In vitro efficacy of cold atmospheric pressure plasma on S. sanguinis biofilms in comparison of two test models

The Antimicrobial Effect of Cold Atmospheric Plasma against Dental Pathogens-A Systematic Review of In-Vitro Studies

Interest in the application of cold atmospheric plasma (CAP) in the medical field has been increasing. Indications in dentistry are surface modifications and antimicrobial interventions. The antimicrobial effect of CAP is mainly attributed to the generation of reactive oxygen and reactive nitrogen species. The aim of this article is to systematically review the available evidence from in-vitro studies on the antimicrobial effect of CAP on dental pathogens. A database search was performed (PubMed, Embase, Scopus). Data concerning the device parameters, experimental set-ups and microbial cultivation were extracted. The quality of the studies was evaluated using a newly designed assessment tool. 55 studies were included (quality score 31-92%). The reduction factors varied strongly among the publications although clusters could be identified between groups of set pathogen, working gases, and treatment time intervals. A time-dependent increase of the antimicrobial effect was observed throughout the studies. CAP may be a promising alternative for antimicrobial treatment in a clinically feasible application time. The introduced standardized protocol is able to compare the outcome and quality of in-vitro studies. Further studies, including multi-species biofilm models, are needed to specify the application parameters of CAP before CAP should be tested in randomized clinical trials.

Low-Temperature Plasma as an Approach for Inhibiting a Multi-Species Cariogenic Biofilm

This study aimed to determine how low-temperature plasma (LTP) treatment affects single- and multi-species biofilms formed by Streptococcus mutans, Streptococcus sanguinis, and Streptococcus gordonii formed on hydroxyapatite discs. LTP was produced by argon gas using the kINPen09™ (Leibniz Institute for Plasma Science and Technology, INP, Greifswald, Germany). Biofilms were treated at a 10 mm distance from the nozzle of the plasma device to the surface of the biofilm per 30 s, 60 s, and 120 s. A 0.89% saline solution and a 0.12% chlorhexidine solution were used as negative and positive controls, respectively. Argon flow at three exposure times (30 s, 60 s, and 120 s) was also used as control. Biofilm viability was analyzed by colony-forming units (CFU) recovery and confocal laser scanning microscopy. Multispecies biofilms presented a reduction in viability (log10 CFU/mL) for all plasma-treated samples when compared to both positive and negative controls (p < 0.0001). In single-species biofilms formed by either S. mutans or S. sanguinis, a significant reduction in all exposure times was observed when compared to both positive and negative controls (p < 0.0001). For single-species biofilms formed by S. gordonii, the results indicate total elimination of S. gordonii for all exposure times. Low exposure times of LTP affects single- and multi-species cariogenic biofilms, which indicates that the treatment is a promising source for the development of new protocols for the control of dental caries.

The Emerging Role of Cold Atmospheric Plasma in Implantology: A Review of the Literature

In recent years, cold atmospheric plasma (CAP) technologies have received increasing attention in the field of biomedical applications. The aim of this article is to review the currently available literature to provide an overview of the scientific principles of CAP application, its features, functions, and its applications in systemic and oral diseases, with a specific focus on its potential in implantology. In this narrative review, PubMed, Medline, and Scopus databases were searched using key words like “cold atmospheric plasma”, “argon plasma”, “helium plasma”, “air plasma”, “dental implants”, “implantology”, “peri-implantitis”, “decontamination”. In vitro studies demonstrated CAP’s potential to enhance surface colonization and osteoblast activity and to accelerate mineralization, as well as to determine a clean surface with cell growth comparable to the sterile control on both titanium and zirconia surfaces. The effect of CAP on biofilm removal was revealed in comparative studies to the currently available decontamination modalities (laser, air abrasion, and chlorhexidine). The combination of mechanical treatments and CAP resulted in synergistic antimicrobial effects and surface improvement, indicating that it may play a central role in surface “rejuvenation” and offer a novel approach for the treatment of peri-implantitis. It is noteworthy that the CAP conditioning of implant surfaces leads to an improvement in osseointegration in in vivo animal studies. To the best of our knowledge, this is the first review of the literature providing a summary of the current state of the art of this emerging field in implantology and it could represent a point of reference for basic researchers and clinicians interested in approaching and testing new technologies.

Medically important biofilms and non-thermal plasma

In recent decades, the non-thermal plasma, i.e. partially or completely ionized gas produced by electric discharges at ambient temperature, has become of interest for its microbiocidal properties with potential of use in the food industry or medicine. Recently, this interest focuses not only on the planktonic forms of microorganisms but also on their biofilms. The works in this interdisciplinary field are summarized in this review. The wide range of biofilm-plasma interactions is divided into studies of general plasma action on bacteria, on biofilm and on its oral and dental application; a short overview of plasma instrumentation is also included. In addition, not only biofilm combating but also an important area of biofilm prevention is discussed. Various DC discharges of the point-to-plane type. Author's photograph, published in Khun et al. (Plasma Sources Sci Technol 27:065002, 2018).

Nonthermal Plasma Jet Treatment Negatively Affects the Viability and Structure of Candida albicans SC5314 Biofilms

Microorganisms are predominantly organized in biofilms, where cells live in dense communities and are more resistant to external stresses than are their planktonic counterparts. With in vitro experiments, the susceptibility of Candida albicans biofilms to a nonthermal plasma treatment (plasma source, kINPen09) in terms of growth, survival, and cell viability was investigated. C. albicans strain SC5314 (ATCC MYA-2876) was plasma treated for different time periods (30 s, 60 s, 120 s, 180 s, 300 s). The results of the experiments, encompassing CFU, fluorescence Live/Dead, and 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide salt (XTT) assays, revealed a negative influence of the plasma treatment on the proliferation ability, vitality, and metabolism of C. albicans biofilms, respectively. Morphological analysis of plasma-treated biofilms using atomic force microscopy supported the indications for lethal plasma effects concomitant with membrane disruptions and the loss of intracellular fluid. Yielding controversial results compared to those of other publications, fluorescence and confocal laser scanning microscopic inspection of plasma-treated biofilms indicated that an inactivation of cells appeared mainly on the bottom of the biofilms. If this inactivation leads to a detachment of the biofilms from the overgrown surface, it might offer completely new approaches in the plasma treatment of biofilms. Because of plasma's biochemical-mechanical mode of action, resistance of microbial cells against plasma is unknown at this state of research.IMPORTANCE Microbial communities are an increasing problem in medicine but also in industry. Thus, an efficient and rapid removal of biofilms is becoming increasingly important. With the aid of the kINPen09, a radiofrequency plasma jet (RFPJ) instrument, decisive new findings on the effects of plasma on C. albicans biofilms were obtained. This work showed that the inactivation of biofilms takes place mainly on the bottom, which in turn offers new possibilities for the removal of biofilms by other strategies, e.g., mechanical treatment. This result demonstrated that nonthermal atmospheric pressure plasma is well suited for biofilm decontamination.

Establishing a laboratory model of dental unit waterlines bacterial biofilms using a CDC biofilm reactor

In this study, a laboratory model to reproduce dental unit waterline (DUWL) biofilms was developed using a CDC biofilm reactor (CBR). Bacteria obtained from DUWLs were filtered and cultured in Reasoner's 2A (R2A) for 10 days, and were subsequently stored at -70°C. This stock was cultivated on R2A in batch mode. After culturing for five days, the bacteria were inoculated into the CBR. Biofilms were grown on polyurethane tubing for four days. Biofilm accumulation and thickness was 1.3 × 10⁵ CFU cm^-2 and 10-14 μm respectively, after four days. Bacteria in the biofilms included cocci and rods of short and medium lengths. In addition, 38 bacterial genera were detected in biofilms. In this study, the suitability and reproducibility of the CBR model for DUWL biofilm formation were demonstrated. The model provides a foundation for the development of bacterial control methods for DUWLs.