RESUMEN
Background and Objectives: Plasma radiation is a widely used technique for sterilization or decontamination in various industries, as well as in some healthcare settings such as dentistry. The primary aim of this study was to assess the potential of plasma radiation to create a new population of Staphylococcus aureus cells with distinct characteristics that could lead to novel healthcare challenges. Materials and Methods: A homemade non-thermal plasma apparatus was applied and the effects of plasma treatment on S. aureus ATCC25923 was assessed. Plasma radiation was applied under controlled conditions to ensure that some bacterial cells remained viable. The treatment was repeated 10 times, with each round followed by a recovery phase to collect any surviving bacterial cells. To assess the potential changes in the bacterial population, we examined the antibiotic susceptibility pattern, micro-structural characteristics using scanning electron microscopy (SEM), and total protein profile using the matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) technique. Results: The experimental results revealed slight variations in the antibiotic susceptibility patterns of certain cell wall agents (imipenem, cephalothin, and cefepime), as well as in the MALDI-TOF spectra. However, no changes were observed in the SEM images. Conclusion: The insufficient application of non-thermal plasma in bacterial decontamination may lead to physiological changes that could enrich or select certain subpopulations of S. aureus.
RESUMEN
Natural preservatives are being extensively investigated for their potential industrial applications in foods and other products. In this work, an essential oil (Thymus daenensis) was formulated as a water-dispersible nanoemulsion (diameter=143nm) using high-intensity ultrasound. The antibacterial activity of the essential oil in both pure and nanoemulsion forms was measured against an important food-borne pathogen bacterium, Escherichia coli. Antibacterial activity was determined by measuring the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The antibacterial activity of the essential oil against E. coli was enhanced considerably when it was converted into a nanoemulsion, which was attributed to easier access of the essential oils to the bacterial cells. The mechanism of antibacterial activity was investigated by measuring potassium, protein, and nucleic acid leakage from the cells, and electron microscopy. Evaluation of the kinetics of microbial deactivation showed that the nanoemulsion killed all the bacteria in about 5min, whereas only a 1-log reduction was observed for pure essential oil. The nanoemulsion appeared to amplify the antibacterial activity of essential oils against E. coli by increasing their ability to disrupt cell membrane integrity.
