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

Lisa Conza,Valeria Gaia,Simona Casati Pagani,Yousef Abu Kwaik

doi:10.1371/journal.pone.0068244

Abstract

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.

Highlights

Legionnaires’ disease (LD) and Pontiac fever may occur after inhalation of bioaerosols contaminated with Legionella
Legionella was detected by co-culture in 52.9% to 83.3% of the composts (68.2613.3%) and in 8.3% to 18.2% of the bioaerosol pools (10.868.4%) with the exception of the CF2 samples, from which Legionella could never be isolated during the sampling period (Table 1)
The 17 composts collected in CF2 were all positive for Free-living amoebae (FLA)

Summary

Introduction

Legionnaires’ disease (LD) and Pontiac fever may occur after inhalation of bioaerosols contaminated with Legionella. The environmental reservoirs of Legionella are ground water, lakes and rivers [1,2]; Legionella, was isolated from potting soils and composts [3,4,5]. Most LD infections are linked to contaminated hot water systems, cooling towers [6], and airconditioning systems [7], but LD cases related to potting soil use or gardening have been described [4]. Some FLA have been described as potential hosts for Legionella: species of Acanthamoeba, Naegleria and Vermamoeba (synonym of Hartmannella) support the intracellular growth of Legionella [9]; some species in these genera are opportunistic human pathogens [10]

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