Survival and nutritional requirements for Legionella in environmental waters

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Legionella are a common yet poorly understood water-born pathogen. These bacteria are ubiquitous in water systems, where protozoan host endoparasitization and biofilm association play important roles in their life cycle. Current knowledge on Legionella ecology is severely lacking in several key areas, including biofilm interactions and the effects environmental conditions have on their growth and survival. A model water distribution system was used to examine the dissemination and survival of Legionella within water systems. After inoculation with L. pneumophila water and biofilm samples were collected from the system and analyzed for concentration of Legionella over a period of 131 days. Legionella were able to maintain stable populations in both water and biofilms in the system for months. In addition, after introduction of 5 mg/L of chlorine, Legionella concentrations decreased, but were not eradicated. A bench scale study was performed in which L. pneumophila cells were inoculated into tubes containing tap water and incubated at 4, 25, and 32° C, with concentrations measured over time. Each temperature showed a steady decrease in concentrations, followed by stabilization. This occurred almost 30 days earlier at 25° C with final population levels 3-fold higher than at 4° C. The results provided by this study document the survival of Legionella under different environmental conditions and provide relevant knowledge in identifying conditions which promote survival and potential growth of Legionella, information that could prove useful for maintenance and monitoring procedures in drinking water distribution systems. To examine beneficial environmental conditions and growth factors for Legionella, two experiments were conducted. To determine the presence and source of two essential nutrients for Legionella growth, iron and L-cysteine, environmental water samples were collected and separated via filtration into different components. In addition, freeze-thawing was used to release potential nutrients from microbial cells. These components were supplemented into modified BCYE media prepared with the following conditions: 1) no iron or L-cysteine added, 2) iron added, 3) L-cysteine added, and 4) both iron and L-cysteine added. Growth of L. pneumophila on these media have demonstrated sufficient levels of iron, L-cysteine, or both to support Legionella growth in environmental waters outside of host cells. Another experiment measured L. pneumophila growth in the previously mentioned components compared with laboratory grade sterile water. Results showing higher and increasing concentrations of Legionella in comparison to sterile water suggest that certain components in environmental water, including some potentially dissolved in the waters, are capable of supporting the growth of this pathogen. The results from this study serve to further elucidate the environmental nutritional requirements for Legionella and provide evidence supporting the theory of their capability for environmental growth in the absence of host organisms.

Original languageEnglish (US)
Title of host publication2013 Water Quality Technology Conference and Exposition, WQTC 2013
StatePublished - 2013
Event2013 Water Quality Technology Conference and Exposition, WQTC 2013 - Long Beach, CA, United States
Duration: Nov 3 2013Nov 7 2013


Other2013 Water Quality Technology Conference and Exposition, WQTC 2013
Country/TerritoryUnited States
CityLong Beach, CA

ASJC Scopus subject areas

  • Water Science and Technology


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