Acanthamoeba keratitis: a sobering case and a promising new treatment

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.

PLGA nanoparticles loaded with Gallic acid- a constituent of Leea indica against Acanthamoeba triangularis

Acanthamoeba, a genus that contains at least 24 species of free-living protozoa, is ubiquitous in nature. Successful treatment of Acanthamoeba infections is always very difficult and not always effective. More effective drugs must be developed, and medicinal plants may have a pivotal part in the future of drug discovery. Our research focused on investigating the in vitro anti- acanthamoebic potential of Leea indica and its constituent gallic acid in different concentrations. Water and butanol fractions exhibited significant amoebicidal activity against trophozoites and cysts. Gallic acid (100 µg/mL) revealed 83% inhibition of trophozoites and 69% inhibition of cysts. The butanol fraction induced apoptosis in trophozoites, which was observed using tunnel assay. The cytotoxicity of the fractions and gallic acid was investigated against MRC-5 and no adverse effects were observed. Gallic acid was successfully loaded within poly (D,L-lactide-co-glycolide) (PLGA) nanoparticles with 82.86% encapsulation efficiency, while gallic acid showed 98.24% in vitro release at 48 hours. Moreover, the gallic acid encapsulated in the PLGA nanoparticles exhibited 90% inhibition against trophozoites. In addition, gallic acid encapsulated nanoparticles showed reduced cytotoxicity towards MRC-5 compared to gallic acid, which evidenced that natural product nanoencapsulation in polymeric nanoparticles could play an important role in the delivery of natural products.

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.

The effect of the disulfideisomerase domain containing protein in the defense against polyhexamethylene biguanide of highly tolerant Acanthamoeba at the trophozoite stage

Acanthamoeba castellanii is a free-living protozoan pathogen capable of causing a blinding keratitis and fatal granulomatous encephalitis. Current treatment generally involves an hourly application of polyhexamethylene biguanide (PHMB) over a period of several days but this is not entirely effective against all strains/isolates. The tolerance mechanisms of PHMB in Acanthamoeba cells remain unclear. In this study, we found that the mRNA expression level of disulfideisomerase domain containing protein (PDI) increased rapidly in surviving cells of the highly PHMB-tolerant Acanthamoeba castellanii strain, NCKH_D, during PHMB treatment, but not in the ATCC standard strain. After PDI-specific silencing, NCKH_D was found to be more vulnerable to PHMB treatment. The results described above show that PDI is an important gene for PHMB tolerance ability in a highly PHMB-tolerant strain of Acanthamoeba and provide a new insight for more efficient medicine development for Acanthamoeba keratitis.

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.

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.

Cationic antimicrobial polymers and their assemblies

Cationic compounds are promising candidates for development of antimicrobial agents. Positive charges attached to surfaces, particles, polymers, peptides or bilayers have been used as antimicrobial agents by themselves or in sophisticated formulations. The main positively charged moieties in these natural or synthetic structures are quaternary ammonium groups, resulting in quaternary ammonium compounds (QACs). The advantage of amphiphilic cationic polymers when compared to small amphiphilic molecules is their enhanced microbicidal activity. Besides, many of these polymeric structures also show low toxicity to human cells; a major requirement for biomedical applications. Determination of the specific elements in polymers, which affect their antimicrobial activity, has been previously difficult due to broad molecular weight distributions and random sequences characteristic of radical polymerization. With the advances in polymerization control, selection of well defined polymers and structures are allowing greater insight into their structure-antimicrobial activity relationship. On the other hand, antimicrobial polymers grafted or self-assembled to inert or non inert vehicles can yield hybrid antimicrobial nanostructures or films, which can act as antimicrobials by themselves or deliver bioactive molecules for a variety of applications, such as wound dressing, photodynamic antimicrobial therapy, food packing and preservation and antifouling applications.

Interaction of polyhexamethylene biguanide hydrochloride (PHMB) with phosphatidylcholine containing o/w emulsion and consequences for microbicidal efficacy and cytotoxicity

Oil-in-water (o/w) emulsions containing egg yolk phosphatidylcholine (EPC) were combined with aqueous polyhexamethylene biguanide hydrochloride (PHMB). The PHMB concentration in the aqueous phase was estimated by filtration centrifugation experiments. In parallel, PHMB concentration was assessed utilizing cytotoxicity assays (neutral red) on cultured murine fibroblasts (L929 cells) and tests of bactericidal efficacy on either Pseudomonas aeruginosa or Staphylococcus aureus. Biological tests were performed in cell culture medium. Filtration centrifugation experiments demonstrated much higher aqueous PHMB concentrations than did the assays for biologically effective PHMB. Therefore, biological test systems should preferably be used to verify effective PHMB concentrations. Tests of microbicidal efficacy in which the same 0.05% PHMB o/w emulsion was re-used 8 times revealed a drug delivery system activated by the presence of test bacteria.

Polyhexamethylene biguanide functionalized cationic silver nanoparticles for enhanced antimicrobial activity

Polyhexamethylene biguanide (PHMB), a broad spectrum disinfectant against many pathogens, was used as a stabilizing ligand for the synthesis of fairly uniform silver nanoparticles. The particles formed were characterized using UV-visible spectroscopy, FTIR, dynamic light scattering, electrophoretic mobility, and TEM to measure their morphology and surface chemistry. PHMB-functionalized silver nanoparticles were then evaluated for their antimicrobial activity against a gram-negative bacterial strain, Escherichia coli. These silver nanoparticles were found to have about 100 times higher bacteriostatic and bactericidal activities, compared to the previous reports, due to the combined antibacterial effect of silver nanoparticles and PHMB. In addition to other applications, PHMB-functionalized silver nanoparticles would be extremely useful in textile industry due to the strong interaction of PHMB with cellulose fabrics.

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.

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 response of Escherichia coli to exposure to the biocide polyhexamethylene biguanide

The global response of Escherichia coli to the broad-spectrum biocide polyhexamethylene biguanide (PHMB) was investigated using transcriptional profiling. The transcriptional analyses were validated by direct determination of the PHMB-tolerance phenotypes of derivatives of E. coli MG1655 carrying either insertionally inactivated genes and/or plasmids expressing the cognate open reading frames from a heterologous promoter in the corresponding chromosomally inactivated strains. The results showed that a wide range of genes was altered in transcriptional activity and that all of the corresponding knockout strains subsequently challenged with biocide were altered in tolerance. Of particular interest was the induction of the rhs genes and the implication of enzymes involved in the repair/binding of nucleic acids in the generation of tolerance, suggesting a novel dimension in the mechanism of action of PHMB based on its interaction with nucleic acids.

Results of penetrating keratoplasty for visual rehabilitation after Acanthamoeba keratitis

PURPOSE

To assess the results of penetrating keratoplasty in quiet eyes after resolution of Acanthamoeba keratitis.

DESIGN

A retrospective interventional case series.

METHODS

Penetrating keratoplasty was undertaken in 13 eyes of 13 patients with an average age of 29 +/- 13 years and a history of Acanthamoeba keratitis that was diagnosed by culture and/or confocal microscopy between January 1995 and September 2004. All eyes were observed for at least 3 months (average, 5 months) after the discontinuation of antiamebic therapy that had been administered for at least 4.5 months. In vivo confocal microscopy was used to ensure that no residual amoeba were present before the operation. Two keratoplasties were combined with a valve insertion; five keratoplasties were combined with cataract extraction, and one keratoplasty was preceded by a ciliary laser ablation.

RESULTS

Postoperative best-corrected visual acuity ranged from 20/40 to 20/15, with the exception of one eye with advanced glaucoma that did not improve from a preoperative vision of light perception. No eye experienced rejection or amoebic recurrences, and 12 grafts remained clear throughout the follow-up period (8 months to 9 years; median, 23 months). One graft failed at 4 months because of uncontrolled glaucoma. The eye was regrafted, and the graft remained clear during the 28 months of follow-up evaluation. Two eyes with preoperatively diagnosed glaucoma needed subsequent surgery to control their intraocular pressure.

CONCLUSION

Penetrating keratoplasty for visual restoration after Acanthamoeba keratitis appears to have an excellent long-term prognosis, provided amoebic infection has resolved and concurrent glaucoma is controlled.

Cooperativity in the binding of the cationic biocide polyhexamethylene biguanide to nucleic acids

The interaction between the broad-spectrum antimicrobial agent, polyhexamethylene biguanide (PHMB), and various nucleic acids was investigated. Titration of either single- or double-stranded 100-bp DNA, or mixed-molecular weight marker DNA, or tRNA with PHMB caused precipitation of a complex between nucleic acid and PHMB in which the nucleotide/biguanide ratio was always close to unity. Binding of PHMB was highly cooperative, with apparent Hill coefficients 10.3-14.6. When a fluorescent derivative of PHMB was titrated with increasing amounts of nucleic acid, all four forms of nucleic acid caused strong polarisation of fluorescence, demonstrating the association with PHMB. The intensity and broad-spectrum binding of PHMB to all forms of nucleic acid has significant implications for the mechanism of action of this biocide.

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.

Acanthamoeba spp. as agents of disease in humans

Acanthamoeba spp. are free-living amebae that inhabit a variety of air, soil, and water environments. However, these amebae can also act as opportunistic as well as nonopportunistic pathogens. They are the causative agents of granulomatous amebic encephalitis and amebic keratitis and have been associated with cutaneous lesions and sinusitis. Immuno compromised individuals, including AIDS patients, are particularly susceptible to infections with Acanthamoeba. The immune defense mechanisms that operate against Acanthamoeba have not been well characterized, but it has been proposed that both innate and acquired immunity play a role. The ameba's life cycle includes an active feeding trophozoite stage and a dormant cyst stage. Trophozoites feed on bacteria, yeast, and algae. However, both trophozoites and cysts can retain viable bacteria and may serve as reservoirs for bacteria with human pathogenic potential. Diagnosis of infection includes direct microscopy of wet mounts of cerebrospinal fluid or stained smears of cerebrospinal fluid sediment, light or electron microscopy of tissues, in vitro cultivation of Acanthamoeba, and histological assessment of frozen or paraffin-embedded sections of brain or cutaneous lesion biopsy material. Immunocytochemistry, chemifluorescent dye staining, PCR, and analysis of DNA sequence variation also have been employed for laboratory diagnosis. Treatment of Acanthamoeba infections has met with mixed results. However, chlorhexidine gluconate, alone or in combination with propamidene isethionate, is effective in some patients. Furthermore, effective treatment is complicated since patients may present with underlying disease and Acanthamoeba infection may not be recognized. Since an increase in the number of cases of Acanthamoeba infections has occurred worldwide, these protozoa have become increasingly important as agents of human disease.

Acanthamoeba keratitis in New Zealand, including two cases with in vivo resistance to polyhexamethylene biguanide

BACKGROUND

Acanthamoeba keratitis is an uncommon corneal infection that can run a protracted course with, at times, serious visual results. Eighty-five per cent of cases occur in soft contact lens wearers. The first New Zealand case occurred in 1990 and only seven cases have been identified in New Zealand to the end of 1996.

METHODS

We surveyed the ophthalmologists looking after these seven cases of acanthamoeba keratitis as to time to diagnosis, treatment and outcome.

RESULTS

New Zealand has a low incidence of this disease. All cases were soft contact lens wearers with defective care in every instance. After an initial two late-diagnosed cases, the time to diagnosis for four of the five other cases has been within 2 weeks. Medical treatment has varied over this series, but since the introduction of the cationic antiseptics polyhexamethylene biguanide (PHMB) and chlorhexidine in 1992, the last five cases were all treated with PHMB. One case diagnosed within 2 weeks ran a devastating course, despite intensive PHMB, and a second case remained culture positive after 1 year of PHMB and the late addition of chlorhexidine. Debridement, 0.1% PHMB and hexamidine eventually settled this eye.

CONCLUSIONS

For treatment PHMB, hexamidine rather than propamidine and surgical debridement are favoured. While all Acanthamoeba isolates show good in vitro sensitivity to PHMB, the in vivo response is not always proportionate. A bacterial endosymbiont may have been a factor in the favourable outcome of one protracted case.

Acanthamoeba keratitis

Acanthamoeba species are an important cause of microbial keratitis that may cause severe ocular inflammation and visual loss. The first cases were recognized in 1973, but the disease remained very rare until the 1980s, when an increase in incidence mainly associated with contact lens wear was reported. There is an increased risk when contact lens rinsing and soaking solutions are prepared with nonsterile water and salt tablets. The clinical picture is often characterized by severe pain with an early superficial keratitis that is often treated as herpes simplex infection. Subsequently a characteristic radial perineural infiltration may be seen, and ring infiltration is common. Limbitis and scleritis are frequent. Laboratory diagnosis is primarily by culture of epithelial samples inoculated onto agar plates spread with bacteria. Direct microscopy of samples using stains for the cyst wall or immunostaining may also be employed. A variety of topically applied therapeutic agents are thought to be effective, including propamidine isethionate, clotrimazole, polyhexamethylene biguanide, and chlorhexidine. Various combinations of these and other agents have been employed, often resulting in medical cure, especially if treatment is commenced early in the course of the disease. Penetrating keratoplasty is preferably avoided in inflamed eyes, but may be necessary in severe cases to preserve the globe or, when the infection has resolved, to restore corneal clarity for optical reasons.

Ultrastructural changes of Acanthamoeba cyst of clinical isolates after treatment with minimal cysticidal concentration of polyhexamethylene biguanide

In order to understand the action mechanism of polyhexamethylene biguanide (PHMB) to the cyst of Acanthamoeba on the morphological basis, the cysts of four corneal isolates of Acanthamoeba were treated with minimal cysticidal concentration (MCC) of PHMB and their ultrastructural changes were examined by transmission electron microscopy. The most striking change of cysts treated with PHMB compared with normal cysts was the shrinkage of intracystic amoebae, which resulted in the separation of the plasma membrane of intracystic amoeba from endocystic wall. Subplasmalemmal lipid droplets became irregularly shaped. In severely damaged cysts, cytoplasm was aggregated and organelles were severely deformed. Cytoplasmic materials were leaked out through the damaged plasma membrane. Most cysts showed aggregation of nuclear chromatin material. Number of mitochondrial cristae was also reduced. Ecto- and endo-cystic walls were relatively well tolerated. Findings in the present study revealed that PHMB affected mainly on plasma membrane, but lesser on organellar membrane of intracystic amoeba. It seemed likely that PHMB might kill cystic forms of Acanthamoeba by similar mechanism in which this environmental biocide can damage the cell wall of Escherichia coli by binding with acidic phospholipids.

Outcome of acanthamoeba keratitis treated with polyhexamethyl biguanide and propamidine

OBJECTIVE

This study investigates the clinical outcome of Acanthamoeba keratitis treated with polyhexamethyl biguanide (PHMB) and propamidine isethionate (Brolene).

DESIGN

A retrospective review of all patients treated for Acanthamoeba keratitis between September 1992 and February 1995 was carried out. All patients were treated with PHMB 0.02% and propamidine 0.1% hourly for 3 days, the frequency reduced to four to six times daily according to clinical response.

MAIN OUTCOME MEASURES

Age, gender, result of laboratory investigation, duration of disease before diagnosis, visual acuity (VA) pretreatment and post-treatment, need for keratoplasty, and presence of adverse reaction were measured.

RESULTS

One hundred eleven cases were identified in 105 patients (60 male, 45 female; mean age, 32). Ninety-two percent of infections were in contact lens wearers. The clinical diagnosis was confirmed by corneal culture or histopathology in 64 cases (57.7%). The diagnosis was made "early" (within 28 days) in 65 cases (58.6%). Twenty-one (18.9%) were "intermediate" (28 days-2 months) and 20 (18%) were "late" (> 2 months) diagnoses. Overall post-treatment VA was 6/12 or better in the majority (88/111, 79.3%) of cases, and 18 (16.2%) had VA of 6/36 or worse. The VA of > or = 6/12 was achieved by 90.8% of the early, 71.4% of the intermediate, and 65% of the late groups. Clinical relapses occurred in 19 patients on reducing the therapy. Treatment toxicity was never serious and consisted only of stinging or superficial punctate keratopathy. Keratoplasty was indicated in only ten patients, and disease activity was controlled adequately in all patients before grafting.

CONCLUSIONS

Combined treatment with PHMB and propamidine is well tolerated, nontoxic, and effective. Typically, visual outcome is favorable and the requirement for keratoplasty reduced markedly.

Treatment of Nocardia asteroides keratitis with polyhexamethylene biguanide

PURPOSE

Polyhexamethylene biguanide (PHMB) is a polymeric biguanide disinfectant that has been used previously in the treatment of Acanthamoeba keratitis. The authors report the first case of Nocardia asteroides keratitis treated successfully with PHMB. Further studies documenting the efficacy of PHMB against N. asteroides in vitro also are presented.

METHODS

A soft contact lens wearer presented with an infectious keratitis. Cultures from the cornea grew N. asteroides. The infection resolved with the treatment with PHMB 0.02%. Serial dilutions of PHMB were performed against N. asteroides in culture.

RESULTS

In vitro dilution studies determined that the minimal inhibitory concentration for PHMB against the tested isolate of N. asteroides was 0.01%. This is a concentration that has been shown to be well tolerated by the cornea in vivo.

CONCLUSIONS

Polyhexamethylene biguanide is effective against both Acanthamoeba and Nocardia and may have a wider range of usefulness than that currently recognized. Further testing, both in vitro and in vivo, is required.

Acanthamoeba keratitis in the south of Sweden

Eight patients with Acanthamoeba keratitis were diagnosed and treated at our clinic between February 1991 and February 1993. Five of these were contact lens wearers, two had suffered recent corneal trauma and one had recently undergone penetrating keratoplasty. The diagnoses were based on both culture and histological examination of biopsy material in three cases, on culture alone in two cases and on histological examination alone in three cases. In all but one primary treatment was Propamidine isethionate and Neomycin/Polymyxin B topically and Ketoconazole orally. Because of poor healing three patients additionally received Paromomycin and Miconazole or Clotrimazol topically; two of these were further treated with Polyhexamethylene biguanide topically. The interval from initial symptoms to accurate diagnoses varied from one to eleven months. In one patient the eye could not be saved; in the remaining patients visual acuity after healing ranged from hand movements to 1.0.

Successful medical therapy of Acanthamoeba keratitis with topical chlorhexidine and propamidine

INTRODUCTION

Following laboratory studies on new potential chemotherapy for Acanthamoeba keratitis, when chlorhexidine and propamidine provided an additive in vitro effect, a series of 12 patients with culture-proven Acanthamoeba keratitis from three UK centres was monitored during and after therapy.

METHODS

In all cases the clinical diagnosis was confirmed by amoebal culture. In some instances identification of the protozoa by direct microscopy of corneal tissue was possible. The medication was provided topically in drop form until the keratitis had resolved. In vitro sensitivity to chlorhexidine and propamidine was performed on all isolates and compared with sensitivity to a range of other drugs used for treatment of the infection.

RESULTS

In vitro drug testing confirmed that trophozoites and cysts of all 12 Acanthamoeba isolates were fully sensitive to chlorhexidine and propamidine. Therapy was satisfactory for controlling and eradicating the acanthamoebal infection in all patients. Three patients developed discrete stromal infiltration at the site of infection that resolved 1 week after commencing therapy, with or without use of steroids. Two patients developed a late inflammatory effect in the stromal scar at 6 months, which resolved with steroids. No clinical evidence of chlorhexidine toxicity was found in any patients.

CONCLUSIONS

The combination of topical chlorhexidine and propamidine was very effective for treating Acanthamoeba keratitis provided the drugs were continued for a sufficient period. No drug toxicity or resistance of Acanthamoeba isolates was observed in the 12 treated patients.

Acanthamoeba keratitis: risk factors and outcome

AIMS/BACKGROUND

This study was initiated to investigate risk factors for and outcome of Acanthamoeba keratitis.

METHODS

Results of treatment were studied in 22 patients (23 eyes) presenting to Bristol Eye Hospital between 1985 and February 1995. Details related to the use and disinfection of contact lenses were also obtained. An additional two patients who were seen at Bristol but mainly treated elsewhere were surveyed for contact lens related information only.

RESULTS

The incidence of Acanthamoeba keratitis rose substantially in the 1990s: three patients presented before 1990, while the remaining 21 presented between January 1990 and February 1995. Eleven patients have presented since january 1994. All of the patients in this series were contact lens wearers, 16 (67%) using daily wear disposable contact lenses. Contact lens disinfection data were available in 22 patients of whom 11 (50%) were using chlorine disinfectant. Other types of disinfection were much less common. Four patients (18%) had not used any disinfectant. During the course of the series the average diagnostic delay has fallen markedly, although in 77% of patients a diagnosis of a viral keratitis, most commonly herpes simplex, was made on first presentation. All but three of the series were treated with a combination of polyhexamethylene biguanide and propamidine isethionate. Penetrating keratoplasty was performed in 9/23 eyes (39%); in all of these eyes diagnosis was delayed for at least 6 weeks. All but one of the eyes in the series achieved a visual acuity of 6/9 or better after treatment, and 18 eyes (78%) saw 6/6 or better.

CONCLUSIONS

Most patients with Acanthamoeba keratitis can now expect a good visual result and cure by medical therapy alone is favoured by early diagnosis.

Acanthamoeba, bacterial, and fungal contamination of contact lens storage cases

BACKGROUND

Microbial corneal infection is the most serious complication of contact lens wear. Contact lens cases are a recognised potential source of pathogens associated with corneal ulcers.

METHODS

This survey established the incidence of protozoal, bacterial, and fungal contact lens case contamination in 101 asymptomatic daily wear cosmetic contact lens wearers from a domiciliary contact lens practice.

RESULTS

Eighty two (81%) contact lens cases were found to be contaminated, with 19 (19%) sterile. Of all contact lens cases, 78 (77%) grew bacteria, 24 (24%) fungi, and 20 (20%) protozoa. Acanthamoeba spp were isolated from eight (8%) contact lens cases. Fifty six (55%) contact lens cases yielded mixed bacterial contamination. This is the first contact lens case survey in which hydrogen peroxide disinfection was the major method of contact lens disinfection (75% of subjects) and no home made saline was used. All the contaminating organisms were shown to possess the enzyme catalase that breaks down hydrogen peroxide to oxygen and water. The polymicrobial nature of the biofilms found in many contact lens cases is illustrated electron micrographically.

CONCLUSION

Based on data from this and previous studies, the authors conclude with recommendations for contact lens wearers: (1) regular scrubbing of contact lens case interior to disrupt biofilms; (2) exposure of contact lens case to very hot water (> or = 70 degrees C) will kill Acanthamoeba contaminants; (3) allow contact lens case to air dry between uses; (4) if hydrogen peroxide disinfection is preferred, use a two step system; (5) replace contact lens case regularly.