Synthesis and Antibacterial Activity of Manganese-Ferrite/Silver Nanocomposite Combined with Two Essential Oils

Abstract

The antimicrobial activity of metal nanoparticles obtained by biogenic routes has been extensively reported. However, their combined use with other antimicrobial formulations, such as essential oils, remains scarcely explored. In this work, a manganese-ferrite/silver nanocomposite (MnFe2O4/Ag-NC) was synthesized in a two-step procedure: first, MnFe2O4 nanoparticles were produced by a coprecipitation method, followed by in situ biogenic reduction of silver ions using Galega officinalis. MnFe2O4/Ag-NC was characterized using transmission electron microscopy (TEM), scanning electron microscopy equipped with an energy dispersive X-ray analyzer (SEM-EDX), and a vibrating sample magnetometer (VSM-SQUID). The antibacterial activity if MnFe2O4/Ag-NC was evaluated against Pseudomonas syringae by determining its minimum inhibitory concentration (MIC) in the presence of two essential oils: eucalyptus oil (EO) and garlic oil (GO). The fractional inhibitory concentration (FIC) was also calculated to determine the interaction between MnFe2O4/Ag-NC and each oil. The MIC of MnFe2O4/Ag-NC was eightfold reduced with the two essential oils (from 20 to 2.5 µg mL−1). However, the interaction with EO was synergistic (FIC: 0.5), whereas the interaction with GO was additive (FIC: 0.75). Additionally, a time-kill curve analysis was performed, wherein the MIC of the combination of MnFe2O4/Ag-NC and EO provoked a rapid bactericidal effect, corroborating a strong synergism. These findings suggest that by combining MnFe2O4/Ag-NC with essential oils, the necessary ratio of the nanocomposite to control phytopathogens can be reduced, thus minimizing the environmental release of silver.