Abstract
Bacteria exist, in most environments, as complex, organised communities of sessile cells embedded within a matrix of self-produced, hydrated extracellular polymeric substances known as biofilms. Bacterial biofilms represent a ubiquitous and predominant cause of both chronic infections and infections associated with the use of indwelling medical devices such as catheters and prostheses. Such infections typically exhibit significantly enhanced tolerance to antimicrobial, biocidal and immunological challenge. This renders them difficult, sometimes impossible, to treat using conventional chemotherapeutic agents. Effective alternative approaches for prevention and eradication of biofilm associated chronic and device-associated infections are therefore urgently required. Atmospheric pressure non-thermal plasmas are gaining increasing attention as a potential approach for the eradication and control of bacterial infection and contamination. To date, however, the majority of studies have been conducted with reference to planktonic bacteria and rather less attention has been directed towards bacteria in the biofilm mode of growth. In this study, the activity of a kilohertz-driven atmospheric pressure non-thermal plasma jet, operated in a helium oxygen mixture, against Pseudomonas aeruginosa in vitro biofilms was evaluated. Pseudomonas aeruginosa biofilms exhibit marked susceptibility to exposure of the plasma jet effluent, following even relatively short (∼10′s s) exposure times. Manipulation of plasma operating conditions, for example, plasma operating frequency, had a significant effect on the bacterial inactivation rate. Survival curves exhibit a rapid decline in the number of surviving cells in the first 60 seconds followed by slower rate of cell number reduction. Excellent anti-biofilm activity of the plasma jet was also demonstrated by both confocal scanning laser microscopy and metabolism of the tetrazolium salt, XTT, a measure of bactericidal activity.
Highlights
Microbial biofilms are organised, multicellular communities held together by a self-produced matrix forming architecturally complex structures [1,2,3]
Whilst a number of studies have examined the effect of atmospheric pressure non-thermal plasmas on microbial biofilms [39,40,41,42,43,44,45,46,47], this study presents a comprehensive investigation of the activity of an in-house designed kHz-driven atmospheric pressure non-thermal plasma jet for the in vitro eradication of the clinically significant P. aeruginosa biofilms grown on inanimate surfaces
Bacterial Growth Inhibition Zones In order to visually demonstrate the effect of the investigated atmospheric pressure plasma jet on the viability of bacterial cells, MH agar plates seeded with P. aeruginosa were exposed to the plasma plume and incubated overnight
Summary
Multicellular communities held together by a self-produced matrix forming architecturally complex structures [1,2,3]. With many millions of medical devices being used each year [11], biofilms constitute a significant public health risk for patients requiring such devices [12]. Among these devices are: intravenous catheters, prosthetic heart valves, joint prostheses, peritoneal dialysis catheters, cardiac pacemakers, cerebrospinal fluid shunts, urethral catheters, urinary stents and endotracheal tubes, which all have an intrinsic risk of surface-associated infections [5]. Biofilms have been associated with many other conditions, on biotic surfaces, including dental plaque, upper respiratory infections, peritonitis, and urogenital infections [11]
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