Abstract
Bacteria can be inactivated through various physical and chemical means, and these have always been the focus of extensive research. To further improve the methodology for these ends, two types of plasma systems were investigated: nano-second pulsed plasma (NPP) as liquid discharge plasma and an Argon gas-feeding dielectric barrier discharge (Ar-DBD) as a form of surface plasma. To understand the sterilizing action of these two different plasma sources, we performed experiments with Staphylococcus aureus (S. aureus) bacteria (wild type) and multidrug resistant bacteria (Penicillum-resistant, Methicillin-resistant and Gentamicin-resistant). We observed that both plasma sources can inactivate both the wild type and multidrug-resistant bacteria to a good extent. Moreover, we observed a change in the surface morphology, gene expression and β-lactamase activity. Furthermore, we used X-ray photoelectron spectroscopy to investigate the variation in functional groups (C-H/C-C, C-OH and C=O) of the peptidoglycan (PG) resulting from exposure to plasma species. To obtain atomic scale insight in the plasma-cell interactions and support our experimental observations, we have performed molecular dynamics simulations to study the effects of plasma species, such as OH, H2O2, O, O3, as well as O2 and H2O, on the dissociation/formation of above mentioned functional groups in PG.
Highlights
Found to be a result of methicillin-resistant S. aureus[1,7]
Many kinds of nano-second pulsed plasma (NPP) and DBD plasma sources have been reported in the literature to inactivate different types of bacteria[9,10,11,20,21,22,23]
We have used an NPP to its 4th discharge because we observed in our earlier work that the flux of reactive species (RS) created by the NPP increases as the number of discharges increases[13]
Summary
Found to be a result of methicillin-resistant S. aureus[1,7]. gentamicin-resistant S. aureus has been clinically isolated, and its mechanism has been observed to be different from that of penicillin and methicillin[8]. Atmospheric pressure non-thermal plasma (APP) provides a means to efficiently and effectively control multidrug resistant microorganisms[9,10]. Many studies have investigated plasma-based sterilization of immobilized microorganisms on a material surface under dry condition[20,21,22]. Reactive species and free radicals in the gas phase directly damage microorganisms[20,21,22], sterilization under wet conditions is important for a variety of practical applications. We investigate two types of APP systems in this work: one is nano-second pulsed plasma (NPP) as liquid discharge plasma and the other is an Argon gas feeding dielectric barrier discharge (Ar-DBD) as surface plasma. We use S. aureus bacteria (wild type) and multidrug-resistant bacteria (Penicillum-resistant S. aureus (PRSA), Methicillin-resistant S. aureus (MRSA) and Gentamicin-resistant S. aureus (GRSA)) to understand the plasma activity. We studied the interaction of the reactive (i.e., O, OH, O3 and H2O2) as well as non-reactive (i.e., O2, H2O) plasma species with PG of S. aureus, using reactive molecular dynamics (MD) simulations
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