*Article* **Antibiotic-Resistant and Non-Resistant Bacteria Display Similar Susceptibility to Dielectric Barrier Discharge Plasma**

**Akikazu Sakudo 1,2,\* and Tatsuya Misawa <sup>3</sup>**


Received: 30 July 2020; Accepted: 31 August 2020; Published: 31 August 2020

**Abstract:** Here, we examined whether antibiotic-resistant and non-resistant bacteria show a differential susceptibility to plasma treatment. *Escherichia coli* DH5α were transformed with pPRO-EX-HT-CAT, which encodes an ampicillin resistance gene and chloramphenicol acetyltransferase (CAT) gene, and then treated with a dielectric barrier discharge (DBD) plasma torch. Plasma treatment reduced the viable cell count of *E. coli* after transformation/selection and further cultured in ampicillin-containing and ampicillin-free medium. However, there was no significant difference in viable cell count between the transformed and untransformed *E. coli* after 1 min- and 2 min-plasma treatment. Furthermore, the enzyme-linked immunosorbent assay (ELISA) and acetyltransferase activity assay showed that the CAT activity was reduced after plasma treatment in both transformed and selected *E. coli* grown in ampicillin-containing or ampicillin-free medium. Loss of lipopolysaccharide and DNA damage caused by plasma treatment were confirmed by a Limulus test and polymerase chain reaction, respectively. Taken together, these findings suggest the plasma acts to degrade components of the bacteria and is therefore unlikely to display a differential affect against antibiotic-resistant and non-resistant bacteria. Therefore, the plasma method may be useful in eliminating bacteria that are recalcitrant to conventional antibiotic therapy.

**Keywords:** antibiotic resistant bacteria; antibiotic resistance gene; disinfection; *E. coli*; inactivation; plasma; sterilization
