Possible environmental sources of Acanthamoeba spp in contact lens wearers

The global epidemiology and clinical diagnosis of Acanthamoeba keratitis

Acanthamoeba keratitis is a rare parasitic infection of the cornea that can lead to permanent blindness if not diagnosed and treated promptly. We collected data on the incidences of Acanthamoeba keratitis from 20 countries and calculated an annual incidence of 23,561 cases, with the lowest rates in Tunisia and Belgium, and the highest in India. We analyzed 3755 Acanthamoeba sequences from the GenBank database across Asia, Europe, North America, South America, and Oceania and genotyped them into T1, T2, T3, T4, T5, T10, T11, T12, and T15. Many genotypes possess different characteristics, yet T4 is the most prevalent genotype. As efficient treatment against Acanthamoeba remains lacking, prevention from early diagnosis via staining, PCR, or in vivo confocal microscopy (IVCM) becomes significant for the condition's prognosis. IVCM is the most recommended approach for the early detection of Acanthamoeba. If IVCM is unavailable, PCR should be used as an alternative.

Acanthamoeba keratitis in contact lens wearers in a tertiary center of Tunisia, North Africa

PURPOSE

To analyze the epidemiological and clinical features of Acanathamoeba keratitis AK and to assess the risk factors of this corneal infection in contact lens CL wearers in a tertiary center of Tunisia, North Africa.

METHODS

We carried out a retrospective study between January 2008 and December 2019 in the ophthtalmology department of a referral center, Sousse, Tunisia. A review of the chart of 248 patients using CL and diagnosed with presumed infectious keratitis was done.Socio demographic, risk behaviors and microbiological findings in case of AK were analyzed. The mean follow-up was 18 months (1 month-4 years).

RESULTS

AK was diagnosed in 29 cases (11.7% of contact lens wearers with infectious keratitis). These 29 cases were analyzed. The mean age at the time of diagnosis was 33, 44 ± 26, 9 years. Almost of the patients (13; 44.82%) used soft monthly disposable contact lenses. Some risk behaviors related to contact lens wearing were found in our study like not washing and drying hands before CL wear, sleeping in CL, topping off, not respecting the adequate replacement frequency and showering or swimming in CL.After treatment, visual acuity improved only in 10 cases (34.48%), remained the same in 11 cases (37.93%) and worsened in 8 cases (27.58%).

CONCLUSION

Clinicians must suspect AK in each CL wearer with suggestive clinical signs to allow earlier treatment and better prognosis. Public prevention messages that encourage CL wearers to respect the hygiene rules should be broadly applicable to each person using any type of CL, to minimize the risk of AK.

The impact of patient behaviour and care system compliance on reusable soft contact lens complications

Reusable soft daily wear contact lenses (CLs) remain popular and were fit to just over half of all wearers in the most recent international CL prescribing survey. Unlike daily disposable CLs, reusables require cleaning and disinfecting after every use, along with storage in a CL case. These additional requirements add a number of steps to the daily wear and care routine, increasing the opportunities for CL wearers to exhibit non-compliant behaviour. The impact of non-compliance ranges from poor lens comfort through to potentially sight-threatening infective keratitis. The coronavirus pandemic has refocused the profession on the importance of hand hygiene in particular, and the need for promoting safe CL wear in general. This review summarises typical non-compliant behaviour related to reusable CLs, and examines strategies and opportunities to better support wearers. Patient education has a central role in encouraging compliant behaviour, although patient recall of information is low, and personal belief systems may result in continuation of non-compliant behaviour despite awareness of the risks. CL care solutions are required for the daily disinfection of lenses, however misuse of multipurpose solutions (MPS) and hydrogen peroxide (H₂O₂)-based care systems can challenge their ability to be fully efficacious. Standard efficacy testing is reviewed, with consideration of how well current protocols model real-world use of CL solutions. Although some recommendations are in place for the inclusion of additional variables such as lens cases, CL materials, organic soil and efficacy against Acanthamoeba, opportunity still exists to reevaluate global standards to ensure consistency of testing in all markets. Finally, potential future innovations are discussed which may further support increased safety in reusable lens wear through novel antimicrobial additions to both CL materials and cases.

Prevalence and seasonal variation of Acanthamoeba in domestic tap water in greater Sydney, Australia

BACKGROUND

This study examined the prevalence of free-living Acanthamoeba in domestic tap water in the greater Sydney region, Australia, and determined any seasonal variation in prevalence.

METHODS

Fifty-four participants were included in this study following approval from an institutional human research ethics committee. Each participant self-collected two samples (one in summer and another in winter) from the surface of the drain of the bathroom sink using an instructional kit. The samples were cultured by inoculating onto a non-nutrient agar plate seeded with Escherichia coli and incubation at 32°C for two weeks. The plates were microscopically examined for the presence of free-living amoeba. DNA was isolated from 20 samples and a polymerase chain reaction (PCR) assay was performed for amplification of the partial sequence of the 18S ribosomal RNA gene. The PCR amplified products were sequenced using Sanger sequencing and genotyping was performed based on the variation in nucleotide sequences.

RESULTS

A total of 97 samples were collected over the two collection periods, with 28.6 per cent of samples morphologically classified as Acanthamoeba. The summer period yielded 16 of 54 (29.6 per cent) samples classified as Acanthamoeba, while the winter period yielded 12 of 43 (27.9 per cent) samples classified as Acanthamoeba. There was no statistically significant difference (p = 0.85) between the prevalence of free-living Acanthamoeba in summer compared to winter. Phylogenetic analysis showed that 15 of 20 (75 per cent) isolates belonged to genotype T4, the most frequent genotype isolated in Acanthamoeba keratitis.

CONCLUSION

The prevalence of free-living Acanthamoeba characterised morphologically in domestic tap water of the greater Sydney region was higher than expected, especially considering the low incidence of Acanthamoeba keratitis in Australia. However, this study did not find variation between seasons. As the T4 genotype was most common, Sydney-based practitioners must always consider Acanthamoeba as a possible causative organism in cases of microbial keratitis, regardless of the season.

The relationship between environmental sources and the susceptibility of Acanthamoeba keratitis in the United Kingdom

PURPOSE

To determine whether Acanthamoeba keratitis (AK) patients have higher rates of Acanthamoeba and free-living amoeba (FLA) colonising domestic sinks than control contact lens (CL) wearers, and whether these isolates are genetically similar to the corneal isolates from their CL associated AK.

METHODS

129 AK patients from Moorefield Eye Hospital, London and 64 control CL wearers from the Institute of Optometry were included in this study. The participants self-collected home kitchen and bathroom samples from tap-spouts, overflows and drains using an instructional kit. The samples were cultured by inoculating onto a non-nutrient agar plate seeded with Escherichia coli, incubated at 32°C and examined for amoebae by microscopy for up to 2 weeks. Partial sequences of mitochondrial cytochrome oxidase genes (coxA) of Acanthamoeba isolates from four AK patients were compared to Acanthamoeba isolated from the patient's home. The association between sampling sites was analysed with the chi-square test.

RESULTS

A total of 513 samples from AK patients and 189 from CL controls were collected. The yield of FLA was significantly greater in patients' bathrooms (72.1%) than CL controls' bathrooms (53.4%) (p<0.05). Spouts (kitchen 6.7%, bathroom 11%) had the lowest rate of Acanthamoeba isolation compared to drains (kitchen 18.2%, bathroom 27.9%) and overflow (kitchen 39.1%, bathroom 25.9%) either in kitchens or bathrooms (p<0.05). There was no statistically significant difference between the average prevalence of Acanthamoeba in all three sample sites in kitchens (16.9%) compared to all three sample sites in bathrooms (21.5%) and no association for Acanthamoeba prevalence between AK patients and CL controls. All four corneal isolates had the same coxA sequence as at least one domestic water isolate from the patients' sink of the kitchen and the bathroom.

CONCLUSION

The prevalence of Acanthamoeba and FLA was high in UK homes. FLA colonisation was higher in AK patients compared to controls but the prevalence of Acanthamoeba between AK patients and CL controls domestic sinks was similar. This study confirms that domestic water isolates are probably the source of AK infection. Advice about avoiding water contact when using CL's should be mandatory.

Water Exposure and the Risk of Contact Lens-Related Disease

PURPOSE

To describe the association of water exposure with contact lens (CL)-related disease and explore the guidelines regarding water exposure to CL wearers, provided by CL manufacturing industry, global public health, and CL-related professional associations.

METHODS

A review of the literature was conducted by searching PubMed, MEDLINE, and Web of Science databases up to September 2017 for articles published or translated in English using keywords: contact lens* AND tap water OR swimming OR showering OR water exposure AND microbial keratitis OR Acanthamoeba keratitis OR corneal infiltrate* OR ocular adverse event*. References in all relevant publications were also reviewed.

RESULTS

Water exposure during CL wear is associated with complications ranging from sterile corneal infiltrative events to sight-threatening infections. Despite the documented risks due to water exposure, water-related habits are common among CL wearers. This suggests a lack of awareness and understanding regarding the risks among CL wearers and potentially CL practitioners. Discrepancies exist in guidelines for CL hygiene and compliance provided by the CL manufacturing industry, global public health, and CL-related professional associations. There is also widespread use of water imagery within CL marketing and packaging materials. These factors may give rise to confusion among wearers and may contribute toward risk-taking behaviors.

CONCLUSIONS

Consensus among stakeholders about water and CL care is needed. Guidelines should unequivocally advocate for the avoidance of any water exposure including handling CLs with wet hands, rinsing CLs or storage cases in tap water, showering while wearing CLs and swimming with CLs without wearing goggles.

3D Hydrogels Containing Interconnected Microchannels of Subcellular Size for Capturing Human Pathogenic Acanthamoeba Castellanii

Porous hydrogel scaffolds are ideal candidates for mimicking cellular microenvironments, regarding both structural and mechanical aspects. We present a novel strategy to use uniquely designed ceramic networks as templates for generating hydrogels with a network of interconnected pores in the form of microchannels. The advantages of this new approach are the high and guaranteed interconnectivity of the microchannels, as well as the possibility to produce channels with diameters smaller than 7 μm. Neither of these assets can be ensured with other established techniques. Experiments using the polyacrylamide substrates produced with our approach have shown that the migration of human pathogenic Acanthamoeba castellanii trophozoites is manipulated by the microchannel structure in the hydrogels. The parasites can even be captured inside the microchannel network and removed from their incubation medium by the porous polyacrylamide, indicating the huge potential of our new technique for medical, pharmaceutical, and tissue engineering applications.

Review of Contact Lens-Related Complications

The purpose of this article is to provide a review of existing literature describing complications with contemporary contact lenses and their management. It is envisioned that this will serve as a useful summary of noninfectious and infectious complications associated with contact lens wear.

Influence of secondary water supply systems on microbial community structure and opportunistic pathogen gene markers

Secondary water supply systems (SWSSs) refer to the in-building infrastructures (e.g., water storage tanks) used to supply water pressure beyond the main distribution systems. The purpose of this study was to investigate the influence of SWSSs on microbial community structure and the occurrence of opportunistic pathogens, the latter of which are an emerging public health concern. Higher numbers of bacterial 16S rRNA genes, Legionella and mycobacterial gene markers were found in public building taps served by SWSSs relative to the mains, regardless of the flushing practice (P < 0.05). In residential buildings, genes of L. pneumomhila, Acanthamoeba and Vermamoeba vermiformis were primarily detected in tanks and taps compared to the mains. Long water retention time, warm temperature and loss of disinfectant residuals promoted microbial growth and colonization of potential pathogens in SWSSs. Varied levels of microbial community shifts were found in different types of SWSSs during water transportation from the distribution main to taps, highlighting the critical role of SWSSs in shaping the drinking water microbiota. Overall, the results provided insight to factors that might aid in controlling pathogen proliferation in real-world water systems using SWSSs.

Epidemiology of contact lens-induced infiltrates: an updated review

Corneal infiltrative events (CIEs) are well established as a risk associated with soft contact lens wear. The incidence of symptomatic CIEs during extended soft lens wear ranges from 2.5 to six per cent; when asymptomatic CIEs are included, the incidence can be as high as 20-25 per cent. In daily soft lens wear, the annual incidence of symptomatic CIEs is about three per cent. There are various accepted methods of categorising CIEs, and a scoring system based on clinical signs and symptoms is a good approach to grade severity. Lens-related risk factors include extended wear, silicone hydrogel material, the use of multipurpose solutions, bacterial bioburden and reusable lenses. Recent studies report that daily disposable lenses reduce the risk of CIEs.

[Good outcome in Acanthamoeba keratitis]

A 31-year-old woman presented with mild keratitis of her left eye. The use of daily disposable contact lenses, regularly rinsed with tap water, and the development of perineural corneal infiltrates resulted in the clinical suspicion of infection with Acanthamoeba. Corneal epithelial scraping probe for polymerase chain reaction on Acanthamoeba confirmed the clinical diagnosis. Although the treatment was limited to low-dose propamidine monotherapy because of reduced tolerability, the keratitis healed with almost no scarring after 13 months of consequent medication.

Acanthamoeba Keratitis among Rigid Gas Permeable Contact Lens Wearers in the United States, 2005 through 2011

PURPOSE

To describe the clinical presentation and outcomes of Acanthamoeba keratitis (AK) in rigid gas permeable (RGP) contact lens wearers and to identify modifiable risk factors.

DESIGN

Case-control investigation.

PARTICIPANTS

Patients were RGP contact lens-wearing United States residents with a diagnosis of AK from 2005 through 2011. Controls were RGP contact lens wearers with no history of AK who were at least 12 years of age.

METHODS

Patients were identified during 2 multistate AK outbreak investigations. Controls from the first investigation in 2007 were identified using a reverse address directory. In the second investigation, controls were recruited from participating ophthalmology and optometry practices. Patients and controls were interviewed by phone using a standardized questionnaire. Odds ratios (ORs) and Fisher exact P values were calculated to assess risk factors associated with infection.

MAIN OUTCOME MEASURES

Acanthamoeba keratitis, a rare eye disease primarily affecting contact lens wearers, is caused by free-living amebae, Acanthamoeba species.

RESULTS

We identified 37 patients in the 2 investigations, 10 (27%) from the 2007 investigation and 27 (73%) from 2011. There were 17 healthy controls, 9 (53%) from 2007 and 8 (47%) from 2011. Among patients, 9 (24%) wore RGP lenses for orthokeratology or therapeutic indication; no controls wore RGP lenses for these indications. Significant risk factors for AK were wearing lenses for orthokeratology (OR, undefined; P = 0.02), sleeping while wearing lenses (OR, 8.00; P = 0.04), storing lenses in tap water (OR, 16.00; P = 0.001), and topping off contact lens solution in the case (OR, 4.80; P = 0.01). After stratifying by use of RGP lenses for orthokeratology, storing lenses in tap water and topping off remained significant exposures.

CONCLUSIONS

Nearly one quarter of patients were orthokeratology wearers. Using tap water to store RGP lenses and topping off solution in the lens case were modifiable risk behaviors identified in RGP wearers who wore lenses for both orthokeratology and nonorthokeratology indications. Rigid gas permeable wearers should avoid exposing their lenses to tap water and should empty their cases and use fresh lens solution each time they take out their lenses.

Corneal infections in the 21st century

Ninety years ago, the first issue of the Postgraduate Medical Journal published a review of an article written by Mr Robert Lindsay-Rea, a consultant ophthalmic surgeon in the Western Ophthalmic Hospital and an oculist in the West End Hospital for Nervous Diseases, entitled "A preliminary report on the treatment of keratitis". Today, microbial keratitis remains an important cause of avoidable visual impairment in the world. The aetiology of microbial keratitis has changed greatly over the past century due to the discovery of antibiotics, improvement in sanitation and education, the rising trend of contact lens wear and increased air travel. Significant advances have also been made in our understanding and management of this important disorder. This article highlights some of these changes and discusses the current management and research.

Isolation and molecular characterization of Acanthamoeba genotypes in recreational and domestic water sources from Jamaica, West Indies

Free living amoebae (FLA) are amphizoic protozoa that are ubiquitous in nature. Infection with FLA may result in neurological, ocular and skin infections. Exposure to Acanthamoeba occurs frequently through water contact and knowledge of the presence of the organisms in water sources is important in understanding transmission dynamics. The distribution of Acanthamoeba was studied in recreational and domestic water samples collected from across Jamaica. Morphological assessment and polymerase chain reaction revealed Acanthamoeba spp. isolates in 50.6% (42/83) and 17.3% (14/81) of recreational and domestic water, respectively. Sequencing of the DF3 region of the 18S rDNA resulted in the identification of genotypes T3, T4, T5, T10 and T11 corresponding to Acanthamoeba spp: A. griffini, A. triangularis, A. lenticulata, A. culbertsoni and A. hatchetti. Moreover, T4 was the most frequently isolated genotype in both recreational and domestic water. Thermotolerance and osmotolerance assays indicated that most isolates were potentially pathogenic. This is the first report of T3 and T10 genotypes in the Caribbean and the first report of these Acanthamoeba spp. in Jamaican waters. The study shows that there is potential risk of infection to contact wearers who practise poor lens care. Further, Acanthamoeba should be considered as a cause of neurological infections in Jamaica.

Influence of the PDMS substrate stiffness on the adhesion of Acanthamoeba castellanii

BACKGROUND

Mechanosensing of cells, particularly the cellular response to substrates with different elastic properties, has been discovered in recent years, but almost exclusively in mammalian cells. Much less attention has been paid to mechanosensing in other cell systems, such as in eukaryotic human pathogens.

RESULTS

We report here on the influence of substrate stiffness on the adhesion of the human pathogen Acanthamoebae castellanii (A. castellanii). By comparing the cell adhesion area of A. castellanii trophozoites on polydimethylsiloxane (PDMS) substrates with different Young's moduli (4 kPa, 29 kPa, and 128 kPa), we find significant differences in cell adhesion area as a function of substrate stiffness. In particular, the cell adhesion area of A. castellanii increases with a decreasing Young's modulus of the substrate.

CONCLUSION

The dependence of A. castellanii adhesion on the elastic properties of the substrate is the first study suggesting a mechanosensory effect for a eukaryotic human pathogen. Interestingly, the main targets of A. castellanii infections in the human body are the eye and the brain, i.e., very soft environments. Thus, our study provides first hints towards the relevance of mechanical aspects for the pathogenicity of eukaryotic parasites.

Amoebicidal efficacy of a novel multi-purpose disinfecting solution: first findings

Free-living amoebae of the genus Acanthamoeba can cause a sight-threatening corneal infection, Acanthamoeba keratitis, mostly in contact lens wearers. The use of ineffective contact lens disinfecting solutions is one of the most important risk factors for this infection. This study concerns a new multi-purpose contact lens disinfecting solution, OPTI-FREE® PureMoist®, tested for its efficacy against Acanthamoeba trophozoites and cysts by using the most probable number technique for amoebic enumeration. Acanthamoeba castellanii ATCC 50373 and an environmental strain of Acanthamoeba genotype T4 isolated from tap water in Istanbul were used during the experiments. OPTI-FREE® PureMoist® achieved total kill (more than a 3-log reduction) of trophozoites of both strains before the manufacturer-recommended disinfection time (6h). In contrast, this solution had limited cysticidal activity against the ATCC strain but more against the environmental strain, with log reductions of 0.75 and 2.20, respectively, after 6h of exposure.

Identification of coagulase-negative staphylococci in daily disposable contact lens wearers

This study aimed to identify and quantify the number of contaminating organisms on daily disposable (DD) soft contact lenses, which may be responsible for mild cases of keratitis that occur with this lens wear modality. Ten participants wore DD lenses, and 10 participants wore planned replacement (PR) lenses. Lenses were collected aseptically and analysed for microbial contamination. Colony-forming units (CFU) were recorded, and representative colonies were used for identification using the API identification system. The DD lenses evaluated in this study were contaminated with coagulase-negative staphylococcus (CNS), ranging from 1 to 653 CFU. PR lenses showed more diversity in the types of contaminating micro-organisms and consisted of CNS, Gram-negative bacteria (Pseudomonas), a yeast (Candida) and a mould (Aspergillus), ranging from 1 to 230 CFU. CNS was the only type of micro-organism found on DD contact lenses and therefore may be the cause of any form of keratitis observed in DD lens wearers.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study to determine the frequency and identify the contaminating organisms found on daily disposable (DD) soft contact lenses. The contaminating organisms identified on DD contact lenses were solely coagulase-negative staphylococcus (CNS), suggesting that CNS may be the causative organism associated with infectious keratitis that occurs with DD contact lens wear.

A case of medication-resistant acanthamoeba keratitis treated by corneal crosslinking in Turkey

Purpose. To report a case of medication-resistant acanthamoeba keratitis (AK) treated successfully by corneal crosslinking (CXL). Methods. A 26-year-old male with medication-resistant AK underwent a standard CXL procedure with local anesthesia, followed by central corneal epithelial debridement, application of riboflavin 0.1%, and UV-A irradiation. Results. The patient experienced a dramatic symptomatic improvement within 24 hours. At two months, keratitis was healed with a semitransparent paracentral scar that did not affect visual acuity. Conclusions. Our experience, considered in the context of recent studies, suggests that CXL may be an option for selected patients with medication-resistant AK and corneal melting. CXL allows patients to avoid emergency keratoplasty and experience rapid symptomatic relief.

Amoebicidal effects of contact lens disinfecting solutions

PURPOSE

To compare the traditional manual hemacytometer method and an automated counter (Vi-cell) to enumerate and distinguish between viable and non-viable amoeba, and to determine the efficacies of contact lens (CL) disinfecting solutions against three species of Acanthamoeba. The efficacies in the presence of a bacterial food source and bovine serum albumin (BSA) were investigated.

METHODS

Four brands of multipurpose solutions and a hydrogen peroxide disinfecting system (Oxysept) for soft CLs, and four disinfecting solutions for Rigid Gas Permeable (RGP) lenses were tested against three species of Acanthamoeba. Page's amoebic saline was included as a negative control and standard solutions of disinfecting agents, 6% hydrogen peroxide and 0.5% chlorhexidine, as positive controls. The effects of the presence of Pseudomonas aeruginosa and BSA on effectiveness were assessed.

RESULTS

None of the CL solutions tested achieved a 1-log reduction in viability of all three Acanthamoeba species within the manufacturer's recommended disinfection times. The presence of P. aeruginosa did not significantly affect disinfecting capacity of multipurpose solution solutions but reduced activity of RGP solutions and the hydrogen peroxide system. BSA reduced trophozoicidal activity of all solutions. Bland and Altman analysis showed good agreement between Vi-cell and hemacytometer.

CONCLUSIONS

The Vi-Cell analyzer offers a simple and effective method of determining amoebicidal activity. Our results show that the CL solutions tested could not satisfactorily kill Acanthamoeba.

Salicylate inhibition of acanthamoebal attachment to contact lenses

PURPOSE

Sodium salicylate has shown potential as a component of contact lens care solutions designed to reduce Acanthamoebal attachment to contact lenses. This study determined the minimum effective concentration required to significantly reduce amoebal attachment.

METHODS

Different concentrations of sodium salicylate (10, 15, and 20 mM) were applied during exposure of unworn or bacterial biofilm-coated hydrogel contact lenses to Acanthamoeba castellanii trophozoites. Salicylate was applied at stage 1 intervention during biofilm formation on lenses, at stage 2 intervention during amoebal exposure, or at both stages.

RESULTS

A significant reduction in amoebal attachment was achieved when 10 mM salicylate was included during stage 1 alone; however, 15 mM was required for stage 2 intervention to significantly reduce attachment to clean or biofilm-coated lenses. For stages 1 and 2 combined intervention, 10 mM sodium salicylate produced a significant reduction in amoebal attachment.

CONCLUSIONS

In situ, within a contact lens case, biofilm formation and amoebal attachment would occur concurrently; therefore, stages 1 and 2 intervention would be closest to the real-life situation, thus indicating that 10 mM of salicylate would be an effective minimum concentration for reducing amoebal attachment to hydrogel contact lenses. Inclusion of components in contact lens care solution, such as sodium salicylate, which reduce Acanthamoebal attachment, has the potential to enhance effectiveness, particularly where amoebicidal efficacy may be limited, thus reducing the risk of contact lens-associated Acanthamoebal infection.

Radial keratoneuritis as a presenting sign in acanthamoeba keratitis

The visual outcomes of Acanthamoeba keratitis, a rare cause of corneal infection, can be devastating. This paper reports two contact lens wearers with severe pain and photophobia who presented to the emergency room. Biomicroscopy revealed radial keratoneuritis in both individuals. Tissue culture on a nonnutrient agar plate with Escherichia coli overlay resulted in a heavy growth of Acanthamoeba. The inpatient treatment included 0.02% polyhexamethylene biguanide, chlorhexidine, neomycin/polymyxin B/bacitracin (Neosporin), and oral fluconazole, which successfully controlled the corneal infection and improvement in the best corrected visual acuity in both patients. Infection did not recur during the 12-month follow-up period. Acanthamoeba keratitis can present as radial keratoneuritis, mimicking other common corneal infections resulting in diagnostic and treatment delays. Early diagnosis and prudent treatment of Acanthamoeba keratitis are the keys to restoring vision and avoiding the subsequent need for penetrating keratoplasty.

Adherence of acanthamoeba to lens cases and effects of drying on survival

PURPOSE

To compare the effects of drying the lens case with tissue on the presence of Acanthamoeba with cases left wet and to determine adherence to the lens case of varying concentrations of Acanthamoeba suspensions. The effect of drying on viability of Acanthamoeba in new, used, and soiled lens cases was compared over a 24 h period.

METHODS

New (16) and scratched (16) lens cases were rinsed with a range of Acanthamoeba suspensions. Eight of each group were dried with tissue and the presence of Acanthamoeba was determined in all cases using polymerase chain reaction. To examine effects of drying, forty-two lens case wells were scratched to simulate use and 21 of these were artificially soiled with serum Bovine albumin. These cases and a further 21 unused wells were contaminated with Acanthamoeba (×10/ml) and then left to dry in a cool, dry environment. Three wells of each group were sampled at time 0, 2, 4, 6, 8, 12, and 24 h, and the number of viable Acanthamoeba were determined.

RESULTS

Acanthamoeba were more likely to adhere to used than unused lens cases (p < 0.05). Detection of Acanthamoeba in wiped lens cases was at 2-log dilutions less than in cases left wet for both new and used lens cases. Adherence were significantly different between rinse and rinse/dried cases (p = 0.015). Air drying significantly reduced the numbers of viable amoebic cysts and trophozoites and the effect was time dependent. Survival was significantly higher in used and soiled wells.

CONCLUSIONS

Drying with tissue after rinsing significantly reduces numbers of adhering Acanthamoeba. Acanthamoeba were found to be able to adhere even to new unused cases, so the importance of proper cleaning and disinfection of lens cases cannot be underestimated. Air drying reduces viability but some viable cells were present at 24 h in soiled cases, confirming the role of biofilm in protecting organisms from desiccation.

Do free-living amoebae in treated drinking water systems present an emerging health risk?

There is an expanding body of evidence that free-living amoebae (FLA) increase both the numbers and virulence of water-based, human-pathogenic, amoeba-resisting microorganisms (ARM). Legionella spp., Mycobacterium spp., and other opportunistic human pathogens are known to be both ARM and also the etiologic agents of potentially fatal human lung infections. However, comparatively little is known about the FLA that may facilitate ARM growth in drinking water. This review examines the available literature on FLA in treated drinking water systems; in total 26 studies from 18 different countries. FLA were reported to breakthrough the water treatment barrier and enter distribution systems, in addition to the expected post-treatment system ingress. Once in the distribution system there is evidence of FLA colonization and regrowth especially in reservoirs and in-premise plumbing storage tanks. At the point of use the average FLA detection rate was 45% but highly variable (n = 16, σ = 31) due to both differences in both assay methods and the type of water systems examined. This review reveals that FLA are consistently detected in treated drinking water systems around the world and present a yet unquantified emerging health risk. However, more research is urgently required before accurate risks assessments can be undertaken to assess the impacts on human health, in households and institutions, due to exposure to FLA facilitated pathogenic ARM.

Prevalence of Acanthamoeba spp. and other free-living amoebae in household water, Ohio, USA--1990-1992

Knowledge of the prevalence of free-living amoebae (FLA) in US household water can provide a focus for prevention of amoeba-associated illnesses. Household water samples from two Ohio counties, collected and examined for amoebae during 1990-1992, were used to describe the prevalence of Acanthamoeba and other FLA in a household setting. Amoebae were isolated and identified by morphologic features. A total of 2,454 samples from 467 households were examined. Amoebae were found in water samples of 371 (79%) households. Sites most likely to contain amoeba were shower heads (52%) and kitchen sprayers (50%). Species of Hartmannella, Acanthamoeba, or Vahlkampfia were most common. Detection was higher in biofilm swab samples than in water samples. Detection of FLA and Acanthamoeba, at 79% and 51%, respectively, exceed estimates that have been published in previous surveys of household sources. We believe FLA are commonplace inhabitants of household water in this sample as they are in the environment.

Sampling strategy, occurrence and diversity of free-living protozoa in domestic refrigerators

AIMS

Evaluation of a sampling method to recover free-living protozoa (FLP) from plastic surfaces. Application of the method on different areas inside domestic refrigerators.

METHODS AND RESULTS

Plastic coupons seeded with representatives of FLP were swabbed with cotton wools. The recovery efficiency was the highest for Chilomonas paramecium, followed by Tetrahymena pyriformis and the lowest for Acanthamoeba polyphaga. From 43 refrigerators, 19 and 26 were considered FLP positive when sample cultures were incubated at 7°C and 20°C, respectively. The number of FLP-positive cultures was the highest in samples taken from vegetable trays followed by discharge gutters, whereas interior walls were rarely FLP positive. Higher numbers of taxa were observed in enrichment cultures incubated at 20°C instead of 7°C. The combination of microscopy and denaturing gradient gel electrophoresis revealed that discharge gutters occasionally were contaminated with a persistent protozoan population of flagellates (Cercozoa) and amoebae (Tubulinea). The FLP-positive status of refrigerator surfaces was correlated with a high aerobic plate count.

CONCLUSIONS

The cotton wool sampling method is useful to sample FLP from plastic surfaces. FLP are part of the microbial communities in domestic refrigerators.

SIGNIFICANCE AND IMPACT OF THE STUDY

Knowledge on the occurrence of FLP in food-related indoor environments is scarce. For the first time, a high protozoan diversity in domestic refrigerators is described.

Microbial keratitis in kingdom of bahrain: clinical and microbiology study

Background:

Microbial keratitis is a potentially vision threatening condition worldwide. Knowing the predisposing factors and etiologic microorganism can help control and prevent this problem. This is the first study of its kind in Kingdom of Bahrain.

Objective:

To study the profile of microbial keratitis in Bahrain with special focus on risk factors, clinical outcome and microbilogical results.

Methods:

A retrospective analysis of all patients admitted in Salmaniya Medical Complex over a period of three years from January 2005 to January 2007 was performed. A total of 285 patients with keratitis were analysed. Non infectious corneal ulceration were excluded. Data collected from medical records were demographic features, predisposing factors, history of corneal trauma, associated ocular conditions, visual acuity at the time of presentation and the clinical course. Predisposing risk factors measured were contact lens use, presence of blepharitis, diabetes, lid abnormalities, dry eyes, keratoplasty and refractive surgery. For contact lens wearers any contact lens related risk factors that can lead to keratitis were measured. Pearson's chi-square test was used to carry out statistical analysis wherever required.

Results:

Contact lens wear, as a risk factor for microbial keratitis, formed 40% of the total study population. Other risk factors identified were dry eyes 24 cases (8%), 10 blepharitis (3%), 22 trauma (8%), abnormal lid position 14 cases (5%). 6 patients keratitis in a graft (2%), 3 had refractive surgery (1%). The most common causative organism isolated was pseudomonas aeroginosa (54%) followed by streptococcus 12%, staph 10%, other organisms 6%. 95% of contact lens wearers had pseudomonas Aeroginosa. This was statistically significant (p< 0.0001). The vast majority, 92% healed with scarring. 1% needed therapeutic keratoplasty and 7% lost to follow up. Risk factors in contact lens wearers were; 41 patients (36%) slept with the contact lenses. 12 (8%) had contact lens related trauma and 8 (7%) had poor hygiene. Sleeping with the contact lenses was statistically significant (p< 0.0001).

Conclusion & Recommendation:

Contact lens wear is the major risk factor for microbial keratitis in Bahrain. Pseudomonas aeroginosa was the commonest bacteria isolated. Sleeping with the contact lenses is the major risk factor among contact lens wearers. Majority of keratitis patients resulted in permanent scarring on the cornea. Educating the public, especially on contact lens care and precaution, can help reduce this visual morbidity.

Acanthamoeba spp. in domestic tap water in houses of contact lens wearers in the metropolitan area of Mexico City

A survey was carried out in the metropolitan area of Mexico City to determine the presence of Acanthamoeba in the tap water of houses of contact lens wearers. Water samples were taken from the mains water entry, bathroom sinks and storage containers (roof tanks, cisterns) of 27 houses; and from the solution contained in the contact lens cases. Samples were filtered and cultured onto NNE medium. The isolates were identified based on their morphological features and pathogenicity. Total and fecal coliforms, water temperature, pH, dissolved oxygen and residual free-chlorine were measured by standard methods. Forty five isolates of Acanthamoeba from 200 water samples were obtained. The highest number of amoebae was isolated from cisterns and roof tanks. Most Acanthamoeba isolates were non-pathogenic, however, their presence in tap water is a potential hazard since some species can cause Acanthamoeba keratitis and granulomatous amoebic encephalitis.

In vitro evaluation of the amoebicidal activity of garlic (Allium sativum) extract on Acanthamoeba castellanii and its cytotoxic potential on corneal cells

Free-living protozoa of the genus Acanthamoeba can cause one of the most severe, potentially sight-threatening infections of the eye, the so-called A. keratitis. A. keratitis is difficult to treat because, under adverse conditions, the amoeba encyst and medical therapy is often less effective against cysts than against trophozoites. The aim of this study was to investigate evaluate the in vitro effect of the nonpolar subfraction of the methanol extract of garlic (Allium sativum) on the growth of A. castellanii trophozoites and cysts and also its cytotoxicity on corneal cells in vitro. Extract was evaluated for its amoebicidal activity, using an inverted light microscope. The effect of the nonpolar extract with the concentrations, ranging from 0.78 to 62.5 mg/mL on the proliferation of A. castellanii trophozoites and cysts, were examined in vitro. For the determination of cytotoxicity of the extract on corneal cells, agar diffusion tests were performed. The present study demonstrates the in vitro effectiveness of the garlic against the A. castellanii growth curve. Evaluations revealed that garlic inhibits trophozoite growth in dose- and time-dependent ways. In the case of the cyctotoxic acitivities, it showed no cytotoxicity for the cornea cells in the concentration of 3.90 mg/mL. These findings indicate that nonpolar subfraction of the methanol extracts of garlic has amoebicidal, as well as its cysticidal, properties on Acanthamoeba trophozoites and cysts. Garlic alone, and in combination with other amoebicidal agents, may be used in clinical practices after further investigations.

Bilateral Acanthamoeba keratitis in an experienced two-weekly disposable contact lens wearer

PURPOSE

To present a case of bilateral Acanthamoeba keratitis in a patient who stored both contact lenses in the same storage case.

METHODS

The case report of a 44-year-old female contact lens wearer who developed bilateral culture-positive Acanthamoeba keratitis. Although an experienced contact lens user for many years, she admitted to occasionally rinsing her dual contact lens case in tap water and leaving it to air dry. She was successfully treated with intensive topical polyhexamethyl biguanide and propamide isethionate in conjunction with a mydriatic agent, topical ofloxacin, and oral flurbiprofen.

RESULTS

The Acanthamoeba keratitis resolved without sequelae. After 6 months, the patient had a visual acuity of 20/20 in each eye.

CONCLUSIONS

Although bilateral Acanthamoeba keratitis is rare, it is essential that the patient is properly educated in contact lens hygiene and disinfection. Regular contact lens follow-up of patients is essential, and lens storage and disinfection techniques must be reviewed with the patient. The use of single-use contact lens storage cases may be advantageous in reducing the incidence of bilateral disease after case contamination.

In vitro effectiveness of Thymus sipyleus subsp. sipyleus var. sipyleus on Acanthamoeba castellanii and its cytotoxic potential on corneal cells

Acanthamoeba species are an important cause of microbial keratitis that may cause severe ocular inflammation and visual loss. Acanthamoeba keratitis is difficult to treat, without total efficacy in some patients because of cysts which is less susceptible than trophozoites to the usual treatments. We investigated here the in vitro amoebicidal activity of methanolic extract of Thymus sipyleus subsp. sipyleus var. sipyleus from Turkish flora against Acanthamoeba castellanii and also its cytotoxicity on corneal cells in vitro. Extract was evaluated for its amoebicidal activity using an inverted light microscope. The effect of the polar extract with the concentrations ranging from 1.0 to 32.0 mg/ml on the proliferation of A. castellanii trophozoites and cysts were examined in vitro. For the determination of cytotoxicity of the extract on corneal cells, agar diffusion tests were performed. According to results obtained from the tests, the extract evaluated here showed remarkable amoebicidal effect on A. castellanii. In the case of the cytotoxic activities, it showed no cytotoxicity for corneal cells in the concentration of 32 mg/ml. As a result, polar subfraction of the methanolic extract of Thymus sipyleus subsp. sipyleus var. sipyleus could be concluded as a new natural agent for the treatment of Acanthamoeba infections. On the other hand, it still needs to be further evaluated by in vivo test systems to confirm the efficiency of its biological effect.

Factors affecting the epidemiology of Acanthamoeba keratitis

Despite being a relatively rare disease in comparison with other forms of infectious keratitis, Acanthamoeba keratitis is a potentially blinding disease. Wide variations in the incidence of Acanthamoeba keratitis have been reported in both developed and developing countries. At the same time that contact lens wear was found to be responsible for the spread of the disease in developed countries, Acanthamoeba keratitis was considered a rare disease in developing countries compared with fungal and bacterial keratitis. In recent decades, the risk of getting Acanthamoeba keratitis has increased because of the increased proportion of contact lens wearers. This article introduces the different factors affecting the epidemiology of Acanthamoeba keratitis worldwide, presents a chronological review of the literature, and shows the progressive spread of Acanthamoeba keratitis in the last two decades in different geographical areas of the world. A detailed comparison of the incidence of the disease as reported in different studies in different countries is made. The impact of contact lenses and other factors, such as hot weather, virulence of Acanthamoeba strains, water sanitation and quality, the occurrence of environmental disasters such as flooding, and the wide environmental presence of Acanthamoeba cysts on the incidence of the disease, are discussed. In addition, the ability of Acanthamoeba cysts to resist different harsh conditions is reviewed.

Efficacy of contact lens storage solutions against trophozoite and cyst of Acanthamoeba castellanii strain 1BU and their cytotoxic potential on corneal cells

Acanthamoeba is a free-living amoeba causing a potentially blinding infection of the cornea. Contact lens wearers are most at risk and account for about 95% of cases. We investigated the in vitro effectiveness of 10 contact lens solutions against Acanthamoeba castellanii and their cytotoxicity on corneal cells in vitro. Contact lens solutions were evaluated for their amoebicidal activities using an inverted light microscope. To determine of their cytotoxicity on corneal cells, agar diffusion tests were performed. According to the results obtained from the tests, AVIZOR Aqua Soft Comfort and Elegance(R) showed the best amoebicidal effect on A. castellanii trophozoites. Cysts were still viable after overnight (8 h) exposure. In the case of the cyctotoxic acitivities, All In One Light, Astek, SOLO-Care Aqua, Maxima, and Horien showed no cytotoxicity on the corneal cells. ReNu MultiPlus, AVIZOR Aqua Soft Comfort, Carrera, and Elegance showed mild cytotoxicity on the corneal cells. Plurisol.M presented moderate cytotoxicity on the corneal cells. All commercial solutions examined in this study are the lack of efficacy against A. castellanii. Improvement or development of new contact lens disinfecting systems by the manufacturers is needed to prevent Acanthamoeba keratitis.

Acanthamoeba: keratopathogenicity of isolates from domestic tap water in Korea

In a previous study, we reported on the contamination rate of free living amoeba, including Acanthamoeba, isolated from contact lens storage cases (CLSC) and domestic tap water in Korea. In an effort to evaluate the potential kerato-pathogenicity of 5 isolates from CLSC and 17 isolates from domestic tap water, we have conducted an investigation into the morphological features, mitochondrial DNA (mtDNA) restriction fragment length polymorphism (RFLP) phenotypes, 18S rDNA sequences, and drug sensitivities of these isolates, and have compared the results with those of 20 amoebic keratitis (AK) isolates from Korea, as well as 14 reference strains. Cysts from 22 isolates obtained from CLSC and domestic tap water showed typical characteristics of morphological group 2. A total of three and five mtDNA RFLP patterns generated by EcoRI were found in 5 of the isolates from CLSC and 17 of the isolates from domestic tap water, respectively. The mtDNA RFLP patterns of four of the five isolates from the CLSC were found to be identical to those of the isolates from domestic tap water of students who had contaminated CLSC. The majority had mtDNA RFLP patterns identical to those of AK isolates in Korea. The results of 18S rDNA sequencing analysis were also shown to coincide with the results of mtDNA RFLP analysis. KA/WP12 was determined to be profoundly sensitive to chlorhexidine (MCC; 6.25microg/ml), and KAWP2 was the most sensitive strain to polyhexamethylene biguanide (PHMB) (MCC; 4.69microg/ml). Some difference in the cytopathic effects of isolates against human corneal epithelial cells was observed according to their mtDNA genotypes. In conclusion, domestic tap water may constitute a source of Acanthamoeba contamination of CLSC, and most isolates from CLSC and domestic tap water appear to be potentially keratopathogenic.

Variable Responses of Acanthamoeba Strains to Three Multipurpose Lens Cleaning Solutions

PURPOSE

A novel method has been developed to compare Acanthamoeba strain differences by testing their susceptibility to multipurpose contact lens cleaning solutions (MPS).

METHODS

This method uses surface-attached amoebae that mimic cells attached to a contact lens. In brief, acanthamoebae were grown on non-nutrient agar plates with Escherichia coli prey. Blocks of agar with cysts or trophozoites (approximately 50 cells) were cut out and transferred to MPS [ReNu MultiPlus; (Bausch & Lomb, Rochester, NY), Complete (Allergan, Irvine, CA), and Opti-Free Express (Alcon, Ft. Worth, TX)] for up to 24 h treatment. After neutralizing in Dey Engley broth (Difco), blocks were washed in amoeba saline and reinoculated onto fresh prey bacteria. Positive growth was indicative of survival.

RESULTS

Testing showed that the efficacy of the three MPS was different. Opti-Free was the most effective against cysts, followed by ReNu while Complete was relatively ineffective. Not surprisingly, trophozoites were more susceptible than cysts.

CONCLUSIONS

Findings for individual MPS complement previous work with other methods. This study has also identified that environmental strains vary in their sensitivity to disinfecting solutions. Overall, Acanthamoeba genotypes T3, T5, and T11 from the environment were more resistant than the T4 isolates from the cornea and beach. This resilience supports previous work on temperature tolerance, in which T3 and T5, and T11 acanthamoebae grew in temperatures up to 41 degrees C. Investigators should therefore consider the strain genotype and its source before embarking on MPS sensitivity testing.

Efficacy of contact lens storage solutions against different acanthamoeba strains

PURPOSE

This study was undertaken in order to determine the susceptibility of acanthamoebae to various contact lens disinfecting systems, with respect to type of disinfectant and exposure time.

METHODS

Ten contact lens solutions, including one new system, were tested for their effectivities against cysts of three Acanthamoeba strains. Of main interest was an incubation time of 8 hours (overnight disinfection) and cyst quantities of 10 and 10, respectively.

RESULTS

Boston Advance (polyaminopropyl biguanide 0.0005%, chlorhexidine 0.003%) for the storage of rigid gas permeable contact lenses destroyed the cysts of all strains at either concentration within one hour of exposure. Meni Care Plus (polyhexamethylene biguanide 0.0005%) also destroyed 10 cysts of all strains, however, 10 cysts only of two strains within one hour; after an exposure time of 8 hours all cysts were killed. The disinfecting solutions for soft contact lenses did not kill 10 cysts of either strain after 8 hours of incubation time.

CONCLUSION

Two of the tested contact lens solutions (the ones for rigid gas permeable lenses) destroyed the cysts of all strains. One of these, containing a combination of two amoebicidal ingredients even after only one hour of exposure time.

Antigens of selected Acanthamoeba species detected with monoclonal antibodies

Acanthamoeba species are ubiquitous soil and freshwater protozoa that have been associated with infections of the human brain, skin, lungs and eyes. Our aim was to develop specific antibodies to aid in rapid and specific diagnosis of clinically important isolates. Mice were variously immunised with live mixtures of Acanthamoeba castellanii strain 112 (AC112) trophozoites and cysts, or with sonicated, formalin-fixed or heat-treated trophozoites, or with a trophozoite membrane preparation. Eight hybridoma cell lines secreting monoclonal antibodies reactive with A. castellanii epitopes were generated. Seven of the new antibodies (designated AMEC1-3 and MTAC1-4) were isotyped as IgMkappa and one (MTAC5) as IgG1kappa. All of the novel antibodies bound to AC112 cysts, and MTAC4 and MTAC5 also bound to trophozoites as measured by flow cytometry on unfixed cells. Single chain antibody fragments that retained parental antibody binding characteristics were engineered from three of the hybridomas (AMEC1, MTAC3 and MTAC4). Four monoclonal antibodies (AMEC1, AMEC3, MTAC1, MTAC3) bound reliably to unfixed cysts of clinical isolates of A. castellanii (two strains) and Acanthamoeba polyphaga (two strains), belonging to Pussard-Pons morphological group II, and to Acanthamoeba lenticulata and Acanthamoeba culbertsoni, belonging to Pussard-Pons morphological group III. None of the antibodies bound to cysts or trophozoites of the environmental group I species, Acanthamoeba tubiashi. Antibodies AMEC1, MTAC3, MTAC4 and MTAC5 reacted with buffered formalin-fixed AC112 by immunohistochemistry, and also stained Acanthamoeba in sections of infected rat cornea and buffered formalin-fixed, paraffin-embedded infected human cornea. These antibodies may be useful in diagnosing pathogenic Acanthamoeba species in clinical specimens, provided that cysts are present.

Attachment of Acanthamoeba to first- and second-generation silicone hydrogel contact lenses

PURPOSE

To investigate the attachment of Acanthamoeba to first- and second-generation silicone hydrogel contact lenses, and to determine if patient wear or the presence of a bacterial biofilm coating affects attachment characteristics.

DESIGN

Experimental study.

PARTICIPANTS AND CONTROLS

Attachment to the silicone hydrogel lenses was compared with that to a conventional hydrogel control lens. Sixteen replicates (n = 16) were carried out for unworn, worn, and biofilm-coated lenses of each type.

METHODS

Unworn, worn, and Pseudomonas aeruginosa biofilm-coated first-generation (lotrafilcon A) and second-generation (galyfilcon A) silicone hydrogel and conventional hydrogel (etafilcon A) lens quarters were incubated for 90 minutes in suspensions of plate-cultured Acanthamoeba castellanii trophozoites.

MAIN OUTCOME MEASURES

Trophozoites attached to one surface of each lens quarter were counted by direct light microscopy. Logarithmic transformation of data allowed the use of parametric analysis of variance for statistical analysis.

RESULTS

Attachment of Acanthamoeba was affected significantly by lens material type (P<0.001), with higher numbers of trophozoites attaching to the first-generation lotrafilcon A silicone hydrogel lens, compared with the second-generation galyfilcon A lens and the conventional hydrogel lens. Attachments to the latter 2 lenses did not differ significantly from each other (P = 0.126). Patient wear and the presence of a bacterial biofilm had no significant effect on attachment to the lotrafilcon A lens (P = 0.426) but did significantly increase attachment to the galyfilcon A (P<0.001) and the etafilcon A (P = 0.009) lenses; attachment to the latter 2 lenses was still significantly less than that found with the first-generation silicone hydrogel (P<0.001).

CONCLUSIONS

Acanthamoeba demonstrated a significantly greater affinity for the first-generation silicone hydrogel lens as compared with the second-generation silicone hydrogel and the conventional hydrogel. If exposed to Acanthamoeba (e.g., when showering or swimming, through noncontinuous wear and ineffective lens care regimes), first-generation silicone hydrogel lenses may promote a greater risk of Acanthamoeba infection due to the enhanced attachment characteristics of this lens material. However, prospective studies in patients are required to determine if these experimental results are clinically significant.

The role of domestic tap water in Acanthamoeba contamination in contact lens storage cases in Korea

A survey was carried out from August to December 2004 in Pusan, Korea to document the presence of free-living amoeba (FLA), including the genus Acanthamoeba, in both contact lens storage cases and domestic tap water. Acanthamoeba was isolated from 5 (4.2%) in 120 contact lens storage cases. Four house tap water samples from residents, whose contact lens storage cases had been contaminated by Acanthamoeba, were also found to be contaminated with Acanthamoeba. Therefore, the contamination rate of FLA and Acanthamoeba in domestic tap water was investigated in order to examine the role of domestic tap water in Acanthamoeba contamination of contact lens storage cases. FLA and Acanthamoeba were identified in 97 (46.8%) and 16 (7.7%) of the 207 domestic tap water samples, respectively. There were no significant differences between the contamination rates of FLA in tap water according to the filtration plant of origin. No FLA was detected in the tap water directly supplied by the water purification plants. Water storage tanks appear to promote FLA colonization, including Acanthamoeba, in domestic tap water. This increases the risk of Acanthamoeba contamination in contact lens storage cases as well as increasing the risk of Acanthamoeba keratitis.