UV-C Disinfection Research Articles

UVC fluencies for preventative treatment of Pseudomonas aeruginosa contaminated polymer tubes

Exposing Pseudomonas aeruginosa biofilm grown on the inner surface of Teflon and silicone tubes to UVC light (265 nm) from light emitting diodes (LED) has previously been shown to substantially reduce biofilm growth. Smaller UVC fluencies were required to disinfect Teflon tubes compared to silicone tubes. Light propagation enhancement in tubes can be obtained if the refractive index of the intra-luminal saline solution is higher than that of the polymer. This condition is achieved by using Teflon tubes with a low refractive index (1.34) instead of the polymers with a high refractive index (1.40–1.50) normally used for tubing in catheter production. Determining whether or not UVC light exposure can disinfect and maintain the intra-luminal number of colony forming units (CFUs) at an exceedingly low level and thus avoid the growth and establishment of biofilm is of interest. The use of UVC diodes is demonstrated to be a preventative disinfection treatment on tubes made of Teflon, which enhances the UVC light propagation, and on tubes made of a softer material, ethylene vinyl acetate (EVA), which is suitable for catheters but much less suitable for UVC light propagation. Simulating an aseptic breach (∼103–104 CFU ml−1), the UVC disinfection set-up was demonstrated using tubes contaminated with planktonic P. aeruginosa. After the tubes (10–20 cm) were inoculated with the bacterial solution for 3 h, they were emptied and filled with saline solutions (0.9–20%). Next UVC fluencies (0–21 mJ cm−2) were applied to the tubes 3 h after inoculation. Colony counts were carried out on liquid samples drawn from the tubes the first day after UVC treatment and liquid and surface samples were collected and analyzed 3–4 days later. A fluence of approximately 1.0 mJ cm−2 was noted as being sufficient for no growth for a period of 3–4 days for the Teflon tubes. Determining the fluence threshold for the EVA tubes was not possible. Almost all of the UVC-treated EVA tubes were disinfected simply by filling the tubes with a saline solution. Direct UVC treatment of the contaminated EVA tubes revealed, however, that a fluence of 21 mJ cm−2 killed the bacteria present in the tubes and kept them disinfected for a period of 3–4 days.

Effect of UV-C Disinfection of Beer - Sensory Analyses and Consumer Ranking

Ultraviolet (UV-C) light irradiation is gaining rapid acceptance within the food and beverage industry as a non-thermal disinfection technique. A series of trials, using a pilot scale UV-C treatment system, were conducted to investigate the effect of UV-C on beer with specific attention to lightstruck flavour formation. Both commercial and micro-brewed beers were treated with UV-C light at 254 nm. Samples were analysed by consumer and trained panels. Sensory analyses revealed that at a low UV-C level, lightstruck flavour was apparent and this increasingly gave way to a more intense burnt rubber off-flavour as the UV-C exposure was increased. A sample enrichment probe technique coupled with a gas chromatography-mass spectrometry (SEP/GCMS) revealed the presence of lightstruck flavour in all the treated beers.

Repression of photoreactivation and dark repair of coliform bacteria by TiO2-modified UV-C disinfection

Photoreactivation and dark repair of damaged DNA can occur after some bacteria are disinfected with UV-C irradiation and thus reduce the disinfection efficiency. We have discovered that the provision of 1mg/L titanium dioxide (TiO2) in suspension during UV-C irradiation at normal disinfection doses repressed the photoreactivation and dark repair. The repressive effect was also observed when a TiO2-coated plate was used during UV-C exposure but removed thereafter, indicating the repressive effect does not require the presence of TiO2 in the post-UV event. The repressive effect was consistently observed with changes of bacteria species, temperature, salinities, UV sources, doses and intensities, and with/without nutrients. The repressive effect is likely associated with the additional radical attack during UV-TiO2 irradiation and/or formation of a small amount of stable residual oxidants (primarily hydrogen peroxide). The TiO2-modified UV-C disinfection represents an innovative means to disinfect water. It is particularly useful in situations where additions of residual chlorine or chloramines are not allowed or not possible. Nevertheless, the TiO2 shall be properly included, by either using the optimum dose in suspension or immobilizing it onto a surface, since too little TiO2 cannot provide the repression while too much TiO2 in suspension gives a detrimental effect on the UV-C disinfection.

Comparison of UV C Light and Chemicals for Disinfection of Surfaces in Hospital Isolation Units

To determine the bactericidal effect on surfaces of ceiling- and wall-mounted UV C (UVC) light (wavelength, 254 nm) in isolation units, compared with standard hospital environmental cleaning and chemical disinfection during final disinfection after patients are treated for infections. Microbial samples were obtained from surfaces in isolation units (patient room, anteroom, and bathroom) before and after irradiation with UVC, chloramine disinfection, and standard hospital environmental cleaning. Samples were tested using standard contact plates. Four identical, negative air-pressure isolation units (patient room, anteroom, and bathroom) with a defined number of ceiling- and wall-mounted UVC light units. The UVC distribution was monitored in one isolation unit after irradiation for approximately 40 minutes, corresponding to doses ranging from 160 J/m2 in a shadowed area to 19,230 J/m2 at the mostly highly exposed site (which is high enough to inactivate most bacterial organisms, including spores). UVC disinfection significantly reduced the number of bacteria on surfaces directly or indirectly exposed to UVC to a very low number, as did 5% chloramine disinfection alone (P<.001 for both). Completely shadowed areas in the isolation unit (eg, the bed rail, lockers, and mattresses) still required disinfection by chemicals. Disinfection with UVC light may significantly reduce environmental bacterial contamination and thereby protect the next patient housed in an isolation room. UVC disinfection may not be used alone but is a good addition to chemical disinfection.