Three encephalitis-causing amoebae and their distinct interactions with the host

Molecular Mechanisms of Acanthamoeba castellanii Response to Different Sources of Oxidative Stress

Oxidative stress is a biological principle affecting all life on Earth and is also an important factor in the pathogen-host relationship. The pathogenic free-living amoeba Acanthamoeba castellanii has several pathways to cope with reactive oxygen species and the damage that they cause. In this study, we aimed to provide a comprehensive analysis of the amoeba's response to different sources of oxidative stress. Using whole-cell proteomic analysis, we obtained a complex picture of the changes in the proteome and identified potential key players in the defense against oxidative stress. Importantly, from the differential proteomics analysis, we identified a candidate efflux pump that may be involved in Acanthamoeba drug resistance.

Secreted small RNAs of Naegleria fowleri are biomarkers for diagnosis of primary amoebic meningoencephalitis

Rapid and accurate diagnostics are needed to effectively detect and treat primary amoebic meningoencephalitis (PAM) caused by Naegleria fowleri (Nf). Delayed diagnosis and similarities to other causes of meningitis contribute to a case mortality rate of >97%. Thus, there is an unmet medical need for a non-invasive liquid biopsy diagnostic method. We sequenced Nf extracellular vesicles (EVs) and identified microRNAs, tRNAs and other small RNAs in Nf-EVs. From these data we selected two prevalent small RNAs as biomarker candidates. We developed an RT-qPCR assay and both small RNAs were detected in Nf-EVs and amoeba-conditioned media. In the mouse model of PAM both small RNA biomarkers were detected in 100% of mouse plasma samples at the end-stage of infection. Notably, smallRNA-1 was detected in the urine of infected mice at timepoints as early as 24h post infection (18/23 mice) and in the plasma as early as 60h post infection (8/8 mice). Additionally, smallRNA-1 was detected in 100% (n=6) of CSF samples from human PAM cases, and in whole blood samples, but not in human plasma from PAM cases. In this study, we discovered small RNAs as biomarkers of Nf infection, one which can be detected reliably in CSF, urine, and whole blood. The RT-qPCR assay is a highly sensitive diagnostic assay that can be conducted in ~3h after receipt of liquid biopsy. The data suggest detection of smallRNA-1 biomarker could provide earlier diagnosis of PAM and be used to monitor biomass of amoebae during treatment.

Acanthamoeba castellanii trophozoites need oxygen for normal functioning and lipids are their preferred substrate, offering new possibilities for treatment

Acanthamoebae, pathogenic free-living amoebae, can cause Granulomatous Amoebic Encephalitis (GAE) and keratitis, and for both types of infection, no adequate treatment options are available. As the metabolism of pathogens is an attractive treatment target, we set out to examine the energy metabolism of Acanthamoeba castellanii and studied the aerobic and anaerobic capacities of the trophozoites. Under anaerobic conditions, or in the presence of inhibitors of the electron-transport chain, A. castellanii trophozoites became rounded, moved sluggishly and stopped multiplying. This demonstrates that oxygen and the respiratory chain are essential for movement and replication. Furthermore, the simultaneous activities of both terminal oxidases, cytochrome c oxidase and the plant-like alternative oxidase, are essential for normal functioning and replication. The inhibition of normal function caused by the inactivity of the respiratory chain was reversible. Once respiration was made possible again, the rounded, rather inactive amoebae formed acanthopodia within 4 h and resumed moving, feeding and multiplying. Experiments with radiolabelled nutrients revealed a preference for lipids over glucose and amino acids as food. Subsequent experiments showed that adding lipids to a standard culture medium of trophozoites strongly increased the growth rate. Acanthamoeba castellanii trophozoites have a strictly aerobic energy metabolism and β-oxidation of fatty acids, the Krebs cycle, and an aerobic electron-transport chain coupled to the ATP synthase, producing most of the used ATP. The preference for lipids can be exploited, as we show that three known inhibitors of lipid oxidation strongly inhibited the growth of A. castellanii. In particular, thioridazine and perhexiline showed potent effects in low micromolar concentrations. Therefore, this study revealed a new drug target with possibly new options to treat Acanthamoeba infections.

Transcriptomic profiling of "brain-eating amoeba" Naegleria fowleri infection in mice: the host and the protozoa perspectives

The free-living amoeba Naegleria fowleri (NF) causes a rare but lethal parasitic meningoencephalitis (PAM) in humans. Currently, this disease lacks effective treatments and the specific molecular mechanisms that govern NF pathogenesis and host brain response remain unknown. To address some of these issues, we sought to explore naturally existing virulence diversity within environmental NF isolates. Herein, we purified two new NF environmental isolates (NF45 and NF1) and tested their in vivo virulence using experimental infection in mice. We found that NF45 was highly virulent (NF45_HV) compared with NF1 (low virulence, NF1_LV), based on in vivo amoeba growth kinetics and mouse survival. To identify underlying differences, we conducted RNA-seq and bioinformatics analyses from the infected mouse brains. Our results showed that NF1_LV and NF45_HV modulated the expression of their genes during mouse brain infection. Differentially expressed genes (DEGs) in NF1_LV were mostly involved in Translational protein, Protein-binding activity modulator, Protein modifying enzyme, while DEGs in NF45_HV were related to DNA metabolism, Cytoskeletal protein, Protein-binding activity modulator. Proteases (namely the virulence factor Cathepsin B) were upregulated in NF1_LV, while downregulated in NF45_HV. When analyzing the host response against infection by these two NF strains, enrichment analyses uncovered genes and mechanisms related to the host immune responses and nervous systems. We detected more DEGs in NF1_LV infected mice compared to NF45_HV, related to blood brain barrier leakage, immune cell recruitment, cytokine production (including IL-6, IFN-Ɣ and TNFα), inflammation of astrocytes and microglia, and oligodendrocyte and neurons degeneration. Increased expression of neuromotor-related genes such as Adam22, Cacnb4 and Zic1 (activated by NF1_LV infection) and ChAt (activated by NF45_LV infection) could explain PAM symptoms such as muscle weakness and seizures. Globally, our results showed that NF isolated from the environment can have different levels of virulence and differentially modulate their gene expression during brain infection. We also provided, for the first time, a comprehensive information for the molecular mechanisms of neuro-immune and host-pathogen interactions during PAM disease. As the host and the protozoa are strongly implicated in PAM lethality, new therapies targeting both the parasite, and the host should be considered to treat PAM infection.

The potential of nanocomposites (patuletin-conjugated with gallic acid-coated zinc oxide) against free-living amoebae pathogens

Free-living amoebae infections are on the rise while the prognosis remains poor. Current therapies are ineffective, and there is a need for novel effective drugs which can target Naegleria, Balamuthia, and Acanthamoeba species. In this study, we determined the effects of a nano-formulation based on flavonoid patuletin-loaded gallic acid functionalized zinc oxide nanoparticles (PA-GA-ZnO) against Acanthamoeba, Balamuthia, and Naegleria trophozoites. Characterization of the nano-formulation was accomplished utilizing analytical tools, namely Fourier-transform infrared spectroscopy, drug entrapment efficiency, polydispersity index, dimensions, and surface morphologies. Anti-amoebic effects were investigated using amoebicidal assay, cytopathogenicity assay, and cytotoxicity of the nano-formulation on human cells. The findings revealed that nano-formulation (PA-GA-ZnO) displayed significant anti-amoebic properties and augmented effects of patuletin alone against all three brain-eating amoebae. When tested alone, patuletin nano-formulations showed minimal toxicity effects against human cells. In summary, the nano-formulations evaluated herein depicts efficacy versus Acanthamoeba, Balamuthia, and Naegleria. Nonetheless, future studies are needed to comprehend the molecular mechanisms of patuletin nano-formulations versus free-living amoebae pathogens, in addition to animal studies to determine their potential value for clinical applications.

Bacterial microbiota management in free-living amoebae (Heterolobosea lineage) isolated from water: The impact of amoebae identity, grazing conditions, and passage number

Free-living amoebae (FLA) are ubiquitous protozoa mainly found in aquatic environments. They are well-known reservoirs and vectors for the transmission of amoeba-resistant bacteria (ARB), most of which are pathogenic to humans. Yet, the natural bacterial microbiota associated with FLA remains largely unknown. Herein, we characterized the natural bacterial microbiota of different FLA species isolated from recreational waters in Guadeloupe. Monoxenic cultures of Naegleria australiensis, Naegleria sp. WTP3, Paravahlkampfia ustiana and Vahlkampfia sp. AK-2007 (Heterolobosea lineage) were cultivated under different grazing conditions, during successive passages. The whole bacterial microbiota of the waters and the amoebal cysts was characterized using 16S rRNA gene metabarcoding. The culturable subset of ARB was analyzed by mass spectrometry (MALDI-TOF MS), conventional 16S PCR, and disk diffusion method (to assess bacterial antibiotic resistance). Transmission electron microscopy was used to locate the ARB inside the amoebae. According to alpha and beta-diversity analyses, FLA bacterial microbiota were significantly different from the ones of their habitat. While Vogesella and Aquabacterium genera were detected in water, the most common ARB belonged to Pseudomonas, Bosea, and Escherichia/Shigella genera. The different FLA species showed both temporary and permanent associations with differentially bacterial taxa, suggesting host specificity. These associations depend on the number of passages and grazing conditions. Additionally, Naegleria, Vahlkampfia and Paravahlkampfia cysts were shown to naturally harbor viable bacteria of the Acinetobacter, Escherichia, Enterobacter, Pseudomonas and Microbacterium genera, all being pathogenic to humans. To our knowledge, this is the first time Paravahlkampfia and Vahlkampfia have been demonstrated as hosts of pathogenic ARB in water. Globally, the persistence of these ARB inside resistant cysts represents a potential health risk. To ensure the continued safety of recreational waters, it is crucial to (i) regularly control both the amoebae and their ARB and (ii) improve knowledge on amoebae-bacteria interactions to establish better water management protocols.

Antiamoebic activities of flavonoids against pathogenic free-living amoebae, Naegleria fowleri and Acanthamoeba species

Free-living amoebae (FLA) rarely cause human infections but can invoke fatal infections in the central nervous system (CNS). No consensus treatment has been established for FLA infections of the CNS, emphasizing the urgent need to discover or develop safe and effective drugs. Flavonoids, natural compounds from plants and plant-derived products, are known to have antiprotozoan activities against several pathogenic protozoa parasites. The anti-FLA activity of flavonoids has also been proposed, while their antiamoebic activity for FLA needs to be emperically determined. We herein evaluated the antiamoebic activities of 18 flavonoids against Naegleria fowleri and Acanthamoeba species which included A. castellanii and A. polyphaga. These flavonoids showed different profiles of antiamoebic activity against N. fowleri and Acanthamoeba species. Demethoxycurcumin, kaempferol, resveratrol, and silybin (A+B) showed in vitro antiamoebic activity against both N. fowleri and Acanthamoeba species. Apigenin, costunolide, (‒)-epicatechin, (‒)-epigallocatechin, rosmarinic acid, and (‒)-trans-caryophyllene showed selective antiamoebic activity for Acanthamoeba species. Luteolin was more effective for N. fowleri. However, afzelin, berberine, (±)-catechin, chelerythrine, genistein, (+)-pinostrobin, and quercetin did not exhibit antiamoebic activity against the amoeba species. They neither showed selective antiamoebic activity with significant cytotoxicity to C6 glial cells. Our results provide a basis for the anti-FLA activity of flavonoids, which can be applied to develope alternative or supplemental therapeutic agents for FLA infections of the CNS.

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

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

Pathogenic free-living amoebic encephalitis from 48 cases in China: A systematic review

Background

Free-living amoebae (FLA) including Naegleria fowleri, Acanthamoeba spp., and Balamuthia mandrillaris can become pathogenic and cause severe cerebral infections, named primary amoebic meningoencephalitis (PAM), granulomatous amoebic encephalitis (GAE), and balamuthia amoebic encephalitis (BAE), respectively. FLA encephalitis has been reported across China, but the clinical data descriptions and analytical results of these different reports vary widely. Currently, no consensus treatment has been established. We conduct a systematic review to evaluate the exposure location, clinical symptoms, diagnosis, treatment, and prognosis of three FLA encephalitis and aim to reveal the differences between three FLA encephalitis in China.

Methods

We used MEDLINE (PubMed interface), EMBASE, China National Knowledge Infrastructure (CNKI), Wanfang database, and China Biology Medicine disc (CBMdisc) databases for literatures published and manually retrieve the hospital records of our hospital. The search time was up to August 30, 2022, with no language restrictions.

Results

After excluding possible duplicate cases, a total of 48 patients of three FLA encephalitis were collected. One from the medical records of our hospital and 47 patients from 31 different studies. There were 11 patients of PAM, 10 patients of GAE, and 27 patients of BAE. The onset of PAM is mostly acute or subacute, and the clinical symptoms are acute and fulminant hemorrhagic meningoencephalitis. Most patients with GAE and BAE have an insidious onset and a chronic course. A total of 21 BAE patients (77.8%) had skin lesions before onset of symptoms. Additionally, 37 cases (77.1%) were diagnosed with FLA encephalitis before death. And there were 4 of PAM, 2 of GAE, and 10 of BAE diagnosed using next generation sequencing. No single agent can be proposed as the ideal therapy by itself. Only 6 cases were successfully treated.

Conclusions

This review provides an overview of the available data and studies of FLA encephalitis in China and identify some potential differences. FLA encephalitis is a rare but pathogenic infection, and physicians should early identify this encephalitis to improve survival.

Naegleria genus pangenome reveals new structural and functional insights into the versatility of these free-living amoebae

Introduction

Free-living amoebae of the Naegleria genus belong to the major protist clade Heterolobosea and are ubiquitously distributed in soil and freshwater habitats. Of the 47 Naegleria species described, N. fowleri is the only one being pathogenic to humans, causing a rare but fulminant primary amoebic meningoencephalitis. Some Naegleria genome sequences are publicly available, but the genetic basis for Naegleria diversity and ability to thrive in diverse environments (including human brain) remains unclear.

Methods

Herein, we constructed a high-quality Naegleria genus pangenome to obtain a comprehensive catalog of genes encoded by these amoebae. For this, we first sequenced, assembled, and annotated six new Naegleria genomes.

Results and Discussion

Genome architecture analyses revealed that Naegleria may use genome plasticity features such as ploidy/aneuploidy to modulate their behavior in different environments. When comparing 14 near-to-complete genome sequences, our results estimated the theoretical Naegleria pangenome as a closed genome, with 13,943 genes, including 3,563 core and 10,380 accessory genes. The functional annotations revealed that a large fraction of Naegleria genes show significant sequence similarity with those already described in other kingdoms, namely Animalia and Plantae. Comparative analyses highlighted a remarkable genomic heterogeneity, even for closely related strains and demonstrate that Naegleria harbors extensive genome variability, reflected in different metabolic repertoires. If Naegleria core genome was enriched in conserved genes essential for metabolic, regulatory and survival processes, the accessory genome revealed the presence of genes involved in stress response, macromolecule modifications, cell signaling and immune response. Commonly reported N. fowleri virulence-associated genes were present in both core and accessory genomes, suggesting that N. fowleri's ability to infect human brain could be related to its unique species-specific genes (mostly of unknown function) and/or to differential gene expression. The construction of Naegleria first pangenome allowed us to move away from a single reference genome (that does not necessarily represent each species as a whole) and to identify essential and dispensable genes in Naegleria evolution, diversity and biology, paving the way for further genomic and post-genomic studies.

Anti-Acanthamoeba activity of a semi-synthetic mangostin derivative and its ability in removal of Acanthamoeba triangularis WU19001 on contact lens

Garcinia mangostana L., also known as the mangosteen tree, is a native medicinal plant in Southeast Asia having a wide variety of pharmacologically active compounds, including xanthonoid mangostin. In this study, we examined the pharmacological activities of the selected semi-synthetic mangostin derivative, namely, amoebicidal activity, encystation inhibition, excystation activity, and removal capacity of adhesive Acanthamoeba from the surface of contact lens (CL). Among the three derivatives, C1 exhibited promising anti-Acanthamoeba activity against Acanthamoeba triangularis WU19001 trophozoites and cysts. SEM images displayed morphological changes in Acanthamoeba trophozoites, including the loss of acanthopodia, pore formation in the cell membrane, and membrane damage. In addition, the treated cyst was shrunken and adopted an irregular flat cyst shape. Under a fluorescence microscope, acridine orange and propidium iodide (AO/PI) staining revealed C1 induced condensation of cytoplasm and chromatin with the loss of cell volume in the treated trophozoites, while calcofluor white staining demonstrated the leakage of cell wall in treated cysts, leading to cell death. Interestingly, at the concentration ranges in which C1 showed the anti-Acanthamoeba effects (IC₅₀ values ranging from 0.035-0.056 mg/mL), they were not toxic to Vero cells. C1 displayed the highest inhibitory effect on A. triangularis encystation at 1/16×MIC value (0.004 mg/mL). While C1 demonstrated the excystation activity at 1/128×MIC value with a high rate of 89.47%. Furthermore, C1 exhibited the removal capacity of adhesive Acanthamoeba from the surface of CL comparable with commercial multipurpose solutions (MPSs). Based on the results obtained, C1 may be a promising lead agent to develop a therapeutic for the treatment of Acanthamoeba infections and disinfectant solutions for CL.

Prevalence of free-living amoebae in swimming pools and recreational waters, a systematic review and meta-analysis

Free-living amoebae (FLA) are cosmopolitan microorganisms known to be pathogenic to humans who often have a history of contact with contaminated water. Swimming pools and recreational waters are among the environments where the greatest human exposure to FLA occurs. This study aimed to determine the prevalence of FLA in swimming pools and recreational waters, through a systematic review and meta-analysis that included studies published between 1977 and 2022. A total of 106 studies were included and an overall prevalence of FLA in swimming pools and recreational waters of 44.34% (95% CI = 38.57–50.18) was found. Considering the studies published up to 2010 (1977–2010), between 2010 and 2015, and those published after 2010 (> 2010–2022), the prevalence was 53.09% (95% CI = 43.33–62.73) and 37.07% (95% CI = 28.87–45.66) and 45.40% (95% CI = 35.48–55.51), respectively. The highest prevalence was found in the American continent (63.99%), in Mexico (98.35%), and in indoor hot swimming pools (52.27%). The prevalence varied with the variation of FLA detection methods, morphology (57.21%), PCR (25.78%), and simultaneously morphology and PCR (43.16%). The global prevalence by genera was Vahlkampfia spp. (54.20%), Acanthamoeba spp. (33.47%), Naegleria spp. (30.95%), Hartmannella spp./Vermamoeba spp. (20.73%), Stenamoeba spp. (12.05%), and Vannella spp. (10.75%). There is considerable risk of FLA infection in swimming pools and recreational waters. Recreational water safety needs to be routinely monitored and, in case of risk, locations need to be identified with warning signs and users need to be educated. Swimming pools and artificial recreational water should be properly disinfected. Photolysis of NaOCl or NaCl in water by UV-C radiation is a promising alternative to disinfect swimming pools and artificial recreational waters.