Distribution of Legionella and bacterial community composition among regionally diverse US cooling towers

Abstract

Cooling towers (CTs) are a leading source of outbreaks of Legionnaires’ disease (LD), a severe form of pneumonia caused by inhalation of aerosols containing Legionella bacteria. Accordingly, proper maintenance of CTs is vital for the prevention of LD. The aim of this study was to determine the distribution of Legionella in a subset of regionally diverse US CTs and characterize the associated microbial communities. Between July and September of 2016, we obtained aliquots from water samples collected for routine Legionella testing from 196 CTs located in eight of the nine continental US climate regions. After screening for Legionella by PCR, positive samples were cultured and the resulting Legionella isolates were further characterized. Overall, 84% (164) were PCR-positive, including samples from every region studied. Of the PCR-positive samples, Legionella spp were isolated from 47% (78), L. pneumophila was isolated from 32% (53), and L. pneumophila serogroup 1 (Lp1) was isolated from 24% (40). Overall, 144 unique Legionella isolates were identified; 53% (76) of these were Legionella pneumophila. Of the 76 L. pneumophila isolates, 51% (39) were Lp1. Legionella were isolated from CTs in seven of the eight US regions examined. 16S rRNA amplicon sequencing was used to compare the bacterial communities of CT waters with and without detectable Legionella as well as the microbiomes of waters from different climate regions. Interestingly, the microbial communities were homogenous across climate regions. When a subset of seven CTs sampled in April and July were compared, there was no association with changes in corresponding CT microbiomes over time in the samples that became culture-positive for Legionella. Legionella species and Lp1 were detected frequently among the samples examined in this first large-scale study of Legionella in US CTs. Our findings highlight that, under the right conditions, there is the potential for CT-related LD outbreaks to occur throughout the US.

Legionnaires’ Disease Cases at a Large Community Hospital—Common and Underdiagnosed

“…Somewhat alarmingly, Legionella pneumophila was found in 14 of 20 (70%) US hospitals surveyed across 13 states [12] and 60% of Paris hospital water systems [13]. Additionally, a survey of 196 cooling towers across the US revealed pathogenic Legionella strains in 53 towers (27%) [14]. In cooling towers, Legionella can grow to outbreak levels within 7 days [15,16].…”

Exploitation of Phosphoinositides by the Intracellular Pathogen,Legionella pneumophila

“…In the human lung, L. pneumophila infects resident alveolar macrophages leading to severe pneumonia, known as Legionnaires' disease, which can be fatal in immunocompromised individuals [14]. Outbreaks stem from contaminated water systems such as those supplying water towers, cooling systems, and decorative fountains [15]. In 2017, a study by the Centers for Disease Control and Prevention (CDC) found that L. pneumophila was the leading bacterial agent responsible for public drinking water-associated outbreaks within the United States [14].…”

Impact of temperature onLegionella pneumophila, its protozoan host cells, and the microbial diversity of the biofilm community of a pilot cooling tower

“…The 98 identity and relative abundance of these microbes is influenced by several parameters. The 99 microbial population residing in cooling towers is shaped by local climate and water sources 100 (Llewellyn et al, 2017;Paranjape et al, 2020). Additionally, the microbiota is affected by the 101 disinfectant residuals and application schedule (Hwang et al, 2012;Paranjape et al, 2020).…”