| Abstract: This study aimed to evaluate the bactericidal, bacteriostatic and sporicidal activity of the essential oils (EOs) of Copaifera multijuga and Thymus vulgaris against Alicyclobacillus acidoterrestris. The combined activity of the EOs and nisin was also assessed by determining the fractional inhibitory concentration (FIC). In addition, the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and minimum sporicidal concentration (MSC) were evaluated by serial microdilution in Bacillus acidoterrestris (BAT) broth with subcultures in BAT agar. The MIC of the C. multijuga and T. vulgaris EOs were 300 μg mL-1 and 500 μg mL-1, respectively, and the MBC of both EOs was >1,000 μg mL-1. The best MSC of C. multijuga was reached at a concentration of 500 μg mL-1 with a reduction of 3.07 log CFU mL-1. For the EO of T. vulgaris, better results were observed at concentrations higher than 500 μg mL-1, and a reduction of 2.05 log CFU mL-1 was achieved at 1,000 μg mL-1. The checkerboard method showed that the combination of EOs and nisin had an additive interaction (FIC index of 0.75). The bactericidal activity was confirmed by the death curve. According to the selectivity index, the treatment was less selective for A. acidoterrestris than for Vero cells. The flow cytometry results indicated that the vegetative forms of A. acidoterrestris had a higher incidence of vegetative cells with alterations in cell membrane integrity compared to their spores; however, we cannot conclude that this is the main mechanism of action of the EOs. Our studies showed that the tested substances had good antibacterial properties because they reduced the viability of A. acidoterrestris. Thus, it is evident that the EOs of C. multijuga and T. vulgaris have potential for use as antibacterial agents against A. acidoterrestris. |