Presence of Legionella spp. in cooling towers: the role of microbial diversity, Pseudomonas, and continuous chlorine application

Legionnaire’s Disease (LD) is a severe pneumonia caused byLegionella pneumophila. Cooling towers are the main source ofL. pneumophiladuring large outbreaks. Colonization, survival, and proliferation ofL. pneumophilain cooling towers are necessary for outbreaks to occur. These steps are affected by chemical and physical parameters of the cooling tower environment. We hypothesize that the bacterial community residing in the cooling tower could also affect the presence ofL. pneumophila. A16S rRNAtargeted amplicon sequencing approach was used to study the bacterial community of cooling towers and its relationship with theLegionella spp.andL. pneumophilacommunities. The results indicated that the water source shaped the bacterial community of cooling towers. Several taxa were enriched and positively correlated withLegionella spp.andL. pneumophila. In contrast,Pseudomonasshowed a strong negative correlation withLegionella spp.and several other genera. Most importantly, continuous chlorine application reduced microbial diversity and promoted the presence ofPseudomonascreating a non-permissive environment forLegionella spp. This suggests that disinfection strategies as well as the resident microbial population influences the ability ofLegionella spp.to colonize cooling towers.