Determination of Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC)

Both MIC and MBC were determined by standardized methods, according to the Clinical and Laboratory Standards Institute (CLSI, 2015). The initial solutions of the NPs were prepared in sterilized distilled water. MIC of the nanoparticles was determined by the broth microdilution method in a 96-well plate (300 μL capacity, sterilized, MicroWell, NUNC, Thermo-Fisher Scientific, Waltham, MA), against Salmonella Typhimurium strains (Table 1). The MIC was determined as the lowest concentration of NPs that inhibited the visible bacterial growth after 24 h of incubation. Then, the broths used for MIC determination were subcultured onto fresh agar plates. After incubation, the number of viable cells was estimated by determining the number of colony-forming units (cfu). Based on this, the MBC was determined as the concentration of antimicrobial agent that causes the death of 99.9% of the initial inoculum, as previously reported (Díaz-García et al., 2020).