Introduction: Nanoparticles with the different sizes, surfaces and chemical characteristics can have different applications. Pseudomonas aeruginosa is an opportunistic bacterium that has the ability to produce pigment. The aim of this study was to investigate the effect of zinc oxide (ZnO) nanoparticles on pigment production of clinical isolates of Pseudomonas aeruginosa.

Materials & methods: In this description cross-sectional study, 15 clinical isolates of Pseudomonas aeruginosa were collected from hospitals in Mashhad. Bacteria were identified using biochemical tests and polymerase chain reaction (PCR) by specific primers of exoA gene. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of zinc oxide nanoparticles (diameter of 4-7 nm) were determined by agar dilution method. Glycerol- alanine (GA) medium containing different concentrations (0, 20, 40 and 60 mg/ml) of nanoparticles were used for investigation of the effect of ZnO nanoparticles on pigment production. The pigment was extracted by adding chloroform. 

Findings: All clinical isolates were identified by biochemical experiments as P. aeruginosa and exoA gene was detected in all bacteria. The average MIC and MBC of ZnO nanoparticles were 60 mg/ml and 70 mg/ml, respectively. All isolates were examined and compared for pyocyanin pigment production. The pigment production was significantly reduced with increasing concentrations the ZnO nanoparticles (p < 0.05).

Discussion & Conclusion: Zinc oxide nanoparticles had inhibitory effect on bacteria and pigment production. Pigment production decreased with increasing concentrations of nanoparticles. ZnO nanoparticles could be used in prevention or helping to treat P. aeruginosa infections.