Biodiversity of amoebae and amoebae‐resisting bacteria in a drinking water treatment plant

Abstract

The complex ecology of free-living amoebae (FLA) and their role in spreading pathogenic microorganisms through water systems have recently raised considerable interest. In this study, we investigated the presence of FLA and amoebae-resisting bacteria (ARB) at various stages of a drinking water plant fed with river water. We isolated various amoebal species from the river and from several points within the plant, mostly at early steps of water treatment. Echinamoeba- and Hartmannella-related amoebae were mainly recovered in the drinking water plant whereas Acanthamoeba- and Naegleria-related amoebae were recovered from the river water and the sand filtration units. Some FLA isolates were recovered immediately after the ozonation step, thus suggesting resistance of these microorganisms to this disinfection procedure. A bacterial isolate related to Mycobacterium mucogenicum was recovered from an Echinamoeba-related amoeba isolated from ozone-treated water. Various other ARB were recovered using co-culture with axenic Acanthamoeba castellanii, including mycobacteria, legionella, Chlamydia-like organisms and various proteobacteria. Noteworthy, a new Parachlamydia acanthamoebae strain was recovered from river water and from granular activated carbon (GAC) biofilm. As amoebae mainly multiply in sand and GAC filters, optimization of filter backwash procedures probably offers a possibility to better control these protists and the risk associated with their intracellular hosts.

Enhanced survival but not amplification of Francisella spp. in the presence of free-living amoebae

“…The isolation and identification of amoebae-resisting bacteria (ARB) using the well-established co-culture method involves inoculation of samples onto a monolayer of axenic amoebae and continuous monitoring of cultures for amoebal lysis, resulting from infection by ARBs (reviewed in [46,47]). From soil, drinking water, ground and surface water, and clinical samples, the amoebal co-culture method, with amoebal lysis as an assay endpoint, has been used by numerous groups to identify human pathogens such as those belonging to the class Chlamydiae and the genera Aeromonas, Bacillus, Enterobacter, Legionella, Mycobacterium, Pseudomonas, Rhodococcus, and Streptococcus as well as novel bacteria belonging to the genera Afipia and Bosea [48][49][50][51][52][53][54][55][56]. Thus, the absence of amoebal lysis observed in this study between each FLA and Francisella spp.…”

Discovery of New Intracellular Pathogens by Amoebal Coculture and Amoebal Enrichment Approaches

“…Amoebae were present at every step of water purification and distribution, indicating a resistance of these protists to ozonation and chlorination. Intracellular bacteria could also be detected in these amoebae, showing the importance of indigenous amoebae in the transmission of intracellular bacteria 14 .…”

“…Thus, when investigating a water treatment plant system and the downstream water network, 25 different amoebal strains have been detected, of which 12 corresponded to new species 14 . Amoebae were present at every step of water purification and distribution, indicating a resistance of these protists to ozonation and chlorination.…”

“…The most common bacteria isolated by amoebal coculture are members of the Mycobacterium genus that could be recovered from water treatment plants and from water networks 13,14,24,27,28 . Legionella and α-proteobacteria species could also be isolated from water treatment plants and from hospital water networks 14,24,[28][29][30][31] . Several Chlamydia-related species were also isolated from river water and water treatment facilities, as for example Estrella lausannensis (Figures 2B-C 12,15,32,33 .…”

“…Free-living amoebae likely represent an important potential reservoir for intracellular bacteria that have yet not been discovered. This led our group to implement in Lausanne two main techniques, called amoebal coculture and amoebal enrichment, which allowed different groups to isolate several new obligate intracellular microorganisms from various environmental samples [9][10][11][12][13][14][15] .…”