Drug resistance and Acanthamoeba keratitis: the quest for alternative antiprotozoal chemotherapy

Development of ophthalmic nanoemulsions of β-caryophyllene for the treatment of Acanthamoeba keratitis

Although rare, amoebic keratitis (AK) is a disease caused by Acanthamoeba spp. that can lead to blindness. The drugs currently available for its treatment are very toxic, which has motivated the investigation for more effective and safe therapeutic options. In this study, the in vitro activity of ß-caryophyllene (BCP) was exploited taking into account its action against other protozoans as well as its well-known healing and anti-inflammatory properties (aspects relevant for the AK pathogenesis). On the other hand, high volatilization and oxidation phenomena are found for this compound, which led to its incorporation into nanoemulsions (NEs). Two emulsifying agents were tested, resulting in monodisperse systems with reduced droplet size (<265 nm) and high surface charge (positive and negative for NEs prepared with cetrimonium bromide -CTAB and Phosal® 50+, respectively). NEs prepared with CTAB were shown to be more stable after long-term storage at 4 and 25 °C than those prepared with Phosal®. Pure BCP, at the highest concentration (500 µM), resulted in a level of inhibition of Acanthamoeba trophozoites equivalent to that of reference drug (chlorhexidine). This activity was even greater after oil nanoencapsulation. The reduced droplet size could improve the interaction of the oil with the microorganism, justifying this finding. Changes in surface charge did not impact the activity. Positively charged NEs improved the interaction and retention of BCP in the cornea and thus should be prioritized for further studies.

Understanding Acanthamoeba Keratitis: An In-Depth Review of a Sight-Threatening Eye Infection

Acanthamoeba keratitis (AK) is a rare but potentially sight-threatening corneal infection caused by the Acanthamoeba parasite. This microorganism is found ubiquitously in the environment, often in freshwater, soil, and other sources of moisture. Despite its low incidence, AK presents significant challenges due to delayed diagnosis and the complex nature of therapeutic management. Early recognition is crucial to prevent severe ocular complications, including corneal ulceration and vision loss. Diagnostic modalities and treatment strategies may vary greatly depending on the clinical manifestation and the available tools. With the growing reported cases of Acanthamoeba keratitis, it is essential for the ophthalmic community to thoroughly understand this condition for its effective management and improved outcomes. This review provides a comprehensive overview of AK, encompassing its epidemiology, risk factors, pathophysiology, clinical manifestations, diagnosis, and treatment.

Acanthamoeba keratitis - A review

This is a comprehensive review after a thorough literature search in PubMed-indexed journals, incorporating current information on the pathophysiology, clinical features, diagnosis, medical and surgical therapy, as well as outcomes of Acanthamoeba keratitis (AK). AK is a significant cause of ocular morbidity, and early diagnosis with timely institution of appropriate therapy is the key to obtaining good outcomes. The varied presentations result in frequent misdiagnosis, and co-infections can increase the morbidity of the disease. The first line of therapy continues to be biguanides and diamidines, with surgery as a last resort.

Antiamoebic Susceptibility in Acanthamoeba Keratitis: Comparison of Isolates From South India and Northern California

PURPOSE

Outcomes of Acanthamoeba keratitis are often worse in India than in the United States. The goal of this study was to determine whether antiamoebic susceptibility patterns were different when comparing Acanthamoeba isolates from India with those of the United States.

METHODS

Acanthamoeba isolates were obtained from corneal scrapings of 43 patients with infectious keratitis seen at the Francis I. Proctor Foundation (N = 23) and Aravind Eye Hospital (N = 20) from 2008 through 2012 and plated on growth media. A previously described minimum cysticidal concentration (MCC) assay was performed by a single laboratory technician to assess susceptibility to 5 antiamoebic agents for all isolates. Testing was conducted in triplicate, with the median MCC chosen for analyses.

RESULTS

The MCC (μg/mL) of polyhexamethylene biguanide was 6.25 [IQR 5.47-12.5] for Aravind isolates and 6.25 [IQR 6.25-9.375] for Proctor isolates ( P = 0.75), corresponding values were 6.25 [IQR 3.125-6.25] and 3.125 [IQR 3.125-9.375] for chlorhexidine ( P = 0.81), 2500 [IQR 2500-5000] and 5000 [IQR 1250-20,000] for voriconazole ( P = 0.25), 15.6 [IQR 15.6-39.0625] and 15.6 [IQR 15.6-31.25] for hexamidine ( P = 0.92), and 15.6 [IQR 7.81-15.6] and 15.6 [IQR 7.81-31.25] for propamidine ( P = 0.42).

CONCLUSIONS

This study found no statistically significant differences in antiamoebic susceptibility of Indian versus US samples from Acanthamoeba keratitis clinical isolates. These findings suggest that differences in antiamoebic susceptibility are likely not responsible for differential outcomes in Acanthamoeba keratitis between the 2 locations.

Treatment of recalcitrant Acanthamoeba Keratitis with Photoactivated Chromophore for Infectious Keratitis Corneal Collagen Cross-Linking (PACK-CXL)

PURPOSE

To describe a case of recalcitrant Acanthamoeba Keratitis (AK) complicated by medical non-compliance and medication intolerance that was successfully treated with photoactivated chromophore for infectious keratitis corneal collagen cross-linking (PACK-CXL).

OBSERVATIONS

A 31-year-old male presented with right eye pain and redness in the setting of fresh water exposure and scleral contact lens wear. He had lack of a response to treatment with antiviral therapy for 3 months by an outside provider. Cultures were found to be positive for Acanthamoeba and the patient was treated with an extended course of various anti-amoebic therapies with poor compliance due to pain and toxicity. He was eventually treated with intrastromal voriconazole and Miltefosine without improvement and eventually had PACK-CXL with resolution of his infection and pain.

CONCLUSION

PACK-CXL was associated with a dramatic improvement in a case of recalcitrant Acanthamoeba keratitis unresponsive to both traditional and novel therapies and may be a viable alternative or adjunctive therapy for Acanthamoeba keratitis.

Amoebicidal Activity of Poly-Epsilon-Lysine Functionalized Hydrogels

Purpose

To determine the amoebicidal activity of functionalized poly-epsilon-lysine hydrogels (pɛK⁺) against Acanthamoeba castellanii.

Methods

A. castellanii trophozoites and cysts were grown in the presence of pɛK solution (0–2.17 mM), pɛK or pɛK⁺ hydrogels, or commercial hydrogel contact lens (CL) for 24 hours or 7 days in PBS or Peptone-Yeast-Glucose (PYG) media (nutrient-deplete or nutrient-replete cultures, respectively). Toxicity was determined using propidium iodide and imaged using fluorescence microscopy. Ex vivo porcine corneas were inoculated with A. castellanii trophozoites ± pɛK, pɛK⁺ hydrogels or commercial hydrogel CL for 7 days. Corneal infection was assessed by periodic acid–Schiff staining and histologic analysis. Regrowth of A. castellanii from hydrogel lenses and corneal discs at 7 days was assessed using microscopy and enumeration.

Results

The toxicity of pɛK⁺ hydrogels resulted in the death of 98.52% or 83.31% of the trophozoites at 24 hours or 7 days, respectively. The toxicity of pɛK⁺ hydrogels resulted in the death of 70.59% or 82.32% of the cysts in PBS at 24 hours or 7 days, respectively. Cysts exposed to pɛK⁺ hydrogels in PYG medium resulted in 75.37% and 87.14% death at 24 hours and 7 days. Ex vivo corneas infected with trophozoites and incubated with pɛK⁺ hydrogels showed the absence of A. castellanii in the stroma, with no regrowth from corneas or pɛK⁺ hydrogel, compared with infected-only corneas and those incubated in presence of commercial hydrogel CL.

Conclusions

pɛK⁺ hydrogels demonstrated pronounced amoebicidal and cysticidal activity against A. castellanii. pɛK⁺ hydrogels have the potential for use as CLs that could minimize the risk of CL-associated Acanthamoeba keratitis.

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.

Acanthamoeba Keratitis, Pathology, Diagnosis and Treatment

Acanthamoeba keratitis is an unusual corneal infection that is recently increasing in frequency and is often contracted by contact lens wearers, someone who experienced recent eye trauma, or someone exposed to contaminated waters. Acanthamoeba survive in air, soil, dust, and water. Therefore, eye trauma and poor contact lens hygiene practices lead to the entrapment of debris and thus infection. Acanthamoeba keratitis results in severe eye pain, inflammation, and defects of the epithelium and stroma that can potentially result in vision loss if not diagnosed early and treated promptly. The disease can be diagnosed using corneal scrape/biopsy, polymerase chain reactions, impression cytology, or in vivo confocal microscopy. Once diagnosed, it is usually treated with an antimicrobial combination therapy of biguanide and aromatic diadine eye drops for several months. Advanced stages of the disease result in vision loss and the need for corneal transplants. Avoiding the risk factors and diagnosing the disease early are the most effective ways to combat Acanthamoeba keratitis.

In vitro effects of multi-purpose contact lens disinfecting solutions towards survivability of Acanthamoeba genotype T4 in Malaysia

The incidence of Acanthamoeba keratitis has been increasing since the previous decades, especially among contact lens users. This infection is majorly caused by the use of ineffective contact lens disinfecting solution. Thus, this study was conducted to evaluate the in vitro effects of multi-purpose disinfecting solutions (MPDS) against Acanthamoeba trophozoites and cysts. Acanthamoeba genotype T4 isolated from contact lens paraphernalia and an environmental strains were propagated for trophozoite or cyst-containing culture and adjusted in final concentration of 1 × 10⁵ cells/ml. Amoebicidal and cysticidal assays were conducted by incubating trophozoites and cysts with OPTI-FREE® Express®, ReNu® Fresh™, Complete® Multi-Purpose Solution and AVIZOR Unica® Sensitive according to the manufacturer’s minimum recommended disinfectant time (MMRDT) for up to 12 h at 30 ⁰C. Trypan blue hemocytometer-based microscopic counts determined amoebicidal and cysticidal effects. The viability of Acanthamoeba trophozoites and cysts was confirmed by re-inoculated them in the 1.5% non-nutrient agar plates. It was found that none of the MPDS showed amoebicidal and cysticidal effects during the MMRDT. However, OPTI-FREE® Express® demonstrated a significant differences in average cell reduction for both stages within MMRDT. When subjected to 12 h exposure, both OPTI-FREE® Express® and ReNu® Fresh™ led to significant reduction in the number of trophozoite and cyst cells. Notably, Complete® Multi-Purpose Solution and AVIZOR Unica® Sensitive did appreciably improve the solution effectiveness towards trophozoite cells when incubated for 12 h. All MPDS were largely ineffective, with 100% survival of all isolates at MMRDT, while OPTI-FREE® Express® showed limited amoebicidal activity against the contact lens paraphernalia isolate, however, it was more against the environmental strains after 12 h incubation time. The commercially available MPDS employed in this research offered minimal effectiveness against the protozoa despite the contact time. Improvement or development of new solution should consider the adjustment of the appropriate disinfectant concentration, adequate exposure time or the incorporation of novel chemical elements, which are effective against Acanthamoeba for accelerated disinfecting and more reduction of potential exposure of contact lens users to Acanthamoeba keratitis.

Alkyl-carbon chain length of two distinct compounds and derivatives are key determinants of their anti-Acanthamoeba activities

The opportunistic pathogen, Acanthamoeba castellanii is the causative agent for the sight threatening infection Acanthamoeba keratitis (AK). It is commonly associated with contact lens wearers, and prevalence is increasing at an alarming rate due to an inadequate preventive strategy to protect the lens from this protist. This problem is compounded by the lack of an effective acanthamoebocide, particularly with cysticidal activity in the contact lens solutions. We have used cytotoxicity assays and a variety of biophysical approaches to show that two molecules with tails made of alkyl carbon, alkylphosphocholines (APCs) and quaternary ammonium compounds (QACs) had significant chain-length dependent efficacy against A. castellanii trophozoites, the latter producing death via permeabilization, and DNA complexing. QACs were more effective than APCs and had activity against cysts. Conversely, the QAC with 12 alkyl carbon chain, was non toxic, its presence increased A. castellanii trophozoites biomass and delayed encystation by 96 h. Interestingly, it was unable to induce excystation and increased trophozoite sensitivity to APC16. These results present a mono- and multi-inhibitor management strategy effective against trophozoites and cysts that may be useful for formulating into contact lense cleaning solutions and reducing AK incidence.

Acanthamoeba Keratitis: Current Status and Urgent Research Priorities

Background:

First discovered in the early 1970s, Acanthamoeba keratitis has remained a major eye infection and presents a significant threat to the public health, especially in developing countries. The aim is to present a timely review of our current understanding of the advances made in this field in a comprehensible manner and includes novel concepts and provides clear directions for immediate research priorities.

Methods:

We undertook a search of bibliographic databases for peer-reviewed research literature and also summarized our published results in this field.

Results:

The present review focuses on novel diagnostic and therapeutic strategies in details which can provide access to management and treatment of Acanthamoeba keratitis. This coupled with the recently available genome sequence information together with high throughput genomics technology and innovative approaches should stimulate interest in the rational design of preventative and therapeutic measures. Current treatment of Acanthamoeba keratitis is problematic and often leads to infection recurrence. Better understanding of diagnosis, pathogenesis, pathophysiology and therapeutic regimens, would lead to novel strategies in treatment and prophylaxis.

In Vitro Evaluation of the Inhibitory Effect of Topical Ophthalmic Agents on Acanthamoeba Viability

Purpose

To compare the antimicrobial effect of topical anesthetics, antivirals, antibiotics, and biocides on the viability of Acanthamoeba cysts and trophozoites in vitro.

Methods

Amoebicidal and cysticidal assays were performed against both trophozoites and cysts of Acanthamoeba castellanii (ATCC 50370) and Acanthamoeba polyphaga (ATCC 30461). Test agents included topical ophthalmic preparations of common anesthetics, antivirals, antibiotics, and biocides. Organisms were exposed to serial two-fold dilutions of the test compounds in the wells of a microtiter plate to examine the effect on Acanthamoeba spp. In addition, the toxicity of each of the test compounds was determined against a mammalian cell line.

Results

Proxymetacaine, oxybuprocaine, and especially tetracaine were all toxic to the trophozoites and cysts of Acanthamoeba spp., but lidocaine was well tolerated. The presence of the benzalkonium chloride (BAC) preservative in levofloxacin caused a high level of toxicity to trophozoites and cysts. With the diamidines, the presence of BAC in the propamidine drops was responsible for the activity against Acanthamoeba spp. Hexamidine drops without BAC showed good activity against trophozoites, and the biguanides polyhexamethylene biguanide, chlorhexidine, alexidine, and octenidine all showed excellent activity against trophozoites and cysts of both species.

Conclusions

The antiamoebic effects of BAC, povidone iodine, and tetracaine are superior to the current diamidines and slightly inferior to the biguanides used in the treatment for Acanthamoeba keratitis.

Translational Relevance

Ophthalmologists should be aware that certain topical anesthetics and ophthalmic preparations containing BAC prior to specimen sampling may affect the viability of Acanthamoeba spp. in vivo, resulting in false-negative results in diagnostic tests.

Acanthamoeba keratitis therapy: time to cure and visual outcome analysis for different antiamoebic therapies in 227 cases

AIMS

To test the hypothesis that Acanthamoeba keratitis (AK) outcomes differ for different topical antiamoebic therapies (AAT) and to provide the detailed patient outcome data.

METHODS

A retrospective cohort study of 227 patients developing AK between 25 July 1991 and 10 August 2012. Inclusion criteria required a complete record of AAT treatment for both the primary outcome of a medical cure rate at 12 months and the secondary outcome of Snellen visual acuity ≤6/24 and/or surgical intervention. Analysis used multivariable regression to control for differences in baseline disease characteristics for both primary and secondary outcomes with unadjusted analyses for other outcomes. Subjects were categorised for analysis both by the AAT used at baseline and also by mutually exclusive AAT (patients exposed to all the drugs in each group, and no others, for some period). AAT categories were PHMB monotherapy, PHMB+diamidine, PHMB+chlorhexidine+diamidine, diamidine monotherapy and other AAT.

RESULTS

Analysis by baseline AAT showed no notable difference between treatments for both a medical cure at 12 months in 60.79% (138/227) or for a poor outcome in 49.34% (112/227). When AATs were analysed by mutually exclusive groups, PHMB monotherapy provided the best outcomes. These findings are subject to bias requiring careful interpretation. Overall cure rates for the 214 subjects with resolved outcomes were 94.27% (214/227), median time to cure 5 months (IQR 3.25-9.00 months) and range 1-26.24 months.

CONCLUSION

PHMB 0.02% monotherapy for the initial treatment of AK is as effective as biguanide+diamidine combination therapy. Chlorhexidine monotherapy was too infrequent for comparison. The outcome data are the most detailed available.

Acanthamoeba in the eye, can the parasite hide even more? Latest developments on the disease

Acanthamoeba spp. is a free living protozoan in the environment, but can cause serious diseases. Acanthamoeba keratitis (AK), a severe and painful eye infection, must be treated as soon as possible to prevent ulceration of the cornea, loss of visual acuity, and eventually blindness or enucleation. Although the disease affects principally contact lens (CLs) wearers, it is recognized nowadays as a cause of keratitis also in non-CLs wearers. Although the number of infections caused by these amoebae is low, AK is an emerging disease presenting an extended number of cases each year worldwide mostly due to the increasing use of CLs, but also to better diagnostic methods and awareness. There are two principal causes that lead to severe outcomes: misdiagnosis or late diagnosis of the causal agent, and lack of a fully effective therapy due to the existence of a highly resistant cyst stage of Acanthamoeba. Recent studies have reported different genotypes that have not been previously associated with this disease. In addition, Acanthamoeba can act as a reservoir for phylogenetically diverse microorganisms. In this regard, recently giant viruses called Pandoravirus have been found within genotypes producing keratitis. What potential risk this poses is not yet known. This review focuses on an overview of the present status and future prospects of this re-emerging pathology, including features of the parasite, epidemiology, clinical aspects, diagnosis, and treatment.

Characterisation of sterol biosynthesis and validation of 14α-demethylase as a drug target in Acanthamoeba

The soil amoebae Acanthamoeba causes Acanthamoeba keratitis, a severe sight-threatening infection of the eye and the almost universally fatal granulomatous amoebic encephalitis. More effective treatments are required. Sterol biosynthesis has been effectively targeted in numerous fungi using azole compounds that inhibit the cytochrome P450 enzyme sterol 14α-demethylase. Herein, using Gas Chromatography Mass Spectrometry (GCMS), we demonstrate that the major sterol of Acanthamoeba castellanii is ergosterol and identify novel putative precursors and intermediate sterols in its production. Unlike previously reported, we find no evidence of 7-dehydrostigmasterol or any other phytosterol in Acanthamoeba. Of five azoles tested, we demonstrate that tioconazole and voriconazole have the greatest overall inhibition for all isolates of Acanthamoeba castellanii and Acanthamoeba polyphaga tested. While miconazole and sulconazole have intermediate activity econazole is least effective. Through GCMS, we demonstrate that voriconazole inhibits 14α-demethylase as treatment inhibits the production of ergosterol, but results in the accumulation of the lanosterol substrate. These data provide the most complete description of sterol metabolism in Acanthamoeba, provide a putative framework for their further study and validate 14α-demethylase as the target for azoles in Acanthamoeba.

In-vitro development of an effective treatment for Acanthamoeba keratitis

The aim of this study was to develop an in-vitro topical treatment for Acanthamoeba keratitis (AK) effective against cysts and trophozoites. Qualitative assays were performed with voriconazole, chlorhexidine, propamidine, cellulase, tobramycin, ciprofloxacin and paromomycin as monotherapy and various combinations. Riboflavin with ultraviolet-A (R + UV-A) as monotherapy or combined with voriconazole and moxifloxacin was also tested. Quantitative assays to assess cyst viability after treatment were performed for the chemicals that showed the highest activity in the qualitative assays. Paromomycin and propamidine did not show antiamoebic activity. Regardless of the total dose, no amoebicidal effect was observed for R + UV-A. Tobramycin, ciprofloxacin, voriconazole, chlorhexidine and cellulase were selected for quantitative assays because they appeared to cause greater damage to the structure of amoebae. Chlorhexidine and ciprofloxacin were the most active against Acanthamoeba spp. as monotherapy. Among the combinations evaluated, ciprofloxacin-voriconazole-chlorhexidine showed the greatest amoebicidal activity, with severe damage of the cellular membrane and an important decrease in cell concentration. In summary, ciprofloxacin as monotherapy and in combination with voriconazole and chlorhexidine has been classified as promising treatment. Additional in-vivo studies in animal models and clinical trials in patients with AK should be considered to confirm the efficacy of ciprofloxacin.

Therapeutic agents and biocides for ocular infections by free-living amoebae of Acanthamoeba genus

Acanthamoeba keratitis is a sight-threatening infectious disease. Resistance of the cystic form of the protozoan to biocides and the potential toxicity of chemical compounds to corneal cells are the main concerns related to long-term treatment with the clinically available ophthalmic drugs. Currently, a limited number of recognized antimicrobial agents are available to treat ocular amoebic infections. Topical application of biguanide and diamidine antiseptic solutions is the first-line therapy. We consider the current challenges when treating Acanthamoeba keratitis and review the chemical properties, toxicities, and mechanisms of action of the available biocides. Antimicrobial therapy using anti-inflammatory drugs is controversial, and aspects related to this topic are discussed. Finally, we offer our perspective on potential improvement of the effectiveness and safety of therapeutic profiles, with the focus on the quality of life and the advancement of individualized medicine.

The Development of Drugs against Acanthamoeba Infections

For the past several decades, there has been little improvement in the morbidity and mortality associated with Acanthamoeba keratitis and Acanthamoeba encephalitis, respectively. The discovery of a plethora of antiacanthamoebic compounds has not yielded effective marketed chemotherapeutics. The rate of development of novel antiacanthamoebic chemotherapies of translational value and the lack of interest of the pharmaceutical industry in developing such chemotherapies have been disappointing. On the other hand, the market for contact lenses/contact lens disinfectants is a multi-billion-dollar industry and has been successful and profitable. A better understanding of drugs, their targets, and mechanisms of action will facilitate the development of more-effective chemotherapies. Here, we review the progress toward phenotypic drug discovery, emphasizing the shortcomings of useable therapies.

Recent trends: Medical management of infectious keratitis

This review article highlights the newer diagnostic modalities and approaches in the medical management of infectious keratitis. A Medline literature search conducted to March 2014 has been included. Recent studies or publications were selected from international indexed journals using suitable key words. Development of specular microscopy and polymerase chain reaction (PCR) has a promising role as diagnostic modalities in infectious keratitis, especially in refractory cases. Previously fortified antibiotics have been the mainstay of treatment for bacterial keratitis. Recently, the advent of fourth-generation fluoroquinolones monotherapy has shown promising results in the management of bacterial keratitis. Corneal collagen cross-linking is being considered in the refractory cases. Topical natamycin and amphotericin B should be considered as the first choice anti-fungal agents in suspected filamentous or yeast infection respectively. Voriconazole and newer routes of administration such as intrastromal and intracameral injection of conventional anti-fungal agents have demonstrated a positive clinical response. Ganciclovir is a newer anti-viral agent with promising results in herpes simplex keratitis. Thus, introduction of newer diagnostic modalities and collagen cross-linking along with fourth-generation fluoroquinolones and newer azoles have a promising role in the management of infectious keratitis.

Medical interventions for acanthamoeba keratitis

BACKGROUND

Acanthamoeba are microscopic, free-living, single-celled organisms which can infect the eye and lead to Acanthamoeba keratitis (AK). AK can result in loss of vision in the infected eye or loss of eye itself; however, there are no formal guidelines or standards of care for the treatment of AK.

OBJECTIVES

To evaluate the relative effectiveness and safety of medical therapy for the treatment of AK.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (2015, Issue 1), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to January 2015), EMBASE (January 1980 to January 2015), PubMed (1948 to January 2015), Latin American and Caribbean Health Sciences Literature Database (LILACS) (1982 to January 2015), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic search for trials. We last searched the electronic databases on 9 January 2015.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of medical therapy for AK, regardless of the participants' age, sex, or etiology of disease. We included studies that compared either anti-amoeba therapy (drugs used alone or in combination with other medical therapies) with no anti-amoeba therapy or one anti-amoeba therapy with another anti-amoeba therapy.

DATA COLLECTION AND ANALYSIS

Two authors independently screened search results and full-text reports, assessed risk of bias, and abstracted data. We used standard methodological procedures as set forth by the Cochrane Collaboration.

MAIN RESULTS

We included one RCT (56 eyes of 55 participants) in this review. The study compared two types of topical biguanides for the treatment of AK: chlorhexidine 0.02% and polyhexamethylene biguanide (PHMB) 0.02%. All participants were contact lens wearers with a median age of 31 years. Treatment duration ranged from 51 to 145 days. The study, conducted in the UK, was well-designed and had low risk of bias overall.Outcome data were available for 51 (91%) of 56 eyes. Follow-up times for outcome measurements in the study were not reported. Resolution of infection, defined as control of ocular inflammation, relief of pain and photosensitivity, and recovery of vision, was 86% in the chlorhexidine group compared with 78% in the PHMB group (relative risk (RR) 1.10, 95% confidence intervals (CI) 0.84 to 1.42). In the chlorhexidine group, 20 of 28 eyes (71%) had better visual acuity compared with 13 of 23 eyes (57%) in the PHMB group at final follow-up (RR 1.26, 95% CI 0.82 to 1.94). Five participants required therapeutic keratoplasty: 2 in the chlorhexidine group compared with 3 in the PHMB group (RR 0.55, 95% CI 0.10 to 3.00). No serious adverse event related to drug toxicity was observed in the study.

AUTHORS' CONCLUSIONS

There is insufficient evidence to evaluate the relative effectiveness and safety of medical therapy for the treatment of AK. Results from the one included study yielded no difference with respect to outcomes reported between chlorhexidine and PHMB. However, the sample size was inadequate to detect clinically meaningful differences between the two groups as indicated by the wide confidence intervals of effect estimates.

[Acanthamoeba keratitis]

Early diagnosis and appropriate therapy are key elements for a good prognosis in Acanthamoeba keratitis (AK). AK should be considered in any case of corneal trauma complicated by exposure to soil or contaminated water, and in all contact lens (CL) wearers. A presumptive diagnosis of AK can be made clinically and with in vivo confocal microscopy, although a definitive diagnosis requires identification of Acanthamoeba on direct scraping, histology, or identification of Acanthamoeba DNA by polymerase chain reaction (PCR). We use cysticidal drugs for treating AK because encysted forms are more resistant than trophozoites to treatment. The treatment protocol used a biguanide (PHMB 0.02% or chlorhexidine 0.02%) and a diamidine (propamidine 0.1% or hexamidine 0.1%). New diagnostic modalities and more specific topical anti-amoebic treatments would substantially benefit patients with AK.

Development of a practical complete-kill assay to evaluate anti-Acanthamoeba drugs

IMPORTANCE

Acanthamoeba keratitis is a debilitating eye disease that requires effective topical drug therapy. Currently, there is no standard in vitro test to evaluate anti-Acanthamoeba drugs.

OBJECTIVE

To develop a practical in vitro complete-kill assay to assess anti-Acanthamoeba drugs.

DESIGN AND SETTING

Isolates of Acanthamoeba strains (n = 15) evaluated in a clinical laboratory. An in vitro laboratory assay was created to determine whether polyhexamethylene biguanide, 0.02%, chlorhexidine digluconate, 0.02%, hexamidine diisethioonate, 0.1%, and voriconazole, 1.0%, were effective in completely killing 15 different isolates of Acanthamoeba at time points of 24, 48, and 72 hours in comparison with a saline control. Each 0.5-mL volume of drug was inoculated with 0.1 mL of Acanthamoeba cysts (range, 1-3 × 10(6)/mL) (determined with a hemacytometer) and allowed to incubate at 30°C. At the time points listed, 0.05 mL from each treatment group was inoculated onto nonnutrient agar overlaid with Enterobacter aerogenes. The plates were microscopically examined for growth 1 and 2 weeks after inoculation. At 2 weeks, all plates were subcultured onto a fresh medium. At another 7 days, the growth in subculture at each time point was graded "1" for growth and "0" for no growth.

MAIN OUTCOMES AND MEASURES

The cumulative grades of 3 time points (range, 0-3) for each drug and isolate were nonparametrically compared to determine differences in growth between the drugs. The "kill" incidence rates over the 3 time points were also compared.

RESULTS

In vitro testing determined that antiacanthamoebal efficacy (determined by the median growth grade and the kill incidence rate) was more prominent for hexamidine diisethioonate (median growth grade, 0.0; kill incidence rate, 93% [14 of 15 isolates]) and polyhexamethylene biguanide (median growth grade, 0.0; kill incidence rate, 80% [12 of 15 isolates]) than for chlorhexidine digluconate (median growth grade, 1.0; kill incidence rate, 40% [6 of 15 isolates]), voriconazole (median growth grade, 2.0; kill incidence rate, 13% [2 of 15 isolates]), and saline (median growth grade, 3.0; kill incidence rate, 0% [0 of 15 isolates]).

CONCLUSIONS AND RELEVANCE

The complete-kill assay appears to provide separation in the effectiveness of different antiamoebic drug solutions. This assay may be helpful for guiding topical Acanthamoeba therapy and providing a practical method to evaluate and screen new anti-infectives in the treatment of Acanthamoeba keratitis.

Treatment of Acanthamoeba keratitis

The treatment of Acanthamoeba keratitis has now been possible since the first successful therapy developed in the mid 1980s with a combination of propamidine 0.1% (Brolene) and neomycin 1%. However, only half the patients responded to this regimen as the cysts were often resistant to neomycin and relatively insensitive to propamidine. This led to research for better therapy, culminating in the mid 1990s with research in Glasgow demonstrating much increased effectiveness with use of the biguanide chlorhexidine 0.02% and in London and Bristol for similar effectiveness with the polymeric polyhexamethylene biguanide (PHMB) 0.02%. Both biguanides were combined with propamidine for enhanced effectiveness but were also shown to be effective as monotherapy. While this therapy inactivates the trophozoites and cysts in Acanthamoeba keratitis in the majority of patients (approximately 90%), there have been notable failures particularly when presentation is late with deep stromal infection. Additional highly acanthamoebicidal drugs are needed that can penetrate the stroma for synergistic action. This role may be taken up by certain antineoplastic drugs, such as alkylphosphocholine-1 (Miltefosine), that also have antiprotozoal activity.

Acanthamoeba-cytopathic protein induces apoptosis and proinflammatory cytokines in human corneal epithelial cells by cPLA2α activation

PURPOSE

We have shown that Acanthamoeba interacts with a mannosylated protein on corneal epithelial cells and stimulates trophozoites to secrete a mannose-induced 133 kDa protease (MIP-133), which facilitates corneal invasion and induces apoptosis. The mechanism of MIP-133-induced apoptosis is unknown. The aim of this study was to determine if MIP-133 induces apoptosis and proinflammatory cytokines/chemokines in human corneal epithelial (HCE) cells via the cytosolic phospholipase A(2α) (cPLA(2α)) pathway.

METHODS

HCE cells were incubated with or without MIP-133 at doses of 7.5, 15, and 50 μg/mL for 6, 12, and 24 hours. The effects of cPLA(2α) inhibitors on cPLA(2α), arachidonic acid (AA) release, and apoptosis were tested in vitro. Inhibition of cPLA(2α) involved preincubating HCE cells for 1 hour with cPLA(2α) inhibitors (10 μM methyl-arachidonyl fluorophosphonate [MAFP] or 20 μM arachidonyl trifluoromethyl ketone [AACOCF3]) with or without MIP-133 for 24 hours. Expression of cPLA(2α) mRNA and enzyme was examined by RT-PCR and cPLA(2) activity assays, respectively. Apoptosis of corneal epithelial cells was determined by caspase-3 and DNA fragmentation assays. Expression of IL-8, IL-6, IL-1β, and IFN-γ was examined by RT-PCR and ELISA.

RESULTS

MIP-133 induced significant cPLA(2α) (approximately two to four times) and AA release (approximately six times) from corneal cells while cPLA(2α) inhibitors significantly reduced cPLA(2α) (approximately two to four times) and AA release (approximately three times) (P < 0.05). cPLA(2α) inhibitors significantly inhibited MIP-133-induced DNA fragmentation approximately 7 to 12 times in HCE cells (P < 0.05). MIP-133 specifically activates cPLA(2α) enzyme activity in HCE cells, which is blocked by preincubation with anti-MIP-133 antibody. In addition, MIP-133 induced significant IL-8, IL-6, IL-1β, and IFN-γ production, approximately two to three times (P < 0.05).

CONCLUSIONS

MIP-133 interacts with phospholipids on plasma membrane of HCE cells and activates cPLA(2α). cPLA(2α) is involved in apoptosis, AA release, and activation of proinflammatory cytokines/chemokines from HCE cells. cPLA(2α) inhibitors may be a therapeutic target in Acanthamoeba keratitis.

Practice patterns and opinions in the treatment of acanthamoeba keratitis

PURPOSE

Management of acanthamoeba keratitis remains challenging for ophthalmologists. We conducted a survey of members of The Cornea Society to elicit expert opinions on the diagnosis and treatment of acanthamoeba keratitis.

METHODS

An online survey was sent to all subscribers of The Cornea Society via the kera-net listserv. Descriptive statistics were performed.

RESULTS

Eighty-two participants completed the online survey. Of the 82 respondents, 76.8% included the combination of clinical examination and culture in their diagnostic strategy and 43.9% used confocal microscopy. Most respondents (97.6%) had used combination therapy with multiple agents to treat acanthamoeba keratitis at some point in the past, whereas a smaller proportion (47.6%) had ever used monotherapy. Respondents most commonly chose polyhexamethylene biguanide as the ideal choice for monotherapy (51.4%), and dual therapy with a biguanide and diamidine as the ideal choice for combination therapy (37.5%). The majority of respondents (62.2%) reported using topical corticosteroids at least some of the time for acanthamoeba keratitis. Keratoplasty was an option considered by most respondents (75.6%), although most (85.5%) would only perform surgery after medical treatment failure.

CONCLUSIONS

There was a wide range of current practice patterns for the diagnosis and treatment of acanthamoeba keratitis. The lack of sufficiently powered comparative effectiveness studies and clinical trials makes evidence-based decision-making for this disease difficult.

Effect of combined chlorhexidine gluconate and neosporin on experimental keratitis with two pathogenic strains of Acanthamoeba

Acanthamoeba keratitis (AK) is a painful, sight-threatening, and difficult-to-treat corneal infection caused by the ubiquitous free-living amoebae Acanthamoeba species. The aim of the present study was to compare the severity of keratitis, caused by Acanthamoeba hatchetii and Acanthamoeba castellanii infections, and to assess the therapeutic effects of combined chlorhexidine (CHX) and Neosporin® treatment in rats. The rats were first divided into two groups, in which the eyes of the animals were infected with A. hatchetii or A. castellanii trophozoites. On day 5, all corneas were examined in order to determine the degree of infection (grade 0 to 3), and animals were divided into two new groups, treatment and infected control groups. The treatment was continued for 28 days, followed by excision and histological evaluation of the corneas. In conclusion, the clinical picture progressed more rapidly and severely in eyes infected by A. castellanii, while it was non-invasive and slower to progress with A. hatchetii. Moreover, eyes infected by A. hatchetii responded quicker and more positively to therapy, consistent with its clinical course, while a longer recovery was seen with A. castellanii. Histological examinations revealed the presence of A. castellanii and A. hatchetii trophozoites in the stroma of eyes of the treatment and control groups. As a result, our findings suggest that a combination of Neosporin with lower doses of CHX may be beneficial to treat patients with early diagnosis of AK.

Double-biguanide therapy for resistant acanthamoeba keratitis

Aims

To report the clinical and diagnostic findings of a patient with Acanthamoeba keratitis resistant to both polyhexamethylene biguanide (PHMB)-hexamidine and chlorhexidine-hexamidine treatment.

Methods

Slit-lamp biomicroscopy, corneal cell scraping and histopathology were performed on a 39-year-old woman presenting with corneal ulcer in her left eye.

Results

The patient was successfully treated with PHMB-chlorhexidine association therapy. Subsequent perforating keratoplasty remained clear at the last follow-up visit after 7 months and increased visual acuity to 20/20 with correction.

Conclusions

This case emphasizes the proteiform aspects of Acanthamoeba drug resistance, and suggests that PHMB-chlorhexidine association might represent an additional option for cases resistant to standard therapy.

Contact lens-related acanthamoeba keratitis

Acanthamoeba keratitis is a rare but severe disease, with more than 95% of cases occurring in contact lens wearers. With a worldwide resurgence of contact lens-related disease, this report illustrates the clinical characteristics and treatment challenges representative of this disease. This report describes Acanthamoeba keratitis in a 47-year-old female using extended wear silicone hydrogel contact lenses, with a history of swimming in a home pool and failure to subsequently disinfect the contact lenses. The diagnosis was based on clinical signs, disease course, and confocal microscopy results despite a negative result for corneal smear and culture. The corneal signs included an epithelial defect, epithelial irregularities, anterior stromal infiltrates, perineural infiltrates, an anterior stromal ring infiltrate, and hypopyon. The case was diagnosed as an infective keratitis and treated promptly using intensive topical administration of fortified gentamicin and cephalothin. The high likelihood Acanthamoeba prompted immediate use of polyhexamethylbiguanide and chlorhexidine, with propamide and adjunct treatment using atropine and oral diclofenac. Steroids were added on day 3, and the frequency of administration of antibacterial treatment was gradually reduced and ceased by day 10. The analgesia was stopped at 3 months. The frequency of administration of antiamoeba therapy and steroid treatment was slowly reduced and all treatment was ceased after 18 months. Despite considerable morbidity in terms of the treatment duration, hospitalization, outpatient appointments, and associated disease costs, the final visual outcome (6/6) was excellent.

Riboflavin and ultraviolet light a therapy as an adjuvant treatment for medically refractive Acanthamoeba keratitis: report of 3 cases

PURPOSE

To present the first 3 cases of Acanthamoeba keratitis (AK), unresponsive to medical treatment, that were successfully treated with a novel adjunctive therapy using ultraviolet light A (UVA) and riboflavin (B2).

DESIGN

Interventional case series.

PARTICIPANTS

Two patients with confirmed AK and 1 patient with presumptive AK, which were all refractive to multidrug conventional therapy.

INTERVENTION

Two treatment sessions involving topical application of 0.1% B2 solution to the ocular surface combined with 30 minutes of UVA irradiation focused on the corneal ulcer.

MAIN OUTCOME MEASURES

Clinical examination by slit lamp, confocal microscopy, and histopathology, when available.

RESULTS

All patients in these series showed a rapid reduction in their symptoms and decreased ulcer size after the first treatment session. The progress of the clinical improvement began to slow after 1 to 3 weeks of the first application and was then renewed after the second application. All ancillary signs of inflammation mostly resolved after the second treatment session. The ulcers in all patients continued to decrease and were closed within 3 to 7 weeks of the first application. Two patients developed dense central corneal scars, and penetrating keratoplasty was performed for visual rehabilitation. Histopathologic examination of the excised tissue revealed no Acanthamoeba organisms. The remaining patient had no symptoms or signs of infection, both clinically and by confocal microscopy, and was left with a semitransparent eccentric scar that did not affect visual acuity.

CONCLUSIONS

The adjunctive use of UVA and B2 therapy seems to be a possible alternative for selected cases of medication-resistant AK.

Acanthamoeba keratitis: diagnosis and treatment update 2009

PURPOSE

To describe the current management of Acanthamoeba keratitis (AK).

DESIGN

A perspective based on the literature and author experience.

RESULTS

Early diagnosis and appropriate therapy are key to a good prognosis. A provisional diagnosis of AK can be made using the clinical features and confocal microscopy, although a definitive diagnosis requires culture, histology, or identification of Acanthamoeba deoxyribonucleic acid by polymerase chain reaction. Routine use of tissue diagnosis is recommended, particularly for patients unresponsive to treatment for AK. Topical biguanides are the only effective therapy for the resistant encysted form of the organism in vitro, if not always in vivo. None of the other drugs that have been used meet the requirements of consistent cysticidal activity and may have no therapeutic role. The use of topical steroids is controversial, but probably beneficial, for the management of severe corneal inflammatory complications that have not responded to topical biguanides alone. The scleritis associated with AK is rarely associated with extracorneal invasion and usually responds to systemic anti-inflammatory treatment combined with topical biguanides. Therapeutic keratoplasty retains a role for therapy of some severe complications of AK but not for initial treatment. With modern management, 90% of patients can expect to retain visual acuity of 6/12 or better and fewer than 2% become blind, although treatment may take 6 months or more.

CONCLUSIONS

Better understanding of the pathogenesis of the extracorneal complications, the availability of polymerase chain reaction for tissue diagnosis, and effective licensed topical anti-amoebics would substantially benefit patients with AK.

The potential pathogenicity of chlorhexidine-sensitive Acanthamoeba strains isolated from contact lens cases from asymptomatic individuals in Tenerife, Canary Islands, Spain

Pathogenic strains of the genus Acanthamoeba are causative agents of a serious sight-threatening infection of the eye known as Acanthamoeba keratitis. The prevalence of this infection has risen in the past 20 years, mainly due to the increase in number of contact lens wearers. In this study, the prevalence of Acanthamoeba in a risk group constituted by asymptomatic contact lens wearers from Tenerife, Canary Islands, Spain, was evaluated. Contact lenses and contact lens cases were analysed for the presence of Acanthamoeba isolates. The isolates' genotypes were also determined after rDNA sequencing. The pathogenic potential of the isolated strains was subsequently established using previously described molecular and biochemical assays, which allowed the selection of three strains with high pathogenic potential. Furthermore, the sensitivity of these isolates against two standard drugs, ciprofloxacin and chlorhexidine, was analysed. As the three selected strains were sensitive to chlorhexidine, its activity and IC(50) were evaluated. Chlorhexidine was found to be active against these strains and the obtained IC(50) values were compared to the concentrations of this drug present in contact lens maintenance solutions. It was observed that the measured IC(50) was higher than the concentration found in these maintenance solutions. Therefore, the ineffectiveness of chlorhexidine-containing contact lens maintenance solutions against potentially pathogenic strains of Acanthamoeba is demonstrated in this study.

Medical management approach to infectious keratitis

This section provides guidelines on medical therapy of patients with infectious keratitis. In addition to initial empirical therapy, preferred medications, once the organisms responsible are isolated, are discussed. Atypical mycobacterial keratitis following lasik is described. General guidelines for supportive therapy and follow-up, of these patients are presented. Clinical response to treatment and indications for intervention are discussed. Possible causes and approach to cases refractory to medical therapy are discussed.