Cold Atmospheric-Pressure Plasma Caused Protein Damage in Methicillin-Resistant Staphylococcus aureus Cells in Biofilms

Staphylococcus aureus strains exhibit heterogenous tolerance to direct cold atmospheric plasma therapy

The global clinical and socioeconomic impact of chronic wounds is substantial. The main difficulty that clinicians face during the treatment of chronic wounds is the risk of infection at the wound site. Infected wounds arise from an accumulation of microbial aggregates in the wound bed, leading to the formation of polymicrobial biofilms that can be largely resistant to antibiotic therapy. Therefore, it is essential for studies to identify novel therapeutics to alleviate biofilm infections. One innovative technique is the use of cold atmospheric plasma (CAP) which has been shown to possess promising antimicrobial and immunomodulatory properties. Here, different clinically relevant biofilm models will be treated with cold atmospheric plasma to assess its efficacy and killing effects. Biofilm viability was assessed using live dead qPCR, and morphological changes associated with CAP evaluated using scanning electron microscopy (SEM). Results indicated that CAP was effective against Candida albicans and Pseudomonas aeruginosa, both as mono-species biofilms and when grown in a triadic model system. CAP also significantly reduced viability in the nosocomial pathogen, Candida auris. Staphylococcus aureus Newman exhibited a level of tolerance to CAP therapy, both when grown alone or in the triadic model when grown alongside C. albicans and P. aeruginosa. However, this degree of tolerance exhibited by S. aureus was strain dependent. At a microscopic level, biofilm treatment led to subtle changes in morphology in the susceptible biofilms, with evidence of cellular deflation and shrinkage. Taken together, these results indicate a promising application of direct CAP therapy in combatting wound and skin-related biofilm infections, although biofilm composition may affect the treatment efficacy.

Inactivation of airborne pathogenic microorganisms by plasma-activated nebulized mist

The airborne microorganisms in the aerosols are one main transmission way of pathogenic microorganisms and therefore inactivation of microorganisms in aerosols could effectively prevent the transmission of pathogenic microorganisms to control epidemics. The mist nebulized by plasma-activated air could effectively inactivate bacteria and could be developed for the sterilization of microorganisms in aerosols. In this study, the plasma-activated nebulized mist (PANM) was applied for the inactivation of microorganisms in aerosols and efficiently inactivated the bacteria, yeast, and viruses in aerosols after 2-min treatment. The PANM treatment caused morphologic changes and damage to the bacteria cells in aerosols. The PANM could also inactivate the microorganisms attached to the surface of the treatment chamber and the bacteria attached to the skin of mice within 6-min treatment. The biosafety assays demonstrated that the PANM treatment exhibited no effects on the behavior, hematological and serum biochemical parameters of blood, and organs from the mice. This study would supply an efficient, broad-spectrum, and safe aerosol sterilization strategy based on plasma technology to prevent the transmission of airborne microorganisms.

Antimicrobial and cleaning effects of ultrasonic-mediated plasma-loaded microbubbles on Enterococcus faecalis biofilm: an in vitro study

BACKGROUND

Enterococcus faecalis (E. faecalis) is the most frequently isolated bacteria from teeth with root canal treatment failure. This study aims to evaluate the disinfection effect of ultrasonic-mediated cold plasma-loaded microbubbles (PMBs) on 7d E. faecalis biofilm, the mechanical safety and the mechanisms.

METHODS

The PMBs were fabricated by a modified emulsification process and the key reactive species, nitric oxide (NO) and hydrogen peroxide (H₂O₂) were evaluated. The 7d E. faecalis biofilm on human tooth disk was constructed and divided into the following groups: PBS, 2.5%NaOCl, 2%CHX, and different concentrations of PMBs (10⁸ mL^-1, 10⁷ mL^-1). The disinfection effects and elimination effects were verified with confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Microhardness and roughness change of dentin after PMBs treatment were verified respectively.

RESULTS

The concentration of NO and H₂O₂ in PMBs increased by 39.99% and 50.97% after ultrasound treatment (p < 0.05) respectively. The CLSM and SEM results indicate that PMBs with ultrasound treatment could remove the bacteria and biofilm components effectively, especially those living in dentin tubules. The 2.5% NaOCl presented an excellent effect against biofilm on dishes, but the elimination effect on dentin tubules is limited. The 2% CHX group exhibits significant disinfection effect. The biosafety tests indicated that there is no significant changes on microhardness and roughness after PMBs with ultrasound treatment (p > 0.05).

CONCLUSION

PMBs combined with ultrasound treatment exhibited significant disinfection effect and biofilm removal effect, the mechanical safety is acceptable.

Inactivation of antibiotic-resistant bacteria and antibiotic-resistance genes in wastewater streams: Current challenges and future perspectives

The discovery of antibiotics, which was once regarded as a timely medical intervention now leaves a bitter aftertaste: antimicrobial resistance (AMR), due to the unregulated use of these compounds and the poor management receiving wastewaters before discharge into pristine environments or the recycling of such treated waters. Wastewater treatment plants (WWTPs) have been regarded a central sink for the mostly unmetabolized or partially metabolised antibiotics and is also pivotal to the incidence of antibiotic resistance bacteria (ARBs) and their resistance genes (ARGs), which consistently contribute to the global disease burden and deteriorating prophylaxis. In this regard, we highlighted WWTP-antibiotics consumption-ARBs-ARGs nexus, which might be critical to understanding the epidemiology of AMR and also guide the precise prevention and remediation of such occurrences. We also discovered the unsophistication of conventional WWTPs and treatment techniques for adequate treatment of antibiotics, ARBs and ARGs, due to their lack of compliance with environmental sustainability, then ultimately assessed the prospects of cold atmospheric plasma (CAP). Herein, we observed that CAP technologies not only has the capability to disinfect wastewater polluted with copious amounts of chemicals and biologicals, but also have a potential to augment bioelectricity generation, when integrated into bio electrochemical modules, which future WWTPs should be retrofitted to accommodate. Therefore, further research should be conducted to unveil more of the unknowns, which only a snippet has been highlighted in this study.

Technologies to decontaminate bacterial biofilm on hospital surfaces: a potential new role for cold plasma?

Healthcare-associated infections (HCAIs) are a major challenge and the near patient surface is important in harbouring causes such as methicillin-resistant Staphylococcus aureus (MRSA) and Clostridioides difficile. Current approaches to decontamination are sub-optimal and many studies have demonstrated that microbial causes of HCAIs may persist with onward transmission. This may be due to the capacity of these microbes to survive in biofilms on surfaces. New technologies to enhance hospital decontamination may have a role in addressing this challenge. We have reviewed current technologies such as UV light and hydrogen peroxide and also assessed the potential use of cold atmospheric pressure plasma (CAPP) in surface decontamination. The antimicrobial mechanisms of CAPP are not fully understood but the production of reactive oxygen and other species is believed to be important. CAPP systems have been shown to partially or completely remove a variety of biofilms including those caused by Candida albicans, and multi-drug-resistant bacteria such as MRSA. There are some studies that suggest promise for CAPP in the challenge of surface decontamination in the healthcare setting. However, further work is required to define better the mechanism of action. We need to know what surfaces are most amenable to treatment, how microbial components and the maturity of biofilms may affect successful treatment, and how would CAPP be used in the clinical setting.

Cold Atmospheric Plasma Ameliorates Skin Diseases Involving Reactive Oxygen/Nitrogen Species-Mediated Functions

Skin diseases are mainly divided into infectious diseases, non-infectious inflammatory diseases, cancers, and wounds. The pathogenesis might include microbial infections, autoimmune responses, aberrant cellular proliferation or differentiation, and the overproduction of inflammatory factors. The traditional therapies for skin diseases, such as oral or topical drugs, have still been unsatisfactory, partly due to systematic side effects and reappearance. Cold atmospheric plasma (CAP), as an innovative and non-invasive therapeutic approach, has demonstrated its safe and effective functions in dermatology. With its generation of reactive oxygen species and reactive nitrogen species, CAP exhibits significant efficacies in inhibiting bacterial, viral, and fungal infections, facilitating wound healing, restraining the proliferation of cancers, and ameliorating psoriatic or vitiligous lesions. This review summarizes recent advances in CAP therapies for various skin diseases and implicates future strategies for increasing effectiveness or broadening clinical indications.

Effect of the Application of Cold Plasma Energy on the Inactivation of Microorganisms, Proteins, and Lipids Deterioration in Adobera Cheese

Cheeses are perishable foods that must fulfill sanitary and quality requirements according to the parameters established globally. Plasma as a nonthermal inactivation technique has been a current research topic for food preservation, so the objective of this work was to study the effect of plasma energy against microorganisms in Adobera cheese (traditional Mexican cheese) as well as evaluate the possible degradation of lipids and protein. 108 CFU/mL of Escherichia coli ATCC 25922, Salmonella ATCC13076, and Staphylococcus aureus ATCC 6538 were inoculated at 0.5 g of Adobera cheese and were subjected to an energy of 30 volts, in a dielectric barrier discharge reactor (DBDR) at intervals of times 1, 3, 5, 7, 10, and 15 min. A flow of a mixture of air and helium at 96% purity was used. The decimal reduction time (D) was determined, and the oxidation of proteins and lipids was analyzed after each treatment. The results showed an annihilating effect of plasma on the indicator bacteria under study, and a reduction of 5 logarithmic cycles was obtained. The maximum degree of lipid oxidation was 23 acid degree values (ADV) after 7 min of exposure to plasma. The oxidation of proteins showed a direct and proportional relationship between the formation of carbonyl groups with the percentage significant loss to the concentration of carbonyl groups with the concentration of protein oxidation, after 3 min of exposure to cold plasma levels of 82% and 99% oxidation of Adobera cheese protein and free casein, respectively. We conclude that the plasma energy applied to Adobera cheese is an effective treatment to inactivate bacteria. However, there is the possibility of causing changes in taste and odor, due to the release of fatty acids and the oxidation of proteins.

Effects of Atmospheric Plasma Corona Discharge on Agrobacterium tumefaciens Survival

Soil-borne pathogenic microorganisms are known to cause extensive crop losses. Agrobacterium tumefaciens, a member of the Proteobacteria, causes the neoplastic crown gall disease in plants. Plant protection is mainly based on toxic chemicals that are harmful to the environment. The use of cold atmospheric-pressure plasma is an attractive method for microbial eradication. Its antimicrobial mechanism includes the formation of large quantities of reactive oxygen species (ROS). The advantages of eradicating bacteria using cold plasma are not needed for chemicals, short treatment, and environmental temperatures. This study examined the impact of plasma corona discharge exposure on A. tumefaciens viability, membrane permeability, relative cell size, and ROS formation. The results showed that 90 s of plasma exposure led to a reduction by four orders of magnitude when the initial concentration was 1 × 107 CFU/mL and in a dry environment. When the initial concentration was 1 × 106 CFU/mL, 45 s of exposure resulted in total bacterial eradication. In a liquid environment, in an initial concentration of 2.02 × 106 CFU/mL, there was no complete bacterial eradication even at the most prolonged examined exposure (90 s). The influence of plasma treatment on the membrane permeability of A. tumefaciens, and their possible recovery, were analyzed using flow cytometer analysis using propidium iodide (PI). When the plasma-treated bacteria were suspended in Luria–Bertani (LB) (rich medium), the PI-positive count of the plasma-treated bacteria after two hours was 12 ± 3.9%. At the 24th hour, this percentage was only 1.74 ± 0.6%, as the control (0.7 ± 0.1%). These results may indicate the repair of the plasma-treated bacteria that were suspended in LB. At the 24th hour, the relative cell size of the treated bacteria shifted to the right, to ~3 × 104 forward side scatter (FSC), about 0.5-fold higher than the untreated cells. Measurement of the ROS showed that the intracellular fluorescence of the 90-s plasma-treated cells led to significant fluorescence formation of 32 relative fluorescence units (RFU)/cell (9 × 104 fold, compared to the nontreated cells). This study showed that cold plasma is a useful method for A. tumefaciens eradication. The eradication mechanism involves ROS generation, membrane permeability, and changes in cell size.

Low-Temperature Gas Plasma Combined with Antibiotics for the Reduction of Methicillin-Resistant Staphylococcus aureus Biofilm Both In Vitro and In Vivo

Biofilm infections in wounds seriously delay the healing process, and methicillin-resistant Staphylococcus aureus is a major cause of wound infections. In addition to inactivating micro-organisms, low-temperature gas plasma can restore the sensitivity of pathogenic microbes to antibiotics. However, the combined treatment has not been applied to infectious diseases. In this study, low-temperature gas plasma treatment promoted the effects of different antibiotics on the reduction of S. aureus biofilms in vitro. Low-temperature gas plasma combined with rifampicin also effectively reduced the S. aureus cells in biofilms in the murine wound infection model. The blood and histochemical analysis demonstrated the biosafety of the combined treatment. Our findings demonstrated that low-temperature gas plasma combined with antibiotics is a promising therapeutic strategy for wound infections.