Biochemical characterization and functional studies of Acanthamoeba mannose-binding protein

Identification of new targets for the diagnosis of cysts (four) and trophozoites (one) of the eye pathogen Acanthamoeba

Acanthamoebae , which are free-living amoebae, cause corneal inflammation (keratitis) and blindness, if not diagnosed and effectively treated. While trophozoites adhere to and damage the cornea, Acanthamoeba cysts, the walls of which contain cellulose and have two layers connected by conical ostioles, are the diagnostic form by microscopy of the eye or of corneal scrapings. We recently used structural and experimental methods to characterize cellulose-binding domains of Luke and Leo lectins, which are abundant in the inner layer and ostioles. However, no antibodies have been made to these lectins or to a Jonah lectin and a laccase, which are abundant in the outer layer. Here we used confocal microscopy to show that rabbit antibodies to recombinant Luke, Leo, Jonah, and laccase generally support localizations of GFP-tagged proteins in walls of transfected Acanthamoebae. Rabbit antibodies to all four wall proteins efficiently detected calcofluor white-labeled cysts of 10 of 11 Acanthamoeba isolates obtained from the ATCC, including five T4 genotypes that cause most cases of keratitis. Laccase shed into the medium during encystation was detected by an enzyme-linked immunoassay. We also used structural and experimental methods to characterize the mannose-binding domain of an Acanthamoeba mannose-binding protein and showed that rabbit antibodies to the mannose-binding domain efficiently detected trophozoites of all 11 Acanthamoeba isolates. We conclude that four wall proteins are all excellent targets for diagnosing Acanthamoeba cysts in the eye or corneal scrapings, while the mannose-binding domain is an excellent target for identifying trophozoites in cultures of corneal scrapings.

Importance

Free-living amoeba in the soil or water cause Acanthamoeba keratitis, which is diagnosed by identification of cysts by microscopy of the eye or of corneal scrapings, using calcofluor-white that unfortunately cross-reacts with fungi and plants. Alternatively, Acanthamoeba infections are diagnosed by identification of trophozoites in cultures of scrapings. Here we showed that rabbit antibodies to four abundant cyst wall proteins (Jonah, Luke, Leo, and laccase) each efficiently detect calcofluor-white-labeled cysts of 10 of 11 Acanthamoeba isolates obtained from the ATCC. Further, laccase released into the medium by encysting Acanthamoebae was detected by an enzyme-linked immunoassay. We also showed that rabbit antibodies to the mannose-binding domain of the Acanthamoeba mannose-binding protein, which mediates adherence of trophozoites to keratinocytes, efficiently identifies trophozoites of all 11 ATCC isolates. In summary, four wall proteins and the ManBD appear to be excellent targets for diagnosis of Acanthamoeba cysts and trophozoites, respectively.

Unravelling mechanisms of bacterial recognition by Acanthamoeba: insights into microbial ecology and immune responses

Acanthamoeba, are ubiquitous eukaryotic microorganisms, that play a pivotal role in recognizing and engulfing various microbes during predation, offering insights into microbial dynamics and immune responses. An intriguing observation lies in the apparent preference of Acanthamoeba for Gram-negative over Gram-positive bacteria, suggesting potential differences in the recognition and response mechanisms to bacterial prey. Here, we comprehensively review pattern recognition receptors (PRRs) and microbe associated molecular patterns (MAMPs) that influence Acanthamoeba interactions with bacteria. We analyze the molecular mechanisms underlying these interactions, and the key finding of this review is that Acanthamoeba exhibits an affinity for bacterial cell surface appendages that are decorated with carbohydrates. Notably, this parallels warm-blooded immune cells, underscoring a conserved evolutionary strategy in microbial recognition. This review aims to serve as a foundation for exploring PRRs and MAMPs. These insights enhance our understanding of ecological and evolutionary dynamics in microbial interactions and shed light on fundamental principles governing immune responses. Leveraging Acanthamoeba as a model organism, provides a bridge between ecological interactions and immunology, offering valuable perspectives for future research.

The gene expression and proteomic profiling of Acanthamoeba isolates

INTRODUCTION

The free-living protozoan Acanthamoeba can cause severe keratitis known as Acanthamoeba Keratitis (AK) and granulomatous amoebic encephalitis (GAE). The pathogenesis of Acanthamoeba includes intricate interactions between the organism and the host's immune system. The downstream analysis of a well-annotated genome assembly along with proteomic analysis can unravel several biological processes and aid in the identification of potential genes involved in pathogenicity.

METHODS

Based on the next-generation sequencing data analysis, genes including lysophospholipase, phospholipase, S8/S53 peptidase, carboxylesterase, and mannose-binding protein were selected as probable pathogenic targets that were validated by conventional PCR in a total of 30 Acanthamoeba isolates. This was followed by real-time PCR for the evaluation of relative gene expression in the keratitis and amoebic encephalitis animal model induced using keratitis (CHA5), encephalitis (CHA24) and non-pathogenic environmental isolate (CHA36). In addition, liquid chromatography-mass spectrometry (LC-MS/MS) was performed for keratitis, encephalitis, and non-pathogenic environmental isolate before and after treatment with polyhexamethylene biguanide (PHMB).

RESULTS

The conventional PCR demonstrated the successful amplification of lysophospholipase, phospholipase, S8/S53 peptidase, carboxylesterase, and mannose-binding protein genes in clinical and environmental isolates. The expression analysis revealed phospholipase, lysophospholipase, and mannose-binding genes to be significantly upregulated in the keratitis isolate (CHA 5) during AK in the animal model. In the case of the amoebic encephalitis model, phospholipase, lysophospholipase, S8/S53 peptidase, and carboxylesterase were significantly upregulated in the encephalitis isolate compared to the keratitis isolate. The proteomic data revealed differential protein expression in pathogenic versus non-pathogenic isolates in the pre and post-treatment with PHMB.

CONCLUSION

The gene expression data suggests that lysophospholipase, phospholipase, S8/S53 peptidase, carboxylesterase, and mannose-binding protein (MBP) could play a role in the contact-dependent and independent mechanisms of Acanthamoeba pathogenesis. In addition, the proteomic profiling of the 3 isolates revealed differential protein expression crucial for parasite growth, survival, and virulence. Our results provide baseline data for selecting possible pathogenic targets that could be utilized for designing knockout experiments in the future.

Extracellular Vesicles Secreted by Acanthamoeba culbertsoni Have COX and Proteolytic Activity and Induce Hemolysis

Several species of Acanthamoeba genus are potential pathogens and etiological agents of several diseases. The pathogenic mechanisms carried out by these amoebae in different target tissues have been documented, evidencing the relevant role of contact-dependent mechanisms. With the purpose of describing the pathogenic processes carried out by these protozoans more precisely, we considered it important to determine the emission of extracellular vesicles (EVs) as part of the contact-independent pathogenicity mechanisms of A. culbertsoni, a highly pathogenic strain. Through transmission electronic microscopy (TEM) and nanoparticle tracking analysis (NTA), EVs were characterized. EVs showed lipid membrane and a size between 60 and 855 nm. The secretion of large vesicles was corroborated by confocal and TEM microscopy. The SDS-PAGE of EVs showed proteins of 45 to 200 kDa. Antigenic recognition was determined by Western Blot, and the internalization of EVs by trophozoites was observed through Dil-labeled EVs. In addition, some EVs biological characteristics were determined, such as proteolytic, hemolytic and COX activity. Furthermore, we highlighted the presence of leishmanolysin in trophozites and EVs. These results suggest that EVs are part of a contact-independent mechanism, which, together with contact-dependent ones, allow for a better understanding of the pathogenicity carried out by Acanthamoeba culbertsoni.

Taurine, a Component of the Tear Film, Exacerbates the Pathogenic Mechanisms of Acanthamoeba castellanii in the Ex Vivo Amoebic Keratitis Model

Acanthamoeba spp. is the etiological agent of amoebic keratitis. In this study, the effect of taurine in physiological concentrations in tears (195 μM) on trophozoites of Acanthamoeba castellanii through the ex vivo amoebic keratitis model was evaluated. Trophozoites were coincubated with the Syrian golden hamster cornea (Mesocricetus auratus) for 3 and 6 h. Group 1: Control (-). Corneas coincubated with amoebic culture medium and taurine. Group 2: Control (+). Corneas coincubated with trophozoites without taurine. Group 3: Corneas coincubated with taurine 15 min before adding trophozoites. Group 4: Trophozoites coincubated 15 min with taurine before placing them on the cornea. Group 5: Corneas coincubated for 15 min with trophozoites; subsequently, taurine was added. Results are similar for both times, as evaluated by scanning electron microscopy. As expected, in the corneas of Group 1, no alterations were observed in the corneal epithelium. In the corneas of Group 2, few adhered trophozoites were observed on the corneal surface initiating migrations through cell junctions as previously described; however, in corneas of Groups 3, 4 and 5, abundant trophozoites were observed, penetrating through different corneal cell areas, emitting food cups and destabilizing corneal surface in areas far from cell junctions. Significant differences were confirmed in trophozoites adherence coincubated with taurine (p < 0.05). Taurine does not prevent the adhesion and invasion of the amoebae, nor does it favor its detachment once these have adhered to the cornea, suggesting that taurine in the physiological concentrations found in tears stimulates pathogenic mechanisms of A. castellanii.

Susceptibility of the Intact and Traumatized Feline Cornea to In Vitro Binding and Invasion by Acanthamoeba castellanii

PURPOSE

Acanthamoeba castellanii ( A. castellanii ) displays host specificity at the level of the ocular surface. This study determined the susceptibility of the intact and traumatized feline cornea to A. castellanii binding and invasion relative to other host species with established susceptibility and resistance to Acanthamoeba binding.

METHODS

Full-thickness buttons of fresh feline, porcine, and canine corneas were prepared. The corneal epithelium was confirmed intact by fluorescein staining or lightly scarified with a 25-G needle to simulate corneal trauma. Acanthamoeba castellanii was axenically cultivated. Corneal buttons were incubated with the parasite suspension or parasite-free medium for 18 hours at 35°C. Corneal buttons were rinsed, fixed, and processed for histopathology and immunohistochemistry using immunoperoxidase and immunofluorescence methods of amoeba detection.

RESULTS

Numerous amoebae were bound to feline and porcine corneas incubated with parasites. In both intact and traumatized corneas, amoebae were detected at all levels in the corneal epithelium and within the anterior stroma. In traumatized corneal sections, amoebae were frequently present in regions of epithelial damage. Corneal architecture was well-preserved in sections incubated with parasite-free medium; however, epithelial cell sloughing, separation of epithelial layers, and epithelial detachment from the stroma were observed in corneas incubated with amoebae. Intact and traumatized canine corneas were relatively free of adherent amoebae, and corneal architecture was indistinguishable between sections incubated with the parasite suspension and parasite-free medium.

CONCLUSIONS

The feline cornea is highly susceptible to in vitro binding and invasion by A. castellanii . Acanthamoeba binding to the feline cornea does not require a previous epithelial defect.

Effectiveness of Polyclonal Antibody Immunoconjugate Treatment with Propamidine Isethionate for Amoebic Keratitis in Golden Hamsters

Acanthamoeba griffini is known to cause amoebic keratitis (AK); its main causes are inadequate hygiene when contact lenses are handled and/or its prolonged use at night, as well as the use of contact lenses during underwater activities. The most used treatment for AK is the combination of propamidine isethionate combined with polyhexamethylene biguanide, which disrupts the cytoplasmic membrane, and damages cellular components and respiratory enzymes. We proposed an immunoconjugate treatment obtained from Acanthamoeba immunized rabbit serum combined with propamidine isethionate; the corneas of hamsters inoculated with A. griffini (MYP2004) were treated with the combined, at 1, 2, and 3 weeks. Propamidine isethionate is frequently used for AK treatment, in vivo study we are found IL-1β and IL-10 expression and caspase 3 activity is significantly increased with respect to the group that was inoculated with the amoeba without receiving any treatment, suggesting that it may be an effect of the toxicity of this drug on the corneal tissue. Application of the immunoconjugate showed enhanced amoebicidal and anti-inflammatory activities, with comparison to propamidine isethionate only. The aim of this study is to evaluate the effect of the immunoconjugate of propamidine isethionate and polyclonal antibodies as a treatment of AK in golden hamsters (Mesocricetus auratus).

Acanthamoeba Mannose and Laminin Binding Proteins Variation across Species and Genotypes

Acanthamoeba is a ubiquitous free-living amoeba capable of being an opportunistic pathogen in humans and animals. A critical step in infection is the adhesion of the amoeba to host cells and tissues, and two major parasite adhesins, mannose-binding protein (MBP) and laminin-binding protein (LBP), are known to recognize the cell surface glycoproteins and those of the extracellular matrix, respectively. In this study, the available genomes of Acanthamoeba were analysed to recover the sequences of MBP and LBP using previously published genetic data. Genes for both proteins were successfully obtained from strains belonging to various genotypes (T4A, T4D, T4G, T4F, T2, T5, T10, T22, T7 and T18), resulting in a single gene for LBP but identifying two types of MBP, MBP1 and MBP2. Phylogenetic analysis based on deduced amino acid sequences shows that both MBP and LBP have a branching pattern that is consistent with that based on 18S rDNA, indicating that changes in both proteins occurred during diversification of Acanthamoeba lines. Notably, all MBPs possess a conserved motif, shared with some bacterial C-type lectins, which could be the recognition site for mannose binding.

Chromosome-scale assemblies of Acanthamoeba castellanii genomes provide insights into Legionella pneumophila infection-related chromatin reorganization

The unicellular amoeba Acanthamoeba castellanii is ubiquitous in aquatic environments, where it preys on bacteria. The organism also hosts bacterial endosymbionts, some of which are parasitic, including human pathogens such as Chlamydia and Legionella spp. Here we report complete, high-quality genome sequences for two extensively studied A. castellanii strains, Neff and C3. Combining long- and short-read data with Hi-C, we generated near chromosome-level assemblies for both strains with 90% of the genome contained in 29 scaffolds for the Neff strain and 31 for the C3 strain. Comparative genomics revealed strain-specific functional enrichment, most notably genes related to signal transduction in the C3 strain and to viral replication in Neff. Furthermore, we characterized the spatial organization of the A. castellanii genome and showed that it is reorganized during infection by Legionella pneumophila Infection-dependent chromatin loops were found to be enriched in genes for signal transduction and phosphorylation processes. In genomic regions where chromatin organization changed during Legionella infection, we found functional enrichment for genes associated with metabolism, organelle assembly, and cytoskeleton organization. Given Legionella infection is known to alter its host's cell cycle, to exploit the host's organelles, and to modulate the host's metabolism in its favor, these changes in chromatin organization may partly be related to mechanisms of host control during Legionella infection.

Potential anti-Acanthamoeba and anti-adhesion activities of Annona muricata and Combretum trifoliatum extracts and their synergistic effects in combination with chlorhexidine against Acanthamoeba triangularis trophozoites and cysts

Plants with medicinal properties have been used in the treatment of several infectious diseases, including Acanthamoeba infections. The medicinal properties of Cambodian plant extracts; Annona muricata and Combretum trifoliatum were investigated against Acanthamoeba triangularis. A total of 39 plant extracts were evaluated and, as a result, 22 extracts showed positive anti-Acanthamoeba activity. Of the 22 extracts, 9 and 4 extracts showed anti-Acanthamoeba activity against trophozoites and cysts of A. triangularis, respectively. The minimum inhibitory concentration of A. muricata and C. trifoliatum extracts against trophozoites and cysts was 500 and 1,000 μg/mL, respectively. The combination of A. muricata at 1/4×MIC with chlorhexidine at 1/8×MIC demonstrated a synergistic effect against trophozoites, but partial synergy against cysts. A 40% reduction in trophozoites and 60% of cysts adhered to the plastic surface treated with both extracts at 1/2×MIC were noted comparing to the control (P < 0.05). Furthermore, a reduction of 80% and 90% of trophozoites adhered to the surface was observed after pre-treatment with A. muricata and C. trifoliatum extracts, respectively. A 90% of cysts adhered to the surface was decreased with pre-treatment of A. muricata at 1/2×MIC (P < 0.05). A 75% of trophozoites and cysts from Acanthamoeba adhered to the surface were removed after treatment with both extracts at 4×MIC (P < 0.05). In the model of contact lens, 1 log cells/mL of trophozoites and cysts was significantly decreased post-treatment with both extracts compared to the control. Trophozoites showed strong loss of acanthopodia and thorn-like projection pseudopodia, while cysts demonstrated retraction and folded appearance treated with both extracts when observed by SEM, which suggests the potential benefits of the medicinal plants A. muricata and C. trifoliatum as an option treatment against Acanthamoeba infections.

Diagnosis of Acanthamoeba keratitis in Mashhad, Northeastern Iran: A Gene-Based PCR Assay

Background:

The genus Acanthamoeba is a free-living opportunistic protozoan parasite, which widely distributed in soil and fresh water. Acanthamoeba keratitis, which causes a sight-threating infection of the cornea, is going to rise in Iran and worldwide. The aim of this study was to compare direct microscopy, culture and PCR for detection of Acanthamoeba spp. in clinical samples and to determine the genotypes of Acanthamoeba spp. by sequencing 18SrRNA gene.

Methods:

Among patients clinically suspected to AK referred to a tertiary ophthalmology center at Mashhad, northeastern Iran. During 2017-18, twenty corneal scrapes specimens obtained. The samples were divided into three parts, subjected to direct microscopic examination, culture onto non-nutrient agar and PCR technique. Sensitivity, specificity, accuracy and likelihood ratio were evaluated.

Results:

Among 20 persons clinically suspected to amoebic keratitis, 13(69.2%) patients definitely diagnosed as Acanthamoeba keratitis. Wearing contact lens, eye trauma due to foreign particle and swimming in fresh water were the main predisposing factors. Most of patients suffered from pain and photophobia. Corneal ring infiltration and epithelial defect were common clinical sings. Direct examination had the lowest sensitivity and sensitivity of both Nelson-PCR and JDP-PCR methods were equal and highest. In addition, the results of sequencing identified that all strains belonged to T4 genotype.

Conclusion:

Amoebic keratitis is a sporadic parasitic keratitis, which is mainly seen in contact lens user in Mashhad. PCR based on 18S ribosomal DNA with JDP primers is a reliable and highly sensitive method for diagnosis of Acanthamoeba keratitis in clinically suspected cases.

Free-living amoebae and other neglected protistan pathogens: Health emergency signals?

Protistan parasites have an undisputed global health impact. However, outside of a few key exceptions, e.g. the agent of malaria, most of these infectious agents are neglected as important health threats. The Symposium entitled "Free-living amoebae and neglected pathogenic protozoa: health emergency signals?" held at the European Congress of Protistology in Rome, July 2019, brought together researchers addressing scientific and clinical questions about some of these fascinating organisms. Topics presented included the molecular basis of pathogenicity in Acanthamoeba; genomics of Naegleria fowleri; and epidemiology of poorly diagnosed enteric protistan species, including Giardia, Cryptosporidium, Blastocystis, Dientamoeba. The Symposium aim was to excite the audience about the opportunities and challenges of research in these underexplored organisms and to underline the public health implications of currently under-appreciated protistan infections. The major take home message is that any knowledge that we gain about these organisms will allow us to better address them, in terms of monitoring and treatment, as sources of future health emergencies.

Curcuma longa rhizome extract and Curcumin reduce the adhesion of Acanthamoeba triangularis trophozoites and cysts in polystyrene plastic surface and contact lens

Curcuma longa and Curcumin have been documented to have a wide spectrum of pharmacological effects, including anti-Acanthamoeba activity. Hence, this study sought to explore the anti-adhesion activity of C. longa extract and Curcumin against Acanthamoeba triangularis trophozoites and cysts in plastic and contact lenses. Our results showed that C. longa extract and Curcumin significantly inhibited the adhesion of A. triangularis trophozoites and cysts to the plastic surface, as investigated by the crystal violet assay (P < 0.05). Also, an 80-90% decrease in adhesion of trophozoites and cysts to the plastic surface was detected following the treatment with C. longa extract and Curcumin at 1/2 × MIC, compared to the control. In the contact lens model, approximately 1 log cells/mL of the trophozoites and cysts was reduced when the cells were treated with Curcumin, when compared to the control. Pre-treatment of the plastic surface with Curcumin at 1/2-MIC reduced 60% and 90% of the adhesion of trophozoites and cysts, respectively. The reduction in 1 Log cells/mL of the adhesion of A. triangularis trophozoites was observed when lenses were pre-treated with both the extract and Curcumin. Base on the results obtained from this study, A. triangularis trophozoites treated with C. longa extract and Curcumin have lost strong acanthopodia, thorn-like projection pseudopodia observed by scanning electron microscope. This study also revealed the therapeutic potentials of C. longa extract and Curcumin, as such, have promising anti-adhesive potential that can be used in the management/prevention of A. triangularis adhesion to contact lenses.

Interactions Between Acanthamoeba culbertsoni and Pathogenic Bacteria and their Inhibition by Lectin-Antibodies

In this study, using pathogenic and non-pathogenic bacteria, it was analyzed whether a polyclonal serum and a monoclonal antibody to A. culbertsoni mannose-binding protein (MBP) could inhibit its interaction. The association of the amoeba with E. coli O157:H7 was very strong at a level of over 100%, but the non-pathogenic E. coli strain was about five times lower at 22%. Pathogenic K. pnueumoniae also showed high association with amoeba by about 92% as compared with pathogenic E. coli O157:H7 and S. agalactiae. The polyclonal serum to MBP inhibited E. coli O157:H7 association to amoeba 2.5 times more than untreated E. coli O157:H7. Monoclonal antibody to MBP also inhibited bacterial association with amoeba but was not stronger than the polyclonal serum. Pathogenic E. coli O157:H7 showed about 88% invasion into amoeba and decreased about 22% as compared with associated E. coli O157:H7. Polyclonal serum to MBP inhibited about 55%, 50%, and 44% in E. coli O157:H7, K. pneumoniae and S. agalactiae, respectively. The invasion of K. pneumoniae and S. agalactiae was not high as polyclonal serum but was about 8% to 10% weaker than polyclonal serum. The pathogenic strains of K. pneumoniae and S. agalactiae showed less decrease in survival as shown at invasion than E. coli O157:H7 without antibody. This study provided the information that the pathogenic bacteria could be more interactive with A. culbertsoni trophozoites as a reservoir host than non-pathogenic E. coli, and the amoeba should interact with bacteria by the MBP lectin.

Lectins as virulence factors in Entamoeba histolytica and free-living amoebae

Currently, there is growing interest in the identification and purification of microbial lectins due to their involvement in the pathogenicity mechanisms of pathogens, such as Entamoeba histolytica and free-living amoebae. The Gal/GalNAc lectin from E. histolytica participates in adhesion, cytotoxicity and regulation of immune responses. Furthermore, mannose- and galactose-binding protein have been described in Acanthamoeba castellanii and Balamuthia mandrillaris, respectively and they also contribute to host damage. Finally, in Naegleria fowleri, molecules containing mannose and fucose are implicated in adhesion and cytotoxicity. Considering their relevance in the pathogenesis of the diseases caused by these protozoa, lectins appear to be promising targets in the diagnosis, vaccination and treatment of these infections.

Description of Virulent Factors and Horizontal Gene Transfers of Keratitis-Associated Amoeba Acanthamoeba Triangularis by Genome Analysis

Acanthamoeba triangularis strain SH 621 is a free-living amoeba belonging to Acanthamoeba ribo-genotype T4. This ubiquitous protist is among the free-living amoebas responsible for Acanthamoeba keratitis, a severe infection of human cornea. Genome sequencing and genomic comparison were carried out to explore the biological functions and to better understand the virulence mechanism related to the pathogenicity of Acanthamoeba keratitis. The genome assembly harbored a length of 66.43 Mb encompassing 13,849 scaffolds. The analysis of predicted proteins reported the presence of 37,062 ORFs. A complete annotation revealed 33,168 and 16,605 genes that matched with NCBI non-redundant protein sequence (nr) and Cluster of Orthologous Group of proteins (COG) databases, respectively. The Kyoto Encyclopedia of Genes and Genomes Pathway (KEGG) annotation reported a great number of genes related to carbohydrate, amino acid and lipid metabolic pathways. The pangenome performed with 8 available amoeba genomes belonging to genus Acanthamoeba revealed a core genome containing 843 clusters of orthologous genes with a ratio core genome/pangenome of less than 0.02. We detected 48 genes related to virulent factors of Acanthamoeba keratitis. Best hit analyses in nr database identified 99 homologous genes shared with amoeba-resisting microorganisms. This study allows the deciphering the genome of a free-living amoeba with medical interest and provides genomic data to better understand virulence-related Acanthamoeba keratitis.

Type 1 Fimbriae and Motility Play a Pivotal Role During Interactions of Salmonella typhimurium with Acanthamoeba castellanii (T4 Genotype)

Amoebic bacterial interactions are the most ancient form of host pathogen interactions. Here, we investigate the fate of Salmonella typhimurium and Acanthamoeba castellanii T4 genotype upon mutual interactions in a nutrition free environment. The role of type 1 fimbriae and motility of S. typhimurium during interactions with A. castellanii has also been investigated. Deletion of genes encoding the type 1 fimbriae subunit FimA, type 1 fimbriae tip protein FimH, chemotaxis regulatory proteins CheA and CheY and major flagella subunits FliC and FljB was performed through homologous recombination. In vitro association, invasion and survival assays of S. typhimurium wild-type and mutant strains were performed upon co-incubation of bacteria with A. castellanii trophozoites in a nutrition free environment. The deletion gene encoding type 1 fimbriae subunit FimA reduced, whereas the deletion of genes encoding flagella subunits FliC and FljB of flagella enhanced the association capability of S. typhimurium with A. castellanii. Invasion of A. castellanii by Salmonella was significantly reduced upon the loss of type 1 fimbriae subunit FimA and type 1 fimbriae tip protein FimH. Co-incubation of S. typhimurium with A. castellanii in phosphate buffered saline medium stimulated the growth of S. typhimurium wild-type and mutant strains. Viable A. castellanii trophozoites count became significantly reduced upon co-incubation with S. typhimurium within 48 h. Type 1 fimbriae play a pivotal role in the adherence of S. typhimurium to the A. castellanii cell surface. Subsequently, this interaction provides S. typhimurium an advantage in growth.

Giant virus vs amoeba: fight for supremacy

Since the discovery of mimivirus, numerous giant viruses associated with free-living amoebae have been described. The genome of giant viruses can be more than 2.5 megabases, and virus particles can exceed the size of many bacteria. The unexpected characteristics of these viruses have made them intriguing research targets and, as a result, studies focusing on their interactions with their amoeba host have gained increased attention. Studies have shown that giant viruses can establish host-pathogen interactions, which have not been previously demonstrated, including the unprecedented interaction with a new group of small viruses, called virophages, that parasitize their viral factories. In this brief review, we present recent advances in virophage-giant virus-host interactions and highlight selected studies involving interactions between giant viruses and amoebae. These unprecedented interactions involve the giant viruses mimivirus, marseillevirus, tupanviruses and faustovirus, all of which modulate the amoeba environment, affecting both their replication and their spread to new hosts.

Host Invasion by Pathogenic Amoebae: Epithelial Disruption by Parasite Proteins

The epithelium represents the first and most extensive line of defence against pathogens, toxins and pollutant agents in humans. In general, pathogens have developed strategies to overcome this barrier and use it as an entrance to the organism. Entamoeba histolytica, Naegleriafowleri and Acanthamoeba spp. are amoebae mainly responsible for intestinal dysentery, meningoencephalitis and keratitis, respectively. These amoebae cause significant morbidity and mortality rates. Thus, the identification, characterization and validation of molecules participating in host-parasite interactions can provide attractive targets to timely intervene disease progress. In this work, we present a compendium of the parasite adhesins, lectins, proteases, hydrolases, kinases, and others, that participate in key pathogenic events. Special focus is made for the analysis of assorted molecules and mechanisms involved in the interaction of the parasites with epithelial surface receptors, changes in epithelial junctional markers, implications on the barrier function, among others. This review allows the assessment of initial host-pathogen interaction, to correlate it to the potential of parasite invasion.

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.

Tupanvirus-infected amoebas are induced to aggregate with uninfected cells promoting viral dissemination

The discovery of giant viruses in the last years has fascinated the scientific community due to virus particles size and genome complexity. Among such fantastic discoveries, we have recently described tupanviruses, which particles present a long tail, and has a genome that contains the most complete set of translation-related genes ever reported in the known virosphere. Here we describe a new kind of virus-host interaction involving tupanvirus. We observed that tupanvirus-infected amoebas were induced to aggregate with uninfected cells, promoting viral dissemination and forming giant host cell bunches. Even after mechanical breakdown of bunches, amoebas reaggregated within a few minutes. This remarkable interaction between infected and uninfected cells seems to be promoted by the expression of a mannose receptor gene. Our investigations demonstrate that the pre-treatment of amoebas with free mannose inhibits the formation of bunches, in a concentration-dependent manner, suggesting that amoebal-bunch formation correlates with mannose receptor gene expression. Finally, our data suggest that bunch-forming cells are able to interact with uninfected cells promoting the dissemination and increase of tupanvirus progeny.

Molecular and biochemical characterization of key enzymes in the cysteine and serine metabolic pathways of Acanthamoeba castellanii

Background

Acanthamoeba spp. can cause serious human infections, including Acanthamoeba keratitis, granulomatous amoebic encephalitis and cutaneous acanthamoebiasis. Cysteine biosynthesis and the L-serine metabolic pathway play important roles in the energy metabolism of Acanthamoeba spp. However, no study has confirmed the functions of cysteine synthase (AcCS) in the cysteine pathway and phosphoglycerate dehydrogenase (AcGDH) or phosphoserine aminotransferase (AcSPAT) in the non-phosphorylation serine metabolic pathway of Acanthamoeba.

Methods

The AcCS, AcGDH and AcSPAT genes were amplified by PCR, and their recombinant proteins were expressed in Escherichia coli. Polyclonal antibodies against the recombinant proteins were prepared in mice and used to determine the subcellular localisation of each native protein by confocal laser scanning microscopy. The enzymatic activity of each recombinant protein was also analysed. Furthermore, each gene expression level was analysed by quantitative PCR after treatment with different concentrations of cysteine or L-serine.

Results

The AcCS gene encodes a 382-amino acid protein with a predicted molecular mass of 43.1 kDa and an isoelectric point (pI) of 8.11. The AcGDH gene encodes a 350-amino acid protein with a predicted molecular mass of 39.1 kDa and a pI of 5.51. The AcSPAT gene encodes a 354-amino acid protein with a predicted molecular mass of 38.3 kDa and a pI of 6.26. Recombinant AcCS exhibited a high cysteine synthesis activity using O-acetylserine and Na₂S as substrates. Both GDH and SPAT catalysed degradation, rather than synthesis, of serine. Exogenous L-serine or cysteine inhibited the expression of all three enzymes in a time- and dose-dependent manner.

Conclusions

This study demonstrated that AcCS participates in cysteine biosynthesis and serine degradation via the non-phosphorylation serine metabolic pathway, providing a molecular basis for the discovery of novel anti-Acanthamoeba drugs.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3188-7) contains supplementary material, which is available to authorized users.

Production of a monoclonal antibody against a mannose-binding protein of Acanthamoeba culbertsoni and its localization

Amoebae from the genus Acanthamoeba are facultative pathogens of humans and other animals. In humans they most frequently infect the eye causing a sight threatening infection known as Acanthamoeba keratitis (AK), and also cause an often fatal encephalitis (GAE). A mannose-binding protein (MBP) has been identified as being important for Acanthamoeba infection especially in AK. This lectin has previously been characterized from Acanthamoeba castellanii as consisting of multiple 130 kDa subunits. MBP expression correlates with pathogenic potential and is expressed in a number of Acanthamoeba species. Here we report the purification of a similar lectin from Acanthamoeba culbertsoni and the production of a monoclonal antibody to it. The A. culbertsoni MBP was isolated by affinity chromatography using α-D-mannose agarose and has an apparent molecular weight of 83 kDa. The monoclonal antibody is an IgM that is useful in both western blots and immunofluorescence. We expect that this antibody will be useful in the study of the pathology of A. culbertsoni and in its identification in clinical samples.

Acanthamoeba-mediated cytopathic effect correlates with MBP and AhLBP mRNA expression

BACKGROUND

In recent years, the concern of Acanthamoeba keratitis has increased since the infection is often associated with contact lens use. Partial 18S rRNA genotypic identification of Acanthamoeba isolates is important to correlate with pathophysiological properties in order to evaluate the degree of virulence. This is the first report of genotypic identification for clinical isolates of Acanthamoeba from corneal scrapings of keratitis in Malaysia. This study is also the first to correlate the mRNA expression of MBP and AhLBP as virulent markers for axenic strains of Acanthamoeba.

RESULTS

In this study, ten clinical isolates were obtained from corneal scrapings. Rns genotype and intra-genotypic variation at the DF3 region of the isolates were identified. Results revealed that all clinical isolates belonged to the T4 genotype, with T4/6 (4 isolates), T4/2 (3 isolates), T4/16 (2 isolates) and one new genotype T4 sequence (T4/36), being determined. The axenic clinical isolates were cytopathogenic to rabbit corneal fibroblasts. MBP and AhLBP mRNA expression are directly correlated to Acanthamoeba cytopathic effect.

CONCLUSIONS

All ten Malaysian clinical isolates were identified as genotype T4 which is predominantly associated with AK. Measuring the mRNA expression of Acanthamoeba virulent markers could be useful in the understanding of the pathogenesis of Acanthamoeba keratitis.

Vaccination with recombinant protein (r22C03), a putative attachment factor of Neoparamoeba perurans, against AGD in Atlantic salmon (Salmo salar) and implications of a co-infection with Yersinia ruckeri

Amoebic gill disease (AGD) affects salmonids during the marine grow-out phase in the Tasmanian industry and in other major salmonid producing countries. During the period post-transfer to seawater, the bacterial condition yersiniosis can also cause high levels of mortality in Atlantic salmon grown in Tasmania, in addition to the hatchery outbreaks. The recombinant protein r22C03, a mannose-binding protein-like (MBP-like) similar to attachment factors of other amoebae, was tested as a vaccine candidate against AGD in a large scale challenge trial. Fish were immunised with r22C03 combined with FCA via intraperitoneal (i.p.) injection, and given a booster five weeks later by either i.p. injection (RP group) or by a dip-immersion (mRP). Fish were then challenged twice with Neoparamoeba perurans: the initial challenge 16 weeks after primary immunisation was terminated due to presence of ulcerative lesions in the skin of salmon; the second challenge was carried out after five weeks of treatment with oxytetracycline. These skin lesions might have been associated with a concurrent infection with Yersinia ruckeri, which was detected by real-time qPCR in serum of a large proportion of moribund and survivor fish after the AGD challenge. Before and during the N. perurans infection, levels of antibodies against r22C03 were measured by ELISA in serum, skin mucus and supernatant from skin and gill explants. For the second challenge, the average size of AGD lesions was recorded from histology sections and survival curves were obtained. Before AGD challenge, r22C03 induced antibody responses in serum and explants with both vaccination strategies. At the end of the challenge, levels of antibodies were lower than before challenge irrespective of treatment. Both vaccinated groups presented increased serum antibody responses, while only mRP presented antibody responses in skin mucus, and no significant antibody responses were measured in the explants. Antibodies did not confer protection to N. perurans infection, as no difference was observed in the survival curves of the vaccinated and control groups, and there was no effect on the gill lesion size. The concurrent yersiniosis infection probably represented more closely infection patterns observed in commercial settings. However, it could have interfered with the survival results and with the ability of the fish to respond to the amoebae infection.

Photochemotherapeutic strategy against Acanthamoeba infections

Acanthamoeba is a protist pathogen that can cause serious human infections, including blinding keratitis and a granulomatous amoebic encephalitis that almost always results in death. The current treatment for these infections includes a mixture of drugs, and even then, a recurrence can occur. Photochemotherapy has shown promise in the treatment of Acanthamoeba infections; however, the selective targeting of pathogenic Acanthamoeba has remained a major concern. The mannose-binding protein is an important adhesin expressed on the surface membranes of pathogenic Acanthamoeba organisms. To specifically target Acanthamoeba, the overall aim of this study was to synthesize a photosensitizing compound (porphyrin) conjugated with mannose and test its efficacy in vitro. The synthesis of mannose-conjugated porphyrin was achieved by mixing benzaldehyde and pyrrole, yielding tetraphenylporphyrin. Tetraphenylporphyrin was then converted into mono-nitrophenylporphyrin by selectively nitrating the para position of the phenyl rings, as confirmed by nuclear magnetic resonance (NMR) spectroscopy. The mono-nitrophenylporphyrin was reduced to mono-aminophenylporphyrin in the presence of tin dichloride and confirmed by a peak at m/z 629. Finally, mono-aminoporphyrin was conjugated with mannose, resulting in the formation of an imine bond. Mannose-conjugated porphyrin was confirmed through spectroscopic analysis and showed that it absorbed light of wavelengths ranging from 425 to 475 nm. To determine the antiacanthamoebic effects of the derived product, amoebae were incubated with mannose-conjugated porphyrin for 1 h and washed 3 times to remove extracellular compound. Next, the amoebae were exposed to light of the appropriate wavelength for 1 h. The results revealed that mannose-conjugated porphyrin produced potent trophicidal effects and blocked excystation. In contrast, Acanthamoeba castellanii incubated with mannose alone and porphyrin alone did not exhibit an antiamoebic effect. Consistently, pretreatment with mannose-conjugated porphyrin reduced the A. castellanii-mediated host cell cytotoxicity from 97% to 4.9%. In contrast, treatment with porphyrin, mannose, or solvent alone had no protective effects on the host cells. These data suggest that mannose-conjugated porphyrin has application for the targeted photodynamic therapy of Acanthamoeba infections and may serve as a model in the development of therapeutic interventions against other eukaryotic infections.

An update on Acanthamoeba keratitis: diagnosis, pathogenesis and treatment

Free-living amoebae of the genus Acanthamoeba are causal agents of a severe sight-threatening infection of the cornea known as Acanthamoeba keratitis. Moreover, the number of reported cases worldwide is increasing year after year, mostly in contact lens wearers, although cases have also been reported in non-contact lens wearers. Interestingly, Acanthamoeba keratitis has remained significant, despite our advances in antimicrobial chemotherapy and supportive care. In part, this is due to an incomplete understanding of the pathogenesis and pathophysiology of the disease, diagnostic delays and problems associated with chemotherapeutic interventions. In view of the devastating nature of this disease, here we present our current understanding of Acanthamoeba keratitis and molecular mechanisms associated with the disease, as well as virulence traits of Acanthamoeba that may be potential targets for improved diagnosis, therapeutic interventions and/or for the development of preventative measures. Novel molecular approaches such as proteomics, RNAi and a consensus in the diagnostic approaches for a suspected case of Acanthamoeba keratitis are proposed and reviewed based on data which have been compiled after years of working on this amoebic organism using many different techniques and listening to many experts in this field at conferences, workshops and international meetings. Altogether, this review may serve as the milestone for developing an effective solution for the prevention, control and treatment of Acanthamoeba infections.

Current Status of Acanthamoeba in Iran: A Narrative Review Article

BACKGROUND

Free-living amoebae belonging to the genus Acanthamoeba have an environmental distribution. Amoebic keratitis due to these protozoan parasites continue to rise in Iran and worldwide. In Iran, there are various researches regarding both morphological and molecular identification of Acanthamoeba spp. in environmental and clinical samples. However, there is no thorough review about Acanthamoeba genotypes and their distribution in environmental sources such as water, dust and biofilm in Iran. Besides, according to increasing cases of Amoebic keratitis in the region awareness regarding the pathogenic potential of these sight-threatening amoebae is of utmost importance.

METHODS

We conducted a thorough review based on the database sources such as MEDLINE, PubMed and Google scholar. No restrictions were placed on study date, study design or language of publication. We searched all valuable and relevant information considering the occurrence of the Acanthamoeba in both environmental and clinical samples.

RESULTS

According to our thorough review Acanthamoeba belonging to T4 genotype is the most prevalent type strain in environmental and clinical samples in several regions in Iran and worldwide, however, there are reports regarding Acanthamoeba belonging to other genotypes such as T2, T3, T5, T6 and T11 and the mentioned point could leads us to more researches with the goal of presenting the real genotype dominance of Acanthamoeba and related disease in the country.

CONCLUSION

Overall, the present review will focus on present status of genotypes of Acanthamoeba in Iran during recent years.

Administration of recombinant attachment protein (r22C03) of Neoparamoeba perurans induces humoral immune response against the parasite in Atlantic salmon (Salmo salar)

This study investigated the use of a recombinant protein of Neoparamoeba perurans, the causative agent of Amoebic gill disease (AGD), as an immunogen to generate systemic and mucosal antibody responses against the parasite. Genes encoding N. perurans homologs of mannose-binding protein (MBP) from Acanthamoeba spp. have been identified. From these, a Neoparamoeba MBP - like EST has been identified and produced as a recombinant fusion protein. Attachment of N. perurans to the gill might be reduced by antibody-mediated interference of this protein, but this is dependent on the presence and level of functional antibodies in the mucus. Fish were immunized with the protein via i.p. injection with Freund's complete adjuvant (FCA); and serum and skin mucus samples were collected before and after immunization. Antibodies (IgM) present in samples were characterized via Western blot and their levels measured with an ELISA. The immunization was able to induce a systemic IgM response 8 weeks after primary exposure and a mucosal response 4 weeks post initial immunization, which were specific to the recombinant protein but not to antigens obtained from crude amoebic preparations. However, adherence of the antibodies to the parasite was observed using immunocytochemistry, and both, serum and skin mucus IgM, were able to bind the surface of formalin-fixed N. perurans. This finding may contribute to further research into the development of a vaccine for AGD.

Biochemical and cellular mechanisms regulatingAcanthamoeba castellaniiadherence to host cells

Free-living amoebae belonging to the genusAcanthamoebaare the causative agents of infections such as amoebic keratitis (AK), granulomatous amoebic encephalitis (GAE) and cutaneous lesions. The mechanisms involved in the establishment of infection are unknown. However, it is accepted that the initial phase of pathogenesis involves adherence to the host tissue. In this work, we analysed surface molecules with an affinity for epithelial and neuronal cells from the trophozoites ofAcanthamoeba castellanii. We also investigated the cellular mechanisms that govern the process of trophozoite adhesion to the host cells. We first used confocal and epifluorescence microscopy to examine the distribution of theA. castellaniiactin cytoskeleton during interaction with the host cells. The use of drugs, as cytochalasin B (CB) and latrunculin B (LB), revealed the participation of cytoskeletal filaments in the adhesion process. In addition, to identify the proteins and glycoproteins on the surface ofA. castellanii, the trophozoites were labelled with biotin and biotinylated lectins. The results revealed bands of surface proteins, some of which were glycoproteins with mannose andN-acetylglucosamine residues. Interaction assays of biotinylated amoebae proteins with epithelial and neuronal cells showed that some surface proteins had affinity for both cell types. The results of this study provide insight into the biochemical and cellular mechanisms of theAcanthamoebainfection process.

Non-contact lens use-related Acanthamoeba keratitis in southern Turkey: evaluation of risk factors and clinical features

PURPOSE

To assess the diagnostic methods, risk factors, and clinical features of Acanthamoeba keratitis cases in patients who do not wear contact lenses.

METHODS

Medical records of 26 consecutive patients with non-contact lens-related Acanthamoeba keratitis, who were followed up at the tertiary eye care center between May 2010 and May 2012, were analyzed. Laboratory, demographic, and clinical findings were evaluated pertaining to the patients.

RESULTS

Twenty-six non-contact lens-related Acanthamoeba keratitis cases were included in the study. The main risk factors were trauma (group 1, n = 13 patients) and ocular surface disease (group 2, n = 12 patients). One patient had both of the risk factors mentioned above. Overall test results showed that Acanthamoeba positivity rates were 15.3% for direct microscopy, 46.1% for culture, 92.3% for conventional polymerase chain reaction (PCR), and 100% for real-time PCR. The rates of full-thickness corneal involvement and ring-shaped infiltrations were higher in group 2, whereas superficial keratitis and radial keratoneuritis were higher in group 1. The final visual acuities were significantly better in group 1 than group 2 (p<0.025).

CONCLUSIONS

This study is the first regional report from Turkey about Acanthamoeba keratitis in non-contact lens users. A majority of cases admitted to a tertiary eye care center were related to trauma or ocular surface disease. Physician suspicion is critically important for the timely diagnosis of these cases. At this point, molecular diagnostic tests (PCR or real-time PCR) seem to support the clinical diagnosis of Acanthamoeba keratitis with the help of fast and reliable results.

Genome of Acanthamoeba castellanii highlights extensive lateral gene transfer and early evolution of tyrosine kinase signaling

BACKGROUND

The Amoebozoa constitute one of the primary divisions of eukaryotes, encompassing taxa of both biomedical and evolutionary importance, yet its genomic diversity remains largely unsampled. Here we present an analysis of a whole genome assembly of Acanthamoeba castellanii (Ac) the first representative from a solitary free-living amoebozoan.

RESULTS

Ac encodes 15,455 compact intron-rich genes, a significant number of which are predicted to have arisen through inter-kingdom lateral gene transfer (LGT). A majority of the LGT candidates have undergone a substantial degree of intronization and Ac appears to have incorporated them into established transcriptional programs. Ac manifests a complex signaling and cell communication repertoire, including a complete tyrosine kinase signaling toolkit and a comparable diversity of predicted extracellular receptors to that found in the facultatively multicellular dictyostelids. An important environmental host of a diverse range of bacteria and viruses, Ac utilizes a diverse repertoire of predicted pattern recognition receptors, many with predicted orthologous functions in the innate immune systems of higher organisms.

CONCLUSIONS

Our analysis highlights the important role of LGT in the biology of Ac and in the diversification of microbial eukaryotes. The early evolution of a key signaling facility implicated in the evolution of metazoan multicellularity strongly argues for its emergence early in the Unikont lineage. Overall, the availability of an Ac genome should aid in deciphering the biology of the Amoebozoa and facilitate functional genomic studies in this important model organism and environmental host.

Exploring the unique N-glycome of the opportunistic human pathogen Acanthamoeba

Glycans play key roles in host-pathogen interactions; thus, knowing the N-glycomic repertoire of a pathogen can be helpful in deciphering its methods of establishing and sustaining a disease. Therefore, we sought to elucidate the glycomic potential of the facultative amoebal parasite Acanthamoeba. This is the first study of its asparagine-linked glycans, for which we applied biochemical tools and various approaches of mass spectrometry. An initial glycomic screen of eight strains from five genotypes of this human pathogen suggested, in addition to the common eukaryotic oligomannose structures, the presence of pentose and deoxyhexose residues on their N-glycans. A more detailed analysis was performed on the N-glycans of a genotype T11 strain (4RE); fractionation by HPLC and tandem mass spectrometric analyses indicated the presence of a novel mannosylfucosyl modification of the reducing terminal core as well as phosphorylation of mannose residues, methylation of hexose and various forms of pentosylation. The largest N-glycan in the 4RE strain contained two N-acetylhexosamine, thirteen hexose, one fucose, one methyl, and two pentose residues; however, in this and most other strains analyzed, glycans with compositions of Hex(8-9)HexNAc(2)Pnt(0-1) tended to dominate in terms of abundance. Although no correlation between pathogenicity and N-glycan structure can be proposed, highly unusual structures in this facultative parasite can be found which are potential virulence factors or therapeutic targets.

Pathogenesis of acanthamoeba keratitis

Acanthamoeba keratitis (AK) is a serious infection of the cornea. At present, diagnosis of the disease is not straightforward and treatment is very demanding. While contact lens wear is the leading risk factor for A K, Acanthamoeba parasites are increasingly recognized as an important cause of keratitis in non-contact lens wearers. The first critical step in the pathogenesis of infection is the adhesion of the microbe to the surface of the host tissues. Acanthamoebae express a major virulence protein, the mannose-binding protein (MBP), which mediates the adhesion of amoebae to the surface of the cornea. The MBP is a transmembrane protein with characteristics of a typical cell surface receptor. Subsequent to the MBP-mediated adhesion to host cells, the amoebae produce a contact-dependent metalloproteinase and several contact-independent serine proteinases. These proteinases work in concert to produce a potent cytopathic effect (CPE ) involving killing of the host cells, degradation of epithelial basement membrane and underlying stromal matrix, and penetration into the deeper layers of the cornea. In the hamster animal model, oral immunization with the recombinant MBP protects against AK, and this protection is associated with an increased level of anti-MBP IgA in tears of protected animals. Normal human tear fluid contains IgA antibodies against Acanthamoeba MBP that is likely to provide protection by inhibiting the adhesion of parasites to host cells. Indeed, in in vitro CPE assays, even a low concentration of tears (10 microL of undiluted tears per milliliter of media) almost completely inhibits Acanthamoeba-induced CPE . In addition to adherence-inhibiting, IgA-mediated protection, human tears also contain IgA-independent factors that provide protection against Acanthamoeba-induced CPE by inhibiting the activity of cytotoxic proteinases. Characterization of the CPE-inhibitory factors of human tears should lead to a better understanding of the mechanism by which the tissues of the host resist the infection and also help decode circumstances that predispose to Acanthamoeba infections.

Molecular Identification and Sequencing of Mannose Binding Protein (MBP) Gene of Acanthamoeba palestinensis

BACKGROUND

Acanthamoeba keratitis develops by pathogenic Acanthamoeba such as A. palestinensis. Indeed this species is one of the known causative agents of amoebic keratitis in Iran. Mannose Binding Protein (MBP) is the main pathogenicity factors for developing this sight threatening disease. We aimed to characterize MBP gene in pathogenic Acanthamoeba isolates such as A. palestinensis.

METHODS

This experimental research was performed in the School of Public Health, Tehran University of Medical Sciences, Tehran, Iran during 2007-2008. A. palestinensis was grown on 2% non-nutrient agar overlaid with Escherichia coli. DNA extraction was performed using phenol-chloroform method. PCR reaction and amplification were done using specific primer pairs of MBP. The amplified fragment were purified and sequenced. Finally, the obtained fragment was deposited in the gene data bank.

RESULTS

A 900 bp PCR-product was recovered after PCR reaction. Sequence analysis of the purified PCR product revealed a gene with 943 nucleotides. Homology analysis of the obtained sequence showed 81% similarity with the available MBP gene in the gene data bank. The fragment was deposited in the gene data bank under accession number EU678895,

CONCLUSION

MBP is known as the most important factor in Acanthamoeba pathogenesis cascade. Therefore, characterization of this gene can aid in developing better therapeutic agents and even immunization of high-risk people.

Elastase secretion in Acanthamoeba polyphaga

Acanthamoeba species are frequently isolated from soil and water collections. In the environment, the organisms multiply as phagotrophic trophozoites and encyst under adverse conditions. Several species are known to infect man, causing keratitis and opportunistic diseases. The mechanisms underlying tissue damage and invasion by the amoebae are being elucidated and the involvement of secreted peptidases, particularly serine peptidases, has been demonstrated. Here, elastase activity was examined in Acanthamoeba-conditioned medium (ACM), making use of elastin-Congo red (ECR) and synthetic peptide p-nitroanilide substrates. ACM hydrolysed ECR over a broad pH range and optimally at a pH of 7.5 and above. Indicating the activity of serine and metallopeptidases, Congo red release was potently inhibited by PMSF, antipain, chymostatin and 1,10-phenanthroline, partially reduced by elastatinal and EDTA, and unaffected by 1,7-phenanthroline and E-64. Screening with synthetic substrates mainly showed the activity of serine peptidases. ACM efficiently hydrolysed Suc-Ala(2)-Pro-Leu-pNA and Suc-Ala(2)-Pro-Phe-pNA over a broad pH range (7.0-9.5) and was weakly active against Suc-Ala(3)-pNA, a substrate found to be optimally hydrolysed at a pH around 7.0. Following ammonium sulfate precipitation of ACM proteins and FPLC analysis, the majority of the ECR-splitting activity, characterised as serine peptidases, bound to CM-sepharose and co-eluted with part of the Suc-Ala(2)-Pro-Phe-pNA-hydrolysing activity in a gradient of 0-0.6M NaCl. In the corresponding FPLC fractions, serine peptidases resolving in the region of 70-130kDa were detected in gelatin gels. Overall, the results demonstrate that trophozoites secrete elastases, and additionally suggest the high molecular weight serine peptidases as possible elastase candidates.

Binding of serum mannan binding lectin to a cell integrity-defective Cryptococcus neoformans ccr4Delta mutant

Mannan binding lectin (MBL) is an innate immune mediator belonging to the collectin family known to bind to the surfaces of many viruses, bacteria, and fungi. However, pathogenic strains of the fungus Cryptococcus neoformans are resistant to MBL binding. To dissect the mechanism of cryptococcal resistance to MBL, we compared MBL binding to an encapsulated wild-type strain, an encapsulated ccr4Delta mutant defective in cell integrity, and an acapsular cap60Delta strain. No MBL binding was detected on wild-type C. neoformans. In contrast, the ccr4Delta mutant bound MBL to the cell wall, predominantly at the ends of enlarged buds, whereas the acapsular strain bound MBL only at the bud neck and bud scars. In addition, the ccr4Delta mutant was sensitive to the cell wall-active antifungal caspofungin and other cell wall stress inducers, and its virulence was reduced in a mouse model of cryptococcosis. Interestingly, treatment of wild-type cells with caspofungin also increased MBL binding to C. neoformans. These results suggest that both the presence of capsule and wild-type cell wall architecture preclude MBL binding to C. neoformans.

Oral immunization with Acanthamoeba castellanii mannose-binding protein ameliorates amoebic keratitis

Acanthamoeba castellanii mannose-binding protein (MBP) mediates adhesion of the amoebae to corneal epithelial cells, a key first step in the pathogenesis of Acanthamoeba keratitis (AK), a devastating corneal infection. In the present study, we demonstrate that oral immunization with recombinant MBP ameliorates AK in a hamster animal model and that this protection is associated with the presence of elevated levels of anti-MBP immunoglobulin A in the tear fluid of the immunized animals.