Annual variations and effects of temperature on Legionella spp. and other potential opportunistic pathogens in a bathroom

Abstract

Opportunistic pathogens (OPs) in drinking water, like Legionella spp., mycobacteria, Pseudomonas aeruginosa, and free-living amobae (FLA) are a risk to human health, due to their post-treatment growth in water systems. To assess and manage these risks, it is necessary to understand their variations and environmental conditions for the water routinely used. We sampled premise tap (N = 26, N = 26) and shower (N = 26) waters in a bathroom and compared water temperatures to levels of OPs via qPCR and identified Legionella spp. by 16S ribosomal RNA (rRNA) gene sequencing. The overall occurrence and cell equivalent quantities (CE L) of Mycobacterium spp. were highest (100 %, 1.4 × 10), followed by Vermamoeba vermiformis (91 %, 493), Legionella spp. (59 %, 146), P. aeruginosa (14 %, 10), and Acanthamoeba spp. (5 %, 6). There were significant variations of OP's occurrence and quantities, and water temperatures were associated with their variations, especially for Mycobacterium spp., Legionella spp., and V. vermiformis. The peaks observed for Legionella, mainly consisted of Legionella pneumophila sg1 or Legionella anisa, occurred in the temperature ranged from 19 to 49 °C, while Mycobacterium spp. and V. vermiformis not only co-occurred with Legionella spp. but also trended to increase with increasing temperatures. There were higher densities of Mycobacterium in first than second draw water samples, indicating their release from faucet/showerhead biofilm. Legionella spp. were mostly at detectable levels and mainly consisted of L. pneumophila, L. anisa, Legionella donaldsonii, Legionella tunisiensis, and an unknown drinking water isolate based on sequence analysis. Results from this study suggested potential health risks caused by opportunistic pathogens when exposed to warm shower water with low chlorine residue and the use of Mycobacterium spp. as an indicator of premise pipe biofilm and the control management of those potential pathogens.

Shotgun Metagenomics Reveals Taxonomic and Functional Shifts in Hot Water Microbiome Due to Temperature Setting and Stagnation

“…M. avium had a higher relative abundance in distal taps than in recirculating lines and a higher abundance from the experimental rig taps than control rig taps. Similarly, higher numbers in stagnated first draw than in flushed hot water were observed in a bathroom distal tap, with a trend of increasing numbers with temperature (20–49°C) ( Dumoulin et al, 1988 ; Lu et al, 2017 ). P. aeruginosa can grow well at 37–42°C ( LaBauve and Wargo, 2012 ), but less Pseudomonas were found in hot water systems characterized by higher numbers of L. pneumophila ( Borella et al, 2004 ), similar to what we observed in Figure 4B .…”

“…P. aeruginosa can grow well at 37–42°C ( LaBauve and Wargo, 2012 ), but less Pseudomonas were found in hot water systems characterized by higher numbers of L. pneumophila ( Borella et al, 2004 ), similar to what we observed in Figure 4B . While these different OPs do share some common features ( Falkinham, 2015 ), their detections and abundances showed different trends with respect to examined factors ( Lu et al, 2017 ), making it difficult to effectively control all of them using a single uniform strategy. The fact that several positive correlations between L. pneumophila and known protozoan hosts were confirmed suggests that the metagenomic approach provides information consistent with known microbial ecological relationships.…”

“…In typical home plumbing and especially in large buildings, it is impossible to maintain water hot at the water heater set point throughout the plumbing or during water use due to heat loss ( Fernández-Seara et al, 2007a , b ; Bedard et al, 2015 ). Stagnant water in distal taps is characterized by greater concentrations of bacteria and OPs ( Rhoads et al, 2015 ; Lu et al, 2017 ) and a distinct microbial composition relative to recirculating hot water ( Ji et al, 2017 ).…”

Ten questions concerning the aerosolization and transmission of Legionella in the built environment

“…Favorable levels of heat, 101, 129 mature biofilm accumulation, 130, 131 and presence of eukaryotic hosts 132, 133 are the most frequently observed factors responsible for proliferation. Source-specific conditions, such as low disinfectant residual 134 and stagnant water, 135 both frequently found within premise plumbing, have also been shown to be conducive to Legionella growth.…”

Nontuberculous mycobacteria in drinking water systems – the challenges of characterization and risk mitigation

“…The complexity and heterogeneity of water systems make it challenging to link NTM growth and persistence to a few definable factors; more work is required to develop distribution system management strategies to mitigate the presence of NTM.In contrast to distribution system studies, research on NTM in building plumbing is plentiful, likely due to the number of NTM infections linked to public buildings. Large surface area to volume ratios, intermittent stagnation, low disinfectant residuals, and warm temperatures make building plumbing a favorable environment for bacterial attachment and growth[50][51][52][53]. NTM have been found in numerous plumbing appurtenances, including faucets and showerheads[12,22,54].…”