Abstract
Pathogenic Legionella species grow optimally inside free-living amoebae to concentrations that increase risks to those who are exposed. The aim of this study was to screen a complete drinking water system and cooling towers for the occurrence of Acanthamoeba spp. and Naegleria fowleri and their cooccurrence with Legionella pneumophila, Legionella anisa, Legionella micdadei, Legionella bozemanii, and Legionella longbeachae. A total of 42 large-volume water samples, including 12 from the reservoir (water source), 24 from two buildings (influents to the buildings and exposure sites (taps)), and six cooling towers were collected and analyzed using droplet digital PCR (ddPCR). N. fowleri cooccurred with L. micdadei in 76 (32/42) of the water samples. In the building water system, the concentrations of N. fowleri and L. micdadei ranged from 1.5 to 1.6 Log10 gene copies (GC)/100 mL, but the concentrations of species increased in the cooling towers. The data obtained in this study illustrate the ecology of pathogenic Legionella species in taps and cooling towers. Investigating Legionella’s ecology in drinking and industrial waters will hopefully lead to better control of these pathogenic species in drinking water supply systems and cooling towers.
Highlights
Free-living amoebae are ubiquitous protozoa that have been found in various natural and engineered water systems, such as surface water, groundwater, drinking water supply systems, hot springs, and cooling towers [1,2,3,4,5,6,7]
Using droplet digital PCR (ddPCR), this study addressed the following objectives (i) identify the cooccurrence of pathogenic Legionella spp. (L. pneumophila, L. anisa, L. longbeachae, L. bozemanii, and L. micdadei) and amoebae species (N. fowleri and Acanthamoeba spp.) in a complete water supply chain and cooling towers, (ii) examine the difference in occurrence and concentration of N. fowleri and Acanthamoeba spp. in a groundwater source, which supplied the building water system, and cooling towers, all located in the state of Michigan
Water samples collected from the cooling towers were higher in percentage positives for Acanthamoeba spp. 83% (5/6) and N. fowleri 83% (5/6) than the drinking water system (Fa, ERC, and RES_IN, and RES_EF) (Table 1)
Summary
Free-living amoebae are ubiquitous protozoa that have been found in various natural and engineered water systems, such as surface water, groundwater, drinking water supply systems, hot springs, and cooling towers [1,2,3,4,5,6,7]. Similar to free-living amoebae, Legionella spp. are found in natural water bodies (surface water, groundwater, and hot springs) [8,9,10,11] and human-made systems (swimming pools, drinking water supply systems, and cooling towers) [12,13,14,15,16,17,18,19,20,21] In their natural and engineered environments, freeliving amoebae serve as a host, reservoir, and vehicle of pathogenic bacteria, including Legionella species [8,9,10,11,12,13,14,15,16,17,18,19,20,21]. To that end, cooling towers and hot-water taps are key sources of human infections with Legionella species [32,33], posing a risk to human health via inhalation as these exposure sites are aerosol spreading units [34,35,36,37]
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