Protozoa in Risk Assessment of Legionellosis—Inadequacy of Guidelines and Monitoring

EPA Grant Number: R825352
Title: Protozoa in Risk Assessment of Legionellosis—Inadequacy of Guidelines and Monitoring
Investigators: Berk, Sharon G. , Newsome, Anthony L. , Wells, Martha J.M.
Institution: Tennessee Technological University , Middle Tennessee State University
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1996 through September 30, 1999 (Extended to September 30, 2000)
Project Amount: $359,300
RFA: Exploratory Research - Environmental Biology (1996) RFA Text |  Recipients Lists
Research Category: Biology/Life Sciences , Ecosystems


Significant gaps exist in the knowledge of conditions leading to outbreaks of legionellosis, with no guidelines for control or monitoring of the protistan hosts of legionellae. This waterborne disease remains a mystery with respect to when, where and why it strikes. Since one risk factor is age greater than 55, this disease may become a greater threat in the near future as the U.S. baby-boomers reach their mid 50s. Studies on interactions between amoebae and Legionella generally concur that amoebae and possibly other protozoa play major roles in maintaining legionellae in man-made environments such as cooling towers, often implicated as sources of outbreaks of legionellosis.

Alarming new observations by the PIs and others, suggest risk assessment should include a look at protozoan production of infectious particles containing Legionella. The investigators found that several species of amoebae release respirable-sized vesicles containing living Legionella; and the vesicles, containing legionellae wrapped in myelin membranes, resist exposure to cooling tower biocides for at least 24 h. Such vesicles are free in the water, and may contain over 1,000 bacteria. Traditional plate count approaches to monitoring cooling tower water may grossly underestimate the risk, since one vesicle may result in only one colony forming unit. Such vesicles may hold an important key to the epidemiology of legionellosis, and may explain paradoxes regarding infective doses.

Objectives include establishing conditions more closely resembling cooling tower environments to study infectivity and vesicle production by cooling tower isolates of amoebae and ciliates. Co-culture experiments will determine whether amplification of legionellae can take place when the "host" protozoa have alternative bacteria as food sources, and will determine the threshold ratios of legionellae to other bacteria leading to amplification of the legionellae. A new relatively inexpensive analytical technique, flow field-flow fractionation, will be evaluated for detection of legionellae-containing vesicles in water samples, and several environmental parameters will be examined for their role in production of such vesicles by protozoa. Biocide efficacy against the host protozoa will be tested, especially to study resistance and cross-resistance to biocides. Such work should help find cost-effective measures of controlling the potential hosts and amplifiers of Legionella. Molecular probes to rRNA sequences will be tested as a tool to confirm the intracellular relationship between legionellae and protozoa in situ.

The proposed work should provide information upon which to base regulatory guidelines, and results could target key factors in production of infectious particles. This work may lead to new strategies for prevention of legionellosis.

Publications and Presentations:

Publications have been submitted on this project: View all 16 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 2 journal articles for this project

Supplemental Keywords:

air, water, microbiology, bacteria., Health, Scientific Discipline, Environmental Chemistry, Chemistry, Epidemiology, Disease & Cumulative Effects, Biology, health effects, microbiology, risk assessment, Legionellosis, bacteria, infective dose, waterborne disease, airway disease, cooling towers, protozoa, biocides

Progress and Final Reports:

  • 1997 Progress Report
  • 1998
  • 1999 Progress Report
  • Final Report