Free-living amoebae (FLA) co-occurring with legionellae in industrial waters

Microbial assessment and performance evaluation of eyewash stations in the laboratory setting

Eyewash stations are an essential component of laboratory safety programs, providing first aid in case of ocular exposure to hazardous materials. However, the presence of microbial contamination in these devices poses a potential risk of ocular infection to laboratory employees. This cross-sectional study aimed to evaluate the microbial quality and performance of 40 eyewash stations fixed in 10 buildings in a laboratory setting. Water quality parameters, including temperature, pH, turbidity, and the presence of Acanthamoeba spp., were measured at various time points (first draw, after 2 min of flushing, and 15 min flushing) from samples collected from each of the 40 eyewash stations. Performance and operational data were also measured according to the American National Standards Institute (ANSI)/International Safety Equipment Association (ISEA) Z358.1-2014 standard. Our results showed variable compliance with this standard across measures of physical condition, performance, access, and maintenance. Out of the 147 water samples collected (130 eyewash samples, 17 building reference samples), 28 samples were suspected to contain Acanthamoeba spp. or other free-living amoeba based on initial testing. Further analysis using polymerase chain reaction (PCR) confirmed the presence of Acanthamoeba spp. in 5 out of 28 samples. The results of this study provide insights into the potential risk of ocular infections associated with using eyewash stations and provide the basis for the recommendations on maintenance protocols to minimize the risk of microbial contamination.

Multiplex Real-Time Polymerase Chain Reaction Assay To Detect Acanthamoeba spp., Vermamoeba vermiformis, Naegleria fowleri, and Balamuthia mandrillaris in Different Water Sources

Free-living amoebae (FLA) are widely distributed in the environment. Among these, Acanthamoeba spp., Naegleria fowleri, Balamuthia mandrillaris, and Vermamoeba vermiformis have been reported as human pathogens with health effects ranging from lethal encephalitis to different epithelial disorders. Despite this, FLA still present many diagnostic challenges. The aim of this study was to develop a rapid and efficient multiplex real-time quantitative polymerase chain reaction (qPCR) to simultaneously detect Acanthamoeba spp., N. fowleri, B. mandrillaris, and V. vermiformis in different water sources. For the validation of the qPCR assay, 38 samples (19 tap water and 19 stagnant water sources) were analyzed. The qPCR assay accurately identified the four types of FLA with no cross-reactivity. Considering water samples with results subsequently confirmed by conventional PCR, the multiplex qPCR assay detected 18/38 (47.4%) positive samples (Acanthamoeba spp. in 44.7% and V. vermiformis in 31.6%) and growth in nonnutritive agar (NNA) cultures identified 7/38 (18.4%) positive samples. Of the tap water samples analyzed, 26.3% of samples positive for FLA were detected by growth in NNA culture whereas 31.6% were identified by qPCR. In addition, FLA were detected in 2/19 stagnant water samples (10.5%) by growth in NNA culture and in 12/19 stagnant water samples (63.2%) by qPCR. Neither N. fowleri nor B. mandrillaris was detected in the water samples analyzed. In conclusion, the qPCR developed showed its potential as a rapid tool for detection of Acanthamoeba spp., N. fowleri, B. mandrillaris, and V. vermiformis. Moreover, FLA species were detected in half of the water sources evaluated, suggesting the importance of the surveillance of these potential infectious agents.

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.

Excessive Ozonation Stress Triggers Severe Membrane Biofilm Accumulation and Fouling

The established benefits of ozone on microbial pathogen inactivation, natural organic matter degradation, and inorganic/organic contaminant oxidation have favored its application in drinking water treatment. However, viable bacteria are still present after the ozonation of raw water, bringing a potential risk to membrane filtration systems in terms of biofilm accumulation and fouling. In this study, we shed light on the role of the specific ozone dose (0.5 mg-O3/mg-C) in biofilm accumulation during long-term membrane ultrafiltration. Results demonstrated that ozonation transformed the molecular structure of influent dissolved organic matter (DOM), producing fractions that were highly bioavailable at a specific ozone dose of 0.5, which was inferred to be a turning point. With the increase of the specific ozone dose, the biofilm microbial consortium was substantially shifted, demonstrating a decrease in richness and diversity. Unexpectedly, the opportunistic pathogen Legionella was stimulated and occurred in approximately 40% relative abundance at the higher specific ozone dose of 1. Accordingly, the membrane filtration system with a specific ozone dose of 0.5 presented a lower biofilm thickness, a weaker fluorescence intensity, smaller concentrations of polysaccharides and proteins, and a lower Raman activity, leading to a lower hydraulic resistance, compared to that with a specific ozone dose of 1. Our findings highlight the interaction mechanism between molecular-level DOM composition, biofilm microbial consortium, and membrane filtration performance, which provides an in-depth understanding of the impact of ozonation on biofilm accumulation.

Phagocytosis-associated genes in Acanthamoeba castellanii feeding on Escherichia coli

Acanthamoeba species are free-living amoebae those are widely distributed in the environment. They feed on various microorganisms, including bacteria, fungi, and algae. Although majority of the microbes phagocytosed by Acanthamoeba spp. are digested, some pathogenic bacteria thrive within them. Here, we identified the roles of 3 phagocytosis-associated genes (ACA1_077100, ACA1_175060, and AFD36229.1) in A. castellanii. These 3 genes were upregulated after the ingestion of Escherichia coli. However, after the ingestion of Legionella pneumophila, the expression of these 3 genes was not altered after the consumption of L. pneumophila. Furthermore, A. castellanii transfected with small interfering RNS (siRNA) targeting the 3 phagocytosis-associated genes failed to digest phagocytized E. coli. Silencing of ACA1_077100 disabled phagosome formation in the E. coli-ingesting A. castellanii. Alternatively, silencing of ACA1_175060 enabled phagosome formation; however, phagolysosome formation was inhibited. Moreover, suppression of AFD36229.1 expression prevented E. coli digestion and consequently led to the rupturing of A. castellanii. Our results demonstrated that the ACA1_077100, ACA1_175060, and AFD36229.1 genes of Acanthamoeba played crucial roles not only in the formation of phagosome and phagolysosome but also in the digestion of E. coli.

Identifying the function of genes involved in excreted vesicle formation in Acanthamoeba castellanii containing Legionella pneumophila

BACKGROUND

Legionella spp. can survive and replicate inside host cells such as protozoa and macrophages. After enough growth, Legionella is released from the host cells as free legionellae or Legionella-filled vesicles. The vesicles support Legionella to survive for a long time in the environment and transmit to a new host. In this study, we identified the differentially expressed genes of Acanthamoeba infected by Legionella (ACA1_114460, ACA1_091500, and ACA1_362260) and examined their roles in the formation of the excreted vesicles and escape of Legionella from the Acanthamoeba.

METHODS

After ingestion of Escherichia coli and Legionella pneumophila, expression levels of target genes in Acanthamoeba were measured by real-time polymerase chain reaction (PCR) analysis. The roles of target genes were investigated by transfection of small interfering RNA (siRNA). The formation of Legionella-containing excreted vesicles and the vesicular co-localization with the lysosomes were examined by Giemsa stain and LysoTracker stain.

RESULTS

ACA1_114460, ACA1_091500, and ACA1_362260 were upregulated after ingestion of Legionella in Acanthamoeba. ACA1_114460- and ACA1_091500-silenced Acanthamoeba failed to form the Legionella-containing excreted vesicles. Legionella was released as free legionellae from the Acanthamoeba. When the ACA1_362260 of Acanthamoeba was silenced, Legionella-containing excreted vesicles were fused with the lysosome.

CONCLUSIONS

These results indicated that ACA1_114460, ACA1_091500, and ACA1_362260 of Acanthamoeba played important roles in the formation of Legionella-containing excreted vesicles and inhibition of the lysosomal co-localization with the phagosome.

Effect of odor treatment systems on bioaerosol microbial concentration and diversity from wastewater treatment plants

Biofiltration, activated carbon and chemical scrubbing are technologies used for odor control in wastewater treatment plants. These systems may also influence the airborne microbial load in treated air. The study objectives were to 1) evaluate the capacity of three odor control system technologies to reduce the airborne concentration of total bacteria, Legionella, L. pneumophila, non-tuberculous mycobacteria (NTM) and Cladosporium in winter and summer seasons and 2) to describe the microbial ecology of the biofiltration system and evaluate its impact on treated air microbial diversity. A reduction of the total bacterial concentration up to 25 times was observed after odor treatment. Quantification by qPCR revealed the presence of Legionella spp. in all air samples ranging between 26 and 1140 GC/m³, while L. pneumophila was not detected except for three samples below the limit of quantification. A significant increase of up to 25-fold of Legionella spp. was noticed at the outlet of two of the three treatment systems. NTM were ubiquitously detected before air treatment (up to 2500 GC/m³) and were significantly reduced by all 3 systems (up to 13-fold). Cladosporium was measured at low concentrations for each system (< 190 GC/m³), with 68 % of the air samples below the limit of detection. Biodiversity results revealed that biofiltration system is an active process that adapts to air pollutants over time. Legionella spp. were detected in significant abundance in the air once treated in winter (up to 27 %). Nevertheless, the abundance of protozoan hosts is low and does not explain the multiplication of Legionella spp. The season remains the most influential factor shaping biodiversity. In summer only, air biofiltration caused a significant enrichment of the biodiversity. Although odor control technologies are not designed for bacterial mitigation, findings from this study suggest their potential to reduce the abundance of some genera harboring pathogenic species.

Evaluation of a novel porous antimicrobial media for industrial and HVAC water biocontrol

A novel treatment method, consisting of pea-gravel with a marine coating supplemented with alkyldimethylbenzylammonium chloride (ADBAC or benzalkonium chloride), has been examined for its antimicrobial performance and coating stability in aqueous environments. Initial column studies examining the porous media's ability to reduce bacterial loads in heating, ventilation, and air conditioning (HVAC) water found average reductions of 94% from pre-flush levels (10⁶ colony forming unit (CFU)/mL) when assessed with R2A spread plates and 83% reductions with SimPlates. There was no observed statistical difference between the average of pre- and post-flush waters from four tests of the media without ADBAC. Taxonomic identification, by 16S rRNA gene sequencing, of colonies drawn from pre- and post-ABDAC R2A plates showed similarities with taxa observed in high frequency from prior cultivation-independent surveys of other cooling tower systems. With this proof of concept, two versions of the media were evaluated for potential coating components released during aqueous exposure. Neither released measurable volatile organic compounds (VOC) components, but one did release bisphenol A and ABDAC compounds. Subsequent column tests of the more durable coating were conducted using cultures of interest in industrial water and demonstrated significant reductions in neutralized post-column Enterococcus faecalis samples and near complete loss of Legionella pneumophila in non-neutralized fluids, but lower reductions in Pseudomonas aeruginosa.

Identifying group-specific primers for environmental Heterolobosa by high-throughput sequencing

Diversity of Heterolobosea (Excavata) in environments is poorly understood despite their ecological occurrence and health‐associated risk, partly because this group tends to be under‐covered by most universal eukaryotic primers used for sequencing. To overcome the limits of the traditional morpho‐taxonomy‐based biomonitoring, we constructed a primer database listing existing and newly designed specific primer pairs that have been evaluated for Heterolobosea 18S rRNA sequencing. In silico taxonomy performance against the current SILVA SSU database allowed the selection of primer pairs that were next evaluated on reference culture amoebal strains. Two primer pairs were retained for monitoring the diversity of Heterolobosea in freshwater environments, using high‐throughput sequencing. Results showed that one of the newly designed primer pairs allowed species‐level identification of most heterolobosean sequences. Such primer pair could enable informative, cultivation‐free assays for characterizing heterolobosean populations in various environments.

Efficient nested-PCR-based method development for detection and genotype identification of Acanthamoeba from a small volume of aquatic environmental sample

Acanthamoeba spp. are opportunistic human pathogens that cause granulomatous amoebic encephalitis and keratitis, and their accurate detection and enumeration in environmental samples is a challenge. In addition, information regarding the genotyping of Acanthamoeba spp. using various PCR methods is equally critical. Therefore, considering the diverse niches of habitats, it is necessary to develop an even more efficient genotyping method for Acanthamoeba spp. detection. This study improved the sensitivity of detection to avoid underestimation of Acanthamoeba spp. occurrence in aquatic environmental samples, and to accurately define the pathogenic risk by developing an efficient PCR method. In this study, a new nested genotyping method was established and compared with various PCR-based methods using in silico, lab, and empirical tests. The in silico test showed that many PCR-based methods could not successfully align specific genotypes of Acanthamoeba, except for the newly designed nested PCR and real-time PCR method. Furthermore, 52 water samples from rivers, reservoirs, and a river basin in Taiwan were analysed by six different PCR methods and compared for genotyping and detection efficiency of Acanthamoeba. The newly developed nested-PCR-based method of genotyping was found to be significantly sensitive as it could effectively detect the occurrence of Acanthamoeba spp., which was underestimated by the JDP-PCR method. Additionally, the present results are consistent with previous studies indicating that the high prevalence of Acanthamoeba in the aquatic environment of Taiwan is attributed to the commonly found T4 genotype. Ultimately, we report the development of a small volume procedure, which is a combination of recent genotyping PCR and conventional real-time PCR for enumeration of aquatic Acanthamoeba and acquirement of biologically meaningful genotyping information. We anticipate that the newly developed detection method will contribute to the precise estimation, evaluation, and reduction of the contamination risk of pathogenic Acanthamoeba spp., which is regularly found in the water resources utilised for domestic purposes.

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.

The wastewater protist Rhogostoma minus (Thecofilosea, Rhizaria) is abundant, widespread, and hosts Legionellales

Wastewater is treated by concerted actions of the microbial communities within bioreactors. Although protists (unicellular eukaryotes) are good bioindicators and important players influencing denitrification, nitrification, and flocculation, they are the least known organisms in WWTPs. The few recent environmental surveys of the protistan diversity in WWTPs show that the most abundant protistan sequences in WWTPs belong to Thecofilosea (Rhizaria). We re-investigated previously published environmental sequencing data and gathered strains from seven WWTPs to determine which species dominate WWTPs worldwide. We found that all highly abundant thecofilosean sequences represent a single species - Rhogostoma minus. Considering that Thecofilosea are frequent hosts for Legionellales, i.e. bacteria linked to waterborne diseases, we confirm that Rhogostoma minus functions as a host for Legionellales in WWTPs. Whether the highly abundant Rhogostoma minus also serves as a host for known human pathogenic Legionellales requires further attention.

The Increasing Importance of Vermamoeba vermiformis

Vermamoeba vermiformis are one of the most prevalent free-living amoebae. These amoebae are ubiquitous and also thermotolerant. Of concern, V. vermiformis have been found in hospital water networks. Furthermore, associations between V. vermiformis and pathogenic bacteria have been reported, such as Legionella pneumophila. Moreover, V. vermiformis are well known to host viruses, bacteria, and other microorganisms and cases of keratitis due to V. vermiformis in conjunction with other amoebae have been reported. Despite the preceding, the medical importance of V. vermiformis is still an ongoing discussion and its genome has been only recently sequenced. Herein, we present a review of the current understanding of the biology and pathogenesis pertaining to V. vermiformis, as well as its' role as an etiological agent and trojan horse. An approach known as theranostics which combines both diagnosis and therapy could be utilized to eradicate and diagnose keratitis cases caused by such amoebae. Given the rise in global warming, it is imperative to investigate these rarely studied amoebae and to understand their importance in human health.

Novel Endosymbionts in Rhizarian Amoebae Imply Universal Infection of Unrelated Free-Living Amoebae by Legionellales

Legionellales-infected water is a frequent cause of local outbreaks of Legionnaires’ disease and Pontiac fever. Decontaminations are difficult because Legionellales reproduce in eukaryotic microorganisms (protists). Most often, Legionellales have been isolated from amoebae; however, the culture-based sampling methods are taxonomically biased. Sequencing studies show that amoebae in the cercozoan class Thecofilosea are dominant in soils and wastewater treatment plants, prompting us to screen their capability to serve as potential hosts of endosymbiotic bacteria. Environmental isolates of Thecofilosea contained a surprising richness of endosymbiotic Legionellales, including Legionella. Considering the widespread dispersal of Legionellales in apparently unrelated amoeboid protist taxa, it appears that the morphotype and not the evolutionary origin of amoebae determines their suitability as hosts for Legionellales. We further provide a protocol for gnotobiotic cultivation of Legionellales and their respective hosts, facilitating future genomic and transcriptomic research of host–symbiont relationships.

A Systematic Review of Intracellular Microorganisms within Acanthamoeba to Understand Potential Impact for Infection

Acanthamoeba, an opportunistic pathogen is known to cause an infection of the cornea, central nervous system, and skin. Acanthamoeba feeds different microorganisms, including potentially pathogenic prokaryotes; some of microbes have developed ways of surviving intracellularly and this may mean that Acanthamoeba acts as incubator of important pathogens. A systematic review of the literature was performed in order to capture a comprehensive picture of the variety of microbial species identified within Acanthamoeba following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Forty-three studies met the inclusion criteria, 26 studies (60.5%) examined environmental samples, eight (18.6%) studies examined clinical specimens, and another nine (20.9%) studies analysed both types of samples. Polymerase chain reaction (PCR) followed by gene sequencing was the most common technique used to identify the intracellular microorganisms. Important pathogenic bacteria, such as E. coli, Mycobacterium spp. and P. aeruginosa, were observed in clinical isolates of Acanthamoeba, whereas Legionella, adenovirus, mimivirus, and unidentified bacteria (Candidatus) were often identified in environmental Acanthamoeba. Increasing resistance of Acanthamoeba associated intracellular pathogens to antimicrobials is an increased risk to public health. Molecular-based future studies are needed in order to assess the microbiome residing in Acanthamoeba, as a research on the hypotheses that intracellular microbes can affect the pathogenicity of Acanthamoeba infections.

Free living amoebae isolation in irrigation waters and soils of an insular arid agroecosystem

The use of freshwater in agricultural systems represents a high percentage of total water consumption worldwide. Therefore, alternative sources of water for irrigation will need to be developed, particularly in arid and semi-arid areas, in order to meet the growing demand for food in the future. The use of recycled wastewater (RWW), brackish water (BW) or desalinated brackish water (DBW) are among the different non-conventional water resources proposed. However, it is necessary to evaluate the health risks for humans and animals associated with the microbiological load of these waters. Protozoa such as free-living amoebae (FLA) are considered an emerging group of opportunistic pathogens capable to cause several diseases in humans (e.g. cutaneous and ocular infections, lung, bone or adrenal gland conditions or fatal encephalitis). In the present study we evaluate FLA presence in three different irrigation water qualities (RWW, BW and DBW) and its survival in irrigated agricultural soils of an extremely arid insular ecosystem (Fuerteventura, Canary Islands, Spain). Samples were cultured on 2% Non-Nutrient Agar (NNA) plates covered with a thin layer of heat killed E. coli and checked daily for the presence of FLA. According to the prevalence of FLA, Vermamoeba vermiformis (53,8%), Acanthamoeba spp. (30,8%), Vahlkampfia avara (7,7%) and Naegleria australiensis (7,7%) were detected in the analysed water samples, while Acanthamoeba (83,3%), Cercozoa spp. (8,3%) and Vahlkampfia orchilla (8,3%) were isolated in irrigated soils. Only Acanthamoeba strains were isolated in no irrigated soils used as control, evidencing the capability of these protozoa to resist environmental harsh conditions. Additionally, all analysed water sources and the irrigated soils presented growth of several pathogenic bacteria. Therefore, the coexistence in water and soils of pathogenic bacteria and FLA, can mean an increased risk of infection in agroecosystems.

Isolation and identification of free-living amoebae isolated from well water in Istanbul

Free-living amoebae (FLA) are ubiquitous protozoa commonly found in water and soil environments. FLA belonging to various genera, including Acanthamoeba, Balamuthia, Naegleria, and Vermamoeba, can cause opportunistic and non-opportunistic infections in humans and animals such as keratitis or meningoencephalitis. In addition, some of them serve as hosts for a large number of pathogenic bacteria, yeasts, and viruses. The purpose of the present study was to assess the prevalence and molecular characterization of FLA in well water samples in İstanbul. Ten well water samples were collected from the taps and the presence of FLA was monitored both by the culture and polymerase chain reaction methods. FLA were isolated in 8 out of the 10 samples (80%) included in this study. Morphological analysis and partial sequencing of the 18S rDNA revealed the presence of Acanthamoeba genotypes T3 and T4, and Vermamoeba vermiformis in the investigated well water samples. This study reports for the first time the detection of Acanthamoeba genotype T3 in well water samples in İstanbul. The presence of potentially pathogenic amoebae in habitats related to human activities supports the relevance of FLA as a potential public health concern.

Determination of the bacterial microbiome of free-living amoebae isolated from wastewater by 16S rRNA amplicon-based sequencing

Free-living amoebae (FLA) are ubiquitous protozoa commonly found in water. FLA are well-established hosts for amoeba-resistant bacteria, most of which are pathogenic, and offer them shelter from adverse environmental conditions or water treatments. Since there is very little knowledge about the complete bacterial microbiome of FLA, in this work the bacterial microbiome of FLA isolated from wastewater both after secondary and tertiary treatments was studied by amplicon-based sequencing. FLA were detected in 87.5% and 50.0% of wastewater samples taken after secondary and tertiary disinfection treatments, respectively. The most abundant bacterial phyla were Proteobacteria, Planctomycetes, Bacteroidetes and Firmicutes, which represented 83.77% of the total bacterial FLA microbiome. The most abundant class of bacteria was Gammaproteobacteria, which contains an important number of relevant pathogenic bacteria. The bacteria of public health concern Aeromonas, Arcobacter, Campylobacter, Helicobacter, Klebsiella, Legionella, Mycobacterium, Pseudomonas and Salmonella were detected as part of the FLA microbiome. Although different microbial communities were identified in each sample, there is no correlation between the microbiome of FLA and the extent of wastewater treatment. To our knowledge, this is the first work in which the bacterial microbiome of FLA isolated from wastewater is studied. Obtained results indicate that FLA are hosts of potentially pathogenic bacteria in treated wastewater used for irrigation, which may pose a public health threat.

A New Active Substance Derived from Lyzed Willaertia magna C2c Maky Cells to Fight Grapevine Downy Mildew

Downy mildew of grapevine is one of the most destructive grapevine diseases worldwide. Nowadays, downy mildew control relies almost exclusively on the use of chemical pesticides, including copper products, which are efficient but controversial due to their environmental toxicity. Natural plant protection products have become important solutions in the quest for the sustainable production of food and pest management. However, most biocontrol agents currently on the market, such as biofungicides or elicitors, have a limited efficacy; thus, they cannot replace chemical compounds in full. Our innovation is a natural active substance, which is a lysate of the amoeba Willaertia magna C2c Maky. This active substance is not only able to elicit grapevine defenses, but it also demonstrates direct fungicidal activity against Plasmopara viticola. The efficacy of this new natural substance was demonstrated both in a greenhouse and in a field. The amoeba lysate provided up to 77% protection to grapevine bunches in the field in a natural and safe way.

Insight into the Lifestyle of Amoeba Willaertia magna during Bioreactor Growth Using Transcriptomics and Proteomics

Willaertia magna C2c maky is a thermophilic free-living amoeba strain that showed ability to eliminate Legionella pneumophila, a pathogenic bacterium living in the aquatic environment. The amoeba industry has proposed the use of Willaertia magna as a natural biocide to control L. pneumophila proliferation in cooling towers. Here, transcriptomic and proteomic studies were carried out in order to expand knowledge on W. magna produced in a bioreactor. Illumina RNA-seq generated 217 million raw reads. A total of 8790 transcripts were identified, of which 6179 and 5341 were assigned a function through comparisons with National Center of Biotechnology Information (NCBI) reference sequence and the Clusters of Orthologous Groups of proteins (COG) databases, respectively. To corroborate these transcriptomic data, we analyzed the W. magna proteome using LC–MS/MS. A total of 3561 proteins were identified. The results of transcriptome and proteome analyses were highly congruent. Metabolism study showed that W. magna preferentially consumed carbohydrates and fatty acids to grow. Finally, an in-depth analysis has shown that W. magna produces several enzymes that are probably involved in the metabolism of secondary metabolites. Overall, our multi-omic study of W. magna opens the way to a better understanding of the genetics and biology of this amoeba.

Intracellular Behaviour of Three Legionella pneumophila Strains within Three Amoeba Strains, Including Willaertia magna C2c Maky

Legionella pneumophila is a facultative intracellular pathogen found in aquatic environments as planktonic cells within biofilms and as intracellular parasites of free-living amoebae such as Acanthamoeba castellanii. This pathogen bypasses the elimination mechanism to replicate within amoebae; however, not all amoeba species support the growth of L. pneumophila. Willaertia magna C2c Maky, a non-pathogenic amoeba, was previously demonstrated to possess the ability to eliminate the L. pneumophila strain Paris. Here, we study the intracellular behaviour of three L. pneumophila strains (Paris, Philadelphia, and Lens) within W. magna C2c Maky and compare this strain to A. castellanii and W. magna Z503, which are used as controls. We observe the intracellular growth of strain Lens within W. magna Z503 and A. castellanii at 22 °C and 37 °C. Strain Paris grows within A. castellanii at any temperature, while it only grows at 22 °C within W. magna Z503. Strain Philadelphia proliferates only within A. castellanii at 37 °C. Within W. magna C2c Maky, none of the three legionella strains exhibit intracellular growth. Additionally, the ability of W. magna C2c Maky to decrease the number of internalized L. pneumophila is confirmed. These results support the idea that W. magna C2c Maky possesses unique behaviour in regard to L. pneumophila strains.

Combinatorial selection in amoebal hosts drives the evolution of the human pathogen Legionella pneumophila

Virulence mechanisms typically evolve through the continual interaction of a pathogen with its host. In contrast, it is poorly understood how environmentally acquired pathogens are able to cause disease without prior interaction with humans. Here, we provide experimental evidence for the model that Legionella pathogenesis in humans results from the cumulative selective pressures of multiple amoebal hosts in the environment. Using transposon sequencing, we identify Legionella pneumophila genes required for growth in four diverse amoebae, defining universal virulence factors commonly required in all host cell types and amoeba-specific auxiliary genes that determine host range. By comparing genes that promote growth in amoebae and macrophages, we show that adaptation of L. pneumophila to each amoeba causes the accumulation of distinct virulence genes that collectively allow replication in macrophages and, in some cases, leads to redundancy in this host cell type. In contrast, some bacterial proteins that promote replication in amoebae restrict growth in macrophages. Thus, amoebae-imposed selection is a double-edged sword, having both positive and negative impacts on disease. Comparing the genome composition and host range of multiple Legionella species, we demonstrate that their distinct evolutionary trajectories in the environment have led to the convergent evolution of compensatory virulence mechanisms.

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

Background and Objectives:Legionella is one of the most important water-related pathogens. Inside the water supply systems and the biofilms, Legionella interact with other bacteria and free-living amoeba (FLA). Several amoebas may serve as hosts for bacteria in aquatic systems. This study aimed to investigate the co-occurrence of Legionella spp. and FLA in drinking water supply systems. Materials and Methods: A total of 268 water samples were collected from apartment buildings, hotels, and public buildings. Detection of Legionella spp. was performed in accordance with ISO 11731:2017 standard. Three different polymerase chain reaction (PCR) protocols were used to identify FLA. Results: Occurrence of Legionella varied from an average of 12.5% in cold water samples with the most frequent occurrence observed in hot water, in areas receiving untreated groundwater, where 54.0% of the samples were Legionella positive. The occurrence of FLA was significantly higher. On average, 77.2% of samples contained at least one genus of FLA and, depending on the type of sample, the occurrence of FLA could reach 95%. In the samples collected during the study, Legionella was always isolated along with FLA, no samples containing Legionella in the absence of FLA were observed. Conclusions: The data obtained in our study can help to focus on the extensive distribution, close interaction, and long-term persistence of Legionella and FLA. Lack of Legionella risk management plans and control procedures may promote further spread of Legionella in water supply systems. In addition, the high incidence of Legionella-related FLA suggests that traditional monitoring methods may not be sufficient for Legionella control.

Occurrence and the first report of Naegleria australiensis presence in a major lake in the Philippines

Laguna de Bay or Laguna Lake is one of the six major lakes in the Philippines to be in close contact with population activities due to the expansion of urban settlements in the immediate cities surrounding the lake, thus pushing the population to settle upon its shores. To date, there are no data showing the biodiversity of free-living amoebae (FLA) present in this lake. The present study aims to isolate and identify the FLA present in Laguna de Bay, Philippines. Thirty subsurface water samples were taken from Laguna De Bay using random purposive sampling in May 2018 and were examined for amoebic growth under light microscopy (LM). Results show that 8 out of 30 (26.6%) water samples were positive for amoebic growth and were further tested for more advanced data and genetic variation of the species. Initial molecular analysis using polymerase chain reaction (PCR) and sequencing showed the presence of potentially pathogenic FLA Naegleria australiensis (MK418954). The detection of potential pathogenic FLA in lakes and dams may prove useful in preventing and controlling possible human infections in the country. More data from this study will aid in public awareness and establishing safety guidelines and control programs.

The all-intracellular order Legionellales is unexpectedly diverse, globally distributed and lowly abundant

Legionellales is an order of the Gammaproteobacteria, only composed of host-adapted, intracellular bacteria, including the accidental human pathogens Legionella pneumophila and Coxiella burnetii. Although the diversity in terms of lifestyle is large across the order, only a few genera have been sequenced, owing to the difficulty to grow intracellular bacteria in pure culture. In particular, we know little about their global distribution and abundance.

Here, we analyze 16/18S rDNA amplicons both from tens of thousands of published studies and from two separate sampling campaigns in and around ponds and in a silver mine. We demonstrate that the diversity of the order is much larger than previously thought, with over 450 uncultured genera. We show that Legionellales are found in about half of the samples from freshwater, soil and marine environments and quasi-ubiquitous in man-made environments. Their abundance is low, typically 0.1%, with few samples up to 1%. Most Legionellales OTUs are globally distributed, while many do not belong to a previously identified species.

This study sheds a new light on the ubiquity and diversity of one major group of host-adapted bacteria. It also emphasizes the need to use metagenomics to better understand the role of host-adapted bacteria in all environments.

Symbiont-Mediated Defense against Legionella pneumophila in Amoebae

Legionella pneumophila is an important opportunistic pathogen for which environmental reservoirs are crucial for the infection of humans. In the environment, free-living amoebae represent key hosts providing nutrients and shelter for highly efficient intracellular proliferation of L. pneumophila, which eventually leads to lysis of the protist. However, the significance of other bacterial players for L. pneumophila ecology is poorly understood. In this study, we used a ubiquitous amoeba and bacterial endosymbiont to investigate the impact of this common association on L. pneumophila infection. We demonstrate that L. pneumophila proliferation was severely suppressed in Acanthamoeba castellanii harboring the chlamydial symbiont Protochlamydia amoebophila The amoebae survived the infection and were able to resume growth. Different environmental amoeba isolates containing the symbiont were equally well protected as different L. pneumophila isolates were diminished, suggesting ecological relevance of this symbiont-mediated defense. Furthermore, protection was not mediated by impaired L. pneumophila uptake. Instead, we observed reduced virulence of L. pneumophila released from symbiont-containing amoebae. Pronounced gene expression changes in the presence of the symbiont indicate that interference with the transition to the transmissive phase impedes the L. pneumophila infection. Finally, our data show that the defensive response of amoebae harboring P. amoebophila leaves the amoebae with superior fitness reminiscent of immunological memory. Given that mutualistic associations between bacteria and amoebae are widely distributed, P. amoebophila and potentially other amoeba endosymbionts could be key in shaping environmental survival, abundance, and virulence of this important pathogen, thereby affecting the frequency of human infection.IMPORTANCE Bacterial pathogens are generally investigated in the context of disease. To prevent outbreaks, it is essential to understand their lifestyle and interactions with other microbes in their natural environment. Legionella pneumophila is an important human respiratory pathogen that survives and multiplies in biofilms or intracellularly within protists, such as amoebae. Importantly, transmission to humans occurs from these environmental sources. Legionella infection generally leads to rapid host cell lysis. It was therefore surprising to observe that amoebae, including fresh environmental isolates, were well protected during Legionella infection when the bacterial symbiont Protochlamydia amoebophila was also present. Legionella was not prevented from invading amoebae but was impeded in its ability to develop fully virulent progeny and were ultimately cleared in the presence of the symbiont. This study highlights how ecology and virulence of an important human pathogen is affected by a defensive amoeba symbiont, with possibly major consequences for public health.

Free-living amoebae and squatters in the wild: ecological and molecular features

Free-living amoebae are protists frequently found in water and soils. They feed on other microorganisms, mainly bacteria, and digest them through phagocytosis. It is accepted that these amoebae play an important role in the microbial ecology of these environments. There is a renewed interest for the free-living amoebae since the discovery of pathogenic bacteria that can resist phagocytosis and of giant viruses, underlying that amoebae might play a role in the evolution of other microorganisms, including several human pathogens. Recent advances, using molecular methods, allow to bring together new information about free-living amoebae. This review aims to provide a comprehensive overview of the newly gathered insights into (1) the free-living amoeba diversity, assessed with molecular tools, (2) the gene functions described to decipher the biology of the amoebae and (3) their interactions with other microorganisms in the environment.

Legionella occurrence in municipal and industrial wastewater treatment plants and risks of reclaimed wastewater reuse: Review

Wastewater treatment plants (WWTPs) have been identified as confirmed but until today underestimated sources of Legionella, playing an important role in local and community cases and outbreaks of Legionnaires' disease. In general, aerobic biological systems provide an optimum environment for the growth of Legionella due to high organic nitrogen and oxygen concentrations, ideal temperatures and the presence of protozoa. However, few studies have investigated the occurrence of Legionella in WWTPs, and many questions in regards to the interacting factors that promote the proliferation and persistence of Legionella in these treatment systems are still unanswered. This critical review summarizes the current knowledge about Legionella in municipal and industrial WWTPs, the conditions that might support their growth, as well as control strategies that have been applied. Furthermore, an overview of current quantification methods, guidelines and health risks associated with Legionella in reclaimed wastewater is also discussed in depth. A better understanding of the conditions promoting the occurrence of Legionella in WWTPs will contribute to the development of improved wastewater treatment technologies and/or innovative mitigation approaches to minimize future Legionella outbreaks.

Vermamoeba vermiformis: a Free-Living Amoeba of Interest

Free-living amoebae are protists that are widely distributed in the environment including water, soil, and air. Although the amoebae of the genus Acanthamoeba are still the most studied, other species, such as Vermamoeba vermiformis (formerly Hartmannella vermiformis), are the subject of increased interest. Found in natural or man-made aquatic environments, V. vermiformis can support the multiplication of other microorganisms and is able to harbor and potentially protect pathogenic bacteria or viruses. This feature is to be noted because of the presence of this thermotolerant amoeba in hospital water networks. As a consequence, this protist could be implicated in health concerns and be indirectly responsible for healthcare-related infections. This review highlights, among others, the consequences of V. vermiformis relationships with other microorganisms and shows that this free-living amoeba species is therefore of interest for public health.

Isolation and identification of Acanthamoeba from pond water of parks in a tropical and subtropical region in the Middle East, and its relation with physicochemical parameters

Background

Free-living amoeba (FLA) are wide-spread protozoa that are found in different environmental sources including water, soil, dust, hospital units and ventilation areas. These amoebas can act as opportunistic or non-opportunistic pathogens. Among FLAs, some genera such as Acanthamoeba are important because of their potential pathogenic ability in humans. The purpose of this study is to identify of Acanthamoeba isolated from pond water of parks in a tropical and subtropical region in the Middle East, and its relation with physicochemical parameters.From August to December 2015, 90 samples were collected from pond water of parks of 13 regions of Mashhad City. Physicochemical parameters were measured in situ. After filtering, the samples were cultured on Bacto-agar enriched with Escherichia coli. PCR analysis was conducted on the culture-positive samples, and then the PCR products were sequenced. Statistical analysis was performed by SPSS software and Fisher’s Exact and Mann-Whitney test.

Results

Among the samples that were examined, 19 samples (21.1%) were positive for Acanthamoeba. The sequencing revealed that Acanthamoeba isolates belonged to T4 genotype of Acanthamoeba. There was no significant relationship between physicochemical parameters and the presence of Acanthamoeba.

Conclusion

The prevalence of Acanthamoeba in pond water of parks was relatively high, but there was no significant relationship between physicochemical parameters and the presence of Acanthamoeba.

Encystation: the most prevalent and underinvestigated differentiation pathway of eukaryotes

Not long ago, protists were considered one of four eukaryote kingdoms, but recent gene-based phylogenies show that they contribute to all nine eukaryote subdomains. The former kingdoms of animals, plants and fungi are now relegated to lower ranks within subdomains. Most unicellular protists respond to adverse conditions by differentiating into dormant walled cysts. As cysts, they survive long periods of starvation, drought and other environmental threats, only to re-emerge when conditions improve. For protists pathogens, the resilience of their cysts can prevent successful treatment or eradication of the disease. In this context, effort has been directed towards understanding the molecular mechanisms that control encystation. We here firstly summarize the prevalence of encystation across protists and next focus on Amoebozoa, where most of the health-related issues occur. We review current data on processes and genes involved in encystation of the obligate parasite Entamoeba histolytica and the opportunistic pathogen Acanthamoeba. We show how the cAMP-mediated signalling pathway that controls spore and stalk cell encapsulation in Dictyostelium fruiting bodies could be retraced to a stress-induced pathway controlling encystation in solitary Amoebozoa. We highlight the conservation and prevalence of cAMP signalling genes in Amoebozoan genomes and the suprisingly large and varied repertoire of proteins for sensing and processing environmental signals in individual species.

Diverse Legionella-Like Bacteria Associated with Testate Amoebae of the Genus Arcella (Arcellinida: Amoebozoa)

Diverse species of Legionella and Legionella-like amoebal pathogens (LLAPs) have been identified as intracellular bacteria in many amoeboid protists. There are, however, other amoeboid groups such as testate amoeba for which we know little about their potential to host such bacteria. In this study, we assessed the occurrence and diversity of Legionella spp. in cultures and environmental isolates of freshwater arcellinid testate amoebae species, Arcella hemispherica, Arcella intermedia, and Arcella vulgaris, via 16S rRNA gene sequence analyses and fluorescent in situ hybridization (FISH). Analysis of the 16S rRNA gene sequences indicated that A. hemispherica, A. intermedia, and A. vulgaris host Legionella-like bacteria with 94-98% identity to other Legionella spp. based on NCBI BLAST search. Phylogenetic analysis placed Legionella-like Arcella-associated bacteria (LLAB) in three different clusters within a tree containing all other members of Legionella and LLAPs. The intracellular localization of the Legionella within Arcella hosts was confirmed using FISH with a Legionella-specific probe. This study demonstrates that the host range of Legionella and Legionella-like bacteria in the Amoebozoa extends beyond members of "naked" amoebae species, with members of the testate amoebae potentially serving an ecological role in the dispersal, protection, and replication of Legionella spp. in natural environments.

Application of modified JDP-DGGE-based molecular genotyping method to predict Acanthamoeba genotype and to analyse community diversity in aquatic environments

Acanthamoeba spp. are ubiquitous, opportunistic potential human pathogens, causing granulomatous amoebic encephalitis and keratitis. They are classified as protozoa, and they include at least 20 different genotypes (T1-T20) based on variation in the 18S rRNA gene. Acanthamoeba spp. are diverse in their production of toxins and in their ability to resist environmental factors. Therefore, it is necessary to develop a rapid genotyping method for Acanthamoeba spp. in aquatic environments. Although the denaturing gradient gel electrophoresis (DGGE) method for analysing microbial genotypes is potentially useful for rapid identification of aquatic environmental species, the technique has been compromised by artificial DGGE profiles in which many DNA fragments of identical sequences are segregated and displayed as different bands. The results indicate that PCR-DGGE genotyping with a GC clamp results in many segregated weaker bands of identical DNA sequences. In contrast, PCR-DGGE genotyping without a GC clamp displays genotype-dependent patterns in the major bands. Thus, DGGE without a GC clamp was performed to compare genotyping efficiency for Acanthamoeba in 21 water samples from rivers and reservoirs in Taiwan. Among them, four samples were found to demonstrate a banding pattern with more than one major band, and these band profiles of major bands were identical to those of positive controls. DNA cloning further confirmed that the sequences of the major bands were identical. In conclusion, more than two genotypes of Acanthamoeba in the four samples were identified by this method, suggesting that PCR-DGGE genotyping without a GC clamp is a useful approach for studying the diversity of Acanthamoeba communities. Graphical abstract.

MALDI-TOF MS analysis as a useful tool for an identification of Legionella pneumophila, a facultatively pathogenic bacterium interacting with free-living amoebae: A case study from water supply system of hospitals in Bratislava (Slovakia)

Legionellae, i.e. Legionella pneumophila, are human bacterial hydrophilic facultative pathogens causing pneumonia (Legionnaires' disease). Free-living amoebae (FLA) can serve as natural hosts and thus as reservoirs of many amoebae-resistant bacteria. An encysted amoeba can contribute to the resistance of intracellular L. pneumophila to various chemical and physical treatments. Humans can be infected by droplets containing bacteria from an environmental source or human-made devices such as shower heads, bathtubs, air-conditioning units or whirlpools. In this study, we were investigating the presence of FLA and L. pneumophila in plumbing systems of healthcare facilities in Bratislava (Slovakia) by standard diagnostic methods, while the presence of L. pneumophila was verified also by MALDI-TOF MS (matrix-assisted laser desorption/ionization time-of-flight mass spectrometry) analysis. The results showed the occurrence of L. pneumophila and FLA in 62.26% and 66.4% of samples taken from four paediatric clinics, respectively. Both standard methods and MALDI-TOF MS showed comparable results and they can be successfully applied for the identification of L. pneumophila strains in environmental samples. Our approach could be useful for further monitoring, prevention and decreasing risk of Legionella infection also in other hospitals.

From Many Hosts, One Accidental Pathogen: The Diverse Protozoan Hosts of Legionella

The 1976 outbreak of Legionnaires' disease led to the discovery of the intracellular bacterial pathogen Legionella pneumophila. Given their impact on human health, Legionella species and the mechanisms responsible for their replication within host cells are often studied in alveolar macrophages, the primary human cell type associated with disease. Despite the potential severity of individual cases of disease, Legionella are not spread from person-to-person. Thus, from the pathogen's perspective, interactions with human cells are accidents of time and space—evolutionary dead ends with no impact on Legionella's long-term survival or pathogenic trajectory. To understand Legionella as a pathogen is to understand its interaction with its natural hosts: the polyphyletic protozoa, a group of unicellular eukaryotes with a staggering amount of evolutionary diversity. While much remains to be understood about these enigmatic hosts, we summarize the current state of knowledge concerning Legionella's natural host range, the diversity of Legionella-protozoa interactions, the factors influencing these interactions, the importance of avoiding the generalization of protozoan-bacterial interactions based on a limited number of model hosts and the central role of protozoa to the biology, evolution, and persistence of Legionella in the environment.

Interactive effects of temperature, organic carbon, and pipe material on microbiota composition and Legionella pneumophila in hot water plumbing systems

BACKGROUND

Several biotic and abiotic factors have been reported to influence the proliferation of microbes, including Legionella pneumophila, in hot water premise plumbing systems, but their combined effects have not been systematically evaluated. Here, we utilize simulated household water heaters to examine the effects of stepwise increases in temperature (32-53 °C), pipe material (copper vs. cross-linked polyethylene (PEX)), and influent assimilable organic carbon (0-700 μg/L) on opportunistic pathogen gene copy numbers and the microbiota composition, as determined by quantitative polymerase chain reaction and 16S rRNA gene amplicon sequencing.

RESULTS

Temperature had an overarching influence on both the microbiota composition and L. pneumophila numbers. L. pneumophila peaked at 41 °C in the presence of PEX (1.58 × 105 gene copies/mL). At 53 °C, L. pneumophila was not detected. Several operational taxonomic units (OTUs) persisted across all conditions, accounting for 50% of the microbiota composition from 32 to 49 °C and 20% at 53 °C. Pipe material most strongly influenced microbiota composition at lower temperatures, driven by five to six OTUs enriched with each material. Copper pipes supported less L. pneumophila than PEX pipes (mean 2.5 log10 lower) at temperatures ≤ 41 °C, but showed no difference in total bacterial numbers. Differences between pipe materials diminished with elevated temperature, probably resulting from decreased release of copper ions. At temperatures ≤ 45 °C, influent assimilable organic carbon correlated well with total bacterial numbers, but not with L. pneumophila numbers. At 53 °C, PEX pipes leached organic carbon, reducing the importance of dosed organic carbon. L. pneumophila numbers correlated with a Legionella OTU and a Methylophilus OTU identified by amplicon sequencing.

CONCLUSIONS

Temperature was the most effective factor for the control of L. pneumophila, while microbiota composition shifted with each stepwise temperature increase. While copper pipe may also help shape the microbiota composition and limit L. pneumophila proliferation, its benefits might be constrained at higher temperatures. Influent assimilable organic carbon affected total bacterial numbers, but had minimal influence on opportunistic pathogen gene numbers or microbiota composition. These findings provide guidance among multiple control measures for the growth of opportunistic pathogens in hot water plumbing and insight into the mediating role of microbial ecological factors.

Occurrence of Infected Free-Living Amoebae in Cooling Towers of Southern Brazil

This study determined the occurrence of potentially pathogenic free-living amoebae (FLA) and bacteria associated with amoebae in air-conditioning cooling towers in southern Brazil. Water samples were collected from 36 cooling systems from air-conditioning in the state of Rio Grande do Sul, Brazil. The organisms were identified using polymerase chain reaction (PCR) and sequencing automated. The results showed that these aquatic environments, with variable temperature, are potential "hot spots" for emerging human pathogens like free-living amoebae and bacteria associated. In total, 92% of the cooling-tower samples analyzed were positive for FLA, and Acanthamoeba was the dominant genus by culture and PCR. Amoebal isolates revealed intracellular bacteria in 39.3% of them and all were confirmed as members of the genus Pseudomonas. The results obtained show the important role of cooling towers as a source of amoebae-associated pathogens.

Longitudinal and Source-to-Tap New Orleans, LA, U.S.A. Drinking Water Microbiology

The two municipal drinking water systems of New Orleans, LA, U.S.A. were sampled to compare the microbiology of independent systems that treat the same surface water from the Mississippi River. To better understand temporal trends and sources of microbiology delivered to taps, these treatment plants and distribution systems were subjected to source-to-tap sampling over four years. Both plants employ traditional treatment by chloramination, applied during or after settling, followed by filtration before distribution in a warm, low water age system. Longitudinal samples indicated microbiology to have stability both spatially and temporally, and between treatment plants and distribution systems. Disinfection had the greatest impact on microbial composition, which was further refined by filtration and influenced by distribution and premise plumbing. Actinobacteria spp. exhibited trends with treatment. In particular, Mycobacterium spp., very low in finished waters, occurred idiosyncratically at high levels in some tap waters, indicating distribution and/or premise plumbing as main contributors of mycobacteria. Legionella spp., another genus containing potential opportunistic pathogens, also occurred ubiquitously. Source water microbiology was most divergent from tap water, and each step of treatment brought samples more closely similar to tap waters.

Free-living amoebae and their associated bacteria in Austrian cooling towers: a 1-year routine screening

Free-living amoebae (FLA) are widely spread in the environment and known to cause rare but often serious infections. Besides this, FLA may serve as vehicles for bacterial pathogens. In particular, Legionella pneumophila is known to replicate within FLA thereby also gaining enhanced infectivity. Cooling towers have been the source of outbreaks of Legionnaires' disease in the past and are thus usually screened for legionellae on a routine basis, not considering, however, FLA and their vehicle function. The aim of this study was to incorporate a screening system for host amoebae into a Legionella routine screening. A new real-time PCR-based screening system for various groups of FLA was established. Three cooling towers were screened every 2 weeks over the period of 1 year for FLA and Legionella spp., by culture and molecular methods in parallel. Altogether, 83.3 % of the cooling tower samples were positive for FLA, Acanthamoeba being the dominating genus. Interestingly, 69.7 % of the cooling tower samples were not suitable for the standard Legionella screening due to their high organic burden. In the remaining samples, positivity for Legionella spp. was 25 % by culture, but overall positivity was 50 % by molecular methods. Several amoebal isolates revealed intracellular bacteria.

Convective Mixing in Distal Pipes Exacerbates Legionella pneumophila Growth in Hot Water Plumbing

Legionella pneumophila is known to proliferate in hot water plumbing systems, but little is known about the specific physicochemical factors that contribute to its regrowth. Here, L. pneumophila trends were examined in controlled, replicated pilot-scale hot water systems with continuous recirculation lines subject to two water heater settings (40 °C and 58 °C) and three distal tap water use frequencies (high, medium, and low) with two pipe configurations (oriented upward to promote convective mixing with the recirculating line and downward to prevent it). Water heater temperature setting determined where L. pneumophila regrowth occurred in each system, with an increase of up to 4.4 log gene copies/mL in the 40 °C system tank and recirculating line relative to influent water compared to only 2.5 log gene copies/mL regrowth in the 58 °C system. Distal pipes without convective mixing cooled to room temperature (23-24 °C) during periods of no water use, but pipes with convective mixing equilibrated to 30.5 °C in the 40 °C system and 38.8 °C in the 58 °C system. Corresponding with known temperature effects on L. pneumophila growth and enhanced delivery of nutrients, distal pipes with convective mixing had on average 0.2 log more gene copies/mL in the 40 °C system and 0.8 log more gene copies/mL in the 58 °C system. Importantly, this work demonstrated the potential for thermal control strategies to be undermined by distal taps in general, and convective mixing in particular.

Strategies for the reduction of Legionella in biological treatment systems

A community-wide outbreak of Legionnaire's disease occurred in Warstein, Germany, in August 2013. The epidemic strain, Legionella pneumophila Serogruppe 1, was isolated from an industrial wastewater stream entering the municipal wastewater treatment plant (WWTP) in Wartein, the WWTP itself, the river Wäster and air/water samples from an industrial cooling system 3 km downstream of the WWTP. The present study investigated the effect of physical-chemical disinfection methods on the reduction of the concentration of Legionella in the biological treatment and in the treated effluent entering the river Wäster. Additionally, to gain insight into the factors that promote the growth of Legionella in biological systems, growth experiments were made with different substrates and temperatures. The dosage rates of silver micro-particles, hydrogen peroxide, chlorine dioxide and ozone and pH stress to the activated sludge were not able to decrease the number of culturable Legionella spp. in the effluent. Nevertheless, the UV treatment of secondary treated effluent reduced Legionella spp. on average by 1.6-3.4 log units. Laboratory-scale experiments and full-scale measurements suggested that the aerobic treatment of warm wastewater (30-35 °C) rich in organic nitrogen (protein) is a possible source of Legionella infection.

Water heater temperature set point and water use patterns influence Legionella pneumophila and associated microorganisms at the tap

BACKGROUND

Lowering water heater temperature set points and using less drinking water are common approaches to conserving water and energy; yet, there are discrepancies in past literature regarding the effects of water heater temperature and water use patterns on the occurrence of opportunistic pathogens, in particular Legionella pneumophila. Our objective was to conduct a controlled, replicated pilot-scale investigation to address this knowledge gap using continuously recirculating water heaters to examine five water heater set points (39-58 °C) under three water use conditions. We hypothesized that L. pneumophila levels at the tap depend on the collective influence of water heater temperature, flow frequency, and the resident plumbing ecology.

RESULTS

We confirmed temperature setting to be a critical factor in suppressing L. pneumophila growth both in continuously recirculating hot water lines and at distal taps. For example, at 51 °C, planktonic L. pneumophila in recirculating lines was reduced by a factor of 28.7 compared to 39 °C and was prevented from re-colonizing biofilm. However, L. pneumophila still persisted up to 58 °C, with evidence that it was growing under the conditions of this study. Further, exposure to 51 °C water in a low-use tap appeared to optimally select for L. pneumophila (e.g., 125 times greater numbers than in high-use taps). We subsequently explored relationships among L. pneumophila and other ecologically relevant microbes, noting that elevated temperature did not have a general disinfecting effect in terms of total bacterial numbers. We documented the relationship between L. pneumophila and Legionella spp., and noted several instances of correlations with Vermamoeba vermiformis, and generally found that there is a dynamic relationship with this amoeba host over the range of temperatures and water use frequencies examined.

CONCLUSIONS

Our study provides a new window of understanding into the microbial ecology of potable hot water systems and helps to resolve past discrepancies in the literature regarding the influence of water temperature and stagnation on L. pneumophila, which is the cause of a growing number of outbreaks. This work is especially timely, given society's movement towards "green" buildings and the need to reconcile innovations in building design with public health.

HACCP-Based Programs for Preventing Disease and Injury from Premise Plumbing: A Building Consensus

Thousands of preventable injuries and deaths are annually caused by microbial, chemical and physical hazards from building water systems. Water is processed in buildings before use; this can degrade the quality of the water. Processing steps undertaken on-site in buildings often include conditioning, filtering, storing, heating, cooling, pressure regulation and distribution through fixtures that restrict flow and temperature. Therefore, prevention of disease and injury requires process management. A process management framework for buildings is the hazard analysis and critical control point (HACCP) adaptation of failure mode effects analysis (FMEA). It has been proven effective for building water system management. Validation is proof that hazards have been controlled under operating conditions and may include many kinds of evidence including cultures of building water samples to detect and enumerate potentially pathogenic microorganisms. However, results from culture tests are often inappropriately used because the accuracy and precision are not sufficient to support specifications for control limit or action triggers. A reliable negative screen is based on genus-level Polymerase Chain Reaction (PCR) for Legionella in building water systems; however, building water samples with positive results from this test require further analysis by culture methods.

Occurrence of Potentially Pathogenic Bacterial-Endosymbionts in Acanthamoeba Spp

BACKGROUND

Acanthamoeba- bacteria interactions enable pathogenic bacteria to tolerate harsh conditions and lead to transmission to the susceptible host. The present study was aimed to address the presence of bacterial endosymbionts of Acanthamoeba isolated from recreational water sources of Tehran, Iran. To the best of our knowledge this is the first study regarding occurrence of bacteria in environmental Acanthamoeba spp. in Iran.

METHODS

A total of 75 samples of recreational water sources were collected. Samples were cultured on non- nutrient agar 1.5% plates. Positive Acanthamoeba spp. were axenically grown. DNA extraction and PCR reaction was performed using JDP1-2 primers. All positive samples of Acanthamoeba were examined for the presence of endosymbionts using staining and molecular methods. The PCR products were then sequenced in order to determine the genotypes of Acanthamoeba and bacteria genera.

RESULTS

Out of 75 samples, 16 (21.3%) plates were positive for Acanthamoeba according to the morphological criteria. Molecular analysis revealed that Acanthamoeba belonged to T4 and T5 genotypes. Five isolates (35.7%) were positive for bacterial endosymbionts using staining method and PCR test. Sequencing of PCR products confirmed the presence of Pseudomonas aeruginosa and Agrobacterium tumefasiens.

CONCLUSION

The presence of Acanthamoeba bearing pathogenic endosymbionts in water sources leads us to public health issues including improved sanitation and decontamination measures in recreational water sources in order to prevent amoebae-related infection. To the best of our knowledge this is the first report regarding the isolation of A. tumefasiens from Acanthamoeba in Iran and worldwide.