Physicochemical, Mechanical, and Molecular Properties of Nonlysogenic and P22-Lysogenic Salmonella Typhimurium Treated with Citrus Oil

The aim of this study was to evaluate the phenotypic and genotypic properties of nonlysogenic Salmonella Typhimurium (ST^P22−) and lysogenic Salmonella Typhimurium (ST^P22+) in the presence of sublethal concentrations (SLC_2D) of citrus essential oils (CEOs), which were used to evaluate antimicrobial susceptibility, cell surface hydrophobicity, autoaggregation ability, bacterial motility, lysogenic conversion, gene expression patterns, and antibiofilm formation. The SLC_2D values of non–heat-treated (N-CEO) and heat-treated (H-CEO) CEO in an autoclave at 121°C for 20 min were 2.0 to 2.1 mg/ml against ST^P22− and 1.7 to 1.9 mg/ml against ST^P22+. The rates of injured ST^P22− and ST^P22+ cells treated with SLC_2D of N-CEO and H-CEO ranged from 67 to 83%. The hydrophobicity and autoaggregation were decreased to 2.5 and 19.5% for ST^P22− and 4.7 and 21.7% for ST^P22+, respectively, in the presence of N-CEO. A noticeable reduction in the swarming motility was observed in ST^P22− with N-CEO (14.5%) and H-CEO (13.3%). The numbers of CEO-induced P22 were 5.40 log PFU/ml for N-CEO and 5.65 log PFU/ml for H-CEO. The relative expression of hilA, hilC, hilD, invA, invC, invE, invF, sirA, and sirB was down-regulated in ST^P22− and ST^P22+ with N-CEO and H-CEO. The numbers of adherent ST^P22− and ST^P22+ were effectively reduced by more than 1 log in the presence of CEO. These results suggest that CEO has potential to be used to control bacterial attachment, colonization, and invasion.