Comparative genomic analysis of Acanthamoeba from different sources and horizontal transfer events of antimicrobial resistance genes.

Acanthamoeba species are among the most common free-living amoeba and ubiquitous protozoa, mainly distributed in water and soil, and cause Acanthamoeba keratitis (AK) and severe visual impairment in patients. Although several studies have reported genomic characteristics of Acanthamoeba, limited sample sizes and sources have resulted in an incomplete understanding of the genetic diversity of Acanthamoeba from different sources. While endosymbionts exert a significant influence on the phenotypes of Acanthamoeba, including pathogenicity, virulence, and drug resistance, the species diversity and functional characterization remain largely unexplored. Herein, our study sequenced and analyzed the whole genomes of 19 Acanthamoeba pathogenic strains that cause AK, and by integrating publicly available genomes, we sampled 29 Acanthamoeba strains from ocular, environmental, and other sources. Combined pan-genomic and comparative functional analyses revealed genetic differences and evolutionary relationships among the different sources of Acanthamoeba, as well as classification into multiple functional groups, with ocular isolates in particular showing significant differences that may account for differences in pathogenicity. Phylogenetic and rhizome gene mosaic analyses of ocular Acanthamoeba strains suggested that genomic exchanges between Acanthamoeba and endosymbionts, particularly potential antimicrobial resistance genes trafficking including the adeF, amrA, and amrB genes exchange events, potentially contribute to Acanthamoeba drug resistance. In conclusion, this study elucidated the adaptation of Acanthamoeba to different ecological niches and the influence of gene exchange on the evolution of ocular Acanthamoeba genome, guiding the clinical diagnosis and treatment of AK and laying a theoretical groundwork for developing novel therapeutic approaches. IMPORTANCE: Acanthamoeba causes a serious blinding keratopathy, Acanthamoeba keratitis, which is currently under-recognized by clinicians. In this study, we analyzed 48 strains of Acanthamoeba using a whole-genome approach, revealing differences in pathogenicity and function between strains of different origins. Horizontal transfer events of antimicrobial resistance genes can help provide guidance as potential biomarkers for the treatment of specific Acanthamoeba keratitis cases.

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.

Use of in vivo confocal microscopy in suspected Acanthamoeba keratitis: a 12-year real-world data study at a Swedish regional referral center.

PURPOSE: To report real-world data (RWD) on the use of in vivo confocal microscopy (IVCM) in handling cases of suspected Acanthamoeba keratitis (AK) cases at a regional referral center during a 12-year period. METHODS: Retrospective study of patients with suspected AK presenting at a regional referral center for IVCM in Sweden from 2010 to 2022. Demographics, symptoms, outcomes, and clinical management were analyzed, and IVCM images were interpreted. RESULTS: Of 74 included patients with suspected AK, 18 (24%) were IVCM-positive, 33 (44%) were IVCM-negative, 15 had inconclusive IVCM results (20.2%), and 8 (11%) were referred for a second opinion based on IVCM, 4 of which were IVCM-positive (5.5%), yielding an overall IVCM-positive rate of 29.5%. Cultures were taken in 38 cases (51%) with only 2 cases (2.7%) culture-positive for AK. Of IVCM-negative cases, cultures were taken in 22 (67%) of cases and 100% of these were AK-negative. IVCM-positive cases had more clinic visits (median 30, P = 0.018) and longer follow-up time (median 890 days, P = 0.009) than IVCM-negative patients, while visual acuity improvement did not differ (P > 0.05). Of IVCM-positive cases, 10 (56%) underwent surgery despite prior anti-amoebic treatment, and 14 (78%) had 3 or more IVCM examinations during follow-up, with cysts (100%), dendritic cells (89%) and inflammatory infiltrate (67%) as the most prevalent features. Longitudinal IVCM indicated improvement in cysts, dendritic cells and subbasal nerves with treatment, while clinical resolution was not always consistent with complete absence of cysts. CONCLUSIONS: In a real-world setting, IVCM has a high reliability in classifying AK-negative cases, while IVCM detects AK-positive cases more frequently than the gold-standard culture method, leading to its preferential use over the culture method where time or resources are limited. Despite this, a subset of cases are IVCM-inconclusive, the clinical course of referred patients is long requiring many hospital visits, and visual acuity in most cases does not improve with medical treatment alone. Information sharing across centers and standardization of referral and diagnostic routines is needed to exploit the full potential of IVCM in AK patient management.

Evaluating the amoeba thioredoxin reductase selenoprotein as potential drug target for treatment of Acanthamoeba infections.

The genus Acanthamoeba comprises facultative pathogens, causing Acanthamoeba keratitis (AK) and granulomatous amoebic encephalitis (GAE). In both diseases, treatment options are limited, and drug development is challenging. This study aimed to investigate the role of the large thioredoxin reductase selenoprotein of Acanthamoeba (AcTrxR-L) as a potential drug target assessing the effects of the thioredoxin reductase inhibitors auranofin, TRi-1, and TRi-2 on AcTrxR-L activity and on the viability of Acanthamoeba trophozoites. Recombinant expression and purification of AcTrxR-L as a selenoprotein allowed assessments of its enzymatic activity, with reduction of various substrates, including different thioredoxin isoforms. Auranofin demonstrated potent inhibition towards AcTrxR-L, followed by TRi-1, and TRi-2 exhibiting lower effectiveness. The inhibitors showed variable activity against trophozoites in culture, with TRi-1 and TRi-2 resulting in strongly impaired trophozoite viability. Cytotoxicity tests with human corneal epithelial cells revealed lower susceptibility to all compounds compared to Acanthamoeba trophozoites, underscoring their potential as future amoebicidal agents. Altogether, this study highlights the druggability of AcTrxR-L and suggests it to be a promising drug target for the treatment of Acanthamoeba infections. Further research is warranted to elucidate the role of AcTrxR-L in Acanthamoeba pathogenesis and to develop effective therapeutic strategies targeting this redox enzyme.

[Purulent scleritis following penetrating keratoplasty for acanthamoeba keratitis]. / Gnoinyi sklerit posle skvoznoi keratoplastiki po povodu akantamebnogo keratita.

The problem of treating purulent scleral infections, rare but extremely severe complication of ophthalmic surgeries, remains unresolved. This article presents a case of successful surgical treatment of purulent scleritis - interlamellar scleral abscess - that developed in a patient after repeat penetrating keratoplasty performed due to infectious lysis of the transplant. Although the first keratoplasty was performed for acanthamoeba keratitis, there were no signs of acanthamoeba invasion in the transplant at the time of the second surgery. Scleritis manifested as an infiltrate with pus penetrating the anterior chamber and development of keratoiridocyclitis. During surgery, the abscess cavity was opened, irrigated with an antiseptic solution, and drained into the subconjunctival space; the anterior chamber was irrigated with balanced salt solution through a separate paracentesis. No infection recurrences were noted in the postoperative period and the corneal transplant remained clear.

Staurosporine as a Potential Treatment for Acanthamoeba Keratitis Using Mouse Cornea as an Ex Vivo Model.

Acanthamoeba is a ubiquitous genus of amoebae that can trigger a severe and progressive ocular disease known as Acanthamoeba Keratitis (AK). Furthermore, current treatment protocols are based on the combination of different compounds that are not fully effective. Therefore, an urgent need to find new compounds to treat Acanthamoeba infections is clear. In the present study, we evaluated staurosporine as a potential treatment for Acanthamoeba keratitis using mouse cornea as an ex vivo model, and a comparative proteomic analysis was conducted to elucidate a mechanism of action. The obtained results indicate that staurosporine altered the conformation of actin and tubulin in treated trophozoites of A. castellanii. In addition, proteomic analysis of treated trophozoites revealed that this molecule induced overexpression and a downregulation of proteins related to key functions for Acanthamoeba infection pathways. Additionally, the ex vivo assay used validated this model for the study of the pathogenesis and therapies of AK. Finally, staurosporine eliminated the entire amoebic population and prevented the adhesion and infection of amoebae to the epithelium of treated mouse corneas.

First report of Acanthamoeba spp. isolation in a recreational hot spring in the Philippines.

Natural hot springs are ideal places and environmental matrices that offer relaxation to people and microorganisms of different types. A total of 40 surface water samples were collected from the five identified collection sites, eight water samples for each site. Collection sites are designated 200 m apart to cover the entire study site. Surface water samples were collected approximately 10-20 cm from the surface. Water samples were filtered, cultured, and microscopically observed for 14 days. After 14 days of cultivation, eight (20%) water samples revealed cystic and trophozoite stages. Polymerase chain reaction using JDP1 and JDP2 specific primers confirmed the presence of Acanthamoeba spp. from two of our isolates in the hot spring, isolates 1.1 and 5.1. Further sequencing revealed that the isolates are Acanthamoeba T20 and Acanthamoeba genotype T7. Sequences were deposited to GenBank and were assigned accession numbers PP741726 and PP741727, respectively. The isolation of Acanthamoeba spp. in hot springs has significant health implications, especially for those who use it for recreational activity. Private resort owners are highly encouraged to regularly monitor and maintain hot spring resorts to avoid future infections.

Isolates of Acanthamoeba species in the marine environment in the Philippines.

Acanthamoebae spp. are considered the most commonly occurring free-living amoebae (FLA) in the environment. Their high resilience enables them to thrive in different types of environments. Using purposive sampling, 80 surface water samples were collected from identified coastal sites in Mariveles, Bataan, and Lingayen Gulf (40 water samples for each). Nineteen (23.75%) of the 80 water samples yielded positive amoebic growth during the 14-day culture and microscopic examination. The polymerase chain reaction confirmed Acanthamoeba spp. DNA in isolates MB1, A3, A4, A7, C5, and D3 using JDP1 and JDP2 primer sets. Further sequencing revealed that the isolates belonged to Acanthamoeba sp., Acanthamoeba culbertsoni, Acanthamoeba castellani, and Acanthamoeba genotype T4. The sequences were deposited in GenBank and registered under accession numbers PP741651, PP767364, PP741728, PP741729, PP767365, and PP767366, respectively. Potential risk factors such as waste disposal, expansion of human settlements to coastal locations, and soil runoffs in these environments should be controlled to mitigate the proliferation of potentially pathogenic strains of FLAs.

A Comprehensive Review on Acanthamoeba Keratitis: An Overview of Epidemiology, Risk Factors, and Therapeutic Strategies.

Acanthamoeba keratitis (AK) is a rare but severe corneal infection caused by the free-living amoeba, Acanthamoeba, which is ubiquitously present in the environment. This condition predominantly affects contact lens wearers but can also occur in non-lens users, particularly those exposed to contaminated water or with compromised immune systems. AK is characterized by progressive corneal inflammation, epithelial defects, and ulceration, which can lead to significant visual impairment or blindness if not promptly diagnosed and treated. This review aims to provide a comprehensive overview of AK by synthesizing current knowledge on its epidemiology, risk factors, pathophysiology, clinical manifestations, diagnostic approaches, and therapeutic strategies. The review also highlights preventive measures and public health strategies to reduce the incidence of this debilitating condition. A detailed examination of existing literature was conducted, focusing on the global incidence of AK, demographic trends, and various risk factors such as contact lens use, environmental exposures, and immunity status. The review also delves into the pathophysiology of Acanthamoeba infection, the host immune response, and the challenges in distinguishing AK from other forms of infectious keratitis. Therapeutic strategies, including medical and surgical interventions, are analyzed, along with emerging treatments. The global incidence of AK has increased, particularly among contact lens users, due to poor hygiene practices and environmental exposures. Early diagnosis remains challenging, often leading to delayed treatment and poorer outcomes. Biguanides and diamidines are the mainstays of medical therapy, with surgical options considered in advanced cases. Emerging therapies, such as photodynamic therapy and antimicrobial peptides, show promise in enhancing treatment outcomes. AK poses a significant threat to ocular health due to its potential for severe visual impairment and the complexities associated with its diagnosis and treatment. Early recognition, appropriate management, and public health initiatives focused on prevention are crucial for improving patient outcomes. Ongoing research and a collaborative approach among healthcare providers are essential to advancing the understanding and management of AK.

Rethinking Keratoplasty for Patients with Acanthamoeba Keratitis: Early "Low Load Keratoplasty" in Contrast to Late Optical and Therapeutic Keratoplasty.

BACKGROUND: Early therapeutic penetrating keratoplasty (TKP) for Acanthamoeba keratitis (AK) is thought to have a worse visual prognosis than the delayed optical penetrating keratoplasty (OKP) after successful conservative treatment of AK. This has led to a tendency to prolong conservative therapy and delay penetrating keratoplasty in patients with AK. This retrospective series presents the results of patients with AK that underwent early penetrating keratoplasty after reducing the corneal amoeba load through intensive conservative therapy, so-called "low load keratoplasty" (LLKP). PATIENTS AND METHODS: The medical records of our department were screened for patients with AK, confirmed by histological examination and/or PCR and/or in vivo confocal microscopy, which underwent ab LLKP and had a follow-up time of at least one year between 2009 and 2023. Demographic data, best corrected visual acuity (BCVA) and intraocular pressure at first and last visit, secondary glaucoma (SG), and recurrence and graft survival rates were assessed. RESULTS: 28 eyes of 28 patients were included. The average time from initiation of therapy to penetrating keratoplasty (PKP) was 68 ± 113 days. The mean follow-up time after LLKP was 53 ± 42 months. BCVA (logMAR) improved from 1.9 ± 1 pre-operatively to 0.5 ± 0.6 at last visit (p < 0.001). A total of 14% of patients were under medical therapy for SG at the last visit, and two of them underwent glaucoma surgery. The recurrence rate was 4%. The Kaplan-Meier graft survival rate of the first graft at four years was 70%. The second graft survival rate at four years was 87.5%. CONCLUSION: LLKP appears to achieve a good visual prognosis with an earlier visual and psychological habilitation, as well as low recurrence and SG rates. These results should encourage us to reconsider the optimal timing of PKP in therapy-resistant AK.

Exploration of the Binding Site of Arachidonic Acid in gp63 of Leishmania mexicana and in Orthologous Proteins in Clinically Important Parasites.

Recently, we published that the monoclonal antibody (D12 mAb) recognizes gp63 of L. mexicana, and it is responsible for COX activity. This D12 mAb exhibited cross-reactivity with Trypanosoma cruzi, Entamoeba histolytica, Acanthamoeba castellanii, and Naegleria fowleri. COX activity assays performed in these parasites suggested the potential presence of such enzymatic activity. In our investigation, we confirmed that wild-type recombinant gp63 exhibits COX-like activity, in contrast to a mutated recombinant gp63 variant. Consequently, our objective was to identify sequences orthologous to gp63 and subsequently analyze the binding of arachidonic acid (AA) to the putative active sites of these proteins. Given the absence of a crystallized structure for this protein in the Protein Data Bank (PDB), it was imperative to first obtain a three-dimensional structure by homology modeling, using leishmanolysin from Leishmania major (PDB ID: LML1) as a template in the Swiss model database. The results obtained through molecular docking simulations revealed the primary interactions of AA close to the Zinc atom present in the catalytic site of gp63-like molecules of several parasites, predominantly mediated by hydrogen bonds with HIS264, HIS268 and HIS334. Furthermore, COX activity was evaluated in commensal species such as E. dispar and during the encystment process of E. invadens.

Acanthamoebae as a protective reservoir for Pseudomonas aeruginosa in a clinical environment.

BACKGROUND: Pseudomonas aeruginosa is a growing concern in healthcare-associated infections and poses significant risk to those with serious underlying health conditions. The antimicrobial resistance traits of the pathogen and ability to form biofilms make effective mitigation and disinfection strategies difficult. Added to this challenge is the role that free-living amoebae such as Acanthamoeba play in the detection, disinfection and transmission of P. aeruginosa. P. aeruginosa can survive intracellularly within amoebae, which has the potential to limit detectability and permit transmission into high-risk areas. METHODS/FINDINGS: We screened for the presence of Acanthamoeba spp. and P. aeruginosa within a functioning general hospital in Scotland using a culture and molecular approach, noting their presence at several sites over a four-month period, particularly within floor drains connecting patient rooms. In addition, microbiome analysis revealed that amoebae harbour a unique microbial community comprised primarily of Pseudomonas spp. that were not readily detected using microbiome sequencing techniques on environmental swabs. Having demonstrated that both organisms were consistently present in hospital settings, we investigated the relationship between acanthamoeba and P. aeruginosa in the laboratory, showing that (i) acanthamoeba growth rate is increased in the presence of pseudomonas biofilms and viable pseudomonas persist within the amoebae and (ii) hydrogen peroxide-based disinfectants are significantly less effective against an isolate of P. aeruginosa in the presence of acanthamoeba than when the bacteria are incubated alone. CONCLUSIONS: These findings suggest that amoebae, and other protists, can influence the detection and persistence of P. aeruginosa in high-risk areas and should be considered when implementing mitigation strategies.

Giant viruses inhibit superinfection by downregulating phagocytosis in Acanthamoeba.

In the context of the virosphere, viral particles can compete for host cells. In this scenario, some viruses block the entry of exogenous virions upon infecting a cell, a phenomenon known as superinfection inhibition. The molecular mechanisms associated with superinfection inhibition vary depending on the viral species and the host, but generally, blocking superinfection ensures the genetic supremacy of the virus's progeny that first infects the cell. Giant amoeba-infecting viruses have attracted the scientific community's attention due to the complexity of their particles and genomes. However, there are no studies on the occurrence of superinfection and its inhibition induced by giant viruses. This study shows that mimivirus, moumouvirus, and megavirus, exhibit different strategies related to the infection of Acanthamoeba. For the first time, we have reported that mimivirus and moumouvirus induce superinfection inhibition in amoebas. Interestingly, megaviruses do not exhibit this ability, allowing continuous entry of exogenous virions into infected amoebas. Our investigation into the mechanisms behind superinfection blockage reveals that mimivirus and moumouvirus inhibit amoebic phagocytosis, leading to significant changes in the morphology and activity of the host cells. In contrast, megavirus-infected amoebas continue incorporating newly formed virions, negatively affecting the available viral progeny. This effect, however, is reversible with chemical inhibition of phagocytosis. This work contributes to the understanding of superinfection and its inhibition in mimivirus, moumouvirus, and megavirus, demonstrating that despite their evolutionary relatedness, these viruses exhibit profound differences in their interactions with their hosts.IMPORTANCESome viruses block the entry of new virions upon infecting a cell, a phenomenon known as superinfection inhibition. Superinfection inhibition in giant viruses has yet to be studied. This study reveals that even closely related viruses, such as mimivirus, moumouvirus, and megavirus, have different infection strategies for Acanthamoeba. For the first time, we have reported that mimivirus and moumouvirus induce superinfection inhibition in amoebas. In contrast, megaviruses do not exhibit this ability, allowing continuous entry of exogenous virions into infected amoebas. Our investigation shows that mimivirus and moumouvirus inhibit amoebic phagocytosis, causing significant changes in host cell morphology and activity. Megavirus-infected amoebas, however, continue incorporating newly formed viruses, affecting viral progeny. This research enhances our understanding of superinfection inhibition in these viruses, highlighting their differences in host interactions.

Contact Lens-related Corneal Infections.

Our review provides an update on the current landscape of contact lens-associated microbial keratitis (MK). We discuss the prevalence and risk factors associated with MK, emphasizing the role of overnight wear, poor hygiene, and contact lens type. CL-related MK is commonly caused by bacteria, though can also be caused by fungi or protozoa. Clinical presentation involves ocular pain, redness, and vision loss, with more specific presenting symptoms based on the culprit organism. Treatment strategies encompass prevention through proper hygiene and broad-spectrum antibiotic, antifungal, or antiprotozoal therapy, with surgical management reserved for severe recalcitrant cases.

Amoebicidal activity of essential oils and essential oil-based microemulsions of Aloysia citrodora Ortega ex Pers., Cymbopogon winterianus Jowitt ex Bor, and Ocimum gratissimum L. against Acanthamoeba polyphaga trophozoites.

AIMS: Evaluate the in vitro efficacy of the essential oils derived from Aloysia citrodora (Verbenaceae), Cymbopogon winterianus (Poaceae), and Ocimum gratissimum (Lamiaceae) against Acanthamoeba polyphaga trophozoites. Additionally, microemulsions formulated with these essential oils, along with their major components, were analyzed. METHODS AND RESULTS: The prepared microemulsions were characterized using polarized light microscopy and rheological techniques. The amoebicidal activity was determined by measuring the inhibitory concentration (IC50). Flow cytometry was employed to detect membrane damage and alterations in trophozoites size. The results revealed transparent and thermodynamically stable microemulsions. The essential oil from O. gratissimum exhibited a lower IC50, with values of 280.66 and 47.28 µg ml-1 after 24 and 48 h, respectively. When microemulsions containing essential oils were tested, the IC50 values exhibited a reduction of over 80% after 24 h. Particularly, eugenol, a constituent of the O. gratissimum essential oil, displayed higher amoebicidal activity. The essential oils also caused damage to the cell membrane, resulting in the subsequent death of the trophozoites. CONCLUSIONS: The EOs of A. citrodora, C. winterianus, and O. gratissimum and their microemulsions showed antiparasitic effect against A. polyphaga trophozoites, representing promising alternatives for the treatment of diseases caused by this protozoan.

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.

EVALUATION OF THE CYSTICIDAL ACTIVITY OF CHLOROCRESOL AGAINST ACANTHAMOEBA POLYPHAGA.

Chlorocresol has antibacterial and antifungal properties, yet its effectiveness in eradicating Acanthamoeba spp. remains unexplored. Acanthamoeba species trophozoites are usually sensitive to biocides, whereas cysts tend to be more resistant. This study aimed to evaluate the cysticidal activity of chlorocresol against Acanthamoeba polyphaga. Chlorocresol concentrations of 0.02, 0.04, and 0.08% were prepared and A. polyphaga cysts were incubated at room temperature (28-37 C) for 1, 24, 48, and 72 hr at each concentration. Cyst viability was evaluated using trypan blue staining and the percentage of nonviable cysts was calculated. For qualification assays, treated cysts were cultured on nonnutrient agar medium coated with Escherichia coli, incubated at 30 C, observed under a stereomicroscope for 30 days, and inoculated into peptone-yeast extract-glucose medium at 30 C for 72 hr. The results revealed that the A. polyphaga cysts were susceptible to 0.02, 0.04, and 0.08% chlorocresol. Chlorocresol made a significant difference in viability (P < 0.001) compared with the nontreated control for the same incubation time. This is the first study to examine the efficacy of chlorocresol against A. polyphaga cysts and it was highly effective. Chlorocresol could thus serve as an alternative chemical disinfectant for the eradication of A. polyphaga cysts as well as a prophylactic against transmission of other pathogenic microorganisms for which Acanthamoeba species can act as a carrier.

Perspectives on the Incidence of Acanthamoeba Keratitis: A Systematic Review and Meta-Analysis.

TOPIC: To provide an overview on the incidence of Acanthamoeba keratitis (AK). CLINICAL RELEVANCE: Although being a sight-threatening cause of infectious keratitis, a comprehensive assessment of the incidence of AK is lacking. METHODS: Incidence of AK was computed as the number of eyes with AK per health care center, per year (annualized center incidence [ACI]). Two meta-analytical ratios also were calculated: (1) the ratio of eyes with AK to the count of eyes with nonviral microbial keratitis (MK) and (2) the ratio of eyes with AK to the overall population (i.e., the total number of people in a nation or region, as indicated by the authors in each study). Center was defined as the health care facility where the study took place. Actual and projected estimates of the number of eyes with AK in years were calculated multiplying the ratio of eyes with AK to the total population and the corresponding population estimates, sourced from the United Nations Population Prospects. RESULTS: Overall, 105 articles were included, published between 1987 and 2022. The total number of eyes identified was 91 951, with 5660 eyes affected by AK and 86 291 eyes affected by nonviral MK. The median ACI was 1.9 eyes with AK per health care center per year (95% confidence interval [CI], 1.5-2.6 eyes), with no statistically significant differences among continents. The ratio of eyes with AK to the total number of eyes with MK was 1.52% (95% CI, 1.03%-2.22%), whereas the ratio of eyes with AK in relationship to the entire population was estimated at 2.34 eyes per 1 000 000 people (95% CI, 0.98-5.55 per 1 000 000 people). The projected increase in the numbers of eyes with AK indicated an increase of 18.5% (n = 15 355 eyes with AK) in 2053 and 25.5% (n = 16 253 eyes with AK) in 2073, compared with the baseline of 2023 (n = 12 953 eyes with AK). DISCUSSION: Acanthamoeba keratitis emerged as a relatively low-incident disorder, and no significant differences in terms of its incidence were found among different continents. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Cellulose binding and the timing of expression influence protein targeting to the double-layered cyst wall of Acanthamoeba.

The cyst wall of the eye pathogen Acanthamoeba castellanii contains cellulose and has ectocyst and endocyst layers connected by conical ostioles. Cyst walls contain families of lectins that localize to the ectocyst layer (Jonah) or the endocyst layer and ostioles (Luke and Leo). How lectins and an abundant laccase bind cellulose and why proteins go to locations in the wall are not known and are the focus of the studies here. Structural predictions identified ß-jelly-roll folds (BJRFs) of Luke and sets of four disulfide knots (4DKs) of Leo, each of which contains linear arrays of aromatic amino acids, also present in carbohydrate-binding modules of bacterial and plant endocellulases. Ala mutations showed that these aromatics are necessary for cellulose binding and proper localization of Luke and Leo in the Acanthamoeba cyst wall. BJRFs of Luke, 4DKs of Leo, a single ß-helical fold (BHF) of Jonah, and a copper oxidase domain of the laccase each bind to glycopolymers in both layers of deproteinated cyst walls. Promoter swaps showed that ectocyst localization does not just correlate with but is caused by early encystation-specific expression, while localization in the endocyst layer and ostioles is caused by later expression. Evolutionary studies showed distinct modes of assembly of duplicated domains in Luke, Leo, and Jonah lectins and suggested Jonah BHFs originated from bacteria, Luke BJRFs share common ancestry with slime molds, while 4DKs of Leo are unique to Acanthamoeba.IMPORTANCEAcanthamoebae is the only human parasite with cellulose in its cyst wall and conical ostioles that connect its inner and outer layers. Cyst walls are important virulence factors because they make Acanthamoebae resistant to surface disinfectants, hand sanitizers, contact lens sterilizers, and antibiotics applied to the eye. The goal here was to understand better how proteins are targeted to specific locations in the cyst wall. To this end, we identified three new proteins in the outer layer of the cyst wall, which may be targets for diagnostic antibodies in corneal scrapings. We used structural predictions and mutated proteins to show linear arrays of aromatic amino acids of two unrelated wall proteins are necessary for binding cellulose and proper wall localization. We showed early expression during encystation causes proteins to localize to the outer layer, while later expression causes proteins to localize to the inner layer and the ostioles.

Ac-HSP20 regulates autophagy and promotes the encystation of Acanthamoeba castellanii by inhibiting the PI3K/AKT/mTOR signaling pathway.

BACKGROUND: The encystation of Acanthamoeba castellanii has important ecological and medical significance. Blocking encystation is the key to preventing transmission and curing infections caused by A. castellanii. The formation of autophagosomes is one of the most important changes that occur during the encystation of Acanthamoeba. Our previous studies have shown that the heat shock protein 20 of A. castellanii (Ac-HSP20) is involved in its encystation. This study aimed to determine the role and mechanism of Ac-HSP20 in regulating autophagy involved in the encystation of A. castellanii. METHODS: Immunofluorescence assay, western blotting and transmission electron microscopy were used to analyze the dynamic changes in autophagy during the initiation and continuation of encystation. The knockdown of Ac-HSP20 was performed to clarify its regulation of encystation and autophagy and to elucidate the molecular mechanism by which Ac-HSP20 participates in autophagy to promote cyst maturation. RESULTS: The encystation rates and autophagosomes were significantly decreased by treatment with the autophagy inhibitor 3-MA. The autophagy marker LC3B and autophagic lysosomes increased with the induced duration of encystation and reached the maximum at 48 h. The encystation rate, LC3B expression and autophagosomes decreased when Ac-HSP20 was knocked down by siRNA transfection. In addition, the expression levels of Ac-HSP20 and LC3B increased and the expressions of p-AKT and p-mTOR decreased after 48 h of encystation without knockdown. However, the expressions of p-AKT and p-mTOR increased while the expression of LC3B decreased under the knockdown of Ac-HSP20. Furthermore, the protein expression of LC3B increased when the PI3K/AKT/mTOR signaling pathway was inhibited but decreased when the pathway was activated. CONCLUSIONS: The results demonstrated that autophagy is positively correlated with the encystation of A. castellanii, and Ac-HSP20 regulates autophagy to maintain the homeostasis of A. castellanii by inhibiting the PI3K /AKT /mTOR signaling pathway, thus promoting the maturation and stability of encystation.