Antibacterial activity and mechanism of thymol against Alicyclobacillus acidoterrestris vegetative cells and spores

Alicyclobacillus acidoterrestris has received much attention due to its unique thermo-acidophilic property and implication in the spoilage of pasteurized juices. The aim of this study was to investigate the antibacterial characteristics and mechanisms of thymol against A. acidoterrestris vegetative cells and spores. Minimum inhibition concentration (MIC) and minimum bactericidal concentration (MBC) of thymol against vegetative cells were both 0.25 mg/mL. MIC of thymol against spores was 0.5 mg/mL, and the MBC was greater than 1.0 mg/mL. Thymol could effectively inhibit A. acidoterrestris growth, spore germination and guaiacol production. When treated by thymol, the leakage of nucleic acids and proteins from A. acidoterrestris cells and spores increased significantly. SDS-PAGE investigation of bacterial proteins showed that the loss of soluble proteins was obvious as well. Scanning electron microscopy observation exhibited that A. acidoterrestris cells or spores treated with thymol had a severe morphological damage. These results demonstrated that thymol exerted its good antibacterial activities by destroying the integrity of the cell and spore. This study provides a new method for the inactivation of A. acidoterrestris in fruit juice.