A Study on the antibacterial mechanism of thymol against Aeromonas hydrophila in vitro

As a zoonotic pathogen, Aeromonas hydrophila (A. hydrophila) not only has important economic significance in aquaculture but also plays an important role in global public health. With the abuse of antibiotics, the drug resistance of A. hydrophila has greatly increased, causing a poor therapeutic effect. It is particularly important to develop antibiotics alternatives against resistant bacteria. Thymol, a natural monoterpene phenolic compound, has been reported to have a variety of pharmacological effects. In this study, the effects of thymol on A. hydrophila were evaluated. The MIC and MBC of thymol to A. hydrophila were 128 μg/mL and 256 μg/mL, respectively. The results of the electron microscope showed that the bacterial cells contracted and deformed, the cell membrane was destroyed, and the cytoplasm was lost when treated with 2MIC thymol. Compared with the control group, the conductivity and the amount of DNA leakage of bacteria treated with 2MIC thymol increased by 2.45% and 66.4 μg/mL, respectively. In addition, LDH activity decreased by 25.93% after 2MIC thymol treatment. DAPI staining results showed that the intensity and quantity of fluorescence were significantly decreased in the drug treatment group. In summary, the antibacterial mechanism of thymol was to destroy the integrity of the cell membrane, make intracellular material exudate, and eventually lead to the death of bacteria. Thymol has the potential to be an antibiotics alternative against resistant bacteria.