Strategies to optimize conditions for testing multipurpose contact lens solution efficacy against Acanthamoeba

In Vitro Effectiveness of Soft Contact Lens Solutions Available on the Dutch Market against Acanthamoeba Species

Acanthamoeba keratitis is almost universally associated with contact lens (CL) use. Until today, however, CL solution manufacturing protocols lack testing of anti-amoebic activity. This study investigates the effectiveness of CL solutions available on the Dutch market against trophozoites and cysts of Acanthamoeba castellanii and Acanthamoeba polyphaga. Sixteen CL solutions were tested: 13 multiple purpose solutions (MPS), 2 hydrogen peroxidase solutions (HPS) and 1 povidone-iodine-based solution (PIS). The Spearman-Karber (SK) log reduction method and an XTT colorimetric assay were used to evaluate the effectiveness at the manufacturer's minimum recommended disinfection time (MMRDT) and after eight hours. At the MMRDT, one MPS showed an SK mean log reduction (MLR) of >3.0 against A. castellanii trophozoites. Two additional MPS and both HPS reached this threshold after eight hours. The SK MLR values for A. polyphaga trophozoites were between 1 and 3 at all time points. Using the XTT colorimetric assay, only HPS 1 showed >99.9% reduction (equivalent to 3 log reduction) in metabolic activity of A. castellanii trophozoites after eight hours. For A. polyphaga, both HPS and PIS showed a metabolic reduction of >99.9% after eight hours. Cysts were resistant against all solutions. We conclude that following the manufacturer's guidelines, few solutions provide sufficient effectiveness against Acanthamoeba trophozoites and none against cysts. The results underline the importance of adequate hygiene when handling CLs.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Variables Affecting the Recovery of Acanthamoeba Trophozoites

While the results of Acanthamoeba testing have been extensively published, laboratories conducting such testing are left to develop their own methods in the absence of a standardized methodology. The wide disparity of methods has resulted in equally inconsistent reported results for contact lens care (CLC) products. This study's objective was to determine the source of these discrepancies by evaluating basic Acanthamoeba biology and their impact on antimicrobial efficacy testing, including the ability of a recovery method to stimulate a single trophozoite to proliferate. Antimicrobial efficacy testing was conducted using well-published Acanthamoeba strains, storage conditions, and growth-based recovery methods. To identify variables that influence results, test solutions with low Acanthamoeba disinfection rates were utilized to prevent differences from being masked by high log reductions. In addition, single-cell proliferation assays were executed to understand the growth requirements to stimulate trophozoite propagation in two recovery methods. These studies indicated that both nutrient density (>106 CFU) and the length of plate incubation (at least 14 days) could significantly influence the accurate recovery of trophozoites. Together, this study emphasizes the need to understand how Acanthamoeba trophozoites biology can impact test methods to create divergent results.

Acanthamoeba: An Overview of the Challenges to the Development of a Consensus Methodology of Disinfection Efficacy Testing for Contact Lens Care Products

With the increasing incidence of more pathogens that can cause microbial keratitis (MK), it is necessary to periodically reassess disinfection multipurpose solutions testing requirements to ensure that relevant organisms to challenge them are being used. Current testing protocols have included common pathogens such as Pseudomonas aeruginosa, Staphylococcus aureus, Serratia marcescens, Candida albicans, and Fusarium solani but have omitted less common pathogens such as Acanthamoeba. Specifically, Acanthamoeba sp. has recently been identified as a prevalent cause of MK in certain countries. Developing an appropriate protocol for this unique organism presents a challenge, given its two distinct life stages, methods to grow the organism, encystment techniques, and many other parameters that can affect testing outcomes. Therefore, the appropriate combination of these parameters is crucial to developing a protocol that ensures consistent, accurate results. The FDA has recognized the importance of establishing a standardized testing protocol for this pathogen and embarked on research efforts to provide a recommended testing protocol for testing contact lens care products.

Optimized Protocol for Testing Multipurpose Contact Lens Solution Efficacy Against Acanthamoeba

OBJECTIVES

To evaluate the interlaboratory and intralaboratory reproducibility of a proposed protocol for multipurpose contact lens solution (MPS) disinfection efficacy against Acanthamoeba.

METHODS

Acanthamoeba castellanii and Acanthamoeba polyphaga and four MPS with different biocidal agents were used to evaluate the protocol in two different laboratories. In addition to the negative control, a positive control and neutralization control were used. One experiment was performed in triplicate, and all other experiments were performed in duplicate in each laboratory. Acanthamoeba trophozoites were grown axenically, and cysts were generated using the starvation method. Trophozoites and cysts at a concentration of 2.0 × 10 to 2.0 × 10 organisms per milliliter were exposed to the test MPS for 0, 4 or 6 (manufacturer's recommended soak time [MRST]), 8, and 24 hr. Survivors were determined by a limiting dilution method that used a most probable number evaluation.

RESULTS

The positive and negative controls displayed consistent results and trends both within each laboratory and between each laboratory for trophozoites and cysts of both A. castellanii and A. polyphaga. The neutralization control consistently demonstrated the ability of the neutralizing agents to neutralize the MPS and the positive control and demonstrated no inhibition of Acanthamoeba by the negative control. Testing in triplicate and duplicate demonstrated the reproducibility of the protocol both within each laboratory and between the laboratories. Our results demonstrated that the MPS at the MRST and at 8 hr (likely overnight soak time) are generally more effective against trophozoites than they are against cysts. Only the MPS with hydrogen peroxide as the biocidal agent was able to provide a greater than three-log kill of cysts at the MRST and longer. Among the MPS we tested, trophozoites of A. castellanii and A. polyphaga showed similar responses. Some variability was observed when testing cysts of both species. In both laboratories, one nonhydrogen peroxide containing MPS had some effect (>1 log kill) on A. polyphaga cysts. This solution had no effect (<1 log kill) on A. castellanii cysts, A. castellanii trophozoites, and A. polyphaga trophozoites.

CONCLUSIONS

The protocol that we have revised and evaluated is a well-controlled and reproducible procedure that can effectively evaluate the efficacy of MPS against Acanthamoeba trophozoites. Some variability was observed when testing the cyst stage.

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

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

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.

Fungi associated with drug recalls and rare disease outbreaks

Fungi rarely cause disease outbreaks associated with use of microbe-contaminated drugs. These rare episodes typically involve a restricted spectrum of common environmental species with relatively low virulence, rather than classical pathogens. Review of data involving over-the-counter contact lens solutions and prescription drug-related recalls revealed six episodes during the past decade with significant adverse health and financial impact (including loss of vision and death). Contaminations involved fungi mostly identified with the genera Aspergillus, Exserohilum, Fusarium, Paecilomyces, and Rhizopus. These organisms are noted for their capacity to produce resistant morphotypes (chlamydoconidia, ascospores) under various adverse conditions, generally with temperature survival/tolerances markedly in excess of maximal growth temperatures. High constituent levels of melanin, trehalose and heat-shock proteins facilitate differential survival of morphotypes following exposures to toxic chemicals and temperatures above 80 °C. Adverse environmental factors that induce resistant morphotypes are suggested to occur more readily in situ than during in vitro testing. Rare unexplained, sporadic drug contamination episodes with select thermotolerant fungi may relate, in part, to resistant dormant stages.

Encystment in Acanthamoeba castellanii: a review

Differentiation of Acanthamoeba castellanii trophozoites involves massive turnover of cellular components and remodelling of organelle structure and function so as to produce a cryptobiotic cell, resistant to desiccation, heat, freezing, and chemical treatments. This review presents a summary of a decade of research on the most studied aspects of the biochemistry of this process, with emphasis on problems of biocide and drug resistances, putative new targets, molecular and cell biology of the process of encystment, and the characteristics of the encysted state. As well as the intrinsic pathogenicity of the organism towards the cornea, and the ability of related species to invade the human brain, its propensity for harbouring and transmitting pathogenic bacteria and viruses is considerable and leads to increasing concerns. The long-term survival and resistance of cysts to drugs and biocides adds another layer of complexity to the problem of their elimination.

PrestoBlue® and AlamarBlue® are equally useful as agents to determine the viability of Acanthamoeba trophozoites

Acanthamoeba is an opportunistic pathogen which is the causal agent of several human infections such as Granulomatous Amoebic Encephalitis, Acanthamoeba keratitis and other disseminated infections. Furthermore, current therapeutic measures against Acanthamoeba infections are arduous, and show limited efficacy against the cyst stage of Acanthamoeba. There is a pressing need to search and evaluate new therapeutic agents against these protozoa. Our approach for evaluating possible new drugs is an initial in vitro screening assay based on general metabolic activity of the cells. In this study we compare two agents, AlamarBlue® and PrestoBlue® for this initial screen. Both reagents can be used to indicate metabolism by changes in their absorbance or fluorescence. The assay is carried out in a 96-well plate format and fluorescence can be measured after an inoculation period of as little as 10 min, but more typically 96 h. This to the best of our knowledge this is the first time that both compounds are directly compared using absorbance and fluorescence measurement. We conclude that for the specific case of Acanthamoeba both agents AlamarBlue® and PrestoBlue® are equally useful to determine cell viability.

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

IMPORTANCE

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

OBJECTIVE

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

DESIGN AND SETTING

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

MAIN OUTCOMES AND MEASURES

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

RESULTS

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

CONCLUSIONS AND RELEVANCE

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

In vitro adhesion of Acanthamoeba castellanii to soft contact lenses depends on water content and disinfection procedure

PURPOSE

To compare the potential of different soft contact lenses to be contaminated with Acanthamoeba castellanii as a function of material parameters and cleaning procedures.

METHODS

Different unworn soft hydrogel and silicone hydrogel contact lenses were incubated with human pathogenic A. castellanii. The adhesion of the acanthamoebae was investigated on the contact lenses and put into relation to their material parameters. The efficacy of a recommended contact lens cleaning procedure in reducing A. castellanii adhesion was investigated.

RESULTS

We found that material parameters such as elastic modulus, silicone content, ionic properties and swelling do not influence the adhesion of acanthamoebae to soft contact lenses. A material parameter that influenced adhesion significantly was the water content of the lens. With increasing water content, the adhesion of acanthamoebae increased. By following the cleaning instructions of the manufacturer the contamination of the lenses with A. castellanii could be reduced to a minimum, as shown both on contact lenses and in control experiments.

CONCLUSION

With this study we show that for the tested lenses, the adhesion of A. castellanii to contact lenses is independent of the silicone content of the lens, but depends nonlinearly on the water content of the lens. Furthermore, we demonstrate that applying proper lens cleaning procedures minimizes the risk of acanthamoebae adhesion to contact lenses.