Effect of preliminary stresses on the resistance of Escherichia coli and Staphylococcus aureus toward non-thermal plasma (NTP) challenge.

As the development of hurdle technology, cross-protection of various stresses for pathogens posed the potential risk to food safety and public health. This study tried to explore various preliminary stresses including acidity, osmosis, oxidation, heat and cold on the resistance of microbial cells toward the non-thermal plasma (NTP) exposure. The results indicated that short-term (4h) exposure of Staphylococcus aureus and Escherichia coli to acidity, osmosis, oxidation, heat and cold stresses did not lead to the resistance to the subsequent NTP treatment. On the contrary, acidity, osmosis and heat preadaptation increased the vulnerability of E. coli cells to NTP treatment. After exposing S. aureus to osmosis, oxidation, heat and cold stress for longer period (24h), the reduction level showed significantly (P<0.05) higher. Interestingly, long-term (24h) preliminary exposure of acidic stress exhibited protective effect for S. aureus against the following NTP exposure with less damage in cell membrane integrity, membrane potential and intracellular enzyme activity. It might be due to the protein production for oxidative stress response during preliminary acidic adaptation. In general, the obtained result helped to grasp better understanding of the microbial stress response to NTP treatment and provided insight for the future research in order to accelerate the development of NTP technology in food industry.