Killing of diverse eye pathogens (Acanthamoeba spp., Fusarium solani, and Chlamydia trachomatis) with alcohols

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 β-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 β-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.

Dead reckoning of protist viability with propidium monoazide (PMA)-quantitative PCR; a case study using Neoparamoeba perurans

The ability to distinguish between viable and non-viable protozoan parasites is central to improved human and animal health management. While conceptually simple, methods to differentiate cell viability in situ remain challenging. Amoebic gill disease, caused by Neoparamoeba perurans is a parasitic disease impacting Atlantic salmon aquaculture globally. Although commercial freshwater treatments alleviate AGD, viable amoebae remain on gills or in used treatment water. Existing PCR-based assays are able to quantify N. perurans abundance but cannot discriminate amoeba viability. We investigated the use of propidium monoazide (PMA) application, prior to real-time PCR, to distinguish between alive and dead cells. We demonstrate that 200 μM PMA can significantly reduce amplification from non-viable (isopropanol treated) cultured amoebae across at least three logs of cell concentrations. Using a serial dilution of viable and non-viable cells, we show that non-PMA PCR amplifies both viable and non-viable amoebae, while PMA exposure suppresses (but does not completely inhibit) amplification from non-viable amoebae. The effect of freshwater treatment on N. perurans viability was assessed using the PMA-PCR. Following PMA exposure, amplification from freshwater treated amoebae was reduced by approximately 94-97 %. Taken together this study demonstrates that PMA combined with traditional real-time PCR can estimate amoeba viability.

Necrotizing Scleritis: A Review

Necrotizing scleritis is the most destructive and vision-threatening form of scleritis. Necrotizing scleritis can occur in systemic autoimmune disorders and systemic vasculitis, as well as following microbial infection. Rheumatoid arthritis and granulomatosis with polyangiitis remain the commonest identifiable systemic diseases associated with necrotising scleritis. Pseudomonas species is the most common organism causing infectious necrotizing scleritis, with surgery the most common risk factor. Necrotizing scleritis has the highest rates of complications and is more prone to secondary glaucoma and cataract than other phenotypes of scleritis. The differentiation between non-infectious and infectious necrotizing scleritis is not always easy but is critical in the management of necrotizing scleritis. Non-infectious necrotizing scleritis requires aggressive treatment with combination immunosuppressive therapy. Infectious scleritis is often recalcitrant and difficult to control, requiring long-term antimicrobial therapy and surgical debridement with drainage and patch grafting due to deep-seated infection and the avascularity of the sclera.

Possible Synergistic Role of Cryo-Alcohol Therapy in Infectious Scleritis-Scope and Rationale for Expanding Indications and Review of the Literature

PURPOSE

The purpose of this study was to highlight the use of topical ethanol as an adjunct to cryotherapy, termed cryo-alcohol therapy, in the management of fungal/acanthamoeba scleritis along with a review of the literature.

METHOD

Retrospective interventional case reports of fungal and acanthamoeba scleritis along with a review of the literature.

RESULTS

The patient with circumferential necrotic fungal scleritis resolved in 6 weeks achieving a best-corrected visual acuity (BCVA) of 20/20, and the patient with acanthamoeba scleritis is awaiting optical keratoplasty after complete resolution in 8 weeks. The literature review from January 1990 to December 2020 revealed BCVA >20/200 in 50% of the eyes with a mean time to resolution being 4.16 ± 2.13 months in fungal scleritis, with 27.02% and 75% of the eyes requiring evisceration in fungal and acanthamoeba scleritis, respectively.

CONCLUSIONS

Cryotherapy is a useful adjunct in managing refractory infectious scleritis, and its efficacy can be enhanced by combining the use of topical ethanol to aid in faster recovery and reduce visual morbidity.

Update on diagnosis and management of refractory corneal infections

Infectious keratitis is a medical emergency resulting in significant visual morbidity. Indiscriminate use of antimicrobials leading to the emergence of resistant or refractory microorganisms has further worsened the prognosis. Coexisting ocular surface diseases, delay in diagnosis due to inadequate microbiological sample, a slow-growing/virulent organism, or systemic immunosuppressive state all contribute to the refractory response of the ulcer. With improved understanding of these varied ocular and systemic factors contributing to the refractory nature of the microbes, role of biofilm formation and recent research on improving the bioavailability of drugs along with the development of alternative therapies have helped provide the required multidimensional approach to effectively diagnose and manage cases of refractory corneal ulcers and prevent corneal perforations or further dissemination of disease. In this review, we explore the current literature and future directions of the diagnosis and treatment of refractory keratitis.

Topical use of alcohol in ophthalmology - Diagnostic and therapeutic indications

Alcohol (ethanol) has been used in medicine since time immemorial. In ophthalmic practice, besides as an antiseptic, it was given as retrobulbar injections to relieve severe ocular pain. Alcohol can be applied topically to the surface of neoplastic or suspicious lesions to kill cells that might desquamate and seed during surgical excision, to treat epithelial ingrowth that can occur following corneal surgeries, particularly laser in situ keratomileusis (LASIK), and to treat superficial infectious keratitis. In view of its ability to achieve a smooth cleavage plane between the epithelium and the Bowman's layer, alcohol-assisted delamination (ALD) of the corneal epithelium has been used widely and effectively for a variety of diagnostic and therapeutic indications, at times delivering both outcomes. Diagnostically, ALD yields an intact epithelial sheet which can be fixed flat to provide excellent orientation for histopathological evaluation. Therapeutically, it is most commonly used to treat recurrent corneal erosion syndrome, where its efficacy is comparable to that of phototherapeutic keratectomy but with several advantages. It has also been used to treat various forms of epithelial/anterior stromal dystrophies, which can obviate or delay the need for corneal transplantation for several years. In addition, ALD is performed in corneal collagen cross-linking and corneal refractive surgery for relatively atraumatic removal of the epithelium. In this review, we aimed to provide a comprehensive overview of the diagnostic and therapeutic use of topical alcohol in ophthalmology, to describe the surgical and fixation techniques of ALD, and to highlight our experience in ALD over the past decade.

Orthokeratology lens-related Acanthamoeba keratitis: case report and analytical review

Acanthamoeba keratitis (AK) is a rare but severe ocular infection with a significant risk of vision loss. Contact lens use is the main risk factor for AK. The orthokeratology (OK) lens, a specially designed contact lens, has been used worldwide as an effective method of myopia control. However, the OK lens is associated with an increased risk of Acanthamoeba infection. Many primary practitioners are concerned about this infection because of its relative rarity, the lack of promising therapeutic medications, and the need for referral. We herein report two cases of AK associated with OK lenses, present a systematic review of such cases, and discuss the possible reasons for the higher incidence rate of this infection in patients who wear OK lenses. We combined the clinical knowledge and skills of corneal specialists and lens experts with the sole objective of addressing these OK lens-related AK cases. We found that the most common risk factors were rinsing the lenses or lens cases with tap water. Prompt and accurate diagnosis along with adequate amoebicidal treatment are essential to ensure desirable outcomes for OK lens wearers who develop AK. Appropriate OK lens parameters and regular checkups are also important.

Anti-Acanthamoeba disinfection: hands, surfaces and wounds

Acanthamoebae are facultative parasites causing rare but serious infections such as keratitis and encephalitis and are also known as vectors for several bacterial pathogens, including legionellae and pseudomonads. Acanthamoeba cysts are particularly resilient and enable the amoebae to withstand desiccation and to resist disinfection and therapy. While the search for new therapeutic options has been intensified in the past years, hand and surface disinfectants as well as topical antiseptics for preventing infections have not been studied in detail to date. The aim of this study was to screen well-known and commonly used antimicrobial products in various formulations and different concentrations for their efficacy against Acanthamoeba trophozoites and cysts, including aliphatic alcohols, quaternary ammonium compounds (QACs), peracetic acid (PAA), potassium peroxymonosulfate sulfate (PPMS) and octenidine dihydrochloride (OCT). Of all products tested, OCT and QACs showed the highest efficacy, totally eradicating both trophozoites and cysts within 1 min. The determined 50% effective concentration (EC₅₀) for cysts was 0.196 mg/mL for OCT and 0.119 mg/mL for QACs after 1 min of exposure. PAA and PPMS showed reliable cysticidal efficacies only with prolonged incubation times of 30 min and 60 min, respectively. Aliphatic alcohols generally had limited efficacy, and only against trophozoites. In conclusion, OCT and QACs are potent actives against Acanthamoeba trophozoites and cysts at concentrations used in commercially available products, within contact times suitable for surface and hand disinfection as well as topical antisepsis.

The most abundant cyst wall proteins of Acanthamoeba castellanii are lectins that bind cellulose and localize to distinct structures in developing and mature cyst walls

Background

Acanthamoeba castellanii, which causes keratitis and blindness in under-resourced countries, is an emerging pathogen worldwide, because of its association with contact lens use. The wall makes cysts resistant to sterilizing reagents in lens solutions and to antibiotics applied to the eye.

Methodology/Principal findings

Transmission electron microscopy and structured illumination microscopy (SIM) showed purified cyst walls of A. castellanii retained an outer ectocyst layer, an inner endocyst layer, and conical ostioles that connect them. Mass spectrometry showed candidate cyst wall proteins were dominated by three families of lectins (named here Jonah, Luke, and Leo), which bound well to cellulose and less well to chitin. An abundant Jonah lectin, which has one choice-of-anchor A (CAA) domain, was made early during encystation and localized to the ectocyst layer of cyst walls. An abundant Luke lectin, which has two carbohydrate-binding modules (CBM49), outlined small, flat ostioles in a single-layered primordial wall and localized to the endocyst layer and ostioles of mature walls. An abundant Leo lectin, which has two unique domains with eight Cys residues each (8-Cys), localized to the endocyst layer and ostioles. The Jonah lectin and glycopolymers, to which it binds, were accessible in the ectocyst layer. In contrast, Luke and Leo lectins and the glycopolymers, to which they bind, were mostly inaccessible in the endocyst layer and ostioles.

Conclusions/Significance

The most abundant A. castellanii cyst wall proteins are three sets of lectins, which have carbohydrate-binding modules that are conserved (CBM49s of Luke), newly characterized (CAA of Jonah), or unique to Acanthamoebae (8-Cys of Leo). Cyst wall formation is a tightly choreographed event, in which lectins and glycopolymers combine to form a mature wall with a protected endocyst layer. Because of its accessibility in the ectocyst layer, an abundant Jonah lectin is an excellent diagnostic target.

A half century ago, investigators identified cellulose in the Acanthamoeba cyst wall, which has two layers and conical ostioles that connect them. Here we showed cyst walls contain three large sets of cellulose-binding lectins, which localize to the ectocyst layer (a Jonah lectin) or to the endocyst layer and ostioles (Luke and Leo lectins). We used the lectins to establish a sequence for cyst wall assembly when trophozoites are starved and encyst. In the first stage, a Jonah lectin and glycopolymers were present in dozens of distinct vesicles. In the second stage, a primordial wall contained small, flat ostioles outlined by a Luke lectin. In the third stage, a Jonah lectin remained in the ectocyst layer, while Luke and Leo lectins moved to the endocyst layer and ostioles. A description of the major events during cyst wall development is a starting point for mechanistic studies of its assembly.

Effect of ethanol pretreatment in Acanthamoeba keratitis: a long-term follow-up study

Purpose

The aim of this study was to evaluate the long-term outcomes of ethanol pretreatment in Acanthamoeba keratitis (AK).

Patients and methods

This single-center, retrospective, interventional study included 22 patients (24 eyes) who developed AK and underwent ethanol pretreatment between 2009 and 2015. Samples for smears, polymerase chain reaction, and culture for evidence of Acanthamoeba were collected. After ethanol pretreatment, the patients were treated with corneal epithelial debridement, topical 0.02% polyhexamethylene biguanide, and 0.1% propamidine isethionate. The primary outcomes were a clinically stable ocular surface, complete recovery from corneal infection, and acceptable corneal haze. The secondary outcome measure was improvement in best-corrected visual acuity. Complications and predictors of the visual outcome were also recorded.

Results

Ethanol pretreatment was successful in 20 (83.3%) of the 24 eyes, and no further optical keratoplasty was required. Four eyes required rescue therapeutic keratoplasty because of rapid progression of AK. Patients in whom ethanol pretreatment was successful achieved good final visual outcomes regardless of sex, age, or causative Acanthamoeba species. Patients with worse initial best-corrected visual acuity and rigid gas permeable lens-related AK had better improvement in vision.

Conclusion

Ethanol as a pretreatment for AK is safe and effective. Combined with corneal epithelial debridement, ethanol pretreatment may preclude the need for optical and therapeutic keratoplasty. This technique is suitable for all stages of AK presenting within 3 weeks of symptom onset and achieves favorable results especially in early AK.