Inactivation kinetics of cold oxygen plasma depend on incubation conditions of Aeromonas hydrophila biofilm on lettuce

Abstract

Disease outbreaks from fresh produce have been increasing as a result of the increasing global consumption of produce. We evaluated the efficiency of cold oxygen plasma (COP), a new technology for the decontamination of fresh produce, in reducing biofilm of Aeromonas hydrophila, an emerging food-borne pathogen on lettuce. Lettuce leaves were inoculated with A. hydrophila at different temperatures to form biofilm and planktonic populations, and the inactivation kinetics of COP were determined using a modified Weibull model. To elucidate the antimicrobial mechanism of COP, we used field emission scanning electron microscopy (FESEM) and a quorum sensing (QS) assay. We found that 5min of treatment with COP significantly (p<0.05) reduced the biofilm populations of A. hydrophila on lettuce by 5.0-log incubation at lower than 15°C, whereas biofilm populations displayed enhanced resistance to COP treatment at higher temperatures (≥15°C). Planktonic populations also decreased by >5.0-log within 15s treatment of COP by incubating at any temperature. The mean Td-values for a 5-log reduction (analogous to the traditional D-value) ranged from 4.4–8.1s and 1.84–25.33min for the planktonic and biofilm populations, respectively. However, higher temperatures (≥15°C) resulted in a significantly higher QS (p<0.05) as well as biofilm formation and internalization in stomata, suggesting that higher biofilm formation and internalization might be the main factors mediating resistance to COP. In summary, this study highlights the impact of temperature on the modulation of QS, biofilm formation, internalization, and COP resistance in lettuce.