Introduction Nosocomial infections are a major problem that nursing and medical staffs and also patients face daily [1]. Pseudomonas is a rod-shaped, aerobic, Gram-negative bacterium belonging to the family Pseudomonadaceae [2]. Risk factors for the growth of infections caused by Pseudomonas include neutropenia, cystic fbrosis, severe burns, and foreign device installations [3-4]. Pseudomonas can be diffused in hospitals by nursing staff, medical equipment, sinks, disinfectants, and food. Pseudomonas Pol. J. Environ. Stud. Vol. 27, No. 4 (2018), 1639-1645 Original Research Synthesizing Colloidal Zinc Oxide Nanoparticles for Effective Disinfection; Impact on the Inhibitory Growth of Pseudomonas aeruginosa on the Surface of an Infectious Unit Mahsa Omrani, Ebrahim Fataei* Department of Environmental Sciences, Ardabil Branch, Islamic Azad University, Ardabil, Iran Received: 19 June 2017 Accepted: 19 September 2017 Abstract Pseudomonas aeruginosa has innate characteristics of developing resistance. Therefore, it is obligatory to fnd the new antipseudomonal agents: Zno colloidal nanoparticles (NPs) synthesized via chemical deposition method. Then, TEM, SEM, DLS, and UV-visible were done. Sampling was achieved from not the same sections of infectious unit and then Pseudomonas aeruginosa was isolated from hospital and its antibiotic resistance pattern was determined. Disc diffusion, cavity, MIC, and MBC tests were done. Absorption of UV-visible occurred at about 350 nm. The mid-range of hydrodynamic diameter and the average size of the ZnO NPs were 1.48 um and 5 nm, respectively. Isolated Pseudomonas aeruginosa was resistant to Trimethoprim, Ampicillin, and Nitrofurantoin. The disc diffusion and cavity test of antibiotic-resistant Pseudomonas aeruginosa showed respectively the least sensitivity to ZnO (DIZ = 8 mm and 5 mm) in comparison of standard strain of Pseudomonas aeruginosa (DIZ = 10 mm and 8 mm). According to the results, ZnO NPs could kill all antibiotic-resistant bacteria at a ratio of 1:16 (MBC = 7.5 ppm). However, it was able to eliminate the standard strain of Pseudomonas aeruginosa at a ratio of 1:64 (MBC = 0.937 ppm). This study demonstrated that ZnO NPs have high potential for disinfection of infectious units of hospitals against nosocomial infection – especially by Pseudomonas aeruginosa. Keywords: zinc oxide, nanoparticles, Pseudomonas aeruginosa, disinfection, infectious unit *e-mail: ebfataei@iauardabil.ac.ir, ebfataei@gmail.com DOI: 10.15244/pjoes/77096 ONLINE PUBLICATION DATE: 2018-03-01