Cooccurrence of Five Pathogenic Legionella spp. and Two Free-Living Amoebae Species in a Complete Drinking Water System and Cooling Towers

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.

Water Age Effects on the Occurrence and Concentration of Legionella Species in the Distribution System, Premise Plumbing, and the Cooling Towers

“…A geometric mean for each sample was calculated using all values from technical and biological replicates. Sample concentrations were transformed from gene copies (GC)/100 mL into Log 10 GC/100 mL for statistical analysis [28]. Statistical results were interpreted at the level of significance p < 0.05.…”

“…The building name description of each building was abbreviated to protect the privacy of the site location. The water samples collected for this study are the same samples from Logan-Jackson et al, 2021 and some of these results in Tables 1 and 4 are available from a previously published paper [28].…”

“…Legionella pneumophila was found in 57% (24/42) of the water samples, followed by L. bozemanii 52% (22/42), L. longbeachae 36% (15/42), L. micdadei 23% (10/42), L. anisa 21% (9/42) at geometric mean concentrations of 1.7, 1.7, 1.4, 1.6 and 1.7 Log 10 GC/100 mL, respectively (Table 1). Some of the results in Table 1 are also available in a previously published paper [28]. Table 1 is adapted with permission from ref.…”

“…While both studies [21,27] described the proportion of the samples that were positive for L. pneumophila relative to non-L. pneumophila, neither author described the co-occurrence of L. pneumophila and non-L. pneumophila in any given sample. Logan-Jackson et al, 2021 [28] investigated several pathogenic Legionella species in a complete water supply system. However, the ecology of L. pneumophila and non-L. pneumophila species in individual, specific samples were not discussed.…”

“…However, the ecology of L. pneumophila and non-L. pneumophila species in individual, specific samples were not discussed. The focus of Logan-Jackson et al, 2021 [28] was on understanding the co-occurrence of five of the most-disease relevant Legionella species to free-living amoebae, Naegleria and Acanthamoeba. The improvement of this study to the studies discussed above is investigating only Legionella ecology in a complete water supply system (from source to tap) and describing how multiple factors (water age, water quality parameters, etc.)…”