Efficacy of Inactivation of Pseudomonas aeruginosa by Multiple-Wavelength UV LEDs
Citation:
Whitham, T., N. Saba, H. Woo, K. Carlson, L. Boczek, AND H. Ryu. Efficacy of Inactivation of Pseudomonas aeruginosa by Multiple-Wavelength UV LEDs . UNC Water Microbiology Conference, Chapel Hill,NC, May 22 - 24, 2018.
Impact/Purpose:
The main objectives of this study were to investigate a range of UV wavelengths to formulate an efficient water treatment strategy for Pseudomonas aeruginosa and to explore the synergistic effect of UV reflective materials and strategic sequential exposure to multiple wavelengths of UV light. Overall, UV LEDs demonstrated the capability to effectively inactivate P. aeruginosa, and all of the LEDs tested greatly outperformed conventional LP UV lamps. Furthermore, the synergistic effects of sequential exposures and the use of UV reflective aluminum foil encourages further studies on its applicability for sustainable water treatment and the development of a low power UV-LED POU device.
Description:
Pseudomonas aeruginosa is one of three major opportunistic premise plumbing pathogens (OPPPs). It is responsible for causing many types of infections including pneumonia and blood, tissue, and bone infections. In the United States, the most common disinfection practice for treatment of drinking water is the addition of chlorine to combat pathogens. However, chlorination has been well documented to produce carcinogenic disinfection by-products (DBPs). Ultraviolet (UV) light technology has been widely adapted for water disinfection in the treatment process, as it does not result in the formation of DBPs. Conventional mercury UV lamps, however, have the risk potential for mercury contamination by the accidental breakage of the lamps. The latest UV technology of light emitting diodes (LEDs) is mercury-free and moreover has enormous potential for point-of-use (POU) water disinfection since they are much smaller, lighter, and less fragile. While extensive studies have been conducted on microorganism inactivation using germicidal UV LEDs targeting microbial indicators, limited studies have been focused on waterborne pathogens. In this study, we investigated a range of UV wavelengths to formulate an efficient water treatment strategy for P. aeruginosa and explored the synergistic effect of UV reflective materials and strategic sequential exposure to multiple wavelengths of UV light. Log phase P. aeruginosa cells were prepared by overnight culture at 35°C for 24 h in nutrient broth. The cells were then washed 3 times with Butterfield’s buffer, and a sample with a concentration of 1.0 E+5 colony forming units (CFU)/mL was created. Bench-scale performance evaluations were conducted using a collimated beam (CB) apparatus with LEDs emitting at 255 nm, 265 nm, and 285 nm; a monochromatic low-pressure (LP) UV lamp emitting at 254 nm was tested for comparison. The samples were exposed to five UV doses (measured in mJ/cm2), with the goal of achieving a 4-log inactivation (i.e., 99.99% reduction). Further samples were tested to determine whether aluminum foil would reflect UV irradiation- resulting in greater inactivation- or if exposure to different wavelengths in a certain sequence would have an observed synergistic effect. Samples were plated on nutrient agar and then incubated at 35°C overnight. The number of colonies present were counted and recorded as CFU/mL. Results showed that the LED emitting at 285 nm demonstrated for the greatest inactivation of P. aeruginosa, followed by 265 nm, 255 nm, and finally LP UV at 254 nm. The inactivation coefficients generated by linear regression were 1.2624, 1.2106, 1.1661, and 0.7368, respectively. A 4-log inactivation was achieved at a dose of 3.7 mJ/cm2 for the LED at 285 nm, while the UV dose had to be increased by 57% (to about 5.8 mJ/ cm2) to obtain the same log inactivation using the LP UV. Greater log inactivation of multiple wavelength exposures when compared to single wavelength exposures of the same UV dose suggested synergistic effects. Specifically, inactivation by sequential exposure to all three wavelengths was determined to yield the greatest efficacy, as this sequence resulted in a 0.4 log credit higher than the most effective 285 nm wavelength. The sample with aluminum foil also resulted in increased efficacy of inactivation when compared to the identical sample without any reflective material. In terms of potential applications, LEDs are not only more energy efficient than LP UV lamps, but they also lower the exposure time dramatically. UV LEDs demonstrated the capability to effectively inactivate P. aeruginosa, and all of the LEDs tested greatly outperformed conventional LP UV lamps. Furthermore, the synergistic effects of sequential exposures and the use of UV reflective aluminum foil encourages further studies on its applicability for sustainable water treatment and the developm