The inactivation efficacy of plasma-activated acetic acid against Salmonella Typhimurium cells and biofilm

Aim: This study aimed to examine the inactivation efficacy of plasma-activated acetic acid (PAAA) against Salmonella Typhimurium cells and biofilm and elucidate underlying chemical inactivation pathway. Methods and Results: PAAA was prepared by discharging plasma to 20 ml of 0.2% (v/v) acetic acid (AA) for 20 min (2.2 kHz and 8.4 kVpp). The count of cells and biofilms decreased by 5.71 log CFU ml⁻¹ and 4 log CFU/cm² after 10 min of treatment with 0.2% PAAA and 0.4% PAAA compared with control group (without any treatment), respectively. In 0.2% PAAA, the concentrations of hydrogen peroxide (H₂O₂) and nitrate anions were directly proportional to the plasma discharge time, whilst nitrite anion (NO₂⁻) was not detected. However, the pH values of both 0.2% PAAA and plasma-activated water were inversely proportional to the plasma discharge time. Treatment with catalase, L-histidine, D-mannitol and sodium azide inhibited the antibacterial activity of PAAA. Conclusion: H₂O₂, singlet oxygen, hydroxyl radical and NO₂⁻ are involved in the generation and decomposition of peroxynitrous acid generated from PAAA functioned as intermediate agent, which could diffuse through cell membranes of bacteria and induce cell injury. Significance and Impact of Study: This study provides the understanding of efficacy and selectivity of PAAA which could be a novel decontamination agent.