Inactivation of Campylobacter jejuni by exposure to high-intensity 405-nm visible light

Although considerable research has been carried out on a range of environmental factors that impact on the survival of Campylobacter jejuni, there is limited information on the effects of violet/blue light on this pathogen. This investigation was carried out to determine the effects of high-intensity 405-nm light on C. jejuni and to compare this with the effects on two other important Gram-negative enteric pathogens, Salmonella enteritidis and Escherichia coli O157:H7. High-intensity 405-nm light generated from an array of 405-nm light-emitting diodes was used to inactivate the test bacteria. The results demonstrated that while all three tested species were susceptible to 405-nm light inactivation, C. jejuni was by far the most sensitive organism, requiring a total dose of 18J cm−2 of 405-nm light to achieve a 5-log10 reduction. This study has established that C. jejuni is particularly susceptible to violet/blue light at a wavelength of 405nm. This finding, coupled with the safety-in-use advantages of this visible (non-ultraviolet wavelength) light, suggests that high-intensity 405-nm light may have applications for control of C. jejuni contamination levels in situations where this type of illumination can be effectively applied

Analysis of the transient process in underwater spark discharges

lf water is stressed with a voltage pulse having a rise time of tens of nanoseconds which creates a sufficiently high electric field, streamers develop and a highly conductive channel forms between the electrodes. The intense Joule heating of the plasma in the channel results in the collapse of its electrical resistance from a few Ohms to a few tens of milliOhms with the behavior of the collapse depending on the parameters of the discharge circuit. The rapid decrease of the resistance occurs during the first quarter of the current oscillation in the circuit. During this time, the pressure inside the channel rises to several GPa, causing the channel to expand in water with a velocity of 100 to 1000 m/s driving a high power ultrasound pulse. In the present paper, a phenomenological model is discussed which describes the dynamics of the resistance of underwater spark discharges during its initial stage and allows the pressure in the acoustic pulse to be obtained. The model is based on the plasma channel energy balance equation used by Braginskii and links the hydrodynamic characteristics of the channel and the parameters of the electric driving circuit. The dynamics of the transient cavity during the dissipation of the electrical energy in the plasma channel is described and the analytical results are compared with experimental measurements of the current in the electrical circuit and the acoustic pulse profiles radiated by the transient cavities

Effect of HINS light on the contraction of fibroblast populated collagen lattices

High intensity narrow spectrum (HINS) light has been shown to have bactericidal effects on a range of medically important bacteria[1]. HINS technology could potentially be useful as a method for disinfecting medical implants, tissue engineered constructs and wounds. The fibroblast populated collagen lattice (FPCL) was used as an in vitro model to investigate the effect of HINS light on the wound contraction phase of wound healing

Optimisation of the spark gap parameters for high powered ultrasound applications

There is considerable interest in the industrial and commercial applications of high power ultrasound (HPU) generated using pulsed power techniques. These applications include metal peening, the treatment of ores and minerals before extraction, drilling technologies and the comminution and recovery of waste materials. In all of these applications, it is important to optimise the parameters of the discharge causing the shock wave in the working medium to maximise the efficiency of the treatment. In a research project at the University of Strathclyde, some applications of HPU to the treatment of waste to assist in recycling have been investigated. Two systems have been considered, slag from the manufacture of stainless steel and bottle glass. With the slag material, it is intended to separate stainless steel from the silicate matrix to permit its recovery. With the bottle glass, the intention is comminution of the material to allow it to be recycled in a more valuable form. Measurements of the efficiency of these processes have been made in terms of the mass of material processed versus the energy input as the parameters of the discharge gap have been varied. In parallel with this work, measurements have been made using pinducer sensors to determine the energy in HPU pulses generated by discharges under identical conditions. Correlations are made between the efficiency of material treatment and the intensity of the HPU pulse measured in the far field. It is hoped that this approach will allow the optimal gap parameters to be determined using pinducer measurements rather than time consuming trials based around materials processing

Impact of varying intensities of blue-light exposure on 3T3 cells

There is the need to develop a compatible sterilisation method for hybrid biomaterials. High-intensity blue light in the 405 nm region has been shown to be an effective bacterial decontamination method [1], to cause no noticeable damage to the gross structure of type-I collagen monomer (when treated at 10 mW/cm2) [2], and to have no noticeable effect on 3T3 cell viability, growth rate, redox state or lactate dehydrogenase (LDH) leakage (at 1.0 mW/cm2) [2]. The purpose of this research was to investigate the effect of varying the blue-light intensity on the 3T3 cell response parameters

Inactivation of pathogens on food and contact surfaces using ozone as a biocidal agent

This study focuses on the inactivation of a range of food borne pathogens using ozone as a biocidal agent. Experiments were carried out using Campylobacter jejuni, E. coli and Salmonella enteritidis in which population size effects and different treatment temperatures were investigate

Combined treatment of biomatrices with nisin and pulsed electric fields as a potential decontamination method?

Pulsed electric field (PEF) treatment has been shown to achieve bacterial inactivation in collagen gels whilst retaining the ability of the collagen to function as a biomaterial [1, 2]. Nisin, an antimicrobial peptide, has been used widely as a food preservative and has shown bactericidal action against a number of Gram-positive bacteria [3]. The potential of nisin to increase the efficacy of PEF disinfection of collagen gels to be used for tissue engineering applications was investigated

Factors affecting the operation of laser-triggered gas switch (LTGS) with multi-electrode spark gap

Multi-electrode spark switches can be used for switching applications at elevated voltages or for command triggering. Symmetrical field graded electrodes allow the electrical stress across individual gaps to be controlled, thus maximising the hold off voltage and reducing switch pre-fire. The paper considers some aspects of multielectrode switch design and their influence on switching behavior. Non-symmetrical, uni-directional electrode topologies can be employed with advantages over traditional symmetrical design. The choice of working gas and gas pressure can influence switching performance in terms of delay-time and jitter. Transient analysis of switch characteristics has been undertaken in order to understand multi-electrode switching

Surface flashover of oil-immersed dielectric materials in uniform and non-uniform fields

The applied electrical fields required to initiate surface flashover of different types of dielectric material immersed in insulating oil have been investigated, by applying impulses of increasing peak voltage until surface flashover occurred. The behavior of the materials in repeatedly over-volted gaps was also analyzed in terms of breakdown mode (some bulk sample breakdown behaviour was witnessed in this regime), time to breakdown, and breakdown voltage. Cylindrical samples of polypropylene, low-density polyethylene, ultra-high molecular weight polyethylene, and Rexolite, were held between two electrodes immersed in insulating oil, and subjected to average applied electrical fields up to 870 kV/cm. Tests were performed in both uniform- and non-uniform-fields, and with different sample topologies. In applied field measurements, polypropylene required the highest levels of average applied field to initiate flashover in all electrode configurations tested, settling at similar to 600 kV/cm in uniform fields, and similar to 325 kV/cm in non-uniform fields. In over-volted point-plane gaps, ultra-high molecular weight polyethylene exhibited the longest pre-breakdown delay times. The results will provide comparative data for system designers for the appropriate choice of dielectric materials to act as insulators for high-voltage, pulsed-power machines

The suitability of N2 to replace SF6 in a triggered spark-gap switch for pulsed power applications

The high dielectric strength of sulphur hexafluoride (SF6) when compared with other gases, coupled with safety benefits such as non-flammability and non-toxicity, has seen the widespread use of SF6 for the insulation of switching components. However, SF6 is now widely recognised as a highly damaging greenhouse gas, and investigations of the switching properties of alternative gases to replace SF6 within the bounds of existing system topologies are required. In the present paper, a comparative study has been carried out on a triggered spark-gap of type presently deployed in industrial pulsed-power machines, to determine the suitability of nitrogen (N2) to replace SF6 as the switching medium, without compromising on functionality. Experiments were performed with fast-rising trigger pulses to minimise the delay time to breakdown and jitter, and three distinct operational regimes have been identified for both gases as the pressure inside the switch is increased. The static breakdown characteristics and upper pressure boundaries of operation have been determined for both gases at a range of dc charging voltages. Measurements of the time to breakdown have shown jitters as low as 1.3 ns when operating in N2, highlighting the potential of N2 to replace SF6 without the need for re-design or replacement of the presently used switch