Bacteria embedded within biofilms present a challenge to surface decontamination by conventional means. Atmospheric pressure non-thermal plasma processes have emerged as a promising approach to overcoming this problem. We used atmospheric pressure non-equilibrium plasmas (APNPs) to assess planktonic versus biofilm-resident bacterial (Neisseria gonorrhoeae) susceptibility to treatment. The decontamination efficiency of the process was evaluated against bacteria embedded within a biofilm, as well as planktonic cells placed on a glass surface. Bacterial survival was assessed using a combination of colony forming unit (CFU) ability and vital staining with a combination of SYTO9 plus propidium iodide. Both methods revealed an increased resistance of biofilm-resident bacteria compared with planktonic cells, after a 20-min exposure to the APNPs. Transmission electron microscopy revealed disruption and damage to the cell wall, resulting in the release of cytoplasmic compounds, alterations in morphology, and a decrease in cell volume, indicating that APNPs may affect the cell wall. Present results show that biofilm-resident bacteria demonstrate augmented survival when exposed to APNP treatment and therefore that decontamination procedures should take into account this survival when evaluating surface decontamination measures.

We confirmed that IGFBP7 is a negative immunohistochemical marker for DFSPs and the combination with CD34, FXIIIa and ST-3 immunostaining could make the distinction more reliable.

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