Infection in a rat model reactivates attenuated virulence after long-term axenic culture of Acanthamoeba spp

Experimental Granulomatous Amebic Encephalitis Caused by Acanthamoeba castellanii

Acanthamoeba genus can affect humans with diseases such as granulomatous amebic encephalitis (GAE), a highly lethal neuroinfection. Several aspects of the disease still need to be elucidated. Animal models of GAE have advanced our knowledge of the disease. This work tested Wistar rats (Rattus norvegicus albinus) as an animal model of GAE. For this, 32 animals were infected with 1 × 106A. castellanii trophozoites of the T4 genotype. Ameba recovery tests were carried out using agar plates, vascular extravasation assays, behavioral tests, and histopathological technique with H/E staining. Data were subjected to linear regression analysis, one-way ANOVA, and Tukey's test, performed in the GraphPad Prism® 8.0 program, with a significance level of p < 0.05. The results revealed the efficiency of the model. Amebae were recovered from the liver, lungs, and brain of infected animals, and there were significant encephalic vascular extravasations and behavioral changes in these animals, but not in the control animals. However, not all infected animals showed positive histopathology for the analyzed organs. Nervous tissues were the least affected, demonstrating the role of the BBB in the defense of the CNS. Supported by the demonstrated evidence, we confirm the difficulties and the feasibilities of using rats as an animal model of GAE.

Experimental keratitis induced in rat by Acanthamoeba from distinct morphological groups/genotypes: a histological and immunohistochemical evaluation

Species of the genus Acanthamoeba are free-living protozoans that occasionally act as parasites, causing a severe, progressive corneal infection termed Acanthamoeba keratitis (AK). The variable pathogenic potential among Acanthamoeba lineages has been shown by in vitro assays, but little is known about the behavior of different strains in animal models of AK. This work aimed to evaluate the infectivity of Acanthamoeba from distinct morphological groups and genotypes in a rat model of AK and apply an immunohistochemical technique for histological characterization of the lesions. Only a strain classified as group I/genotype T17, isolated from a soil source, caused ulcerated corneal lesions in two Wistar rats (n = 9) subjected to intrastromal inoculation. Two strains derived from AK human cases (group II/genotype T4 and group III/genotype T5) did not induce corneal lesions in the rats. A previous association of group II/genotype T4 trophozoites with lethally irradiated Escherichia coli did not influence the infectivity. A hyperimmune serum produced in Wistar rats was validated by an immunocytochemical technique using the three distinct strains and then applied for immunohistochemistry. The abundance of antigenic residues was observed in both corneas with keratitis, suggesting that the infectious process tended to resolve. Despite the low infection rate of the AK Wistar rat model, we produced an immunochemical tool with a potential diagnostic application. We also showed for the first time the ability of Acanthamoeba from T17 genotype to cause AK in experimental conditions.

A history of over 40 years of potentially pathogenic free-living amoeba studies in Brazil - a systematic review

Free-living amoeba (FLA) group includes the potentially pathogenic genera Acanthamoeba, Naegleria, Balamuthia, Sappinia, and Vermamoeba, causative agents of human infections (encephalitis, keratitis, and disseminated diseases). In Brazil, the first report on pathogenic FLA was published in the 70s and showed meningoencephalitis caused by Naegleria spp. FLA studies are emerging, but no literature review is available to investigate this trend in Brazil critically. Thus, the present work aims to integrate and discuss these data. Scopus, PubMed, and Web of Science were searched, retrieving studies from 1974 to 2020. The screening process resulted in 178 papers, which were clustered into core and auxiliary classes and sorted into five categories: wet-bench studies, dry-bench studies, clinical reports, environmental identifications, and literature reviews. The papers dating from the last ten years account for 75% (134/178) of the total publications, indicating the FLA topic has gained Brazilian interest. Moreover, 81% (144/178) address Acanthamoeba-related matter, revealing this genus as the most prevalent in all categories. Brazil’s Southeast, South, and Midwest geographic regions accounted for 96% (171/178) of the publications studied in the present work. To the best of our knowledge, this review is the pioneer in summarising the FLA research history in Brazil.

Long-Term In Vitro Passaging Had a Negligible Effect on Extracellular Vesicles Released by Leishmania amazonensis and Induced Protective Immune Response in BALB/c Mice

Depending on Leishmania species and the presence/absence of virulence factors, Leishmania extracellular vesicles (EVs) can differently stimulate host immune cells. This work is aimed at characterizing and evaluating the protective role of EVs released by Leishmania amazonensis promastigotes under different maintenance conditions. Initially, using a control strain, we standardized 26°C as the best release temperature to obtain EVs with a potential protective role in the experimental leishmaniasis model. Then, long-term (LT-P) promastigotes of L. amazonensis were obtained after long-term in vitro culture (100 in vitro passages). In vivo-derived (IVD-P) promastigotes of L. amazonensis were selected after 3 consecutive experimental infections in BALB/c mice. Those strains developed similar lesion sizes except for IVD-P at 8 weeks post infection. No differences in EV production were detected in both strains. However, the presence of LPG between LT-P and IVD-P EVs was different. Groups of mice immunized with EVs emulsified in the adjuvant and challenged with IVD-P parasites showed decreased lesion size and parasitic load compared with the nonimmunized groups. The immunization regimen with two doses showed high IFN-γ and IgG2a titers in challenged mice with either IVD-P or LT-P EVs. IL-4 and IL-10 were detected in immunized mice, suggesting a mixed Th1/Th2 profile. EVs released by either IVD-P or LT-P induced a partial protective effect in an immunization model. Thus, our results uncover a potential protective role of EVs from L. amazonensis for cutaneous leishmaniasis. Moreover, long-term maintenance under in vitro conditions did not seem to affect EV release and their immunization properties in mice.

Super aggregated amphotericin B with a thermoreversible in situ gelling ophthalmic system for amoebic keratitis treatment

Acanthamoeba spp. are the causative agents of a sight-threatening infection of the cornea known as Acanthamoeba keratitis (AK). Amphotericin B - deoxycholate (AB) is used in the treatment of infectious keratitis, however, its topical administration has side effects as blepharitis, iritis, and painful instillation. In this context, the preheating of AB can decrease its toxicity by the formation of super aggregates (hAB). hAB associated with a thermoreversible in situ gelling ophthalmic system is a promising option due to the latter biocompatibility, low toxicity, and high residence time on the ocular surface. Our objective was to develop a topical ocular formulation of hAB for the treatment of AK. After heating at 70°C for 20 min, hAB was incorporated into a thermoreversible gelling system. The amebicidal activity of AB and hAB was evaluated against trophozoites and cysts of A. castellanii (ATCC 50492) and a regional clinical isolate (IC01). The results showed that the preheating of AB did not change the pharmacological action of the drug, with the amebicidal effect of AB and hAB under trophozoites and cysts of Acanthamoeba spp. The thermoreversible system remained stable, allowing the increase of drug retention time. For assessment of cytotoxicity, HUVEC (ATCC® CRL-1730) cells were challenged with AB and hAB for 48h. Cell viability was assessed, and hAB did not show cytotoxicity for HUVEC cells. As far as we know this was the first study that showed the preheated AB associated with a thermoreversible in situ gelling ophthalmic system as a promising system for topical ocular topical administration of hAB for AK therapy.

Comparative proteomic profiling of newly acquired, virulent and attenuated Neoparamoeba perurans proteins associated with amoebic gill disease

The causative agent of amoebic gill disease, Neoparamoeba perurans is reported to lose virulence during prolonged in vitro maintenance. In this study, the impact of prolonged culture on N. perurans virulence and its proteome was investigated. Two isolates, attenuated and virulent, had their virulence assessed in an experimental trial using Atlantic salmon smolts and their bacterial community composition was evaluated by 16S rRNA Illumina MiSeq sequencing. Soluble proteins were isolated from three isolates: a newly acquired, virulent and attenuated N. perurans culture. Proteins were analysed using two-dimensional electrophoresis coupled with liquid chromatography tandem mass spectrometry (LC-MS/MS). The challenge trial using naïve smolts confirmed a loss in virulence in the attenuated N. perurans culture. A greater diversity of bacterial communities was found in the microbiome of the virulent isolate in contrast to a reduction in microbial community richness in the attenuated microbiome. A collated proteome database of N. perurans, Amoebozoa and four bacterial genera resulted in 24 proteins differentially expressed between the three cultures. The present LC-MS/MS results indicate protein synthesis, oxidative stress and immunomodulation are upregulated in a newly acquired N. perurans culture and future studies may exploit these protein identifications for therapeutic purposes in infected farmed fish.

Distinct immunomodulatory properties of extracellular vesicles released by different strains of Acanthamoeba

Free living amoeba of the genus Acanthamoeba are opportunist protozoan involved in corneal, systemic, and encephalic infections in humans. Most of the mechanisms underlying intraspecies variations and pathogenicity are still unknown. Recently, the release of extracellular vesicles (EVs) by Acanthamoeba was reported. However, comparative characterization of EVs from distinct strains is not available. The aim of this study was to evaluate EVs produced by Acanthamoeba from different genotypes, comparing their proteases profile and immunomodulatory properties. EVs from four environmental or clinical strains (genotypes T1, T2, T4, and T11) were obtained by ultracentrifugation, quantitated by nanoparticle tracking analysis and analyzed by scanning and transmission electron microscopy. Proteases profile was determined by zymography and functional properties of EVs (measure of nitrite and cytokine production) were determined after peritoneal macrophage stimulation. Despite their genotype, all strains released EVs and no differences in size and/or concentration were detected. EVs exhibited a predominant activity of serine proteases (pH 7.4 and 3.5), with higher intensity in T4 and T1 strains. EVs from the environmental, nonpathogenic T11 strain exhibited a more proinflammatory profile, inducing higher levels of Nitrite, tumor necrosis factor alpha and interleukin-6 via TLR4/TLR2 than those strains with pathogenic traits (T4, T1, and T2). Preincubation with EVs treated with protease inhibitors or heating drastically decreased nitrite concentration production in macrophages. Those data suggest that immunomodulatory effects of EVs may reflect their pathogenic potential depending on the Acanthamoeba strains and are dependent on protease integrity.

Differential expression of Acanthamoeba castellanii proteins during amoebic keratitis in rats

Amoebic keratitis (AK) is a sight-threatening infection characterized by a severe inflammation of the cornea, caused by the free-living protozoan of the genus Acanthamoeba. Identification of amoebic proteins involved in AK pathogenesis may help to elucidate molecular mechanisms of infection and contribute to indicate diagnostic and therapeutic targets. In this study, we evaluated changes in the expression profile of Acanthamoeba proteins triggered by the invasive process, using an approach involving two-dimensional polyacrylamide gel electrophoresis (2DE PAGE), followed by mass spectrometry identification (ESI-IT-TOF LC-MSn). AK was induced by intrastromal inoculation in Wistar rats, using trophozoites from a T4 genotype, human case-derived A. castellanii strain under prolonged axenic culture. Cultures re-isolated from the lesions after two successive passages in the animals were used as biological triplicate for proteomic experiments. Analysis of the protein profile comparing long-term and re-isolated cultures indicated 62 significant spots, from which 27 proteins could be identified in the Acanthamoeba proteome database. Five of them (Serpin, Carboxypeptidase A1, Hypothetical protein, Calponin domain-containing protein, aldo/keto reductase) were exclusively found in the re-isolated trophozoites. Our analysis also revealed that a concerted modulation of several biochemical pathways is triggered when A. castellanii switches from a free-living style to a parasitic mode, including energetic metabolism, proteolytic activity, control of gene expression, protein degradation and methylation of DNA, which may be also involved in gain of virulence in an animal model of AK.

Isolation and Identification of Pathogenic Acanthamoeba Species from Air Conditioning Systems, Egypt

Acanthamoeba are free-living amoebae that cause granulomatous amoebic encephalitis and keratitis. In this study, we aimed to isolate and identify Acanthamoeba from air conditioning systems using in vitro cell culture and polymerase chain reaction assays. We also estimated the pathogenicity of the isolates by measuring their thermotolerance and studying mice models inoculated with these isolates. Of the 80 dust samples acquired, 41 (51.25%) were found to be positive for Acanthamoeba spp. using in vitro cell culture and the results were validated using PCR. Out of these 41 samples, 27 (65.9%) were thermotolerant and 16 (39%) samples could infect mice and cause histopathological effects. Highly pathogenic Acanthamoeba isolates were characterized by their thermotolerance and the ability to disseminate in all organs after infection, causing early death of infected animals. Our study thus validated the presence of pathogenic isolates of Acanthamoeba in air conditioners that may be potentially infectious to humans.

Generation of Paramoeba perurans clonal cultures using flow cytometry and confirmation of virulence

Amoebic gill disease (AGD) in farmed Atlantic salmon is caused by the amoeba Paramoeba perurans. The recent establishment of in vitro culture techniques for P. perurans has provided a valuable tool for studying the parasite in detail. In this study, flow cytometry was used to generate clonal cultures from single-sorted amoeba, and these were used to successfully establish AGD in experimental Atlantic salmon. The clonal cultures displayed differences in virulence, based on gill scores. The P. perurans load on gills, determined by qPCR analysis, showed a positive relationship with gill score, and with clonal virulence, indicating that the ability of amoebae to proliferate and/or remain attached on gills may play a role in virulence. Gill scores based on gross signs and histopathological analysis were in agreement. No association between level of gill score and specific gill arch was observed. It was found that for fish with lower gill scores based on histopathological examination, gross examination and qPCR analysis of gills from the same fish were less successful in detecting lesions and amoebae, respectively.

Acanthamoeba and Fusarium interactions: A possible problem in keratitis

The incidence of Acanthamoeba and Fusarium species has increased in contact lens-related infectious keratitis. They share several environments and cases of co-infection have been reported. The interaction between the amoebae and other microorganisms may result in significant changes for both, like increased virulence in mammalian hosts. In this study, we evaluated the interaction of three Acanthamoeba castellanii strains with Fusarium conidia and the possible implications on keratitis. F. conidia were internalized by A. castellanii strains and were able to germinate inside the amoebae. The co-culture with the live amoebae, as well as the amoebal culture supernatant and lysate, increased the fungal growth significantly. Moreover, live F. solani and its culture supernatant enhanced the survival of amoebae, but in a different way in each amoebal strain. The encystment of the A. castellanii strain re-isolated from rat lung was increased by the fungus. These results show that A. castellanii and F. solani interaction may have an important influence on survival of both, and specially indicate a possible effect on virulence characteristics of these microorganisms. These data suggest that the A. castellanii-F. solani interaction may cause severe impacts on keratitis.

Neoparamoeba perurans loses virulence during clonal culture

Amoebic Gill Disease affects farmed salmonids and is caused by Neoparamoeba perurans. Clonal cultures of this amoeba have been used for challenge experiments, however the effect of long-term culture on virulence has not been investigated. Here we show, using in vitro and in vivo methods, that a clone of N. perurans which was virulent 70 days after clonal culture lost virulence after 3 years in clonal culture. We propose that this is related either to the lack of attachment to the gills or the absence of an extracellular product, as shown by the lack of cytopathic effect on Chinook salmon embryo cells. The avirulent clonal culture of N. perurans allowed us to propose two potential virulence mechanisms/factors involved in Amoebic Gill Disease and is an invaluable tool for host-pathogen studies of Amoebic Gill Disease.

Proteomic profiling of the infective trophozoite stage of Acanthamoeba polyphaga

Acanthamoeba polyphaga is a free-living protozoan pathogen, whose infective trophozoite form is capable of causing a blinding keratitis and fatal granulomatous encephalitis in humans. The damage caused by A. polyphaga trophozoites in human corneal or brain infections is the result of several different pathogenic mechanisms that have not yet been elucidated at the molecular level. We performed a comprehensive analysis of the proteins expressed by A. polyphaga trophozoites, based on complementary 2-DE MS/MS and gel-free LC-MS/MS approaches. Overall, 202 non-redundant proteins were identified. An A. polyphaga proteomic map in the pH range 3-10 was produced, with protein identification for 184 of 370 resolved spots, corresponding to 142 proteins. Additionally, 94 proteins were identified by gel-free LC-MS/MS. Functional classification revealed several proteins with potential importance for pathogen survival and infection of mammalian hosts, including surface proteins and proteins related to defense mechanisms. Our study provided the first comprehensive proteomic survey of the trophozoite infective stage of an Acanthamoeba species, and established foundations for prospective, comparative and functional studies of proteins involved in mechanisms of survival, development, and pathogenicity in A. polyphaga and other pathogenic amoebae.