Microbial and legionella dynamics within cooling towers (16S)
Legionella, primarily L. pneumophila, is the causative agent of Legionnaires' Disease (LD). LD prevalence has increased over the past 20 years, with spikes during summer. Cooling towers (CTs) are a major source of outbreaks. Resident CT microbial communities, especially amoebae and ciliate hosts, foster Legionella growth. Seasonal fluctuations in CT physicochemical parameters cause stochastic changes in microbial communities. However, CT microbiomes dynamics and how it affects Legionella communities remain poorly understood. Although biofilm serves as a Legionella niche within CTs, the dynamics of CT biofilm communities remains unclear. This study aims to determine the dynamics of CT microbial communities and their role in L. pneumophila spikes during summer. We collected water and biofilm samples from four CTs bi-weekly from June to September 2022 to measure physicochemical parameters, quantify L. pneumophila by culture, and Legionella and L. pneumophila via qPCR, and determine the CT microbiomes with 16S and 18S rRNA sequencing. Culture seems better to capture L. pneumophila dynamics in CTs. L. pneumophila culture-positive CTs showed fluctuating biocide concentrations and warmer temperatures. Drops in biocide concentration led to increased microbial diversity, higher amoebae abundance, and higher L. pneumophila concentrations. Acanthamoeba and Echinamoebae sp. were uniquely present in culture-positive CTs.  The CT treated exclusively with non-oxidant biocides showed high Legionella concentration but no culturable L. pneumophila suggested intra-species competition. Biofilm-forming bacteria correlated positively with Legionella and L. pneumophila presence, and Legionella and hosts ASVs were continuously found in biofilm samples. In summary, warmer temperatures and fluctuations in biocide concentration led to abundant biofilm-forming bacteria and amoebae that seem to support L. pneumophila growth during summer. To mitigate risks, CT operators should aim for minimum water temperatures and maintain stable biocide concentrations. Biofilm control is strongly recommended as it serves as a chronic L. pneumophila niche.
Legionella, primarily L. pneumophila, is the causative agent of Legionnaires' Disease (LD). LD prevalence has increased over the past 20 years, with spikes during summer. Cooling towers (CTs) are a major source of outbreaks. Resident CT microbial communities, especially amoebae and ciliate hosts, foster Legionella growth. Seasonal fluctuations in CT physicochemical parameters cause stochastic changes in microbial communities. However, CT microbiomes dynamics and how it affects Legionella communities remain poorly understood. Although biofilm serves as a Legionella niche within CTs, the dynamics of CT biofilm communities remains unclear. This study aims to determine the dynamics of CT microbial communities and their role in L. pneumophila spikes during summer. We collected water and biofilm samples from four CTs bi-weekly from June to September 2022 to measure physicochemical parameters, quantify L. pneumophila by culture, and Legionella and L. pneumophila via qPCR, and determine the CT microbiomes with 16S and 18S rRNA sequencing. Culture seems better to capture L. pneumophila dynamics in CTs. L. pneumophila culture-positive CTs showed fluctuating biocide concentrations and warmer temperatures. Drops in biocide concentration led to increased microbial diversity, higher amoebae abundance, and higher L. pneumophila concentrations. Acanthamoeba and Echinamoebae sp. were uniquely present in culture-positive CTs.  The CT treated exclusively with non-oxidant biocides showed high Legionella concentration but no culturable L. pneumophila suggested intra-species competition. Biofilm-forming bacteria correlated positively with Legionella and L. pneumophila presence, and Legionella and hosts ASVs were continuously found in biofilm samples. In summary, warmer temperatures and fluctuations in biocide concentration led to abundant biofilm-forming bacteria and amoebae that seem to support L. pneumophila growth during summer. To mitigate risks, CT operators should aim for minimum water temperatures and maintain stable biocide concentrations. Biofilm control is strongly recommended as it serves as a chronic L. pneumophila niche.
McGill University