Legionella pneumophila transcriptional response following exposure to CuO nanoparticles

Effects of Copper on Legionella pneumophila Revealed via Viability Assays and Proteomics

Cu is an antimicrobial that is commonly applied to premise (i.e., building) plumbing systems for Legionella control, but the precise mechanisms of inactivation are not well defined. Here, we applied a suite of viability assays and mass spectrometry-based proteomics to assess the mechanistic effects of Cu on L. pneumophila. Although a five- to six-log reduction in culturability was observed with 5 mg/L Cu2+ exposure, cell membrane integrity only indicated a <50% reduction. Whole-cell proteomic analysis revealed that AhpD, a protein related to oxidative stress, was elevated in Cu-exposed Legionella relative to culturable cells. Other proteins related to cell membrane synthesis and motility were also higher for the Cu-exposed cells relative to controls without Cu. While the proteins related to primary metabolism decreased for the Cu-exposed cells, no significant differences in the abundance of proteins related to virulence or infectivity were found, which was consistent with the ability of VBNC cells to cause infections. Whereas the cell-membrane integrity assay provided an upper-bound measurement of viability, an amoebae co-culture assay provided a lower-bound limit. The findings have important implications for assessing Legionella risk following its exposure to copper in engineered water systems.

Exposure of Legionella pneumophila to low-shear modeled microgravity: impact on stress response, membrane lipid composition, pathogenicity to macrophages and interrelated genes expression

Here, we studied the effect of low-shear modeled microgravity (LSMMG) on cross stress resistance (heat, acid, and oxidative), fatty acid content, and pathogenicity along with alteration in expression of stress-/virulence-associated genes in Legionella pneumophila. The stress resistance analysis result indicated that bacteria cultivated under LSMMG environments showed higher resistance with elevated D-values at 55 °C and in 1 mM of hydrogen peroxide (H2O2) conditions compared to normal gravity (NG)-grown bacteria. On the other hand, there was no significant difference in tolerance (p < 0.05) toward simulated gastric fluid (pH-2.5) acid conditions. In fatty acid analysis, our result showed that a total amount of saturated and cyclic fatty acids was increased in LSMMG-grown cells; as a consequence, they might possess low membrane fluidity. An upregulated expression level was noticed for stress-related genes (hslV, htrA, grpE, groL, htpG, clpB, clpX, dnaJ, dnaK, rpoH, rpoE, rpoS, kaiB, kaiC, lpp1114, ahpC1, ahpC2, ahpD, grlA, and gst) under LSMMG conditions. The reduced virulence (less intracellular bacteria and less % of induce apoptosis in RAW 264.7 macrophages) of L. pneumophila under LSMMG conditions may be because of downregulation related genes (dotA, dotB, dotC, dotD, dotG, dotH, dotL, dotM, dotN, icmK, icmB, icmS, icmT, icmW, ladC, rtxA, letA, rpoN, fleQ, fleR, and fliA). In the LSMMG group, the expression of inflammation-related factors, such as IL-1α, TNF-α, IL-6, and IL-8, was observed to be reduced in infected macrophages. Also, scanning electron microscopy (SEM) analysis showed less number of LSMMG-cultivated bacteria attached to the host macrophages compared to NG. Thus, our study provides understandings about the changes in lipid composition and different genes expression due to LSMMG conditions, which apparently influence the alterations of L. pneumophila' stress/virulence response.

Quantification of silver nanoparticle interactions with yeast Saccharomyces cerevisiae studied using single-cell ICP-MS

Silver nanoparticles (AgNPs) have been used in many fields due to their anticancer, antimicrobial, and antiviral potential. Single-cell ICP-MS (SC-ICP-MS) is an emerging technology that allows for the rapid characterization and quantification of a metal analyte across a cell population in a single analysis. In this study, a new rapid and sensitive SC-ICP-MS method was developed to quantitatively study the interactions of AgNPs with yeast Saccharomyces cerevisiae. The method can quantify the cell concentration, silver concentration per cell, and profile the nanoparticle distribution in a yeast cell population. AgNP dosing time, concentration, and AgNP size were quantitatively evaluated for their effects on AgNP-yeast cell interactions. The results showed that the initial uptake of AgNPs was rapid and primarily driven by the mass of Ag per cell. The optimal dosing particle concentrations for highest uptake were approximately 1820, 1000, and 300 AgNPs/cell for 10, 20, and 40 nm AgNPs, respectively. Furthermore, this study also validated a washing method for the application to a microorganism for the first time and was used to quantitatively determine the amount of cell surface-adsorbed AgNPs and intracellular AgNPs. These results indicated that the mass (Ag in ag/cell) ratios of intracelluar vs cell surface-adsorbed AgNPs were similar for different AgNP sizes. This high throughput and ultrasensitive SC-ICP-MS method is expected to have many potential applications, such as optimization of methods for green synthesis of AgNPs, nanotoxicity studies, and drug delivery. This is the first quantification study on the interactions of AgNPs and S. cerevisiae using SC-ICP-MS.

Nano drug delivery in intracellular bacterial infection treatments

The present work aimed to review the potential mechanisms used by macrophages to kill intracellular bacteria, their entrance to the cell, and mechanisms of escape of cellular immunity and applications of various nanoparticles. Since intracellular bacteria such as Mycobacterium and Brucella can survive in host cells and can resist the lethal power of macrophages, they can cause chronic disease or recur in 10-30% of cases in improved patients Nano drug-based therapeutics are promising tools for treating intracellular bacteria and preventing recurrence of the disease caused by these bacteria. In addition, among their unique features, we can mention the small size and the ability of these compounds to purposefully reach the target location.

Molecular Mechanisms of Nanomaterial-Bacterial Interactions Revealed by Omics-The Role of Nanomaterial Effect Level

Nanotechnology is employed across a wide range of antibacterial applications in clinical settings, food, pharmaceutical and textile industries, water treatment and consumer goods. Depending on type and concentration, engineered nanomaterials (ENMs) can also benefit bacteria in myriad contexts including within the human body, in biotechnology, environmental bioremediation, wastewater treatment, and agriculture. However, to realize the full potential of nanotechnology across broad applications, it is necessary to understand conditions and mechanisms of detrimental or beneficial effects of ENMs to bacteria. To study ENM effects, bacterial population growth or viability are commonly assessed. However, such endpoints alone may be insufficiently sensitive to fully probe ENM effects on bacterial physiology. To reveal more thoroughly how bacteria respond to ENMs, molecular-level omics methods such as transcriptomics, proteomics, and metabolomics are required. Because omics methods are increasingly utilized, a body of literature exists from which to synthesize state-of-the-art knowledge. Here we review relevant literature regarding ENM impacts on bacterial cellular pathways obtained by transcriptomic, proteomic, and metabolomic analyses across three growth and viability effect levels: inhibitory, sub-inhibitory or stimulatory. As indicated by our analysis, a wider range of pathways are affected in bacteria at sub-inhibitory vs. inhibitory ENM effect levels, underscoring the importance of ENM exposure concentration in elucidating ENM mechanisms of action and interpreting omics results. In addition, challenges and future research directions of applying omics approaches in studying bacterial-ENM interactions are discussed.

Mitigation of Expression of Virulence Genes in Legionella pneumophila Internalized in the Free-Living Amoeba Willaertia magna C2c Maky

Legionella pneumophila is a human pathogen responsible for a severe form of pneumonia named Legionnaire disease. Its natural habitat is aquatic environments, being in a free state or intracellular parasites of free-living amoebae, such as Acanthamoeba castellanii. This pathogen is able to replicate within some amoebae. Willaertia magna C2c Maky, a non-pathogenic amoeba, was previously demonstrated to resist to L. pneumophila and even to be able to eliminate the L. pneumophila strains Philadelphia, Lens, and Paris. Here, we studied the induction of seven virulence genes of three L. pneumophila strains (Paris, Philadelphia, and Lens) within W. magna C2c Maky in comparison within A. castellanii and with the gene expression level of L. pneumophila strains alone used as controls. We defined a gene expression-based virulence index to compare easily and without bias the transcript levels in different conditions and demonstrated that W. magna C2c Maky did not increase the virulence of L. pneumophila strains in contrast to A. castellanii. These results confirmed the non-permissiveness of W. magna C2c Maky toward L. pneumophila strains.

An in vivo protease activity assay for investigating the functions of the Escherichia coli membrane protease HtpX

Escherichia coli HtpX is an M48 family zinc metalloproteinase located in the cytoplasmic membrane. Previous studies suggested that it is involved in the quality control of membrane proteins. However, its in vivo proteolytic function has not been characterized in detail, mainly because the physiological substrates have not been identified and no model substrate that allows sensitive detection of the protease activity is available. We constructed a new model substrate of HtpX and established an in vivo semiquantitative and convenient protease activity assay system for HtpX. This system enables detection of differential protease activities of HtpX mutants carrying mutations in conserved regions. This system would also be useful for investigating the functions of HtpX and its homologs in other bacteria.

The Combined Effect of Cold and Copper Stresses on the Proliferation and Transcriptional Response of Listeria monocytogenes

Listeria monocytogenes is a foodborne pathogen that can cause severe disease in susceptible humans. This microorganism has the ability to adapt to hostile environmental conditions such as the low temperatures used by the food industry for controlling microorganisms. Bacteria are able to adjust their transcriptional response to adapt to stressful conditions in order to maintain cell homeostasis. Understanding the transcriptional response of L. monocytogenes to stressing conditions could be relevant to develop new strategies to control the pathogen. A possible alternative for controlling microorganisms in the food industry could be to use copper as an antimicrobial agent. The present study characterized three L. monocytogenes strains (List2-2, Apa13-2, and Al152-2A) adapted to low temperature and challenged with different copper concentrations. Similar MIC-Cu values were observed among studied strains, but growth kinetic parameters revealed that strain List2-2 was the least affected by the presence of copper at 8°C. This strain was selected for a global transcriptional response study after a 1 h exposition to 0.5 mM of CuSO4 × 5H2O at 8 and 37°C. The results showed that L. monocytogenes apparently decreases its metabolism in response to copper, and this reduction is greater at 8°C than at 37°C. The most affected metabolic pathways were carbohydrates, lipids and nucleotides synthesis. Finally, 15 genes were selected to evaluate the conservation of the transcriptional response in the other two strains. Results indicated that only genes related to copper homeostasis showed a high degree of conservation between the strains studied, suggesting that a low number of genes is implicated in the response to copper stress in L. monocytogenes. These results contribute to the understanding of the molecular mechanisms used by bacteria to overcome a combination of stresses. This study concluded that the application of copper in low concentrations in cold environments may help to control foodborne pathogens as L. monocytogenes in the industry.

Electrically heatable carbon nanotube point-of-use filters for effective separation and in-situ inactivation of Legionella pneumophila

Despite municipal chlorination and secondary disinfection, opportunistic waterborne pathogens (e.g., Legionella spp.) persist in public and private water distribution systems. As a potential source of healthcare-acquired infections, this warrants development of novel pathogen removal and inactivation systems. In this study, electrically heatable carbon nanotube (CNT) point-of-use (POU) filters have been designed to remove and inactivate Legionella pneumophila in water. The CNT/polymer composite membranes effectively removed Legionella (> 99.99%) (i.e., below detection limit) and were able to inactive them on the membrane surface at 100% efficiency within 60 s using ohmic heating at 20 V. The novel POU filters could be used as a final barrier to provide efficient rejection of pathogens and thereby simultaneously eliminate microorganisms in public and private water supplies.

Multiwall Carbon Nanotubes Induce More Pronounced Transcriptomic Responses in Pseudomonas aeruginosa PG201 than Graphene, Exfoliated Boron Nitride, or Carbon Black

Carbonaceous and boron nitride (BN) nanomaterials have similar applications and hydrophobic properties suggesting common release pathways and exposure to bacteria. While high nanomaterial concentrations can be bactericidal or growth-inhibitory, little is known regarding bacterial transcriptional responses to non-growth-inhibitory nanomaterial concentrations. Here, using one strain of Pseudomonas aeruginosa-a clinically and environmentally important bacterial taxon-we analyzed the comparative transcriptomic response to carbonaceous or BN nanomaterials. We show that, at non-growth-inhibitory, equal mass concentrations (10 mg/L), multiwall carbon nanotubes (MWCNTs) induced differential regulation of 111 genes in P. aeruginosa, while graphene, BN, and carbon black caused differential regulation of 44, 26, and 25 genes, respectively. MWCNTs caused the upregulation of genes encoding general stress response (9 genes), sulfur metabolism (15), and transport of small molecules (7) and downregulation of genes encoding flagellar basal-body rod proteins and other virulence-related factors (6), nitrogen metabolism (7), and membrane proteins (12), including a two-component regulatory system CzcS/R. Because two-component systems are associated with antibiotic resistance, the antibiotic susceptibility of P. aeruginosa was tested following MWCNT exposure. In MWCNT-treated cultures, the minimal inhibitory concentrations (MICs) of meropenem and imipenem decreased from 0.06 to 0.03 μg/mL and from 0.25 to 0.125 μg/mL, respectively. Taken together, whole genome analysis indicated that, in the absence of growth inhibition, nanomaterials can alter bacterial physiology and metabolism. For MWCNTs, such alterations may include downregulation of antibiotic resistance pathways, suggesting that pre-exposure to MWCNTs could potentially render bacteria more susceptible to carbapenems which are often the last resort for the globally concerning, highly antibiotic resistant P. aeruginosa.

Omics tools: New challenges in aquatic nanotoxicology?

In recent years, the implication of genomics into ecotoxicological studies has been studied closely to allow a better understanding of organism's responses to environmental contaminants including engineering nanomaterials (ENMs). ENMs are increasingly produced for various applications including cosmetics, electronics, sports equipment, biomedicine and agriculture. Because of their small size, ENMs possess chemical or physical characteristics improved compared to the corresponding macro-sized material. As their application expend, the release of manufactured ENMs into the environment is likely to increase and concern over impacts for the aquatic ecosystem is growing. Several studies reported deleterious effect of ENMs to aquatic organisms, but there is little information about the molecular mechanisms of toxicity. The development of ecotoxicogenomic approaches will improve the characterization of cellular and molecular modes of action of ENMs to aquatic organisms and allow a better prediction of contaminants toxicity. This paper presents an overview of transciptomic/proteomic studies in freshwater and marine organisms exposed to ENMs. Overall, induction of gene expression in relations to defense mechanisms, immune responses, growth and reproduction were measured after ENMs exposures of organisms, but with different patterns depending on exposure duration and concentrations used. In addition, some studies reported a positive correlation between gene expression and cellular modifications, but not at the individual level.

Resistance of Legionella and Acanthamoeba mauritaniensis to heat treatment as determined by relative and quantitative polymerase chain reactions

Legionella and Acanthamoeba spp. persist in harvested rainwater pasteurized at high temperatures (> 72°C) and the interaction mechanisms exhibited between these organisms need to be elucidated. The resistance of two Legionella reference strains (Legionella pneumophila ATCC 33152 and Legionella longbeachae ATCC 33462), three environmental strains [Legionella longbeachae (env.), Legionella norrlandica (env.) and Legionella rowbothamii (env.)] and Acanthamoeba mauritaniensis ATCC 50676 to heat treatment (50-90°C) was determined by monitoring culturability and viability [ethidium monoazide quantitative polymerase chain reaction (EMA-qPCR)]. The expression of metabolic and virulence genes of L. pneumophila ATCC 33152 (lolA, sidF, csrA) and L. longbeachae (env.) (lolA) in co-culture with A. mauritaniensis ATCC 50676 during heat treatment (50-90°C) was monitored using relative qPCR. While the culturability (CFU/mL) and viability (gene copies/mL) of the Legionella strains reduced significantly (p < 0.05) following heat treatment (60-90°C), L. longbeachae (env.) and L. pneumophila ATCC 33152 were culturable following heat treatment at 50-60°C. Metabolically active trophozoites and dormant cysts of A. mauritaniensis ATCC 50676 were detected at 50°C and 60-90°C, respectively. For L. pneumophila ATCC 33152, lolA expression remained constant, sidF expression increased and the expression of csrA decreased during co-culture with A. mauritaniensis ATCC 50676. For L. longbeachae (env.), while lolA was up-regulated at 50-70°C, expression was not detected at 80-90°C and in co-culture. In conclusion, while heat treatment may reduce the number of viable Legionella spp. in monoculture, results indicate that the presence of A. mauritaniensis increases the virulence of L. pneumophila during heat treatment. The virulence of Legionella spp. in co-culture with Acanthamoeba spp. should thus be monitored in water distribution systems where temperature (heat) is utilized for treatment.

Effect of temperature and colonization of Legionella pneumophila and Vermamoeba vermiformis on bacterial community composition of copper drinking water biofilms

It is unclear how the water-based pathogen, Legionella pneumophila (Lp), and associated free-living amoeba (FLA) hosts change or are changed by the microbial composition of drinking water (DW) biofilm communities. Thus, this study characterized the bacterial community structure over a 7-month period within mature (> 600-day-old) copper DW biofilms in reactors simulating premise plumbing and assessed the impact of temperature and introduction of Lp and its FLA host, Vermamoeba vermiformis (Vv), co-cultures (LpVv). Sequence and quantitative PCR (qPCR) analyses indicated a correlation between LpVv introduction and increases in Legionella spp. levels at room temperature (RT), while at 37°C, Lp became the dominant Legionella spp. qPCR analysis suggested Vv presence may not be directly associated with Lp biofilm growth at RT and 37°C, but may contribute to or be associated with non-Lp legionellae persistence at RT. Two-way PERMANOVA and PCoA revealed that temperature was a major driver of microbiome diversity. Biofilm community composition also changed over the seven-month period and could be associated with significant shifts in dissolved oxygen, alkalinity and various metals in the influent DW. Hence, temperature, biofilm age, DW quality and transient intrusions/amplification of pathogens and FLA hosts may significantly impact biofilm microbiomes and modulate pathogen levels over extended periods.

Antimicrobial applications of copper

Copper has long been known to have antimicrobial activity and is used in drinking water treatment and transportation. It has been recognized by the American Environmental Protection Agency as the first metallic antimicrobial agent in 2008. With ongoing waterborne hospital-acquired infections and antibiotic resistance, research on copper as an antimicrobial agent is again very attractive. Many studies have shown that the use of copper surface and copper particles could significantly reduce the environmental bioburden. This review highlights in its first part all the conditions described in the literature to enhance copper antimicrobial activity. Secondly, the different antimicrobial applications of copper in water treatment, hospital care units and public applications are presented. Finally, the future research needs on copper as an antimicrobial agent are discussed.

Transcriptomic changes of Legionella pneumophila in water

Background

Legionella pneumophila (Lp) is a water-borne opportunistic pathogen. In water, Lp can survive for an extended period of time until it encounters a permissive host. Therefore, identifying genes that are required for survival in water may help develop strategies to prevent Legionella outbreaks.

Results

We compared the global transcriptomic response of Lp grown in a rich medium to that of Lp exposed to an artificial freshwater medium (Fraquil) for 2, 6 and 24 hours. We uncovered successive changes in gene expression required for the successful adaptation to a nutrient-limited water environment. The repression of major pathways involved in cell division, transcription and translation, suggests that Lp enters a quiescent state in water. The induction of flagella associated genes (flg, fli and mot), enhanced-entry genes (enh) and some Icm/Dot effector genes suggests that Lp is primed to invade a suitable host in response to water exposure. Moreover, many genes involved in resistance to antibiotic and oxidative stress were induced, suggesting that Lp may be more tolerant to these stresses in water. Indeed, Lp exposed to water is more resistant to erythromycin, gentamycin and kanamycin than Lp cultured in rich medium. In addition, the bdhA gene, involved in the degradation pathway of the intracellular energy storage compound polyhydroxybutyrate, is also highly expressed in water. Further characterization show that expression of bdhA during short-term water exposure is dependent upon RpoS, which is required for the survival of Lp in water. Deletion of bdhA reduces the survival of Lp in water at 37 °C.

Conclusions

The increase of antibiotic resistance and the importance of bdhA to the survival of Lp in water seem consistent with the observed induction of these genes when Lp is exposed to water. Other genes that are highly induced upon exposure to water could also be necessary for Lp to maintain viability in the water environment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1869-6) contains supplementary material, which is available to authorized users.

Environmental (Saprozoic) Pathogens of Engineered Water Systems: Understanding Their Ecology for Risk Assessment and Management

Major waterborne (enteric) pathogens are relatively well understood and treatment controls are effective when well managed. However, water-based, saprozoic pathogens that grow within engineered water systems (primarily within biofilms/sediments) cannot be controlled by water treatment alone prior to entry into water distribution and other engineered water systems. Growth within biofilms or as in the case of Legionella pneumophila, primarily within free-living protozoa feeding on biofilms, results from competitive advantage. Meaning, to understand how to manage water-based pathogen diseases (a sub-set of saprozoses) we need to understand the microbial ecology of biofilms; with key factors including biofilm bacterial diversity that influence amoebae hosts and members antagonistic to water-based pathogens, along with impacts from biofilm substratum, water temperature, flow conditions and disinfectant residual—all control variables. Major saprozoic pathogens covering viruses, bacteria, fungi and free-living protozoa are listed, yet today most of the recognized health burden from drinking waters is driven by legionellae, non-tuberculous mycobacteria (NTM) and, to a lesser extent, Pseudomonas aeruginosa. In developing best management practices for engineered water systems based on hazard analysis critical control point (HACCP) or water safety plan (WSP) approaches, multi-factor control strategies, based on quantitative microbial risk assessments need to be developed, to reduce disease from largely opportunistic, water-based pathogens.

Nanoscale copper in the soil-plant system - toxicity and underlying potential mechanisms

Nanoscale copper particles (nano-Cu) are used in many antimicrobial formulations and products for their antimicrobial activity. They may enter deliberately and/or accidentally into terrestrial environments including soils. Being the major 'eco-receptors' of nanoscale particles in the terrestrial ecosystem, soil-microbiota and plants (the soil-plant system) have been used as a model to dissect the potential impact of these particles on the environmental and human health. In the soil-plant system, the plant can be an indirect non-target organism of the soil-associated nano-Cu that may in turn affect plant-based products and their consumers. By all accounts, information pertaining to nano-Cu toxicity and the underlying potential mechanisms in the soil-plant system remains scanty, deficient and little discussed. Therefore, based on some recent reports from (bio)chemical, molecular and genetic studies of nano-Cu versus soil-plant system, this article: (i) overviews the status, chemistry and toxicity of nano-Cu in soil and plants, (ii) discusses critically the poorly understood potential mechanisms of nano-Cu toxicity and tolerance both in soil-microbiota and plants, and (iii) proposes future research directions. It appears from studies hitherto made that the uncontrolled generation and inefficient metabolism of reactive oxygen species through different reactions are the major factors underpinning the overall nano-Cu consequences in both the systems. However, it is not clear whether the nano-Cu or the ion released from it is the cause of the toxicity. We advocate to intensify the multi-approach studies focused at a complete characterization of the nano-Cu, its toxicity (during life cycles of the least-explored soil-microbiota and plants), and behavior in an environmentally relevant terrestrial exposure setting. Such studies may help to obtain a deeper insight into nano-Cu actions and address adequately the nano-Cu-associated safety concerns in the 'soil-plant system'.

Toxicity of metal oxide nanoparticles: mechanisms, characterization, and avoiding experimental artefacts

Metal oxide nanomaterials are widely used in practical applications and represent a class of nanomaterials with the highest global annual production. Many of those, such as TiO2 and ZnO, are generally considered non-toxic due to the lack of toxicity of the bulk material. However, these materials typically exhibit toxicity to bacteria and fungi, and there have been emerging concerns about their ecotoxicity effects. The understanding of the toxicity mechanisms is incomplete, with different studies often reporting contradictory results. The relationship between the material properties and toxicity appears to be complex and diifficult to understand, which is partly due to incomplete characterization of the nanomaterial, and possibly due to experimental artefacts in the characterization of the nanomaterial and/or its interactions with living organisms. This review discusses the comprehensive characterization of metal oxide nanomaterials and the mechanisms of their toxicity.

Exposure to synthetic gray water inhibits amoeba encystation and alters expression of Legionella pneumophila virulence genes

Water conservation efforts have focused on gray water (GW) usage, especially for applications that do not require potable water quality. However, there is a need to better understand environmental pathogens and their free-living amoeba (FLA) hosts within GW, given their growth potential in stored gray water. Using synthetic gray water (sGW) we examined three strains of the water-based pathogen Legionella pneumophila and its FLA hosts Acanthamoeba polyphaga, A. castellanii, and Vermamoeba vermiformis. Exposure to sGW for 72 h resulted in significant inhibition (P < 0.0001) of amoebal encystation versus control-treated cells, with the following percentages of cysts in sGW versus controls: A. polyphaga (0.6 versus 6%), A. castellanii (2 versus 62%), and V. vermiformis (1 versus 92%), suggesting sGW induced maintenance of the actively feeding trophozoite form. During sGW exposure, L. pneumophila culturability decreased as early as 5 h (1.3 to 2.9 log10 CFU, P < 0.001) compared to controls (Δ0 to 0.1 log10 CFU) with flow cytometric analysis revealing immediate changes in membrane permeability. Furthermore, reverse transcription-quantitative PCR was performed on total RNA isolated from L. pneumophila cells at 0 to 48 h after sGW incubation, and genes associated with virulence (gacA, lirR, csrA, pla, and sidF), the type IV secretion system (lvrB and lvrE), and metabolism (ccmF and lolA) were all shown to be differentially expressed. These results suggest that conditions within GW may promote interactions between water-based pathogens and FLA hosts, through amoebal encystment inhibition and alteration of bacterial gene expression, thus warranting further exploration into FLA and L. pneumophila behavior in GW systems.

Impact of drinking water conditions and copper materials on downstream biofilm microbial communities and Legionella pneumophila colonization

AIMS

This study examined the impact of pipe materials and introduced Legionella pneumophila on downstream Leg. pneumophila colonization and microbial community structures under conditions of low flow and low chlorine residual.

METHODS AND RESULTS

CDC biofilm(™) reactors containing either unplasticized polyvinylchloride (uPVC) or copper (Cu) coupons were used to develop mature biofilms on Norprene(™) tubing effluent lines to simulate possible in-premise biofilm conditions. The microbial communities were characterized through 16S and 18S rRNA gene clone libraries and Leg. pneumophila colonization was determined via specific qPCR assays. The Cu significantly decreased downstream microbial diversity, approximately halved bacterial and eukaryotic abundance, with some groups only detected in uPVC-reactor tubing biofilms. However, some probable amoeba-resisting bacteria (ARB) like Mycobacterium spp. and Rhodobacteraceae were significantly more abundant in the Cu than uPVC-reactor tubing biofilms. In particular, Leg. pneumophila only persisted (postinoculation) within the Cu-reactor tubing biofilms, and the controlled low chlorine residue and water flow conditions led to a general high abundance of possible free-living protozoa in all tubing biofilms. The higher relative abundance of ARB-like sequences from Cu-coupons vs uPVC may have been promoted by amoebal selection and subsequent ARB protection from Cu inhibitory effects.

CONCLUSIONS

Copper pipe and low flow conditions had significant impact on downstream biofilm microbial structures (on plastic pipe) and the ability for Leg. pneumophila colonization post an introduction event.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report that compares the effects of copper and uPVC materials on downstream biofilm communities grown on a third (Norprene(™)) surface material. The downstream biofilms contained a high abundance of free-living amoebae and ARB, which may have been driven by a lack of residual disinfectant and periodic stagnant conditions. Given the prevalence of Cu-piping in buildings, there may be increased risk from drinking water exposures to ARB following growth on pipe/fixture biofilms within premise drinking water systems.

Analysis of the transcriptome of Legionella pneumophila hfq mutant reveals a new mobile genetic element

Hfq is a small RNA-binding protein involved in the post-transcriptional regulation of gene expression by affecting the stability of the mRNA and by mediating efficient pairing between small regulatory RNAs and their target mRNAs. In Legionella pneumophila, the aetiological agent of Legionnaires' disease, mutation of hfq results in increased duration of the lag phase and reduced growth in low-iron medium. In an effort to uncover genes potentially regulated by Hfq, the transcriptome of an hfq mutant strain was compared to that of the wild-type. Unexpectedly, many genes located within a 100 kb genomic island, including a section of the previously identified efflux island, were overexpressed in the hfq mutant strain. Since this island contains a putative conjugative system and an integrase, it was postulated that it could be a new integrated mobile genetic element. PCR analysis revealed that this region exists both as an integrated and as an episomal form in the cell population and that it undergoes differential excision in the hfq mutant background, which was further confirmed by trans-complementation of the hfq mutation. This new plasmid-like element was named pLP100. Differential excision did not affect the copy number of pLP100 at the population level. This region contains a copper efflux pump encoded by copA, and increased resistance to copper was observed for the hfq mutant strain that was abrogated in the complemented strain. A strain carrying a mutation of hfq and a deletion of the right side recombination site, attR, showed that overexpression of pLP100 genes and increased copper resistance in the hfq mutant strain were dependent upon excision of pLP100.