Investigation of critical inter-related factors affecting the efficacy of pulsed light for inactivating clinically relevant bacterial pathogens

Abstract

Aims: To investigate critical electrical and biological factors governing the efficacy of pulsed light (PL) for the in vitro inactivation of bacteria isolated from the clinical environment. Development of this alternative PL decontamination approach is timely, as the incidence of health care-related infections remains unacceptably high. Methods and Results: Predetermined cell numbers of clinically relevant Gram-positive and Gram-negative bacteria were inoculated separately on agar plates and were flashed with £60 pulses of broad-spectrum light under varying operating conditions, and their inactivation measured. Significant differences in inactivation largely occurred depending on the level of the applied lamp discharge energy (range 3AE2-20 J per pulse), the amount of pulsing applied (range 0-60 pulses) and the distance between light source and treatment surface (range 8-20 cm) used. Greater decontamination levels were achieved using a combination of higher lamp discharge energies, increased number of pulses and shorter distances between treatment surface and the xenon light source. Levels of microbial sensitivity also varied depending on the population type, size and age of cultures treated. Production of pigment pyocynanin and alginate slime in mucoid strains of Pseudomonas aeruginosa afforded some protection against lethal action of PL; however, this was evident only by using a combination of reduced amount of pulsing at the lower lamp discharge energies tested. A clear pattern was observed where Gram-positive bacterial pathogens were more resistant to cidal effects of PL compared to Gram negatives. While negligible photoreactivation of PL-treated bacterial strains occurred after full pulsing regimes at the different lamp discharge energies tested, some repair was evident when using a combination of reduced pulsing at the lower lamp discharge energies. Strains harbouring genes for multiple resistances to antibiotics were not significantly more resistant to PL treatments. Slight temperature rises (£4AE2°C) were measured on agar surfaces after extended pulsing at higher lamp discharge energies. Presence of organic matter on treatment surface did not significantly affect PL decontamination efficacy, nor did growth of PL-treated bacteria on selective agar diminish survival compared to similarly treated bacteria inoculated and enumerated on nonselective agar plates. Conclusions: Critical inter-related factors affecting the effective and repeatable in vitro decontamination performance of PL were identified during this study that will aid further development of this athermal process technology for applications in health care and in industry. Very rapid reductions (c. 7 log 10 CFU cm )2

Effects of shading and growth phase on the microbial inactivation by pulsed light

“…Previously, Farrell et al (2010) reported that the resistance of E. coli to PL inactivation was higher in 24-h cultures versus 16-h cultures. Two inactivation mechanisms may have played a role in the lethal effects observed in this work, the photochemical effect (DNA damage), and the photophysical one (structural damage).…”

“…While those results are relevant from the point of view of a real scenario, where both events occur together, their separate study allows to identify the actual effect of the growth phase on PL efficiency. In this regard, Farrell et al (2010) reported that 16-h cultures of Escherichia coli are more sensitive to PL than 24-h cultures. Therefore, the aim of this study was to determine the effect of the shading and microbial growth phase on the efficacy of PL.…”

“…Furthermore, the patent of Hiramoto (1984) also claimed that this phenomenon occurs with the conventional UV lamps and is overcome by the photothermal effect of PL. On the other side, Farrell et al (2010) reported a population density effect in the inactivation curves of staphylococcus aureus and pseudomonas aeruginosa, where tailing was only observed at very high initial sizes.The susceptibility of microorganisms to inactivation by physical methods depends on several factors, which depend in turn on the specific method. The effect of the growth phase of the microor- …”

Efficacy and Mechanisms of Murine Norovirus Inhibition by Pulsed-Light Technology

“…This result is consistent with the finding of Bialka (50), who reported that penetration of the UV portion to depths up to 1 cm occurs in opaque solid materials, such as whey protein gels. In addition, several authors have noted that the alginate slime of mucoid strains of Pseudomonas aeruginosa does not provide any protection against the lethal action of pulsed light (51,52). The viability of P. aeruginosa in biofilms was reduced by 5.8 Ϯ 0.2 log 10 when up to 21.6 J cm Ϫ2 UV fluence was used (52).…”

Post-packaging application of pulsed light for microbial decontamination of solid foods: A review

“…Also, mucoid-and pigment-forming bacteria can have a lower susceptibility to PL. Furthermore, fungi seem to be more resistant than bacteria, bacterial spores are more resistant than their corresponding vegetative cells and smaller bacteria are more than larger ones, due to the faster dissipation of heat from the surface (Anderson, Rowan, MacGregor, Fouracre, & Farish, 2000;Farrell, Garvey, Cormican, Laffey, & Rowan, 2010;Rowan et al, 1999). Since high population density and stationary growth phase can impair the decontamination efficiency, it is recommended to start the PL treatment as soon as possible after the contamination takes place (Anderson et al, 2000;Farrell et al, 2010;Gómez-López, Devlieghere, Bonduelle, & Debevere, 2005b;Hiramoto, 1984;Rajkovic, Tomasevic, et al, 2010).…”