The role of biofilms and protozoa inLegionellapathogenesis: implications for drinking water

Abstract

Summary Current models to study Legionella pathogenesis include the use of primary macrophages and monocyte cell lines, various free‐living protozoan species and murine models of pneumonia. However, there are very few studies of Legionella spp. pathogenesis aimed at associating the role of biofilm colonization and parasitization of biofilm microbiota and release of virulent bacterial cell/vacuoles in drinking water distribution systems. Moreover, the implications of these environmental niches for drinking water exposure to pathogenic legionellae are poorly understood. This review summarizes the known mechanisms of Legionella spp. proliferation within Acanthamoeba and mammalian cells and advocates the use of the amoeba model to study Legionella pathogenicity because of their close association with Legionella spp. in the aquatic environment. The putative role of biofilms and amoebae in the proliferation, development and dissemination of potentially pathogenic Legionella spp. is also discussed. Elucidating the mechanisms of Legionella pathogenicity development in our drinking water systems will aid in elimination strategies and procedural designs for drinking water systems and in controlling exposure to Legionella spp. and similar pathogens.

The novel Legionella pneumophila type II secretion substrate NttC contributes to infection of amoebae Hartmannella vermiformis and Willaertia magna

“…Human infection most often occurs via the inhalation of L. pneumophila-containing water droplets that are produced by man-made devices (Pagnier et al, 2009). The environmental persistence of L. pneumophila is dependent upon its ability to infect and grow in amoebae (Lau & Ashbolt, 2009;Taylor et al, 2009;Thomas et al, 2010). Legionella-laden amoebae or amoebal vesicles and cysts harbouring bacteria might also be part of the inoculum that precipitates lung infection (Berk et al, 1998;Brieland et al, 1997).…”

Genome Dynamics in Legionella: The Basis of Versatility and Adaptation to Intracellular Replication

“…Legionella are able to parasitize at least 20 different species of amoeba, two species of ciliated protozoa, and one slime mold (Lau and Ashbolt 2009), but are associated most frequently with amoeba belonging to the genera Acanthamoeba, Hartmanella, and Naegleria (Fields 1996). Interestingly, not all Legionella will grow in the same amoebal host (Rowbotham 1986) and certain amoeba seem also to be resistant to Legionella infection (Atlan et al 2012).…”

The risk of contracting infectious diseases in public swimming pools. A review

“…Symbiotic or parasitic growth in free-living protozoans have been shown to yield further benefits to Legionella, not only by conferring protection against harsh environments like biocids, but also imparting higher invasiveness and human pathogenicity [66]. There is though some controversion in the scientific literature whether Legionella can multiply in biofilm without having recourse to parasitic multiplication in amoebae [67], but there is no doubt about the significant selective benefits of this mechanism for the organism [68].…”