Ultrasonic irradiation enhanced the efficacy of antimicrobial photodynamic therapy against methicillin-resistant Staphylococcus aureus biofilm

Antimicrobial photodynamic therapy (aPDT) is a non-pharmacological antimicrobial regimen based on light, photosensitizer and oxygen. It has become a potential method to inactivate multidrug-resistant bacteria. However, limited by the delivery of photosensitizer (PS) in biofilm, eradicating biofilm-associated infections by aPDT remains challenging. This study aimed to explore the feasibility of combining ultrasonic irradiation with aPDT to enhance the efficacy of aPDT against methicillin-resistant staphylococcus aureus (MRSA) biofilm. A cationic benzylidene cyclopentanone photosensitizer with much higher selectivity to bacterial cells than mammalian cells were applied at the concentration of 10 μM. 532 nm laser (40 mW/cm², 10 min) and 1 MHz ultrasound (500 mW/cm², 10 min, simultaneously with aPDT) were employed against MRSA biofilms in vitro. In addition to combined with ultrasonic irradiation and aPDT, MRSA biofilms were treated with laser irradiation only, photosensitizer only, ultrasonic irradiation only, ultrasonic irradiation and photosensitizer, and aPDT respectively. The antibacterial efficacy was determined by XTT assay, and the penetration depth of PS in biofilm was observed using a photoluminescence spectrometer and a confocal laser scanning microscopy (CLSM). In addition, the viability of human dermal fibroblasts (WS-1 cells) after the same treatments mentioned above and the uptake of P3 by WS-1 cells after ultrasonic irradiation were detected by CCK-8 and CLSM in vitro. Results showed that the percent decrease in metabolic activity resulting from the US + aPDT group (75.76%) was higher than the sum of the aPDT group (44.14%) and the US group (9.88%), suggesting synergistic effects. Meanwhile, the diffusion of PS in the biofilm of MRSA was significantly increased by 1 MHz ultrasonic irradiation. Ultrasonic irradiation neither induced the PS uptake by WS-1 cells nor reduced the viability of WS-1 cells. These results suggested that 1 MHz ultrasonic irradiation significantly enhanced the efficacy of aPDT against MRSA biofilm by increasing the penetration depth of PS. In addition, the antibacterial efficacy of aPDT can be enhanced by ultrasonic irradiation, the US + aPDT treatment demonstrated encouraging in vivo antibacterial efficacy (1.73 log₁₀ CFU/mL reduction). In conclusion, the combination of aPDT and 1 MHz ultrasound is a potential and promising strategy to eradicate biofilm-associated infections of MRSA.     

TOF-SIMS imaging of chlorhexidine-digluconate transport in frozen hydrated biofilms of the fungus Candida albicans

The diffusion of the anti-microbial chlorhexidine digluconate (CHG) has been studied in C. albicans biofilms by time-of-flight secondary-ion mass spectrometry (TOF-SIMS). C. albicans has been shown to become resistant to common anti-microbial agents, including CHG, when growing as a biofilm. Mass transport resistance within biofilms has commonly been suggested as a resistance mechanism, but measurement of transport for most anti-microbial agents in biofilms has proven extremely difficult because of the heterogeneity of the biofilms and the difficulty in detecting these agents within an intact biofilm. In this study, TOF-SIMS has been used to study the transport of CHG and glucose in a frozen hydrated biofilm. The TOF-SIMS images reveal a progression of CHG from the top of the biofilm to its base with time. Images suggest that there are channels within the biofilm and show preferential binding of CHG to cellular components of the biofilm. Additionally, both living and dead cells can be identified in the TOF-SIMS images by the sequestration of K⁺ and the presence of cell markers. This study demonstrates that TOF-SIMS has the unique potential to simultaneously observe the presence of an antimicrobial agent, concentration of nutrients, and the viability of the cell population.     

Arc Cathode Processes in the Transition Region between Vacuum Arcs and Gaseous Arcs

The cathode processes of electric ares on cleaned Cu cathodes were investigated in the transition region between vacuum and atmospheric pressure (argon). The plasma density in the cathode plane was estimated by probe measurements to be n = r are current, r – distance from the spot). It was observed that several cathode spot parameters have an extremum at p ～ 10⁴ Pa. The crater diameter has a minimum independently of the cathode temperature. The diffusion constant of the chaotic motion determined by framing photographs was found to have a maximum. Some additional, large displacements occurred at that pressure. The diameter of the bright plasma cloud obtained by open-shutter photographs showed a maximum, the current per spot was found to decrease from 20 A in vacuum to 10 A at atmospheric pressure. It is thus concluded that the spot with the smallest crater radius and a low current per spot, occurring at ～ 10⁴ Pa, represents the single spot, whereas the spot at higher pressures, and probably also in vacuum, has a complicated nature where the large craters are formed by a cooperation of single spots.     

Indirect plasma inactivation by a low temperature atmospheric pressure plasma (LTAPP) system

The aim of this paper is to evaluate the inactivation effect of indirect low temperature plasma exposure at atmospheric pressure produced by the original Low Temperature Atmospheric Pressure Plasma (LTAPP) system. In this system, the low temperature plasma is generated using a high voltage power supply in oxygen at atmospheric pressure. The obtained survivor curves for Escherichia coli (G⁻), Bacillus subtilis (G⁺), Staphylococcus aureus (G⁺), Candida albicans (Yeast), and Saccharomyces cerevisiae (Yeast) showed that the LTAPP system could inactivate them. The optical microscope images of B. subtilis and S. cerevisiae treated have confirmed the inactivation effect of the LTAPP system.     

Quasi-Isentropic Compressibility of Deuterium at a Pressure of ~12 TPa

An experimental result for the quasi-isentropic compressibility of a strongly nonideal deuterium plasma compressed in a spherical device by the pressure P = 11400 GPa (114 Mbar) to the density ρ ≈ 10g/cm³ has been reported. The characteristics of the experimental device, diagnostic methods, and experimental results have been described. The trajectory of motion of metallic shells compressing a deuterium plasma has been recorded using intense pulsed sources of X rays with the boundary energy of electrons up to 60 MeV. The deuterium plasma density ρ ≈ 10g/cm³ has been determined from the measured radius of the shell at the time of its “stop.” The pressure of the compressed plasma has been determined from gas-dynamic calculations taking into account the real characteristics of the experimental device.     

Plasma pencil — A new small scale source for atmospheric surface modifications

Plasma pencil is a device which can produce plasma jet at atmospheric pressure and low power (10–200 W) from DC to HF. The jet character of the plasma makes this device very efficient in aimed local (1 – 10² mm²) modifications of surfaces. Great variability in possible power sources allow to achieve a broad range of effects on materials. We have tested bipolar discharges with a metal object and a unipolar HF discharge to burn the glazing on ceramics. Both technologies could be prospective.     

Prevention of biofilm re‐development on Ti‐6Al‐4V alloy by cometary discharge with a metallic grid

The influence of a non‐thermal plasma (NTP) on the gram‐negative bacteria Escherichia coli and Pseudomonas aeruginosa, the gram‐positive bacterium Staphylococcus epidermidis, and the yeast Candida albicans grown on agar or in the biofilm form was compared. NTP was produced by a DC cometary discharge. The biofilms were grown on the surface of Ti‐6Al‐4V alloy often used in the manufacture of prosthetic implants. The exposure by NTP not only inhibited the surface growth of microorganisms in agar cultures but also significantly suppressed the viability of bacteria and yeast in biofilms and prevented its re‐developed from persistent cells remaining in the lower layers of the biofilm. An almost complete prevention of biofilm re‐development was achieved in the case of S. epidermidis; other microorganisms displayed substantial lowering of biofilm biomass and its metabolic activity.     

Comparison of the cytotoxic effect of polystyrene latex nanoparticles on planktonic cells and bacterial biofilms

The cytotoxic effect of positively charged polystyrene latex nanoparticles (PSL NPs) was compared between planktonic bacterial cells and bacterial biofilms using confocal laser scanning microscopy, atomic force microscopy, and a colony counting method. Pseudomonas fluorescens, which is commonly used in biofilm studies, was employed as the model bacteria. We found that the negatively charged bacterial surface of the planktonic cells was almost completely covered with positively charged PSL NPs, leading to cell death, as indicated by the NP concentration being greater than that required to achieve single layer coverage. In addition, the relationship between surface coverage and cell viability of P. fluorescens cells correlated well with the findings in other bacterial cells (Escherichia coli and Lactococcus lactis). However, most of the bacterial cells that formed the biofilm were viable despite the positively charged PSL NPs being highly toxic to planktonic bacterial cells. This indicated that bacterial cells embedded in the biofilm were protected by self-produced extracellular polymeric substances (EPS) that provide resistance to antibacterial agents. In conclusion, mature biofilms covered with EPS exhibit resistance to NP toxicity as well as antibacterial agents.     

Non-LTE diagnostic of an argon arc plasma

The plasma of an argon arc has been investigated by applying the partial LTE model (overpopulation of the ground state) and accounting for different kinetic temperatures of electrons and atoms. The plasma analysis is performed without making use of atomic constants (e.g. transition probabilities) from the literature. The experimental results show that LTE is obtained in the 4mm arc at atmospheric pressure for electron densities above 6×10¹⁶cm^-3. Below this value, increasing under-population of the excited levels with decreasing arc current can be observed. This deviation from LTE may explain some not understood results from previously published spectroscopic observations of argon plasmas.     

Optical properties of nonstoichiometric ZrO<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript> according to spectroellipsometry data

Amorphous nonstoichiometric ZrO_x films of different composition have been synthesized by the method of ion-beam sputtering deposition of metallic zirconium in the presence of oxygen at different partial oxygen pressures in the growth zone, and their optical properties have been studied in the spectral range of 1.12–4.96 eV. It is found that light-absorbing films with metallic conductivity are formed at the partial oxygen pressure below 1.04 × 10^–3 Pa and transparent films with dielectric conductivity are formed at the pressure above 1.50 × 10^–3 Pa. It is shown that the spectral dependences of optical constants of ZrO_x films are described well by the corresponding dispersion models: the Cauchy polynomial model for films with dielectric conductivity and the Lorentz–Drude oscillator model for films with metallic conductivity.     

Thermodynamics and correlation functions of an ultracold nonideal Rydberg plasma

A pseudopotential model is suggested to describe the thermodynamics and correlation functions of an ultracold, strongly nonideal Rydberg plasma. The Monte Carlo method is used to determine the energy, pressure, and correlation functions in the ranges of temperatures T=0.1–10 K and densities n=10^?2–10¹⁶ cm^?3. For a weakly nonideal plasma, the results closely agree with the Debye asymptotic behavior. For a strongly nonideal plasma, many-particle clusters and a spatial order in the arrangement of plasma electrons and ions have been found to be formed.     

The OH collision broadening parameter in the 2900°K H2-NO flame

The collision broadening parameter of the Q₁6 line in the OH (0, 0) A → X u.v. transition has been determined by the curve of growth method in atmospheric pressure nitric oxide-hydrogen flames, in the temperature range 2800–2900°K. An average value of 0.05 was found for this parameter for five flames varying in feed composition between 40 and 65% NO. The exact flame gas compositions and temperatures for which these determinations were made are given in the paper. The data obtained are in agreement with those obtained by Carrington² for atmospheric hydrogen-oxygen flames at 2600°K.     

Modeling the elimination of mature biofilms formed by Staphylococcus aureus and Salmonella spp. Using combined ultrasound and disinfectants

Biofilm formation by foodborne pathogens on food processing surfaces has contributed to numerous disease outbreaks and food recalls. We evaluated the following strategies for elimination of mature biofilm formed by Staphylococcus aureus and Salmonella spp. on stainless steel surfaces: acidic electrolyzed water (AEW), ozone water (OW), or ultrasound (40 kHz) alone, and combinations of ultrasound and disinfectants. The dynamics of elimination by combinations were determined using the Weibull and biphasic models. Treatment with AEW alone reduced the number of biofilm cells by approximately 3.0 log cfu/cm², whereas less than 0.8 log cfu/cm² of cells reduction was observed in biofilm exposed to OW or ultrasound alone, even with treatment for 20 min. The combination of AEW and ultrasound produced an obvious synergistic effect on biofilm reduction, achieving approximately 4.8 log cfu/cm² reduction in Salmonella spp. biofilm. Interestingly, the biphasic model was a better fit than the Weibull model for the elimination process of mature biofilm formed by both pathogens and subjected to a combination of ultrasound and AEW, as determined by smaller values of the statistical parameters RMSE and AIC, although both models could evaluate the dynamic processes. Our findings indicated that a combination of ultrasound and AEW could effectively reduce the biofilm formed by pathogens on food contact surfaces, and that the biphasic model could predict the number of residual cells after biofilm exposure to this intervention approach.     

OH number densities and plasma jet behavior in atmospheric microwave plasma jets operating with different plasma gases (Ar,Ar/N<Subscript>2</Subscript>, and Ar/O<Subscript>2</Subscript>)

OH radical number density in multiple atmospheric pressure microwave plasma jets is measured using UV cavity ringdown spectroscopy of the OH (A–X) (0–0) band at 308 nm. The plasma cavity was excited by a 2.45 GHz microwave plasma source and plasma jets of 2–12 mm long were generated by using three different plasma gases, argon (Ar), Ar/N₂, and Ar/O₂. Comparative characterization of the plasma jets in terms of plasma shape, stability, gas temperature, emission intensities of OH, NO, and N₂, and absolute number density of the OH radical was carried out under different plasma gas flow rates and powers at various locations along the plasma jet axis. With three different operating gases, the presence of OH radicals in all of the plasma jets extended to the far downstream. As compared to the argon plasma jets, the plasma jets formed with Ar/N₂ and Ar/O₂ are more diffuse and less stable. Plasma gas temperatures along the jet axis were measured to be in the range of 470–800 K for all of the jets formed in the different gas mixtures. In each plasma jet, OH number density decreases along the jet axis from the highest OH density in the vicinity of the jet tip to the lowest in the far downstream. OH density ranges from 1.3 × 10¹² to 1.1 × 10¹⁶, 4.1 × 10¹³ to 3.9 × 10¹⁵, and 7.0 × 10¹² to 4.6 × 10¹⁶ molecule/cm³ in the Ar, Ar/N₂, and Ar/O₂ plasma jets, respectively. The OH density dependence on plasma power and gas flow rate in the three plasma jets is also investigated.     

Applications of Laser-Induced Breakdown Spectrometry

INTRODUCTION

When a high-powered laser beam is focused onto a small area or spot of a solid surface, the temperature of the locally heated region rises rapidly to the vaporization temperature of the solid material and an optically induced plasma, frequently called a laser-induced plasma (LIP) or laser-ablated plasma (LAP) or laser spark is formed at the surface. The plasma will be formed when the laser power density exceeds the breakdown threshold value of the solid surface. Although different materials have different breakdown thresholds, an optical plasma is produced when the laser power density exceeds several megawatts per centimeter squared (10⁶ - 10⁹ W/cm²). This plasma has been used for sampling, atomization, excitation, and ionization in analyhcal atomic spectroscopy. It has also been frequently used and proposed as a source for atomic emission spectrometry (AES). In this case the technique is most ofien referred to as laser microprobe optical emission spectrometry (LM-OES) developed by Brech and Cross [1] in early nineteen-sixties or more recently called laser-induced breakdown spectrometry (LIBS) [2,3]. Generally, this analyhcal technique involves two steps; the pulsed focused laser beam directed into a gaseous sample or the surface of a solid or liquid, to produce a transient LIP, followed by the measurement of a characteristic atomic emission signal related to some species present in the plasma. The LIP formed is tightly focused and consists of vaporized atoms, ions, electrons, and molecular fragments. The application of LIBS for direct spectrochemical analysis is a rapidly growing field ranging from the detection of atmospheric pollutants to monitoring of material production processes, and even to “clean-room” technology. Laser ablation techniques have also been applied for solid sample introduction into other plasma sources [4–9]. In recent years, the powerful technique of LIBS as an analytical tool has been recognized by a number of research groups, and has led to an increasing number of publications on the applications of LIBS both in the laboratory and in industry. This growing success of LIBS is a result of thorough research carried out to understand the related plasma physical processes, aided by marked improvements in laser systems and photodetector technology.     

Magnetic moment of pressure quenched cadmium sulfide

Magnetic moment measurements of CdS polycrystalline samples, pressure quenched from above the semiconducting to conducting transition pressure (40 kbars) at rates approaching 10⁶ bars/sec, have been made in a vibrating sample magneto-meter to fields approaching 1000 Oersted. The samples exhibit the complex magnetic behavior of low field diamagnetism (χ > - 5 × 10^-5cgsunits) transforming at fields of several hundred Oersted to positive magnetism (χ > + 3 × 10^-4cgsunits). This magnetic behavior contrasts with unquenched samples which yield the normal diamagnetism of CdS (χ = - 1.5 × 10^-6cgsunits). These anomalous magnetic effects are observed at both room temperatures and LN₂ temperatures at atmospheric pressure.     

Collison nebulizer as a new soft ionization source for mass spectrometry

We have proposed that a Collison-type nebulizer be used as an ionization source for mass spectrometry with ionization under atmospheric pressure. This source does not require the use of electric voltage, radioactive sources, heaters, or liquid pumps. It has been shown that the number of ions produced by the ⁶³Ni radioactive source is three to four times larger than the number of ions produced by acoustic ionization sources. We have considered the possibility of using a Collison-type nebulizer in combination with a vortex focusing system as an ion source for extractive ionization of compounds under atmospheric pressure. The ionization of volatile substances in crossflows of a charged aerosol and an analyte (for model compounds of the amine class, viz., diethylaniline, triamylamine, and cocaine) has been investigated. It has been shown that the limit of detecting cocaine vapor by this method is on the level of 4.6 × 10^–14 g/cm³.     

Thermal conductivity of gold and silver at high pressures

The thermal diffusivities of gold and silver have been measured under pressure up to 2.5 GPa at room temperature. From the measured data the pressure dependence of the thermal conductivity, λ, has been calculated. The values found for the pressure coefficient λ^?1$\text{δλ}\text{δP}$ were 3.9 × 10^?2GPa^?1 for gold and 4.0 × 10^?2 GP silver at atmospheric pressure. The results are compared to theoretical predictions of the pressure dependence and also to previous experimental results for copper and aluminium. For the noble metals, small angle or “vertical” scattering of electrons is shown to have a stronger volume dependence than “horizontal” scattering.     

Investigation of the thermal structure of the upper atmosphere of Venus by 10 μm heterodyne spectroscopy

The Venusian atmosphere has been investigated using a 10 μm heterodyne spectrometer (spectral resolution λ/Δλ = 3 × 10⁶) during upper conjunction and during elongation in 1983. In both cases a variety of spectra from the subsolar region were taken with high spatial resolution showing fully-resolved lines of the 10μm laser transition of CO₂. From these measurements kinetic and rotational temperatures are derived (T∼200K.). These spectroscopically-derived temperatures represent the atmospheric temperature for extended areas (1000–6000 km dia) at an altitude of 100–120 km. They are in agreement with on-the-spot temperature measurements indirectly obtained by space probes during descent. Multiple-line structures have been observed in the 10 μm spectra, which indicate a wave-like perturbation of the vertical temperature profile above a cloud layer at ∼ 20 mb atmospheric pressure.