Abstract
Legionella pneumophila (Lp) is an opportunistic pathogen that causes respiratory infections primarily through inhalation of contaminated aerosols. Lp can colonize premise plumbing systems due to favorable growth conditions (e.g., lower disinfectant residual, stagnation, warm temperatures). UV-C light-emitting diodes (UV-C LEDs) are an emerging water treatment technology and have been shown to effectively inactivate waterborne pathogens. In this study, the inactivation of four Lp strains (three clinical sg1, 4, and 6; and one sg1 drinking water (DW) isolate) was evaluated using a UV-C LED collimated beam at three wavelengths (255, 265, and 280 nm) and six fluence rates (0.5–34 mJ/cm2). Exposure to 255 nm resulted in higher log reductions at the lower fluences compared to exposures at 265 and 280 nm. Efficacy testing was also performed using a UV-C LED point-of-entry (POE) flow-through device. Based on the log inactivation curves, at 255 nm, the sg4 and sg6 clinical isolates were more susceptible to inactivation compared to the two sg1 isolates. However, at 265 and 280 nm, the sg1 and sg4 clinical isolates were more resistant to inactivation compared to the sg6 clinical and sg1 DW isolates. Differential log reductions were also observed using the POE device. Results indicate that although UV-C LED disinfection is effective, variations in Lp inactivation, wavelengths, and technology applications should be considered, especially when targeting specific isolates within premise plumbing systems.
Highlights
At 255 nm, there were 1.6–2.3 log10 colony-forming units (CFU) decreases at 0.5 mJ/cm2 and 2.5–4.1 log10 decreases at 1 mJ/cm2 for each of the four strains
1.7 log10 CFU/mL were detectable for the sg1 drinking water (DW) strain at 2 mJ/cm2 compared to below the limit of detection (LOD) for sg4 and sg6 and about 1 log10 CFU/mL for the sg1 clinical strain (Figure 2B, black line, indicated with *, p < 0.01)
This suggests that at 255 nm, the sg1 DW strain was more resistant to UV-C light-emitting diodes (LEDs) disinfection compared to the other strains, but at 5 mJ/cm2, no culturable cells were detected for all strains
Summary
Legionellae are facultative intracellular Gram-negative bacteria [1]. They are commonly found in freshwater and soil environments [2,3], Legionella infection, or legionellosis, is mainly a result of exposure to engineered water systems due to favorable conditions enabling their growth and the generation of respirable aerosols for transmission [4,5,6]. There are currently over 60 known species within the Legionella genus, more than half of which have been associated with human disease [7,8]. There are currently 15 known serogroup(sg)s of Lp with sg constituting the majority of Lp clinical isolates [9,10,11]
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