Manganese oxide nanoparticles (Mn3O4-NPs) were prepared using precipitation method. The prepared nanoparticles were characterized by a number of techniques, including X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transforms infra red (FT-IR) spectroscopy. The XRD pattern showed that the structure of Mn3O4-NPs was tetragonal hausmannite. The average particle size, revealed by TEM images, has been about 10-30 nm. The tibacterial activities of various concentrations of Mn3O4-NPs against human pathogenic bacteria, mainly Escherichia coli and Staphylococcus aureus have been studied using the Broth Microdilution Method. The antibacterial assay showed that the Mn3O4-NPs prepared in this work inhibited the growth and multiplication of these tested microorganisms. The results of qualitative antibacterial tests revealed that gram negative bacteria (E. coli) were more sensitive to Mn3O4-NPs than gram positive bacteria (S. aureus).

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