Successful medical therapy of Acanthamoeba keratitis with topical chlorhexidine and propamidine

Free-Living Amoebas in Extreme Environments: The True Survival in our Planet

Free-living amoebas (FLAs) are microorganisms, unicellular protozoa widely distributed in nature and present in different environments, such as water or soil; they are maintained in ecosystems and play a fundamental role in the biological control of bacteria, other protozoa, and mushrooms. In particular circumstances, some can reach humans or animals, promoting several health complications. Notably, FLAs are characterized by a robust capacity to survive in extreme environments. However, currently, there is no updated information on the existence and distribution of this protozoan in inhospitable places. Undoubtedly, the cellular physiology of these protozoan microorganisms is very particular. They can resist and live in extreme environments due to their encysting capacity and tolerance to different osmolarities, temperatures, and other environmental factors, which give them excellent adaptative resistance. In this review, we summarized the most relevant evidence related to FLAs and the possible mechanism, which could explain their adaptative capacity to several extreme environments.

Management of Filamentous Fungal Keratitis: A Pragmatic Approach

Filamentous fungal infections of the cornea known as filamentous fungal keratitis (FK) are challenging to treat. Topical natamycin 5% is usually first-line treatment following the results of several landmark clinical trials. However, even when treated intensively, infections may progress to corneal perforation. Current topical antifungals are not always effective and are often unavailable. Alternatives topical therapies to natamycin include voriconazole, chlorhexidine, amphotericin B and econazole. Surgical therapy, typically in the form of therapeutic penetrating keratoplasty, may be required for severe cases or following corneal perforation. Alternative treatment strategies such as intrastromal or intracameral injections of antifungals may be used. However, there is often no clear treatment strategy and the evidence to guide therapy is often lacking. This review describes the different treatment options and their evidence and provides a pragmatic approach to the management of fungal keratitis, particularly for clinicians working in tropical, low-resource settings where fungal keratitis is most prevalent.

Acanthamoeba Keratitis: an update on amebicidal and cysticidal drug screening methodologies and potential treatment with azole drugs

Introduction: Acanthamoeba encompasses several species of free-living ameba encountered commonly throughout the environment. Unfortunately, these species of ameba can cause opportunistic infections that result in Acanthamoeba keratitis, granulomatous amebic encephalitis, and occasionally systemic infection.Areas covered: This review discusses relevant literature found through PubMed and Google scholar published as of January 2021. The review summarizes current common Acanthamoeba keratitis treatments, drug discovery methodologies available for screening potential anti-Acanthamoeba compounds, and the anti-Acanthamoeba activity of various azole antifungal agents.Expert opinion: While several biguanide and diamidine antimicrobial agents are available to clinicians to effectively treat Acanthamoeba keratitis, no singular treatment can effectively treat every Acanthamoeba keratitis case.Efforts to identify new anti-Acanthamoeba agents include trophozoite cell viability assays, which are amenable to high-throughput screening. Cysticidal assays remain largely manual and would benefit from further automation development. Additionally, the existing literature on the effectiveness of various azole antifungal agents for treating Acanthamoeba keratitis is incomplete or contradictory, suggesting the need for a systematic review of all azoles against different pathogenic Acanthamoeba strains.

Biguanides drugs: Past success stories and promising future for drug discovery

Biguanides have attracted much attention a century ago and showed resurgent interest in recent years after a long period of dormancy. They constitute an important class of therapeutic agents suitable for the treatment of a wide spectrum of diseases. Therapeutic indications of biguanides include antidiabetic, antimalarial, antiviral, antiplaque, and bactericidal applications. This review presents an extensive overview of the biological activity of biguanides and different mechanisms of action of currently marketed biguanide-containing drugs, as well as their pharmacological properties when applicable. We highlight the recent developments in research on biguanide compounds, with a primary focus on studies on metformin in the field of oncology. We aim to provide a critical overview of all main bioactive biguanide compounds and discuss future perspectives for the design of new drugs based on the biguanide fragment.

Chlorhexidine gluconate 0.2% as a treatment for recalcitrant fungal keratitis in Uganda: a pilot study

OBJECTIVE

Fungal keratitis is a major ophthalmic public health problem, particularly in low-income and middle-income countries. The options for treating fungal keratitis are limited. Our study aimed to describe the outcomes of using chlorhexidine 0.2% eye-drops as additional treatment in the management of patients with recalcitrant fungal keratitis.

METHODS

This study was nested within a large cohort study of people presenting with microbial keratitis in Uganda. We enrolled patients with recalcitrant fungal keratitis not improving with topical natamycin 5% and commenced chlorhexidine 0.2%. Follow-up was scheduled for 3 months and 1 year. The main outcome measures were healing, visual acuity and scar size at final follow-up.

RESULTS

Thirteen patients were followed in this substudy. The patients were aged 27-73 years (median 43 years). Filamentous fungi were identified by microscopy of corneal scrape samples in all cases. Isolated organisms included Aspergillus spp, Fusarium spp, Candida spp, Bipolaris spp and Acremoninum spp. At the final follow-up, nine patients (75%) had healed; three had vision of better than 6/18. Three patients lost their eyes due to infection. In the remaining nine cases, corneal scarring was variable ranging from 4.6 to 9.4 mm (median 6.6 mm, IQR 5.9-8.0 mm); of these five had dense scars, three had moderate scars and one had a mild scar. None of the patients demonstrated signs of chlorhexidine toxicity during the follow-up.

CONCLUSION

Chlorhexidine 0.2% was found to be a useful sequential adjunctive topical antifungal in cases of fungal keratitis not responding to natamycin 5%, which warrants further evaluation.

Review, analysis, and education of antiseptic related ocular injury in the surgical settings

Preoperative skin antiseptic preparation is the gold standard for prevention of surgical infection. However, improper use of antiseptics may lead to severe ocular damage. Currently, the most common surgical antiseptics can be divided into aqueous-based and alcohol-based disinfectants, with chlorhexidine and iodine/iodophors being the two major components. Chlorhexidine has a persistent antimicrobial effect and is resistant to neutralization by blood or organic products in surgical wounds. Nevertheless, due to its toxicity to the ears, meninges, and eyes, application of chlorhexidine should be prohibited in these surgical fields. Iodine/iodophor is better tolerated by the ocular surface and is the recommended antiseptic for ophthalmic or head and neck surgeries close to the periocular area. Alcohol is less pricey and has a rapid antiseptic effect, though its desiccating effect and flammability restrict the use in mucosal or laser surgeries. The single or combined use of these antiseptics may inadvertently induce severe ocular damage, especially during time-consuming head and neck surgeries with prone, hyperextension, or lateral tilt positions, or surgeries under general anesthesia. Apart from the choice of antiseptics, appropriate selection and attachment of bio-occlusive dressings are key to avoiding antiseptic-related ocular injuries. In this review, we provided a comprehensive summary of the characteristics of antiseptics used in surgical settings and the possible mechanisms and outcomes of antiseptic-related ocular injuries. The prevention, diagnosis, and acute management of these complications were also discussed.

Acanthamoeba keratitis and contact lens wear

Acanthamoeba keratitis is a rare but serious complication of contact lens wear that may cause severe visual loss. The clinical picture is usually characterised by severe pain, sometimes disproportionate to the signs, with an early superficial keratitis that is often misdiagnosed as herpes simplex virus (HSV) keratitis. Advanced stages of the infection are usually characterised by central corneal epithelial loss and marked stromal opacification with subsequent loss of vision. In this paper, six cases of contact lens-related Acanthamoeba keratitis that occurred in Australia and New Zealand over a three-year period are described. Three of the patients were disposable soft lens wearers, two were hybrid lens wearers and one was a rigid gas permeable lens wearer. For all six cases, the risk factors for Acanthamoeba keratitis were contact lens wear with inappropriate or ineffective lens maintenance and exposure of the contact lenses to tap or other sources of water. All six patients responded well to medical therapy that involved topical use of appropriate therapeutic agents, most commonly polyhexamethylene biguanide and propamidine isethionate, although two of the patients also subsequently underwent deep lamellar keratoplasty due to residual corneal surface irregularity and stromal scarring. Despite the significant advances that have been made in the medical therapy of Acanthamoeba keratitis over the past 10 years, prevention remains the best treatment and patients who wear contact lenses must be thoroughly educated about the proper use and care of the lenses. In particular, exposure of the contact lenses to tap water or other sources of water should be avoided.

Biguanides: Species with versatile therapeutic applications

Biguanides are compounds in which two guanidine moieties are fused to form a highly conjugated system. Biguanides are highly basic and hence they are available as salts mostly hydrochloride salts, these cationic species have been found to exhibit many therapeutic properties. This review covers the research and development carried out on biguanides and accounts the various therapeutic applications of drugs containing biguanide group-such as antimalarial, antidiabetic, antiviral, anticancer, antibacterial, antifungal, anti-tubercular, antifilarial, anti-HIV, as well as other biological activities. The aim of this review is to compile all the medicinal chemistry applications of this class of compounds so as to pave way for the accelerated efforts in finding the drug action mechanisms associated with this class of compounds. Importance has been given to the organic chemistry of these biguanide derivatives also.

Effectiveness and Safety of Topical Chlorhexidine and Vitamin E TPGS in the Treatment of Acanthamoeba Keratitis: A Survey on 29 Cases

This study aimed to test the effectiveness of a solution of chlorhexidine (CHX) and D-α-tocopheryl polyethylene glycol succinate (Vitamin E TPGS or TPGS) in the treatment of Acanthamoeba keratitis (AK) via a prospective, interventional case series study. Twenty-nine consecutive patients with AK were enrolled. At baseline, best-corrected visual acuity (BCVA), slit lamp examination, confocal microscopy, and polymerase chain reaction (PCR) were performed. Topical therapy with CHX 0.02% and VE-TPGS 0.2% was administered hourly/24 h for the first day, hourly in the daytime for the next three days, and finally, every two hours in the daytime up to one month. BCVA and ocular inflammation were recorded after two weeks, four weeks, and three months from baseline. Mean logMAR BCVA significantly improved at two weeks (0.78) compared to baseline (1.76), remaining stable over time (0.80 at four weeks, 0.77 at three months). Ocular inflammation improved in 14 eyes at 2 weeks, with further slow improvements in all cases. At three months, no patient had signs of corneal inflammation. The presence of corneal scars was first recorded at the two-week follow-up, with an enlargement at the four-week follow-up. At the three-month follow-up, 19 eyes still showed corneal opacities. In conclusion, the tested solution was shown to be effective for the treatment of AK. Furthermore, it might represent a good first-line treatment.

Topical chlorhexidine 0.2% versus topical natamycin 5% for fungal keratitis in Nepal: rationale and design of a randomised controlled non-inferiority trial

INTRODUCTION

Fungal infections of the cornea, fungal keratitis (FK), are challenging to treat. Current topical antifungals are not always effective and are often unavailable, particularly in low-income and middle-income countries where most cases occur. Topical natamycin 5% is usually first-line treatment, however, even when treated intensively, infections may progress to perforation of the eye in around a quarter of cases. Alternative antifungal medications are needed to treat this blinding disease.Chlorhexidine is an antiseptic agent with antibacterial and antifungal properties. Previous pilot studies suggest that topical chlorhexidine 0.2% compares favourably with topical natamycin. Full-scale randomised controlled trials (RCTs) of topical chlorhexidine 0.2% are warranted to answer this question definitively.

METHODS AND ANALYSIS

We will test the hypothesis that topical chlorhexidine 0.2% is non-inferior to topical natamycin 5% in a two-arm, single-masked RCT. Participants are adults with FK presenting to a tertiary ophthalmic hospital in Nepal. Baseline assessment includes history, examination, photography, in vivo confocal microscopy and cornea scrapes for microbiology. Participants will be randomised to alternative topical antifungal treatments (topical chlorhexidine 0.2% and topical natamycin 5%; 1:1 ratio, 2-6 random block size). Patients are reviewed at day 2, day 7 (with reculture), day 14, day 21, month 2 and month 3. The primary outcome is the best spectacle corrected visual acuity (BSCVA) at 3 months. Primary analysis (intention to treat) will be by linear regression, with treatment arm and baseline BSCVA prespecified covariates. Secondary outcomes include epithelial healing time, scar/infiltrate size, ulcer depth, hypopyon size, perforation and/or therapeutic penetrating keratoplasty (corneal transplant), positive reculture rate (day 7) and quality of life (EuroQol-5 dimensions, WHO/PBD-VF20, WHOQOL-BREF).

ETHICS AND DISSEMINATION

The Nepal Health Research Council, the Nepal Department of Drug Administration and the London School of Hygiene and Tropical Medicine ethics committee have approved the trial. The results will be presented at local and international meetings and submitted to peer-reviewed journals for publication.

TRIAL REGISTRATION NUMBER

ISRCTN14332621; pre-results.

18S rDNA sequencing aided diagnosis of Acanthamoeba jacobsi keratitis -A case report

Identification of Acanthamoeba cysts and trophozoites in cases of keratitis is traditionally done with microbiological techniques such as smear examination with 10% potassium hydroxide (KOH) and culture. Double walled cyst with hexagonal inner wall is characteristic of Acanthamoeba. We report a unique case of a 9 year old boy who presented with dense anterior corneal stromal infltration, which on smear examination showed atypical double walled spherical cysts, leading to a diagnostic dilemma. An 18S rRNA gene-based PCR done on the growth on culture, subsequently identifed a rarely reported species of Acanthamoeba. The patient was advised combination therapy with polyhexamethylene biguanide (PHMB 0.02%) and chlorhexidine (0.02%) eye drops. Three weeks post treatment, the keratitis resolved with scarring and vascularisation and visual acuity improved to 20/60. At 8 weeks follow up Best corrected visual acuity further improved to 20/30 with contact lens.

Metformin-coated silver nanoparticles exhibit anti-acanthamoebic activities against both trophozoite and cyst stages

Acanthamoeba castellanii is an opportunistic protozoan responsible for serious human infections including Acanthamoeba keratitis and granulomatous amoebic encephalitis. Despite advances in antimicrobial therapy and supportive care, infections due to Acanthamoeba are a major public concern. Current methods of treatment are not fully effective against both the trophozoite and cyst forms of A. castellanii and are often associated with severe adverse effects, host cell cytotoxicity and recurrence of infection. Therefore, there is an urgent need to develop new therapeutic approaches for the treatment and management of Acanthamoebic infections. Repurposing of clinically approved drugs is a viable avenue for exploration and is particularly useful for neglected and rare diseases where there is limited interest by pharmaceutical companies. Nanotechnology-based drug delivery systems offer promising approaches in the biomedical field, particularly in diagnosis and drug delivery. Herein, we conjugated an antihyperglycemic drug, metformin with silver nanoparticles and assessed its anti-acanthamoebic properties. Characterization by ultraviolet-visible spectrophotometry and atomic force microscopy showed successful formation of metformin-coated silver nanoparticles. Amoebicidal and amoebistatic assays revealed that metformin-coated silver nanoparticles reduced the viability and inhibited the growth of A. castellanii significantly more than metformin and silver nanoparticles alone at both 5 and 10 μM after 24 h incubation. Metformin-coated silver nanoparticles also blocked encystation and inhibited the excystation in Acanthamoeba after 72 h incubation. Overall, the conjugation of metformin with silver nanoparticles was found to enhance its antiamoebic effects against A. castellanii. Furthermore, the pretreatment of A. castellanii with metformin and metformin-coated silver nanoparticles for 2 h also reduced the amoebae-mediated host cell cytotoxicity after 24 h incubation from 73% to 10% at 10 μM, indicating that the drug-conjugated silver nanoparticles confer protection to human cells. These findings suggest that metformin-coated silver nanoparticles hold promise in the improved treatment and management of Acanthamoeba infections.

The Effect of Antiamoebic Agents on Viability, Proliferation and Migration of Human Epithelial Cells, Keratocytes and Endothelial Cells, In Vitro

PURPOSE

To analyze the effect of diamidines (hexamidine-diisethionat (HD), propamidin-isethionate (PD), dibromopropamidine-diisethionat (DD)), and biguanides (polyhexamethylen biguanid (PHMB), chlorhexidine (CH)) on human corneal epithelial cell, keratocyte and endothelial cell viability, proliferation, and migration, in vitro.

METHODS

For epithelial and endothelial cells a human cell line and for keratocytes primary cultures were used (n = 6 each). We used 3.9x10^-4-0.1% HD, PD or DD, 3.9x10^-4-0.0125% PD, 7.8x10^-5-0.02% PHMB or CH concentration for 24 h to determine viability (Cell Proliferation Kit XTT), proliferation (Cell Proliferation ELISA BrdU kit), and migration using wound healing assay. Viability/proliferation/migration values of each drug were summarized as "area under curve" (AUC) together with a Mann-Whitney test.

RESULTS

HCEC, keratocyte, and HCEC-12 viability AUC, comparing PD and PHMB (p ≤ 0.014 for all; PD better) or PD and HD (p ≤ 0.011 for all; PD better) differed significantly. Keratocyte and HCEC-12 viability AUC comparing CH and HD (p ≤ 0.027; CH better), HCEC-12 viability AUC comparing PD and HD (p = 0.005; PD better) and HCEC viability AUC comparing CH and PHMB (p = 0.014; CH better) differed significantly. HCEC proliferation AUC, comparing PD with PHMB, CH, DD, HD (p ≤ 0.016; PD worse for all) and keratocyte proliferation AUC, comparing PHMB with HD, PD (p = 0.004; p = 0.002; PHMB better for both), CH with HD, PD (p ≤ 0.001; CH better for both) and DD with PD (p = 0.043; DD better) differed significantly. Keratocyte migration AUC comparing PD with control, PHMB, CH, DD and HD differed significantly (p ≤ 0.012; PD worse for all).

CONCLUSIONS

Propamidin-isethionate as diamidine and chlorhexidin as biguanide may be used clinically to reduce cytotoxicity of antiamoebic treatment on human corneal cells. Diamidines reduce proliferation of human epithelial cells and keratocytes more than biguanides and propamidin-isethionate reduces migration of keratocytes. Therefore, in spite of lower cytotoxicity, the inhibitory effect on proliferation and migration indicates that extended use of propamidin-isethionate should be avoided in patients.

Non-contact lens related Acanthamoeba keratitis

The purpose of the study is to describe epidemiology, clinical features, diagnosis, and treatment of Acanthamoeba keratitis (AK) with special focus on the disease in nonusers of contact lenses (CLs). This study was a perspective based on authors' experience and review of published literature. AK accounts for 2% of microbiology-proven cases of keratitis. Trauma and exposure to contaminated water are the main predisposing factors for the disease. Association with CLs is seen only in small fraction of cases. Contrary to classical description experience in India suggests that out of proportion pain, ring infiltrate, and radial keratoneuritis are seen in less than a third of cases. Majority of cases present with diffuse infiltrate, mimicking herpes simplex or fungal keratitis. The diagnosis can be confirmed by microscopic examination of corneal scraping material and culture on nonnutrient agar with an overlay of Escherichia coli. Confocal microscopy can help diagnosis in patients with deep infiltrate; however, experience with technique and interpretation of images influences its true value. Primary treatment of the infection is biguanides with or without diamidines. Most patients respond to medical treatment. Corticosteroids play an important role in the management and can be used when indicated after due consideration to established protocols. Surgery is rarely needed in patients where definitive management is initiated within 3 weeks of onset of symptoms. Lamellar keratoplasty has been shown to have good outcome in cases needing surgery. Since the clinical features of AK in nonusers of CL are different, it will be important for ophthalmologists to be aware of the scenario wherein to suspect this infection. Medical treatment is successful if the disease is diagnosed early and management is initiated soon.

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.

Microwave Irradiation as a Promising Method of Sterilization for Acanthamoeba polyphaga in Cultures

PURPOSE

To determine the killing effect of microwave irradiation on Acanthamoeba polyphaga.

METHODS

The trophozoites and cysts of A. polyphaga both in water and on agar were exposed to microwave irradiation with a capacity of 750 W for 0, 1, 3, 5, and 10 minutes, respectively. Furthermore, the trophozoites and cysts of A. polyphaga in water were exposed to microwave irradiation with a capacity of 100, 300, and 500 W for 1 minute, respectively.

RESULTS

The trophozoites and cysts of A. polyphaga on agar were completely killed by 3 minutes of microwave irradiation with a capacity of 750 W. The trophozoites and cysts of A. polyphaga in water were completely killed by microwave irradiation with a capacity of 300 W for 1 minute.

CONCLUSIONS

We demonstrate that microwave treatment is effective in killing A. polyphaga both in water and on agar and may be a helpful modality to prevent Acanthamoeba keratitis.

Parasites

Parasites are an important cause of human disease worldwide. The clinical severity and outcome of parasitic disease is often dependent on the immune status of the host. Specific parasitic diseases discussed in this chapter are amebiasis, giardiasis, cryptosporidiosis, cyclosporiasis, cystoisosporiasis, microsporidosis, granulomatous amebic encephalitis, toxoplasmosis, leishmaniasis, Chagas disease, malaria, babesiosis, strongyloidiasis, and scabies.

In vitro anti-Acanthamoeba synergistic effect of chlorhexidine and cationic carbosilane dendrimers against both trophozoite and cyst forms

Acanthamoeba sp. are the causative agents of severe illnesses in humans such as Acanthamoeba keratitis (AK) and granulomatous amoebic encephalitis (GAE). Medical therapy is not yet well established. Treatments of AK last for several months and generate toxicity, resistances appear due to the cysts stage and recurrences can occur. In this study has been demonstrated that the combination of chlorhexidine digluconate (CLX) and carbosilane dendrimers containing ammonium or guanidine moieties has in vitro synergistic effect against Acanthamoeba polyphaga. This synergy provokes an important reduction in the minimal trophozoite amoebicidal concentration (MTAC) of CLX, which means a reduction of their toxic effects on human cells. Moreover, some CLX/dendrimer combinations show important activity against the cyst resistance stage.

Chlorhexidine Monotherapy with Adjunctive Topical Corticosteroids for Acanthamoeba Keratitis

PURPOSE

To assess the efficacy of chlorhexidine monotherapy for Acanthamoeba keratitis, and to determine the therapeutic outcomes of concomitant topical corticosteroids.

METHODS

In this prospective interventional case series, 31 eyes of 31 patients with Acanthamoeba keratitis (AK) were treated with chlorhexidine 0.02% as monotherapy, from April 2010 to April 2011. The diagnosis of AK was made based on clinical manifestations and positive confocal microscopic (confoscan 3.4, Nidek Co. Ltd., Gamagori, Japan) results. We report the percentage of a favorable clinical response within two weeks of initiating treatment, worsening of the infection while receiving chlorhexidine, recovery of visual acuity (VA), duration of treatment with chlorhexidine and corticosteroids, necessity for addition of other anti-Acanthamoeba agents, presence of corneal scar at the end of the treatment, and need for penetrating keratoplasty (PK).

RESULTS

Two weeks after initiation of chlorhexidine, improvement in signs and symptoms was observed in 26 (83.9%) patients but 3 eyes required the addition of propamidine. After initial improvement in one patient, the infection worsened, necessitating the addition of Polyhexamethylene Biguanide (PHMB) and propamidine. A total of 26 (83.9%) patients received topical corticosteroids with mean duration of 65.8 ± 45.1 days. In 22 (71%) eyes, final visual acuity was ≥0.80. Improved VA occurred in 29 eyes (93.5%). Optical PK was considered in 3 (9.7%) eyes and a corneal scar developed in 8 (25.8%) eyes.

CONCLUSION

Chlorhexidine is effective for monotherapy in AK and could be a good choice for initiating treatment. After the initial response to anti-Acanthamoeba agents, corticosteroids can be used as adjunctive therapy depending on the clinical condition.

In vitro amoebicidal activities of Satureja cuneifolia and Melissa officinalis on Acanthamoeba castellanii cysts and trophozoites

Amoebic keratitis is difficult to treat without total efficacy in some patients because of cysts, which are less susceptible than trophozoites to the usual treatments. The aim of this study is to evaluate the in vitro amoebicidal activity of the methanolic extracts of Satureja cuneifolia and Melissa officinalis. In the presence of methanolic extracts (ranging from 1.0 to 32.0 mg/ml), numbers of the viable Acanthamoe castellanii trophozoites and cysts were decreased during the experimental process. Both extracts showed a time- and dose-dependent amoebicidal action on the trophozoites and cysts. Among the extracts tested, S. cuneifolia showed the strongest amoebicidal effect on the trophozoites and cysts. In the presence of 32 mg/ml extract, no viable trophozoites were observed within 24 h. At the same concentration value, the extract was found effective against the cysts at a rate of 46.3% within 72 h of the experimental process. At 16 mg/ml extract concentration, no viable trophozoites were also observed in the 24th hour of the experiment. At the end of the experimental process, 34.7% of the cysts were killed by the extract. M. officinalis showed moderate amoebicidal effect. At the concentration of 32 mg/ml, 44.3% and 30.0% of the trophozoites and cysts were killed by the extract, respectively. Results obtained from these concentration values were found statistically different in terms of their actions both on trophozoites and cysts (p<0.05).

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.

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.

Rapidly progressive cataract and iris atrophy during treatment of Acanthamoeba keratitis

PURPOSE

To identify characteristics associated with cataract occurring during the course of Acanthamoeba keratitis.

DESIGN

Retrospective observational case series.

PARTICIPANTS

Eighty-one laboratory-confirmed patients with Acanthamoeba keratitis.

METHODS

Review of clinical records.

MAIN OUTCOME MEASURES

Development of cataract during management of Acanthamoeba keratitis.

RESULTS

Rapidly progressive crystalline lens opacification occurred in 9 eyes within 4 to 15 weeks after diagnosis of Acanthamoeba keratitis. Three were associated with inflammatory complications, including anterior scleritis (2 eyes) and iridocyclitis (1 eye). Six others had the abrupt onset of a dense cataract, including 5 with iris atrophy, that occurred during the initial 6 months of therapy with chlorhexidine, a diamidine, and adjunctive corticosteroid. Extracapsular cataract extraction was performed with or after penetrating keratoplasty. Secondary glaucoma developed in 6 of 9 eyes subsequent to iris atrophy (4 eyes) or a cyclitic membrane (2 eyes), and 3 eyes underwent trabeculectomy.

CONCLUSIONS

Cataract may occur and progress during the management of Acanthamoeba keratitis in association with anterior segment inflammation, iris atrophy, and secondary glaucoma.

The effect of propolis in experimental Acanthamoeba keratitis

PURPOSE

To examine the effect of propolis in a rat model of Acanthamoeba keratitis and to determine its in vitro cytotoxicity in cultured corneal epithelial cells.

METHODS

Eighteen Wistar albino rats were used. Cultured corneal epithelial cells obtained from two healthy rats for in vitro cytotoxicity of propolis. Corneal stromal inoculation was performed in 16 rats with amoebic culture containing 1 x 10(6) amoeba/mL. Rats with Acanthamoeba keratitis 5 days later after the inoculation were divided randomly into four groups, and eight eyes of each group were treated with study drugs. The propolis, chlorhexidine (CHX), propolis plus CHX and control eyes were treated with topical propolis, 0.002% CHX, propolis plus 0.002% CHX and lubricant eye drops, respectively. The study drugs were instilled every one hour for 10 days. All eyes were examined and keratitis graded by slit-lamp biomicroscopy on days 2, 5 and 10 during the administration of the study drugs. After the completion of keratitis grading, all the 16 rats were humanely killed and their corneas were excised and used for Acanthamoeba culture to evaluate presence of Acanthamoeba growth after treatment 14 days later.

RESULTS

Concentrations of propolis higher than 7.81 mg/mL cause damage to corneal epithelial cells in the experiment of in vitro cytotoxicity of propolis on corneal epithelial cells. The keratitis grade on day 2 in the CHX eyes was significantly lower than that in the control eyes (P < 0.05). The keratitis grades on days 5 and 10 in the propolis, CHX and propolis plus CHX eyes were significantly lower compared with those on days 5 and 10 in the control eyes (P < 0.05). In the propolis eyes, the keratitis grade on day 5 was significantly lower than that on day 2 (P < 0.05), and it was significantly lower on day 10 compared with that on day 5 (P < 0.05). In the CHX and propolis plus CHX eyes, the keratitis grade on day 10 was significantly lower compared with that on days 2 and 5 (P < 0.05). In the control eyes, there was no significant difference in the keratitis grades on days 2, 5 and 10 (P > 0.05). The culture positivity at Acanthamoeba growth after treatment experiment in the propolis, CHX and propolis plus CHX eyes was significantly lower than that in the control eyes (P < 0.05).

CONCLUSIONS

We suggest that propolis had amoebicidal properties in this rat model of Acanthamoeba keratitis. Further investigations to evaluate the antimicrobial activity of the individual fractions of the resin could yield more information about its mechanism of action in treating this disease.

Comparison of polyhexamethylene biguanide and chlorhexidine as monotherapy agents in the treatment of Acanthamoeba keratitis

PURPOSE

To compare the therapeutic outcomes of polyhexamethylene biguanide (PHMB) and chlorhexidine for Acanthamoeba keratitis.

DESIGN

Prospective, double-masked, randomized comparative study.

METHODS

Fifty-six eyes of 55 patients with Acanthamoeba keratitis were randomized to receiving PHMB 0.02% or chlorhexidine 0.02%. Diagnosis was made based on positive culture results (cornea or contact lens case) or on clinical grounds. The primary outcome measure was treatment failure defined as failure to induce a favorable clinical response within two weeks. Secondary outcomes were: 1) recovery of visual acuity (VA), 2) the degree of corneal scarring posttreatment, or 3) the need for penetrating keratoplasty.

RESULTS

Fifty-one eyes completed the study. Twenty-three eyes received PHMB and 28 received chlorhexidine. Ninety-eight percent were contact lens wearers. Eighteen (78%) PHMB patients were treatment successes compared with 24 (85.7%) chlorhexidine patients (P = .71). Diagnosis was confirmed by positive corneal culture results in 26 cases (51%). Diagnosis was made within 28 days in 29 cases (56.9%), between one and two months in 13 cases (25.5%), and after more than two months in eight cases (15.7%). Improvement in VA was seen in 13 eyes (56.5%) receiving PHMB vs 20 eyes (71.4%) receiving chlorhexidine. Mild one-quadrant corneal scarring was seen in 43.5% of eyes receiving PHMB and 71.4% of eyes receiving chlorhexidine, whereas moderate corneal scarring in two or three quadrants was seen in 21.7% of eyes receiving PHMB and in 10.7% of eyes receiving chlorhexidine. Five eyes worsened while receiving PHMB vs four eyes worsening while receiving chlorhexidine. Penetrating keratoplasty was required in three eyes from PHMB group and in two eyes from chlorhexidine group.

CONCLUSIONS

Outcomes were similar when using PHMB and chlorhexidine as monotherapy agents in treating Acanthamoeba keratitis.

A comparison of topical chlorhexidine, ciprofloxacin, and fortified tobramycin/cefazolin in rabbit models of Staphylococcus and Pseudomonas keratitis

AIMS

Chlorhexidine was evaluated as a potential topical therapy for experimental bacterial keratitis.

METHODS

Chlorhexidine (0.01%) was compared to ciprofloxacin (0.3%) and tobramycin (1.36%)/cefazolin (5%) both in vitro and in vivo for the treatment of Staphylococcus aureus and Pseudomonas aeruginosa infections. The minimum inhibitory concentration (MIC) was established for each organism for each antibiotic, using a standardized method. One thousand (1000) colony-forming units (CFU) of S. aureus or P. aeruginosa was intrastromally injected into rabbit cornea. A total of 92 corneas were infected and then treated topically with antibiotics. The control eyes were treated with artificial tears. The rabbits were later sacrificed, and the corneal buttons were harvested.

RESULTS

The MIC for chlorhexidine was <or=40 microg/mL for both organisms. In the rabbit model of S. aureus keratitis, following the treatments, the median number of CFU of recoverable bacteria for chlorhexidine (n = 10), ciprofloxacin (n = 12), tobramycin/cefazolin (n = 12), and controls (n = 10) was 1.1 x 10(3), 4.7 x 10(4), 1.9 x 10(5), and 6.7 x 10(4), respectively. For S. aureus, the only treatment that showed a statistically significant reduction in CFU was chlorhexidine. In the P. aeruginosa keratitis group, CFU were significantly reduced with all treatments, compared to the control.

CONCLUSIONS

Chlorhexidine short-term treatment was an effective topical therapy for bacterial keratitis in the rabbit model, when compared with ciprofloxacin and tobramycin/cefazolin, in particular for S. aureus.

Cysticidal Effect on Acanthamoeba and Toxicity on Human Keratocytes by Polyhexamethylene Biguanide and Chlorhexidine

PURPOSE

To evaluate the cysticidal effect of polyhexamethylene biguanide (PHMB) and chlorhexidine on Acanthamoeba and its toxic effect on cultured human keratocytes.

METHODS

Each well of a twofold-diluted Acanthamoeba cyst-containing suspension of 5 x 10(4) cysts/mL was treated with PHMB and chlorhexidine for 8, 24, and 48 hours to determine the minimal cysticidal concentration (MCC) of each disinfectant. Human corneal keratocytes (5 x 10(4) cells/mL) were exposed to PHMB and chlorhexidine for the same time to determine the survival rate of keratocytes. Inverted phase-contrast and electron microscopy were used to observe the morphologic changes.

RESULTS

The mean MCC of PHMB for 8, 24, and 48 hours was 9.42, 5.62, and 2.37 microg/mL, respectively. The mean MCC of chlorhexidine for 8, 24, and 48 hours was 24.32, 10.02, and 7.02 microg/mL, respectively. The respective survival rate of keratocytes at the MCC was 91.7%, 64.6%, and 49.7% for PHMB and 95.7%, 90.6%, and 78.1% for chlorhexidine, respectively. The cysts and keratocytes showed more damaged appearances after treatment with PHMB than chlorhexidine.

CONCLUSIONS

PHMB and chlorhexidine showed a similar amoebicidal efficacy. However, PHMB seemed to be more toxic to keratocytes than chlorhexidine.

Acanthamoeba Keratitis

PURPOSE

To report a recent significant increase of the number of patients diagnosed with Acanthamoeba keratitis (AK) at Wills Eye Hospital between 2004 and 2005. To determine the risk factors, clinical characteristics, treatments, and outcomes of patients with AK.

METHODS

Retrospective consecutive case series of 20 eyes with AK. The information included the incidence from 1995 to 2005, initial and final best-corrected visual acuity (BCVA) at 3-month follow-up, risk factors [contact lenses (CL) history, history of swimming with CL, and exposure to well water and/or contaminated water], clinical characteristics, methods of diagnosis, and treatments.

RESULTS

A statistically significant increased incidence of AK was seen in 2004 and 2005 compared with cases from 1995 to 2003 (P < 0.01). All patients wore CL; 19 of 20 wore frequent-replacement soft CL and used multipurpose disinfecting solutions. Other risk factors were exposure to well water in 40%, swimming with CL in 25%, and overnight wear in 25%. The diagnosis was made by histopathology in 50%, by microbiology in 15%, and by initial classic clinical signs and response to treatments in 35%. Herpes simplex virus was the misdiagnosis in 70%. Patients who presented with dendritiform keratitis or radial keratoneuritis had a BCVA better than 20/30 in 8 of 9 (89%) and patients with ring ulcers or stromal disease who had a BCVA less than finger counting in 5 of 8 (62.5%).

CONCLUSIONS

We observed an increased incidence of AK. Patients with proper use of frequent-replacement CL and multipurpose solutions can develop AK. Advanced stromal disease at diagnosis is associated with worse outcome.

[Keratitis due to Acanthamoeba]

Free-living amebae appertaining to the genus Acanthamoeba, Naegleria and Balamuthia are the most prevalent protozoa found in the environment. These amebae have a cosmopolitan distribution in soil, air and water, providing multiple opportunities for contacts with humans and animals, although they only occasionally cause disease. Acanthamoeba spp. are the causative agent of granulomatous amebic encephalitis, a rare and often fatal disease of the central nervous system, and amebic keratitis, a painful disease of the eyes. Keratitis usually follows a chronic course due to the delay in diagnosis and subsequent treatment. The clear increase in Acanthamoeba keratitis in the last 20 years is related to the use and deficient maintenance of contact lenses, and to swimming while wearing them. The expected incidence is one case per 30,000 contact lens wearers per year, with 88% of cases occurring in persons wearing hydrogel lenses. This review presents information on the morphology, life-cycle and epidemiology of Acanthamoeba, as well as on diagnostic procedures (culture), appropriate antimicrobial therapy, and prevention measures.

Diagnosis and management of Acanthamoeba keratitis

PURPOSE OF REVIEW

This paper reviews the literature generated on Acanthamoeba keratitis since 1998.

RECENT FINDINGS

Acanthamoeba infections may be on the rise. Contact lenses are the biggest risk factor for their development. Silicone hydrogel lenses are increasingly prescribed and may be 'more sticky' to Acanthamoeba organisms. Orthokeratology for the treatment of myopia has been associated with many new cases of Acanthamoeba keratitis. Daily disposable contact lenses are the safest form of soft contact lens. Patients continue to be misdiagnosed as having herpetic keratitis. Impression cytology and confocal microscopy are newer diagnostic modalities. Topical polyhexamethylene biguanide, chlorhexidine and propamidine are the mainstay of medical therapy. Amniotic membrane may be used for cases of persistent epithelial defect and to control inflammation. Penetrating keratoplasty in a medically treated eye affords a good chance of positive outcome.

SUMMARY

Acanthamoeba keratitis continues to be a difficult infection to diagnose and manage. The frequency of these infections may be on the rise, most commonly associated with frequent replacement soft contact lenses. The best chance for a good outcome is based on early diagnosis, so it is important for ophthalmologists consider it in patients, especially in the contact lens wearer with suspected herpes simplex keratitis.

Aromatic diamidines as antiparasitic agents

Parasitic infections are widespread in developing countries and frequently associated with immunocompromised patients in developed countries. Consequently, such infections are responsible for a significant amount of human mortality, morbidity and economic hardship. A growing consensus has identified the urgent need for the development of new antiparasitic compounds, mostly due to the large number of drug-resistant parasites and the fact that currently available drugs are expensive, highly toxic, require long treatment regimens and frequently exhibit significantly reduced activity towards certain parasite strains and evolutive stages. In this context, the activity of aromatic diamidines has been explored against a widespread range of micro-organisms, and the authors' present aim is to review the current status of chemotherapy with these compounds against human parasitic infections.

In vitro acanthamoebicidal activity of a killer monoclonal antibody and a synthetic peptide

OBJECTIVES

To evaluate the in vitro microbicidal activity against Acanthamoeba castellanii of a murine monoclonal anti-idiotypic antibody (KTmAb) and a synthetic killer mimotope (KP), which mimic a yeast killer toxin (KT) characterized by a wide spectrum of antimicrobial activity through interaction with specific cell wall receptors, mainly constituted by beta-glucans.

METHODS

Amoebicidal activity was investigated after incubation of trophozoites under different experimental conditions with laminarinase, KTmAb, KP and a scrambled decapeptide (SP). To confirm the specific interaction of KP with beta-glucans, the experiments were also carried out in the presence of laminarin (beta1-3-glucan) or pustulan (beta1-6-glucan); both glucan molecules were co-incubated with KP or SP.

RESULTS

KTmAb and KP exhibited a time-dependent killing activity, in comparison with SP or heat-inactivated KTmAb; this activity was completely abolished by pre-incubation with laminarin, but not by pustulan. Notably, in vitro amoebicidal activity was observed in the presence of laminarinase, an enzyme that specifically hydrolyses beta-glucans. Furthermore, KP specifically inhibited the growth of Acanthamoeba on infected contact lenses and the remaining adherent KP-treated trophozoites appeared strongly damaged.

CONCLUSIONS

The results indicate that the expression of beta1-3-glucan receptors in the cell membrane is probably modulated during cell growth of A. castellanii and is critical for the killing activity of KT-like molecules. Our data confirm the broad antimicrobial spectra of KTmAb and KP, emphasize the crucial role of beta1-3-glucan in microbial physiology and suggest the potential use of KTmAb and KP in the prevention and therapy of Acanthamoeba infections or in preventing Acanthamoeba contamination during storage of contact lenses.

[Acanthamoeba stromal keratitis: epidemiology and prognosis factors]

PURPOSE

Early treatment of amebic stromal keratitis can change patients' final visual and esthetic prognosis. The aim of this study was to review all proven Acanthamoeba stromal keratitis cases presenting at our ophthalmology emergency department over the past 3 years, in order to delineate the incidence and the factors still leading to this serious complication.

PATIENTS

and methods: All cases of Acanthamoeba stromal keratitis confirmed with a parasitology examination and treated between January 2000 and December 2002 were recorded. During this period of time, eight patients were identified with this condition. Their charts, as well as biomicroscopic, therapeutic, and outcome data were analyzed.

RESULTS

All patients were referred in a second or third intention. Only one patient did not usually wear contact lenses. Six patients had an associated bacterial abscess. The typical amebic annular infiltrate was only observed in one patient. Three patients received an effective antiamebic treatment in the 15 days following the first symptoms and five patients 1 month or more after. An emergency keratoplasty was carried out in one patient. Finally, visual acuity was lower than 5/10 in all cases. The patients treated in the first 15 days had the best final visual acuity.

DISCUSSION

Soft contact lenses are still responsible for the majority of serious amebic corneal complications. Late diagnosis remains the main cause of Acanthamoeba stromal keratitis development, particularly in the absence of contact lens history, because of the delay in treatment.

CONCLUSION

The catastrophic consequences of this complication justify a systematic treatment against ameba in each case of suspected diagnosis. An early and effective treatment of the stromal amebic keratitis can increase the final visual prognosis.

Clinical Science. Six-year review of Acanthamoeba keratitis in New South Wales, Australia: 1997-2002

AIM

To assess the incidence and risk factors for Acanthamoeba keratitis (AK), the diagnostic interval, and the efficacy and outcome of current treatment among the population of New South Wales, Australia.

METHODS

A retrospective review was carried out of all cases of AK treated at the Sydney Eye Hospital between January 1997 and December 2002.

RESULTS

Twenty patients were identified with a mean follow up of 24.8 +/- 21.5 months. Acanthamoeba keratitis constitutes 4.7% of severe infective keratitis treated at Sydney Eye Hospital. The mean interval from first presentation to diagnosis was 26.6 +/- 35.1 days overall; 17.2 +/- 33.1 days for those presenting directly to our unit (69% being diagnosed within 72 h of presentation), and 44.1 +/- 34.0 days for those first presenting elsewhere. Of those with a diagnostic delay >1 month, 57% had been mistakenly diagnosed with Herpes simplex keratitis. Sixteen (80%) wore contact lenses, and eight (40%) had additional risk factors including poor lens hygiene. Complications occurred in 16 (80%), with seven (35%) requiring surgical intervention. Visual acuity improved in 18 (90%), worsened in two patients (10%), and 75% achieved 6/12 or better at last follow up.

CONCLUSIONS

Acanthamoeba keratitis is a rare infection, and contact lens wear remains the commonest association, with poor hygiene constituting significant additional risk. The visual outcome has improved with the availability of effective amoebicidal agents, but patients with a diagnostic delay and non-contact lens wearers are at increased risk of recurrent disease. A high index of clinical suspicion remains the most effective strategy in implementing early treatment, and enabling a favourable outcome.

Laser in situ keratomileusis treatment for myopia after Acanthamoeba keratitis

PURPOSE

We report a case of a patient with a history of Acanthamoeba keratitis in the right eye who was successfully treated with Laser in situ keratomileusis (LASIK) for myopia correction.

METHODS

A 39-year-old woman with a history of wearing daily soft contact lens had early (epithelial phase) Acanthamoeba keratitis in the right eye. The corneal infection resolved with 5 months of topical polyhexamethylene biguanide and propamidine treatment. Recurrence of Acanthamoeba keratitis did not occur after the first episode, and no scarring of the cornea was noted. Laser in situ keratomileusis was performed in both eyes 2 years later.

RESULTS

The patient successfully underwent LASIK procedures in both eyes. No complications were observed intraoperatively and postoperatively in the right eye. The cornea remained clear 3 months postoperatively, and she achieved 6/6 uncorrected visual acuity.

CONCLUSIONS

Following successful treatment of Acanthamoeba keratitis, the LASIK procedure can be performed on previously infected cornea with successful results. There is no recurrence of Acanthamoeba keratitis at 3-month follow-up.

Resistance, biguanide sorption and biguanide-induced pentose leakage during encystment of Acanthamoeba castellanii

AIMS

This study investigates the effects of biguanides during encystment of Acanthamoeba castellanii.

METHODS AND RESULTS

A non-nutrient encystment system was used to investigate the changes in the levels of sorption (uptake) of three non-cysticidal concentrations (10, 20 and 50 microg ml(-1)) of chlorhexidine diacetate (CHA) and polyhexamethylene biguanide (PHMB) as well as their effects on viability and leakage of pentose sugars during the first 36 h of encystment. Trophozoites treated with CHA or PHMB were more sensitive and generally sorbed more of each biocide than cysts. During encystment, the largest increases in resistance developed between 18 and 36 h for both biguanides with the resistance emerging to biguanide concentrations of 10 or 20 microg ml(-1) between 18 and 24 h. At 50 microg ml(-1) resistance emerged between 24 and 36 h. There was a general decrease in biocide sorption during encystment between 0-24 and 0-21 h for CHA and PHMB, respectively, at a concentration of 50 microg ml(-1). The greatest decline in biguanide-induced pentose leakage was between 0 and 12 h.

CONCLUSIONS

The results suggest that during encystment some of the changes in the susceptibility to CHA or PHMB may be related to decreases in the levels of biocide sorption, which is limited by the developing cyst wall.

SIGNIFICANCE AND IMPACT OF THE STUDY

During encystation, changes occur in biguanide sensitivity. The physical barrier of the cyst wall may be an important factor in limiting biocide sorption.

Are cataract and iris atrophy toxic complications of medical treatment of acanthamoeba keratitis?

PURPOSE

Two cases of acanthamoeba keratitis with almost identical clinical courses developed mature cataract and iris atrophy after prolonged treatment with chlorhexidine 0.02% and propamidine isethionate 0.1%. It is suggested that these complications were caused by the chemicals, rather than resulting from the amoebae-induced inflammation.

METHODS

Penetrating keratoplasty was performed in both cases when perforation from peripheral ulceration was threatening.

RESULTS AND CONCLUSIONS

The immediate results were good. From these two cases it seems possible that there is a maximum level of intensity of the medical treatment and also that surgery should be considered at an earlier stage, before intraocular complications develop.