Biosynthesis and antibacterial activity of manganese oxide nanoparticles prepared by green tea extract

Amongst chemical and physical techniques, the biosynthesis method of metal nanoparticles has received the interest of many researchers owing to its environmental safety, simplicity and inexpensiveness. Manganese oxide nanoparticles (MnO NPs) were successfully synthesised using green tea extract as the reducing agent and characterised by UV–Vis spectroscopy, X-ray diffractometry and Fourier transform infrared spectroscopy. The shape and size of the MnO NPs were obtained by scanning electron microscopy. The size of the MnO NPs was 20–30 nm. The MnO NPs exhibited strong antibacterial activity against pathogenic bacteria, namely, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa, with inhibition zones of 12, 14 and 18 mm, respectively. Moreover, the minimum inhibitory concentration (MIC) of the MnO NPs was 12.5 U/mL as determined by resazurin microtitre assay. The activities of some antibiotics remarkably increased when combined with MnO NPs (at MIC).