Abstract
Legionella pneumophila is an increasingly recognized threat to public health via aerosol exposures; with a variety of control measures including: water temperature/flow management and free chlorine used to reduce the risk of infection within healthcare centers. Despite these efforts, L. pneumophila often recolonizes plumbing systems after specific treatments, which prompted us to examine ultraviolet (UV) irradiation for a point-of-use, secondary control measure. Currently, there is no data on the efficacy of high (>254 nm) wavelength UV-C (100–280 nm) light inactivation of L. pneumophila with resuscitation of viable but non-culturable (VBNC) cells. We report for the first time L. pneumophila dose-responses for 268.6 nm and 288.6 nm UV-C, as compared to 256 nm, and demonstrate UV induced VBNC L. pneumophila remaining infectious to Acanthamoeba polyphaga during co-culture experiments. Findings were correlated to molecular-based activity assays to identify additional measures of L. pneumophila viability following UV disinfection compared to culture. A collection of viability markers may provide a more representative measure of risk compared to current culture-based detection, since UV-C irradiated L. pneumophila lose culturability, yet retain activity, increased ATP production, and the ability to be resuscitated by amoeba co-culture. This finding is significant as it identifies potential concern from VBNC cells following UV-C disinfection and the need for further research into the efficacy of UV inactivation as a point-of-use application for L. pneumophila control and management.
Highlights
Legionella pneumophila is a Gram-negative, water-based, opportunistic pathogen that can cause two distinct diseases, a mild one known as Pontiac fever and potentially fatal Legionnaires’ disease (LD)
Several studies have demonstrated the re-colonization of buildings after thermal shock or superchlorination treatments, as L. pneumophila residing within biofilms and protozoan hosts remain protected [5,6]
We have reported for the first time, higher UV-wavelength dose-response curves, comparative photoreactivity plots, and UV-C induced viable but non-culturable (VBNC) L. pneumophila remaining infectious to an amoeba host
Summary
Legionella pneumophila is a Gram-negative, water-based, opportunistic pathogen that can cause two distinct diseases, a mild one known as Pontiac fever and potentially fatal Legionnaires’ disease (LD). Major exposure sources include premise plumbing, cooling towers, and hot tubs, where warm water can stagnate, allowing for L. pneumophila to amplify within biofilms and free-living protozoa [2,3]. Due to these concerns, risk managers have resorted to numerous chemical disinfectants, thermal treatments, and point-of-use (POU) measures to reduce viable L. pneumophila levels within premise plumbing, in healthcare centers [4]. Chlorination and water temperature management are the most common control measures for L. pneumophila within premise plumbing.
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