We assessed the efficacy of bacterial inactivation using a dielectric barrier discharge in three different plasma setups: plasma gas (PG), and direct and indirect plasma activated water (PAW), where deionized water was placed either between or away from the electrodes, respectively. We used bioluminescent Escherichia coli K12 lux as a model bacteria in a biosensor format to study the inactivation kinetics and mechanism of action of produced PG and PAW. The results showed that uninterrupted application of PG decreased bioluminescence rapidly by 1-log within the first minute and 3.6-log after 10 min of treatment. Exposing the bacterial culture with a sublethal dose of PAW (1 mL) rapidly decreased the bioluminescence; however, luminescence slowly recovered after exposure. Subsequent treatment with PAW decreased the bioluminescence to a lesser extent. In addition, direct PAW induced a greater decrease in bioluminescence compared to indirect treatments for both single and multiple exposures. In contrast to the PG, PAW treatments induced a lower bactericidal effect with 0.11 to 0.22-log reduction for indirect PAW and 0.2 to 0.32-log for direct PAW. Our results also indicate that antimicrobial activity of PAW decreased slowly within 20 min of its preparation. The rapid decrease in bioluminescence followed by a partial recovery in a repeatable pattern suggests an incomplete inactivation, and that the reducing power of the cell helps them to survive. Moreover, the complete and partial oxidation of NADH solutions in vitro by PG and PAW, respectively, strongly suggest that the lux fluorophore FMNH₂ and other reducing cofactors could be the target of such treatment before other cell components. This hypothesis was supported by the tendency to recover luminescence by potentially replenishing the pool of FMNH₂ after plasma treatment. It is also important to consider that the reducing power of the cell (NADH, NADPH, and FMNH₂) is crucial for cell viability mostly due to reducing potential for critical metabolic reactions. Therefore, in situ bioluminescence monitoring technology can potentially serve as a unique approach to elucidate the mechanism of bacteria inactivation in real time.

Industrial relevance

The present study developed three dielectric barrier discharge (DBD) plasma setups to produce plasma gas and plasma activated water, which can disinfect both food products and their contact surfaces regardless of geometry. Our in situ bioluminescent technology elucidated bacterial inactivation mechanisms of plasma treatments, which may potentially suggest sufficient exposures to plasma resulting in safe food products without deteriorating their quality. The results will help food manufacturers apply new plasma-based disinfection methods with appropriate treatments.

中文翻译：

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利用生物发光技术表征大气等离子气体和活化水的细菌失活机理

我们在三种不同的等离子体设置中使用介电势垒放电评估了细菌灭活的功效：等离子体气体（PG），直接和间接等离子体活化水（PAW），分别将去离子水置于电极之间或远离电极。我们使用了生物发光大肠杆菌K12 lux以生物传感器的形式作为模型细菌来研究所产生的PG和PAW的失活动力学和作用机理。结果表明，不间断地应用PG可以在第一分钟内迅速降低1log的生物发光，而在处理10分钟后降低3.6log的生物发光。将亚致死剂量的PAW（1 mL）暴露于细菌培养物中会迅速降低生物发光。但是，曝光后发光缓慢恢复。随后用PAW处理降低了生物发光的程度。另外，与单次和多次暴露的间接治疗相比，直接PAW引起的生物发光更大的减少。与PG相比，PAW处理具有较低的杀菌效果，间接PAW降低0.11至0.22 log，直接PAW降低0.2至0.32 log。我们的结果还表明，PAW的抗菌活性在制备后20分钟内缓慢下降。生物发光的迅速下降，然后以可重复的模式部分恢复，表明其不完全失活，并且细胞的降低能力有助于它们存活。此外，NADH溶液的全部和部分氧化PG和PAW分别在体外进行的实验强烈表明，在其他细胞组分之前，lux荧光团FMNH ₂和其他还原性辅助因子可能是此类治疗的目标。通过在等离子处理后潜在地补充FMNH ₂库来恢复发光的趋势支持了该假设。同样重要的是要考虑到，细胞的还原能力（NADH，NADPH和FMNH ₂）对于细胞活力至关重要，这主要是因为降低了关键代谢反应的潜力。因此，原位生物发光监测技术可以潜在地用作实时阐明细菌灭活机理的独特方法。

行业相关性

本研究开发了三种介电势垒放电（DBD）等离子装置，以产生等离子气体和等离子活化水，可以对食品及其接触表面进行消毒，而不管其几何形状如何。我们的原位生物发光技术阐明了血浆处理的细菌失活机制，这可能潜在地表明对血浆的充分暴露可产生安全的食品而不降低其质量。结果将有助于食品制造商采用经过适当处理的基于血浆的新型消毒方法。