Assessment of Microbicidal Activity of Atmospheric Pressure Non-Thermal Plasma Against Planktonic and Biofilm Forms

Background:Atmospheric pressure non-thermal plasma (APNTP) is a promising, relatively novel method for destroying microorganisms either in planktonic or biofilm form, alternative to “conventional” methods which have numerous drawbacks. Aim of the work: To assess the microbicidal activity of atmospheric pressure non-thermal plasma (APNTP) on planktonic and biofilm forms. Subjects and methods: This study was performed on Staphylococcus aureus (S. aureus), coagulase negative staphylococci (CoNS), Pseudomonas (P.) aeruginosa and Escherichia (E.) coli isolates from patients with indwelling medical devices associated infections in different intensive care units (ICUs), Zagazig University Hospitals. Detection of biofilm forming ability of these isolates was done by tube method (TM). Planktonic and biofilm counterpart of selected biofilm forming isolates were exposed to APNTP for different durations to assess the biocidal efficacy of plasma on both microbial forms by colony forming unit (CFU) count and/or 2,3-Bis-(2-Methoxy-4-Nitro-5- Sulfophenyl)-2H-Tetrazolium-5-Carboxanilide (XTT), assay. APNTP morphological changes in E. coli and S. aureus were assessed by transmission electron microscopic (TEM) imaging. Results: APNTP treatment of S. aureus, E. coli suspensions caused progressive reduction in surviving bacterial count and metabolic activity with increasing treatment duration and at 180 seconds of exposure complete sterilization achieved. Similar but more prolonged effect was detected on CoNS and P. aeruginosa suspensions. Its exposure for 240 seconds was needed for their complete sterilization. There was no difference between bacterial percentage reduction calculated by CFU count and XTT assay except in P. aeruginosa suspension for 60 seconds. No observed difference between APNTP effect on planktonic gram positive (GP) and gram negative (GN) bacteria. On the other hand, GN bacterial biofilm was more resistant to APNTP than GP bacterial biofilm. TEM showed that in both S. aureus and E. coli there were significant morphological changes after exposure to plasma. Conclusion: The efficacy of APNTP was proved for in vitro decontamination of planktonic and biofilm forms of S. aureus, CoNS, P. aeruginosa and E. coli that are responsible for many healthcare-acquired infections (HCAIs).