Non-thermal microwave argon plasma affects interactions of Listeria monocytogenes with mammalian cells but it does not kill the intracellular pathogen

Effects of microwave argon non-thermal plasma (NTP) on the facultative intracellular pathogen Listeria monocytogenes were studied. NTP treatment for 2 min caused a 3 log 10 decrease of wild type strain EGDe extracellular bacteria. Similar treatment of infected HEK293 cells caused a 1.5-fold decrease of intracellular EGDe bacteria. The intraphagosomal EGDeΔhly lacked the pore-forming toxin LLO was resistant to NTP. Cell pretreatment with NTP before infection increased EGDe invasion of human HEK293 and murine C26 cells 2.5 and 1.7-fold, respectively. HEK293 cell pretreatment did not affect invasion by EGDe ΔinlA that lacked the invasion factor InlA. Taken together, obtained results demonstrated that a direct NTP effect on intracellular L. monocytogenes was low, still NTP affected interactions between L. monocytogenes and the host cell.