In vitro evaluation of antimicrobial compounds for cysticidal activity against Acanthamoeba

Comparing cytotoxicity and efficacy of miltefosine and standard antimicrobial agents against Acanthamoeba trophozoites and cyst forms: An in vitro study

Acanthamoeba keratitis (AK) is an eye disease often occurring in contact lens wearers. AK treatment is prolonged and requires multiple drugs, which can lead to adverse effects. Our study aimed to compare the in vitro activities and safety of Miltefosine with that of conventional antimicrobial agents used to treat AK. Acanthamoeba castellanii genotype T4 was obtained from a patient with keratitis and subjected to in vitro susceptibility testing with various antimicrobial agents, including Chlorhexidine (CHX), Pentamidine isethionate (PI)Polyhexamethylene biguanide (PHMB), and Miltefosine to assess their efficacy against Acanthamoeba trophozoites and cyst. The cytotoxicity of the agents was evaluated in Vero cells, and their selectivity indexes (SI) were calculated. Chlorhexidine exhibited the highest amoebicidal activity with the highest selectivity index against the trophozoite and cyst, ranging from 1.17 to 8.35. The selectivity index of PHMB is slightly comparable to Chlorhexidine, exhibiting significant anti-Acanthamoeba activity. On the other hand, Pentamidine isethionate and Miltefosine displayed low SI among the compounds. Pentamidine isethionate was effective at high concentrations, which was toxic. Miltefosine exhibited the lowest cytotoxicity; nevertheless, due to the lowest anti-Acanthamoeba activity presented a low selectivity against the parasite. Further studies on more clinical samples and prolonged incubation time should be done to investigate the effectiveness and toxicity of drugs in both in vitro and in vivo conditions.

Evaluation of in vitro activity of five antimicrobial agents on Acanthamoeba isolates and their toxicity on human corneal epithelium

BACKGROUND

Acanthamoeba keratitis (AK) is an important cause of ocular morbidity in both contact lens wearers and non wearers. Medical management comprises prolonged empiric treatment with multiple drugs, leading to adverse effects and suboptimal cure. The present study evaluated the efficiency and safety of common antimicrobial agents used in treatment of AK.

METHODS

Six Acanthamoeba isolates (four AK, two water samples) were axenized and subjected to in vitro susceptibility testing against chlorhexidine, pentamidine isethionate, polymyxin B, miltefosine, and fluconazole to check for trophocidal and cysticidal activity. The safety profile was analysed by observing the cytotoxicity of the highest cidal concentration toward human corneal epithelial cell (HCEC) line.

RESULTS

Chlorhexidine had the lowest cidal concentration against both cysts and trophozoites (range 4.16-25 μg/ml) followed by pentamidine isethionate (range 25-166.7 μg/ml). Both agents were nontoxic to HCEC. Polymyxin B (range 25-200 μg/ml) and fluconazole (range 64-512 μg/ml) had relatively higher minimum inhibitory concentrations (MIC); fluconazole was nontoxic even at 1024 μg/ml, but cytotoxicity was observed at 400 μg/ml with polymyxin B. Miltefosine was not effective against cysts at tested concentrations. A. castellanii were more susceptible to all agents (except pentamidine isethionate) than A. lenticulata. Clinical isolates were less susceptible to polymyxin B and fluconazole than environmental isolates, reverse was true for miltefosine.

CONCLUSION

Chlorhexidine and pentamidine isethionate were the most effective and safe agents against both trophozoites and cysts forms of our Acanthamoeba isolates. Fluconazole had higher MIC but was nontoxic. Polymyxin B was effective at high MIC but therapeutic dose was found toxic. Miltefosine, at tested concentrations, could not inhibit cysts of Acanthamoeba. Clinical isolates had higher MICs for polymyxin B and fluconazole.

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.

Corticosteroid eye drop instillation aggravates the development of Acanthamoeba keratitis in rabbit corneas inoculated with Acanthamoeba and bacteria

The role of topical corticosteroids in management of Acanthamoeba keratitis (AK) remains controversial. Using a rabbit AK model, we investigated whether corticosteroid use is a risk factor of AK. Acanthamoeba (1 × 10⁵/ml) was incubated with two densities of P. aeruginosa (PA; high-PA: 1 × 10⁸/ml, low-PA: 3 × 10⁵/ml) before corneal inoculation. Rabbit corneas were inoculated with Acanthamoeba alone or Acanthamoeba plus PA and administered levofloxacin and betamethasone sodium phosphate (BSP) eye drops for 5 or 7 days. Infected rabbit eyes were evaluated for clinical score and Acanthamoeba by histological examination. Acanthamoeba alone and BSP treatment did not produce keratitis. Corneas inoculated with Acanthamoeba plus low-PA treated immediately with levofloxacin and BSP remained clear with few infiltrates. Corneas inoculated with Acanthamoeba plus low-PA treated with levofloxacin immediately and BSP 12 h later developed severe keratitis. Corneas inoculated with Acanthamoeba plus high-PA treated immediately with levofloxacin and BSP also developed severe keratitis. Acanthamoebae were detected by PAS staining in corneas inoculated with Acanthamoeba plus high-PA treated with levofloxacin and BSP. Topical corticosteroids have the potential to aggravate AK when cornea is infected by Acanthamoeba with a critical number of bacteria or when corticosteroids are given after infection has established by Acanthamoeba with small number of bacteria.

In-vitro development of an effective treatment for Acanthamoeba keratitis

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

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

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

Evaluation of the activity of new cationic carbosilane dendrimers on trophozoites and cysts of Acanthamoeba polyphaga

Dendrimers are repetitively branched molecules with a broad spectrum of applications, mainly for their antimicrobial properties and as nanocarriers for other molecules. Recently, our research group have synthesized and studied their activity against Acanthamoeba sp., causative agent of a severe ocular disease in humans: Acanthamoeba keratitis. New cationic carbosilane dendrimers were tested against the protozoa forms at different concentrations and for different incubation times. Trophozoite viability was determined by manual counting and cyst viability by observing excystment in microplates with fresh culture medium. Cytotoxicity was checked on HeLa cells using the microculture tetrazolium assay. Alterations were observed by optical microscopy and by flow cytometry staining with propidium iodide. Six out of the 18 dendrimers tested were non-cytotoxic and effective against the trophozoite form, having one of them (dendrimer 14 with an IC50 of 2.4 + 0.1 mg/L) a similar activity to chlorhexidine digluconate (IC50 1.7 + 0.1 mg/L). This dendrimer has a polyphenoxo core and a sulphur atom close to the six -NH3+ terminal groups. On the other hand, only two dendrimers showed some effect against cysts (dendrimers 14 and 17). However, their minimum cysticidal concentrations were cytotoxic and less effective than the control drug. The alterations on the amoeba morphology produced by the treatment with dendrimers were size reduction, increased complexity, loss of acanthopodia and cell membrane disruption. In conclusion, these results suggest that some dendrimers may be studied in animal models to test their effect and that new dendrimers with similar features should be synthesized.

The impact of topical corticosteroid use before diagnosis on the outcome of Acanthamoeba keratitis

OBJECTIVE

To examine the impact of topical corticosteroid use before the diagnosis of Acanthamoeba keratitis (AK) on final visual outcomes and to determine the prognostic factors predicting poorer outcomes.

DESIGN

Cohort study.

PARTICIPANTS

A total of 209 eyes of 196 patients with retrievable medical records, diagnosed with AK at Moorfields Eye Hospital, London, between January 1991 and April 2012. One eye was randomly excluded from analysis in the 13 cases of bilateral AK.

METHODS

Patient demographic, initial clinical examination findings, and management details were collected. The outcomes of patients treated with topical corticosteroids before diagnosis of AK were compared with those not treated with topical corticosteroids before diagnosis. A multivariable logistic model, optimized for prior corticosteroid use, was used to derive the odds ratios (ORs) of a suboptimal visual outcome.

MAIN OUTCOME MEASURES

Suboptimal visual outcome was defined as final visual acuity (VA) ≤ 20/80, corneal perforation, or need for keratoplasty.

RESULTS

Acanthamoeba keratitis was diagnosed on microbiological culture in 94 eyes (48.0%), on histopathologic examination in 27 eyes (13.8%), on confocal microscopy in 38 eyes (19.4%), and on the basis of a typical clinical course and response to treatment in 37 eyes (18.9%). Final VA and prior corticosteroid use data were available for 174 eyes (88.8%). In multivariable analysis, corticosteroid use before diagnosis was associated with suboptimal visual outcome (OR, 3.90; 95% confidence interval [CI], 1.78-8.55), as were disease stage 3 at presentation (OR, 5.62; 95% CI, 1.59-19.80) and older age (60+ years) at diagnosis (OR, 8.97; 95% CI, 2.13-37.79).

CONCLUSIONS

Corticosteroid use before diagnosis of AK is highly predictive of a poorer visual outcome. This is largely due to the initial misdiagnosis of AK as herpetic keratitis. It is important to include AK in the differential diagnosis of keratitis in all contact lens users with keratitis, particularly before making a diagnosis of herpes keratitis and before the use of topical corticosteroids in the therapy of any indolent keratitis.

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).

In vitro amoebicidal activities of Teucrium polium and T. chamaedrys on Acanthamoeba castellanii trophozoites and cysts

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 Teucrium polium and Teucrium chamaedrys. In the presence of methanolic extracts (ranging from 1.0 to 32.0 mg/ml), numbers of the viable Acanthamoeba castellani trophozoites and cysts were decreased during the experimental process. Both extracts showed time- and dose-dependent amoebicidal action on the trophozoites and cysts. Among the extracts tested, T. chamaedrys showed the strongest amoebicidal effect on the trophozoites. In the presence of 16 mg/ml or above extract concentrations, no viable trophozoites were observed within 48 h. In the case of T. polium, no viable trophozoites were observed within 48 h at 32 mg/ml concentration. As expected, cysts were found more resistant to the extracts than the trophozoites.

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

PURPOSE

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

DESIGN

Interventional case series.

PARTICIPANTS

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

INTERVENTION

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

MAIN OUTCOME MEASURES

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

RESULTS

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

CONCLUSIONS

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

Acanthamoeba: a review of its potential to cause keratitis, current lens care solution disinfection standards and methodologies, and strategies to reduce patient risk

BACKGROUND

The recent outbreaks of Acanthamoeba keratitis (AK), a rare but serious infection of the cornea, has increased the attention on the pathology of the organism and safety standards as they relate to soft contact lens (SCL) disinfection and solution formulations.

OBJECTIVE

To review the pathologic potential of Acanthamoeba to produce keratitis in patients at risk, discuss the complex issues involved in Acanthamoeba SCL disinfection efficacy standards and testing methods, and present strategies for patients as well as governmental agencies to reduce the risk for future outbreaks of this organism.

METHODS

Studies that investigated the pathology and occurrence of AK and the various methods for testing SCL disinfection products for efficacy against Acanthamoeba were reviewed and the results were summarized. RESULTS.: Acanthamoeba is a ubiquitous organism in nature and has pathogenic and nonpathogenic strains. Trophozoites--not cysts--bind to specific mannosylated proteins on the corneal surface abraded by SCL wear. These bound trophozoites produce a cytotoxic serine protease enzyme that destroys corneal integrity and provides the mechanism for Acanthamoeba to produce keratitis. To date, nowhere in the world are Acanthamoeba challenges included in product approval of SCL disinfection products. Nonstandardized microbiologic methods for SCL disinfection efficacy against Acanthamoeba continue to produce highly variable data from study to study. There are no detailed and standardized methods as yet for trophozoite cell culture, trophozoite-to-cyst conversion, product challenge with amoeba, neutralization of the test sample's antimicrobial activity, and accurate quantification of viable survivor cells.

CONCLUSIONS

Reducing the incidence of AK is multifaceted and includes education of SCL wearers in the hygienic wear and care of their lenses, implementation of standardized and rigorous SCL solution disinfection requirements, and can also include improvements in the antimicrobial quality of municipal water supplies.

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.

A case of successful treatment of cutaneous Acanthamoeba infection in a lung transplant recipient

Acanthamoeba species are known to cause 2 well-described entities: (1) granulomatous amoebic encephalitis (GAE), which usually affects immunocompromised hosts, and (2) keratitis, which typically follows trauma associated with contamination of water or contact lenses. Less common manifestations include pneumonitis and a subacute granulomatous dermatitis. We describe a case of granulomatous dermatitis secondary to Acanthamoeba infection in a lung transplant recipient and a successful outcome following treatment with lipid formulation of amphotericin B and voriconazole. We believe this is the second case report describing disseminated Acanthamoeba infection in a lung transplant recipient. We also describe successful outcome with a combination of lipid formulation of amphotericin B and voriconazole, drugs that have not been previously reported to treat Acanthamoeba.

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.

Resistance of Acanthamoeba castellanii cysts to physical, chemical, and radiological conditions

Resistance of Acanthamoeba castellanii cysts to disinfection agents, antimicrobial agents, heat, freeze-thawing, ultraviolet radiation (UV), gamma irradiation, and cellulase were evaluated in vitro. Following exposure to different agents, the cysts were removed and cultured for A. castellanii trophozoites for 3-14 days. Solutions containing 20% isopropyl alcohol or 10% formalin effectively killed A. castellanii cysts. Hydrogen peroxide (3%, AOSept Disinfectant) effectively killed A. castellanii cysts after 4 hr of exposure. Polyhexamethylene biguanide (0.02%), clotrimazole (0.1%), or propamidine isethionate (Brolene) were effective in killing A. castellanii cysts in vitro. Acanthamoeba castellanii cysts were resistant to both 250 K rads of gamma irradiation and 800 mJ/cm2 of UV irradiation. Excystment of trophozoites was accelerated after exposure to 10, 100, and, 1,000 units of cellulase. These results suggest that A. castellanii cysts benefit by enhanced survival because of their resistance to very harsh environmental conditions.

Antimicrobial susceptibility of 19 Australian corneal isolates of Acanthamoeba

PURPOSE

To determine the in vitro drug susceptibility of Australian corneal isolates of Acanthamoeba and to correlate the results with patient treatment and visual outcome.

METHODS

Acanthomoeba isolates were obtained from a reference laboratory Cyst suspensions were prepared from 19 strains and exposed to 10 antimicrobial agents for 7 days. The minimum drug concentrations required to inhibit excystation were determined. Inhibited cells were then plated out to determine minimum cysticidal concentrations.

RESULTS

Overall, propamidine proved to be the most active anti-Acanthamoeba agent tested. The disinfectant polyhexamethylene biguanide, either pure or in Baquacil, was also effective. Pentamidine, hexamidine, chlorhexidine and chloroxylenol had intermediate activity, while neomycin, amphotericin B and povidone-iodine had poor activity. There was no clear relationship between in vitro susceptibility and visual outcome.

CONCLUSIONS

Propamidine and polyhexamethylene biguanide drops are recommended as initial choices for the treatment of Acanthamoeba keratitis. The variability in the susceptibility to any one agent suggests that individual testing of isolates is necessary to identify the most appropriate treatment. A number of factors influence visual outcome in these cases; further studies are required to resolve the importance or otherwise of in vitro susceptibility.

Acanthamoeba Sinusitis with Subsequent Dissemination in an AIDS Patient

Otolaryngologists can play an important role in the care of patients with acquired immunodeficiency syndrome (AIDS) and/or human immunodeficiency virus infection. We present the case of an AIDS patient who was hospitalized for dehydration and who was soon found to have sinusitis and subsequent disseminated infection caused by Acanthamoeba. To treat the Acanthamoeba infection, the patient was started on oral itraconazole and intravenous metronidazole; IV pentamidine was added 2 days later. Despite aggressive therapy, on the eleventh day of hospitalization, the patient was obtundent and provided minimal response to noxious stimuli. He died on the sixteenth day of hospitalization.

This case is one of only six reported cases of Acanthamoeba associated with sinusitis. Current therapeutic regimens have not been successful for most of these patients, and the prognosis is poor.

In vitro evaluation of the amebicidal activity of Buddleia cordata (Loganiaceae, H.B.K.) on several strains of Acanthamoeba

Infectious diseases produced by free-living amoebae from the genus Acanthamoeba have been recently recognized. The need for antiamebic compounds is urgent as the occurrence of these diseases is being registered more frequently since the late sixties. We screened the aqueous and methanolic extract of a plant used by folk medicine (Buddleia cordata) against eye and skin inflammation for antiamebic activity. We tested the extracts on 29 strains of free-living amoebae, with the result that they were amebostatic for 14 and 15 strains, respectively. We obtained linarin and vanillic acid from the extracts, but only linarin was amebostatic to all the strains and vanillic acid had no activity. However, acetyl vanillic acid had similar effects on amoebae to linarin. Threshold values of these two active compounds ranged from 31.25 microg/ml to 4 mg/ml and from 31.25 microg/ml to 8 mg/ml for linarin and acetyl vanillic acid, respectively. These differences in threshold values were observed even on several strains belonging to the same species (as in the case of A. castellanii and A. polyphaga) indicating the need of susceptibility testing for each clinical isolate of free-living amoebae.

Results of a trial of combined propamidine isethionate and neomycin therapy for Acanthamoeba keratitis. Brolene Study Group

PURPOSE

To characterize patients with Acanthamoeba keratitis and to evaluate the safety and efficacy of propamidine isethionate 0.1% ophthalmic solution (Brolene) when administered concomitantly with neomycin-polymyxin B-gramicidin ophthalmic solution (Neotricin) in the treatment of Acanthamoeba keratitis.

DESIGN

Prospective, noncomparative case series.

METHODS

The authors report the clinical characteristics and outcomes of patients who entered this multicentered, open-label, clinical trial. Eighty-three patients with Acanthamoeba keratitis representing 87 infected eyes entered the trial.

RESULTS

Sixty (69%) of the 87 eyes enrolled had data analyzed for treatment efficacy and safety. Of these 60 eyes, 50 (83%) experienced treatment success. Thirty (60%) patients successfully treated adhered to treatment protocol guidelines. Patients who broke protocol had disease exacerbation during the maintenance therapy phase. The only eyes lost/enucleated were 7 of 17 in which penetrating keratoplasty was performed before eradication of the infectious agent.

CONCLUSION

Propamidine isethionate and neomycin are an effective treatment for Acanthamoeba keratitis. Penetrating keratoplasty should be performed only for visual rehabilitation and not to "debulk" an active infection. The authors advocate treating patients with topical medications, mainly Brolene, until all organisms are eradicated. There should be no signs of infection for at least 3 months in the patients not receiving antiamebic medications before penetrating keratoplasty is performed.

Anti-Acanthamoeba activity of contact lens solutions

AIMS

This study was undertaken to investigate the effects of contact lens disinfecting solutions on strains of Acanthamoeba from the United Kingdom and southern Africa and to compare the results with those of other researchers. No information was previously available for southern African isolates.

METHODS

11 contact lens solutions were tested on cysts of 10 strains of Acanthamoeba.

RESULTS

Not all solutions used in the study were effective, with some for hard and gas permeable contact lenses being more satisfactory than those for soft contact lenses. The most effective of the gas permeable and hard contact lens solutions tested was Transoak (0.01% (wt/vol) benzalkonium chloride), which killed cysts of all strains within 4 hours of exposure. Oxysept 1 (31 mg hydrogen peroxide/ml) was the best soft contact lens solution tested. It eliminated cysts of certain strains within 4 hours, whereas cysts of other strains were only inactivated within either 8 or 72 hours.

CONCLUSIONS

Manufacturers should be aware of the killing time for Acanthamoeba by contact lens solutions and should provide appropriate guidelines for the use thereof. The killing time for cysts of the African and UK isolates studied is, in general, similar. Therefore, it must in the present state of knowledge be assumed that usage guidelines suggested in the UK are also appropriate for travellers to South Africa and for local residents in South Africa.

In vitro effectiveness of povidone-iodine on Acanthamoeba isolates from human cornea

Acanthamoeba keratitis is a severe ocular infection secondary to accidental macro- or microscopic trauma of the cornea. Starting in 1985, a dramatic increase of this infection was recorded along with the spread of contact lens use. This protozoal disease is difficult to treat because of the scarcity of efficacious topical and systemic drugs. We evaluated the in vitro effectiveness of povidone-iodine (PVP-I [Betadine]), an agent with broad antibacterial and antiviral activity, compared to that of chlorhexidine (CXD), a cationic antiseptic, on Acanthamoeba isolates from patients with amebic keratitis. The results showed that PVP-I solution from 0.5 to 2.5% has a better antiamebic activity both on trophic and cystic stages of Acanthamoeba spp. than does CXD.

Effects of polyhexamethylene biguanide and chlorhexidine on four species of Acanthamoeba in vitro

We determined the relative minimal inhibitory and minimal amoebicidal concentrations of chlorhexidine digluconate and polyhexamethylene biguanide for four species of Acanthamoeba. The amoebae were grown in peptone-glucose-yeast extract broth for 72 h in tissue culture flasks. Either washed trophozoites (approximately 10(5)) or cysts (approximately 10(5)) were incubated in the enrichment broth in 96 well microtiter trays. Antimicrobial concentrations of the biguanides were determined from microscopic examinations of methylene blue uptake and from subcultures. In general, killing was time dependent. Minimal amoebicidal concentrations at 24 h ranged from 50 to 100 mg/ml and to as low as 25 mg/ml by 72 h. Trophozoites were killed more rapidly than cysts. Both biguanides had similar levels of activity. A synergistic combination of chlorhexidine and polyhexamethylene biguanide (total concentration 25 mg/ml) was most evident for A. castellanii and A. polyphaga. Cysts of A. culbertsoni and A. hatchetti stained more rapidly after exposure to the combination of biguanides than to the single biguanides, but there were no statistically significant differences in the final numbers of dead or stained cysts after exposure to the combination or to the single biguanides.

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

Trophozoites and cysts of 20 isolates of Acanthamoeba from the cornea and five from related samples were tested in vitro for sensitivity to ten drugs (three aromatic diamidines, two aminoglycosides, two macrolides, a polyene macrolide antibiotic, an organoarsenical and an antimetabolite) and two cationic antiseptics (chlorhexidine and polyhexamethylene biguanide, PHMB). Only chlorhexidine and PHMB showed uniform amoebacidal activity. Aromatic diamidines (pentamidine isethionate, propamidine isethionate and diminazene aceturate) generally proved effective against both forms of the amoeba; only pentamidine gave synergy with the biguanide while propamidine gave an additive effect. Other drugs tested proved erratic or ineffective against different isolates. Chlorhexidine alone, or together with propamidine, was subsequently used in two patients with proven Acanthamoeba keratitis; the causative isolates were sensitive to the individual compounds and to the combination in vitro. The treatment provided resolution of the clinical disease; amoebae were shown to be nonviable by histology and culture. The combination of chlorhexidine and propamidine is recommended for treatment of proven Acanthamoeba keratitis.

Acanthamoeba keratitis: a sobering case and a promising new treatment

This case report describing Acanthamoeba keratitis in a 41-year-old male disposable contact lens wearer, adds some sobering and some encouraging information for the future management of this infection. Initial treatment with topical propamidine isethionate (Brolene) and polymyxin B/neomycin/gramicidin (Neosporin) led to an unsatisfactory clinical response. Topical miconazole 1%, prednisolone acetate 0.12% and oral itraconazole were then added to his treatment. This was later discontinued on noticing ipsilateral toxic cataract formation and an unresponsive pupil. The above medications were replaced with topical polyhexamethylene biguanide (PHMB) 0.02%, which we had shown to have superior in-vitro amoebicidal activity when compared to the other antiamoebic agents used in this case. Withdrawal of the multitreatment schedule and commencement of PHMB was associated with resolution of his keratitis, healing of a large epithelial defect and settling of severe conjunctivitis. The identical Acanthamoeba strain was isolated from the patient's contact lens storage case and cornea, possibly implicating the contaminated contact lens case in the aetiology of his keratitis. This is the first Australasian experience using PHMB to treat Acanthamoeba keratitis. It appears to be a promising new treatment for this infection.

Acanthamoeba keratitis. A masquerade of presentation in six cases

Acanthamoeba keratitis is an uncommon but devastating complication of contact lens wear causing significant ocular morbidity. Six consecutive cases occurring in Western Australia in an 18-month period are reported. In all cases either poor contact lens hygiene or an association with swimming pools and contact lens use is a feature. There is invariably a delay in making the diagnosis, with the appearance frequently mistaken for herpes simplex keratitis. In all cases corneal biopsy was required to confirm the diagnosis. Of the six patients, four responded to medical therapy alone, one required a corneal graft and one required enucleation. We suggest that earlier rather than later corneal biopsy is important in unresponsive cases of culture-negative keratitis, especially in contact lens wearers. We would agree that the treatment of choice is intensive topical propamidine and neosporin. Prevention by strict adherence to contact lens care and hygiene is urged.

A review of 72 consecutive cases of Acanthamoeba keratitis, 1984-1992

A review of consecutive cases of Acanthamoeba keratitis presenting since 1984 was undertaken in order to assess prognostic factors, the success of culture procedures and the outcome of medical and surgical management, with reference to current clinical practice. Seventy-two consecutive cases (77 eyes) of Acanthamoeba keratitis have been managed. Sixty-four patients were contact lens wearers, 28 of these wearing disposable lenses. Superficial corneal involvement and perineural infiltrates were common in those diagnosed less than a month after first symptoms, designated 'early' presentation. Ring infiltrates and ulceration with stromal lysis characterised those presenting at 1-2 months ('intermediate') or after 2 months ('late'); these groups also progressed more frequently to hypopyon, scleritis, glaucoma and cataract formation. Positive corneal cultures were obtained in 10 of 14 (71%) intermediate and 17 of 23 (74%) late cases; early cases underwent epithelial biopsy but formal trephine biopsy was not usually justified (1 of 35 cases) and only 19 of 35 (54%) were tissue-positive. Microbial co-isolates were obtained from 20 corneas. Thirty-four penetrating keratoplasties were performed in 23 eyes, 21 whilst inflamed and 13 when quiet. Of 13 failures in inflamed eyes, 9 were due to recurrence of Acanthamoeba infection. Medical cure is known to have been achieved in 64 of 73 (88%) eyes, 4 of the original 77 having been lost to follow-up abroad. Fifty-eight of 73 eyes (79%) achieved a final visual acuity of 6/12, and of the culture-positive cases, 32 of 46 (70%) achieved 6/12.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of magainins on ameba and cyst stages of Acanthamoeba polyphaga

Amebic keratitis produced by Acanthamoeba spp. is an increasingly important ocular infection in extended-use contact lens wearers. Problems associated with the infection are compounded by the lack of effective and well-tolerated chemotherapeutic agents. The magainins, a group of naturally occurring and synthetic membrane-active peptide compounds, have been shown to be active in vitro against a clinical isolate of Acanthamoeba polyphaga. Two magainins tested extensively had minimal inhibitory and minimal amebicidal values of 20 and 25 micrograms/ml for magainin MSI-103 and 25 and 40 micrograms/ml for magainin MSI-94, respectively. Both amebastatic and amebicidal activities are enhanced by combining the magainins with silver nitrate (200 micrograms/ml) and/or other marginally effective antimicrobial agents. These combinations have activity against both trophic and cystic stages in the Acanthamoeba life cycle and have promise as antimicrobial agents in the treatment of amebic keratitis.