Presence of Legionella and free-living Amoebae in composts and bioaerosols from composting facilities

PLoS One. 2013 Jul 2;8(7):e68244. doi: 10.1371/journal.pone.0068244. Print 2013.


Several species of Legionella cause Legionnaires' disease (LD). Infection may occur through inhalation of Legionella or amoebal vesicles. The reservoirs of Legionella are water, soil, potting soil and compost. Some species of free-living amoebae (FLA) that are naturally present in water and soil were described as hosts for Legionella. This study aimed to understand whether or not the composting facilities could be sources of community-acquired Legionella infections after development of bioaerosols containing Legionella or FLA. We looked for the presence of Legionella (by co-culture) and FLA (by culture) in composts and bioaerosols collected at four composting facilities located in southern Switzerland. We investigated the association between the presence of Legionella and compost and air parameters and presence of FLA. Legionella spp. (including L. pneumophila) were detected in 69.3% (61/88) of the composts and FLA (mainly Acanthamoeba, Vermamoeba, Naegleria and Stenamoeba) in 92.0% (81/88). L. pneumophila and L. bozemanii were most frequently isolated. FLA as potential host for Legionella spp. were isolated from 40.9% (36/88) of the composts in all facilities. In Legionella-positive samples the temperature of compost was significantly lower (P = 0.012) than in Legionella-negative samples. Of 47 bioaerosol samples, 19.1% (9/47) were positive for FLA and 10.6% (5/47) for L. pneumophila. Composts (62.8%) were positive for Legionella and FLA contemporaneously, but both microorganisms were never detected simultaneously in bioaerosols. Compost can release bioaerosol containing FLA or Legionella and could represent a source of infection of community-acquired Legionella infections for workers and nearby residents.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aerosols / analysis*
  • Air Microbiology
  • Amoeba / cytology
  • Amoeba / isolation & purification*
  • Coculture Techniques
  • Environmental Monitoring / methods
  • Humans
  • Hydrogen-Ion Concentration
  • Legionella / cytology
  • Legionella / isolation & purification*
  • Legionellosis / microbiology
  • Soil Microbiology
  • Soil*
  • Switzerland
  • Temperature
  • Water Microbiology


  • Aerosols
  • Soil

Grant support

The work has been partially supported by the Ticino Pulmonary League. A special thanks to Lung Leagues of the Canton Ticino and to the Dr. Pierluigi Crivelli Foundation for financial support. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. No additional external funding was received for this study.