PEG/PVP, Ag@EG/PVP). For each type of nanoparticle, we grown the strains in 96 well-plates, concentration 0.5 McFarland, and a dilution of 10% in 150microL liquid Mueller Hinton, with 8 binary dilutions of nanoparticles from 0.5mg/mL to 0.0039mg/mL. After 24 hours of incubation at 37°C, the growth was spectrophotometrically evaluated at 620nm. Subsequently, the wells were fixed with cold methanol, stained with crystal violet 1%, observed at the inversed microscope and resuspended with acetic acid 33% to be spectrophotometrically read at 492nm for biofilm production. Results / Discussion: We determined the median of minimum inhibitory concentration, mode and range for each type of AgNP. All parameters investigated were lowest for nanoparticles functionalised with ethylene glycol and polyvinylpyrrolidone (Ag@EG/PVP), lower than 0.0039 mg/mL. We noticed a reduction of the biofilm production with 0.01-0.05 for concentration of 0.5 mg/mL, most important effect noticed for Ag@EG/PVP. Conclusion: We underline the efficiency of AgNPs in reducing growth and biofilm production. These findings show that nanosystems could be promising antimicrobial agents for highly antibiotic-resistant Pseudomonas aeruginosa. AgNPs may overcome severe microbial infections, since they are useful agents against resistant pathogens and also biofilms. [ABSTRACT FROM AUTHOR]