Biological responses of Bacillus stratosphericus to Floating Electrode-Dielectric Barrier Discharge Plasma Treatment

Aims: Dielectric barrier discharge (DBD) plasma is used for sterilization of contaminated inanimate surfaces but seldomly optimized and depends upon the type of organisms and the plasma treatment duration, (net energy deposited) this efficacy varies. The proposed study was designed to see biological responses of one of the robust organism, Bacillus stratosphericus. Methods and Results: DBD plasma was applied over various durations to B. stratosphericus either surface-dried or suspension in de-ionized water, and viability, culturability, and viable but nonculturability (VBNC) were assayed using standard techniques. Depending upon the exposure of B. stratosphericus to DBD plasma resulted in three viability states, viable and culturable at low plasma doses and VBNC or disintegrated bacteria at higher plasma doses. Although organism's respiration levels at relatively low levels, immediately after plasma treatment, over the course of 24- h respiratory activity was increased c. eight times (and found still nonculturable during colony assays). Conclusions: The loss of culturability is hypothesized to be induced as one of the responses to oxidative stress and it remains to be unclear if the response is temporary or indefinite. Appropriate plasma powers should be used to avoid VBNC-like status. 2,3-Bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay is a good alternative method to detect VBNC state. Significance and Impact of the Study: Bacillus stratosphericus has the potential to turn into VBNC upon plasma application, and XTT assay can be an alternative method to detect VBNC state.