Control of methicillin-resistant Staphylococcus aureus in planktonic form and biofilms: A biocidal efficacy study of nonthermal dielectric-barrier discharge plasma

Background: Bacterial contamination of surfaces with methicillin-resistant Staphylococcus aureus (MRSA) is a serious problem in the hospital environment and is responsible for significant nosocomial infections. The pathogenic contaminants form biofilms, which are difficult to treat with routine biocides. Thus, a continuous search for novel disinfection methods is essential for effective infection control measures. This demonstration of a novel technique for the control of virulent pathogens in planktonic form as well as in established biofilms may provide a progressive alternative to standard methodology. Methods: We evaluated a novel technique of normal atmospheric nonthermal plasma known as floating-electrode dielectric-barrier discharge (FE-DBD) plasma against a control of planktonic and biofilm forms of Escherichia coli, S aureus, multidrug-resistant methicillin-resistant S aureus (MRSA)-95 (clinical isolate), -USA300, and -USA400, using widely accepted techniques such as colony count assay, LIVE/DEAD BacLight Bacterial Viability assay, and XTT (2,3-Bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5- carboxanilide) assay. Results: Exposure of free living planktonic forms of E coli, S aureus, and MRSA were rapidly inactivated by DBD plasma. Approximately 10(7) bacterial cells were completely (100%) killed, whereas 10(8) and 10(9) were reduced by approximately 90% to 95% and 40% to 45%, respectively, in less than 60 seconds (7.8 J/cm(2)) and completely disinfected in <= 120 seconds. In established biofilms, the susceptibility of MRSA USA400 was comparable with USA300 but less susceptible than MRSA95 (clinical isolate), S aureus, and E coli (P<.05) to FE-DBD plasma, and plasma was able to kill MRSA more than 60% within 15 seconds (1.95 J/cm(2)). The killing responses were plasma exposure-time dependent, and cell density dependent. The plasma was able disinfect surfaces in a less than 120 seconds. Conclusion: Application of DBD plasma can be a valuable decontamination technique for the removal of planktonic and biofilm-embedded bacteria such as MRSA-USA 300,-USA 400, methicillin-sensitive S aureus (MSSA), and E coli, the more common hospital contaminants. Of interest, E coli was more resistant than S aureus phenotypes.