Co-Occurrence of Free-Living Amoeba and Legionella in Drinking Water Supply Systems

Prevalence and distribution of Legionella in municipal drinking water supply systems in Madrid (Spain) and risk factors associated

The presence and concentration of Legionella in drinking water supply systems, in hot water (DHW) for human consumption in public buildings in Madrid with potential health risk was studied. Sampling covered a total of 1695 DHW samples and 30 cold water (DCW) as a control taken in the 21 districts of the city over a period of 14 years (2007-2020). The detection and quantification of Legionella was carried out by plate culture and quantitative qPCR. The study evaluated a series of variables including sampling year, districts, type of building, seasonality, sampling points (taps, tanks and showers), water temperature and type of disinfection used. The degree of compliance of Legionella in the water supply network of Madrid was very high (96.1 %). The degree of colonization of the positive samples ranged from 0.3 × 103 and 1.5 × 105 GU/L for a 97 % of the samples. A higher presence of this bacterium was detected in older facilities in the peripheral districts and end points able to produce aerosols such as showers. The highest number of samples with Legionella growth occurred in the 35-40 °C range. The strategies implemented have contributed to a remarkable decrease in the presence of Legionella in the last years of sampling.

Development of a machine learning model to support low cost real-time Legionella monitoring in premise plumbing systems

Legionella pneumophila (L. pneumophila) is a pathogenic bacterium primarily known for causing Legionnaires' Disease which is known for high mortality rates, particularly in the elderly. With caseloads continuing to increase, further research is needed to improve our understanding of optimized sampling schema and safe limits of L. pneumophila, in part to target improved treatment options and realistic population-level risk modeling. Particularly in healthcare and other high-risk locations these become crucial and time sensitive needs. Therefore, we conceptualized this research as a means of incorporating easily measured physiochemical water quality parameters and generalization of the unique ecology of building water systems to build a computational model that can allow for more rapid and accurate decision making. This research uses the specific machine learning (ML) method called statistical learning theory to incorporate concentration of host cells, such as native amoeba, and physiochemical water quality parameters to estimate the probability of observing ranges of Legionella gene copy concentrations. Using data from previously published research on Legionella prevalence in a large building, our ML method trains the model on the relative impacts of physiochemical parameters on likely amoeba host cell occurrences. The model is expanded to estimate host cell concentrations using correlations and regressions operated through LASSO algorithms. After categorization variables from these results are then used to inform a logistic regression to provide an estimate of the probability of Legionella gene copy concentration ranges. In summary, conventional results generated by logistic regression and multiple linear regression quantified the associations among ecological conditions in the water and ability to predict a likely range of Legionella concentration in a management focused way. Further, two ML methods, PCA and LASSO, demonstrated feasibility in accurate real-time monitoring of Legionella through physiochemical indicators as evidenced with good accuracy of predictions based for validation results. Furthermore results demonstrate the vital need to account for the impact of water quality on building on host cells, and via their quantified water microbial ecology, not just Legionella concentrations.

Diversity of Free-Living Amoebae in New Zealand Groundwater and Their Ability to Feed on Legionella pneumophila

Free-living amoebae (FLA) are common in both natural and engineered freshwater ecosystems. They play important roles in biofilm control and contaminant removal through the predation of bacteria and other taxa. Bacterial predation by FLA is also thought to contribute to pathogen dispersal and infectious disease transmission in freshwater environments via the egestion of viable bacteria. Despite their importance in shaping freshwater microbial communities, the diversity and function of FLA in many freshwater ecosystems are poorly understood. In this study, we isolated and characterized FLA from two groundwater sites in Canterbury, New Zealand using microbiological, microscopic, and molecular techniques. Different methods for groundwater FLA isolation and enrichment were trialed and optimized. The ability of these isolated FLA to predate on human pathogen Legionella pneumophila was assessed. FLA were identified by 18S metagenomic amplicon sequencing. Our study showed that Acanthamoeba spp. (including A. polyphaga) and Vermamoeba veriformis were the main FLA species present in both groundwater sites examined. While most of the isolated FLA co-existed with L. pneumophila, the FLA populations in the L. pneumophila co-culture experiments predominantly consisted of A. polyphaga, Acanthamoeba spp., Naegleria spp., V. vermiformis, Paravahlkampfia spp., and Echinamoeba spp. These observations suggest that FLA may have the potential to act as reservoirs for L. pneumophila in Canterbury, New Zealand groundwater systems and could be introduced into the local drinking water infrastructure, where they may promote the survival, multiplication, and dissemination of Legionella. This research addresses an important gap in our understanding of FLA-mediated pathogen dispersal in freshwater ecosystems.

A challenge in washing water with the sun: 24h of SODIS fails to inactivate Acanthamoeba castellanii cysts and internalized Pseudomonas aeruginosa under strong real sun conditions

Despite access to drinking water being a basic human right, the availability of safe drinking water remains a privilege that many do not have and as a result, many lives are lost each year due to waterborne diseases associated with the consumption of biologically unsafe water. To face this situation, different low-cost household drinking water treatment technologies (HDWT) have been developed, and among them is solar disinfection (SODIS). Despite the effectiveness of SODIS and the epidemiological gains being consistently documented in the literature, there is a lack of evidence of the effectiveness of the batch-SODIS process against protozoan cysts as well as their internalized bacteria under real sun conditions. This work evaluated the effectiveness of the batch-SODIS process on the viability of Acanthamoeba castellanii cysts, and internalized Pseudomonas aeruginosa. Dechlorinated tap water contaminated with 5.6 × 103 cysts/L, contained in PET (polyethylene terephthalate) bottles, was exposed for 8 h a day to strong sunlight (531-1083 W/m2 of maximum insolation) for 3 consecutive days. The maximum water temperature inside the reactors ranged from 37 to 50 °C. Cyst viability was assessed by inducing excystment on non-nutrient agar, or in water with heat-inactivated Escherichia coli. After sun exposure for 0, 8, 16 and 24 h, the cysts remained viable and without any perceptible impairment in their ability to excyst. 3 and 5.5 log CFU/mL of P. aeruginosa were detected in water containing untreated and treated cysts, respectively, after 3 days of incubation at 30 °C. The batch-SODIS process is unable to inactivate A. castellanii cysts as well as its internalized bacteria. Although the use of batch SODIS by communities should continue to be encouraged, SODIS-disinfected water should be consumed within 3 days.

Evaluation of Genetic Diversity and Virulence Potential of Legionella pneumophila Isolated from Water Supply Systems of Residential Buildings in Latvia

Legionella is an opportunistic pathogen with a biphasic life cycle that occasionally infects humans. The aim of the study was to assess the distribution of virulence genes and genetic diversity among L. pneumophila isolated from water supply systems of residential buildings in Latvia. In total, 492 water samples from 200 residential buildings were collected. Identification of Legionella spp. was performed according to ISO 11731, and 58 isolates were subjected to whole-genome sequencing. At least one Legionella-positive sample was found in 112 out of 200 apartment buildings (56.0%). The study revealed extensive sequence-type diversity, where 58 L. pneumophila isolates fell into 36 different sequence types. A total of 420 virulence genes were identified, of which 260 genes were found in all sequenced L. pneumophila isolates. The virulence genes enhC, htpB, omp28, and mip were detected in all isolates, suggesting that adhesion, attachment, and entry into host cells are enabled for all isolates. The relative frequency of virulence genes among L. pneumophila isolates was high. The high prevalence, extensive genetic diversity, and the wide range of virulence genes indicated that the virulence potential of environmental Legionella is high, and proper risk management is of key importance to public health.

Multiple Cross Displacement Amplification Coupled with Lateral Flow Biosensor (MCDA-LFB) for rapid detection of Legionella pneumophila

Background

Legionella pneumophila is an opportunistic waterborne pathogen of significant public health problems, which can cause serious human respiratory diseases (Legionnaires’ disease). Multiple cross displacement amplification (MCDA), a isothermal nucleic acid amplification technique, has been applied in the rapid detection of several bacterial agents. In this report, we developed a MCDA coupled with Nanoparticles-based Lateral Flow Biosensor (MCDA-LFB) for the rapid detection of L. pneumophila.

Results

A set of 10 primers based on the L. pneumophila specific mip gene to specifically identify 10 different target sequence regions of L. pneumophila was designed. The optimal time and temperature for amplification are 57 min and 65 °C. The limit of detection (LoD) is 10 fg in pure cultures of L. pneumophila. No cross-reaction was obtained and the specificity of MCDA-LFB assay was 100%. The whole process of the assay, including 20 min of DNA preparation, 35 min of L. pneumophila-MCDA reaction, and 2 min of sensor strip reaction, took a total of 57 min (less than 1 h). Among 88 specimens for clinical evaluation, 5 (5.68%) samples were L. pneumophila-positive by MCDA-LFB and traditional culture method, while 4(4.55%) samples were L. pneumophila-positive by PCR method targeting mip gene. Compared with culture method, the diagnostic accuracy of MCDA-LFB method was higher.

Conclusions

In summary, the L. pneumophila-MCDA-LFB method we successfully developed is a simple, fast, reliable and sensitive diagnostic tool, which can be widely used in basic and clinical laboratories.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02363-3.

Using Genomic Deletion Mutants to Investigate Effector-Triggered Immunity During Legionella pneumophila Infection

Legionella pneumophila is an intracellular bacterial pathogen that uses a type IV secretion system (T4SS), termed Dot/Icm, to secrete more than 330 virulence effector proteins into the infected host cell. Many Dot/Icm effectors are involved in biogenesis of the Legionella-containing vacuole (LCV), which allows intracellular bacterial replication in environmental amoebae and alveolar macrophages. Through their activity, some effectors trigger the mammalian host immune response in a phenomenon termed effector-triggered immunity (ETI). Here, we describe a protocol to create and use L. pneumophila genome deletion mutants to identify effector(s) that alter pro-inflammatory cytokine production and bacterial clearance in the lungs of mice.

Water Age Effects on the Occurrence and Concentration of Legionella Species in the Distribution System, Premise Plumbing, and the Cooling Towers

In this study, droplet digital PCR^TM (ddPCR^TM) was used to characterize total Legionella spp. and five specific Legionella species from source (groundwater) to exposure sites (taps and cooling towers). A total of 42–10 L volume water samples were analyzed during this study: 12 from a reservoir (untreated groundwater and treated water storage tanks), 24 from two buildings (influents and taps), and six from cooling towers, all part of the same water system. The approximate water age (time in the system) for all sample locations are as follows: ~4.5, 3.4, 9.2, 20.8, and 23.2 h (h) for the groundwater to the reservoir influent, reservoir influent to the reservoir effluent, reservoir effluent to building Fa (building names are abbreviated to protect the privacy of site location), building ERC and the cooling towers, respectively. Results demonstrated that gene copies of Legionella spp. (23S rRNA) were significantly higher in the cooling towers and ERC building (p < 0.05) relative to the reservoir and building Fa (closest to reservoir). Legionella spp. (23S rRNA) were found in 100% (42/42) of water samples at concentrations ranging from 2.2 to 4.5 Log10 GC/100 mL. More specifically, L. pneumophila was found in 57% (24/42) of the water samples, followed by L. bozemanii 52% (22/42), L. longbeachae 36% (15/42), L. micdadei 23% (10/42) and L. anisa 21% (9/42) with geometric mean concentrations of 1.7, 1.7, 1.4, 1.6 and 1.7 Log₁₀ GC/100 mL, respectively. Based on this study, it is hypothesized that water age in the distribution system and the premise-plumbing system as well as building management plays a major role in the increase of Legionella spp., (23S rRNA) and the diversity of pathogenic species found as seen in the influent, and at the taps in the ERC building—where the building water quality was most comparable to the industrial cooling towers. Other pathogenic Legionella species besides L.pneumophila are also likely amplifying in the system; thus, it is important to consider other disease relevant species in the whole water supply system—to subsequently control the growth of pathogenic Legionella in the built water environment.

Legionella: A Promising Supplementary Indicator of Microbial Drinking Water Quality in Municipal Engineered Water Systems

Opportunistic pathogens (OPs) are natural inhabitants and the predominant disease causative biotic agents in municipal engineered water systems (EWSs). In EWSs, OPs occur at high frequencies and concentrations, cause drinking-water-related disease outbreaks, and are a major factor threatening public health. Therefore, the prevalence of OPs in EWSs represents microbial drinking water quality. Closely or routinely monitoring the dynamics of OPs in municipal EWSs is thus critical to ensuring drinking water quality and protecting public health. Monitoring the dynamics of conventional (fecal) indicators (e.g., total coliforms, fecal coliforms, and Escherichia coli) is the customary or even exclusive means of assessing microbial drinking water quality. However, those indicators infer only fecal contamination due to treatment (e.g., disinfection within water utilities) failure and EWS infrastructure issues (e.g., water main breaks and infiltration), whereas OPs are not contaminants in drinking water. In addition, those indicators appear in EWSs at low concentrations (often absent in well-maintained EWSs) and are uncorrelated with OPs. For instance, conventional indicators decay, while OPs regrow with increasing hydraulic residence time. As a result, conventional indicators are poor indicators of OPs (the major aspect of microbial drinking water quality) in EWSs. An additional or supplementary indicator that can well infer the prevalence of OPs in EWSs is highly needed. This systematic review argues that Legionella as a dominant OP-containing genus and natural inhabitant in EWSs is a promising candidate for such a supplementary indicator. Through comprehensively comparing the behavior (i.e., occurrence, growth and regrowth, spatiotemporal variations in concentrations, resistance to disinfectant residuals, and responses to physicochemical water quality parameters) of major OPs (e.g., Legionella especially L. pneumophila, Mycobacterium, and Pseudomonas especially P. aeruginosa), this review proves that Legionella is a promising supplementary indicator for the prevalence of OPs in EWSs while other OPs lack this indication feature. Legionella as a dominant natural inhabitant in EWSs occurs frequently, has a high concentration, and correlates with more microbial and physicochemical water quality parameters than other common OPs. Legionella and OPs in EWSs share multiple key features such as high disinfectant resistance, biofilm formation, proliferation within amoebae, and significant spatiotemporal variations in concentrations. Therefore, the presence and concentration of Legionella well indicate the presence and concentrations of OPs (especially L. pneumophila) and microbial drinking water quality in EWSs. In addition, Legionella concentration indicates the efficacies of disinfectant residuals in EWSs. Furthermore, with the development of modern Legionella quantification methods (especially quantitative polymerase chain reactions), monitoring Legionella in ESWs is becoming easier, more affordable, and less labor-intensive. Those features make Legionella a proper supplementary indicator for microbial drinking water quality (especially the prevalence of OPs) in EWSs. Water authorities may use Legionella and conventional indicators in combination to more comprehensively assess microbial drinking water quality in municipal EWSs. Future work should further explore the indication role of Legionella in EWSs and propose drinking water Legionella concentration limits that indicate serious public health effects and require enhanced treatment (e.g., booster disinfection).

Cooccurrence of Five Pathogenic Legionella spp. and Two Free-Living Amoebae Species in a Complete Drinking Water System and Cooling Towers

Pathogenic Legionella species grow optimally inside free-living amoebae to concentrations that increase risks to those who are exposed. The aim of this study was to screen a complete drinking water system and cooling towers for the occurrence of Acanthamoeba spp. and Naegleria fowleri and their cooccurrence with Legionella pneumophila, Legionella anisa, Legionella micdadei, Legionella bozemanii, and Legionella longbeachae. A total of 42 large-volume water samples, including 12 from the reservoir (water source), 24 from two buildings (influents to the buildings and exposure sites (taps)), and six cooling towers were collected and analyzed using droplet digital PCR (ddPCR). N. fowleri cooccurred with L. micdadei in 76 (32/42) of the water samples. In the building water system, the concentrations of N. fowleri and L. micdadei ranged from 1.5 to 1.6 Log₁₀ gene copies (GC)/100 mL, but the concentrations of species increased in the cooling towers. The data obtained in this study illustrate the ecology of pathogenic Legionella species in taps and cooling towers. Investigating Legionella’s ecology in drinking and industrial waters will hopefully lead to better control of these pathogenic species in drinking water supply systems and cooling towers.

Causes, Factors, and Control Measures of Opportunistic Premise Plumbing Pathogens—A Critical Review

This review critically analyses the chemical and physical parameters that influence the occurrence of opportunistic pathogens in the drinking water distribution system, specifically in premise plumbing. A comprehensive literature review reveals significant impacts of water age, disinfectant residual (type and concentration), temperature, pH, and pipe materials. Evidence suggests that there is substantial interplay between these parameters; however, the dynamics of such relationships is yet to be elucidated. There is a correlation between premise plumbing system characteristics, including those featuring water and energy conservation measures, and increased water quality issues and public health concerns. Other interconnected issues exacerbated by high water age, such as disinfectant decay and reduced corrosion control efficiency, deserve closer attention. Some common features and trends in the occurrence of opportunistic pathogens have been identified through a thorough analysis of the available literature. It is proposed that the efforts to reduce or eliminate their incidence might best focus on these common features.