Determining Garlic and Ginger Oil's Sub-Inhibitory Concentration

The sub-inhibitory concentration (SIC) of garlic and ginger oil was determined according to a previously published protocol [10 (link)]. Two-fold dilutions of garlic and ginger oil (0, 2.5, 1.25, 0.625, 0.312, 0.156, 0.078, 0.039%) were prepared in a sterile 96-well plate (Costar, Corning, NY, USA) containing 100 μL of TSB broth. Ethanol was also included at the concentrations found in the corresponding garlic and ginger samples. Wells were subsequently inoculated with 100 μL of S. infantis, S. typhimurium, or S. enteritidis (~10⁶ CFU/mL). Plates were placed in a Cytation 5 multimode microplate reader (Agilent, Santa Clara, CA, USA) and incubated at 37 °C for 24 h with OD600 readings taken every 30 min. Following incubation, samples were diluted, plated onto XLD plates, and incubated for 24 h at 37 °C for Salmonella enumeration. All concentrations were run in duplicate, and experiments were repeated three times for each Salmonella strain. The highest concentration of phytochemicals that did not inhibit Salmonella growth was selected as the SIC and used in subsequent experiments.