The effects of freezing and antibiotics on the viability of Acanthamoeba cysts

Global prevalence of free-living amoebae in solid matrices - A systematic review with meta-analysis

The ubiquitous free-living amoebae (FLA) are microorganisms of significant medical, sanitary, and ecological importance. However, their characterization within solid matrices such as soil, dust, sediment, mud, sludge, and compost remain to be systematized. In this study, we conducted a systematic review with meta-analysis to explore the global distribution of FLA in solid matrices. From the analysis of 104 out of 4,414 scientific articles retrieved from different databases, it was found that the general global prevalence of FLA in solid matrices was of 55.13% (95% confidence interval (CI) 49.32-60.94). Specifically, FLA prevalence was high in soil (72.40%, 95% CI 69.08-75.73), sediment (57.91%, 95% CI 50.01-65.81), mud (52.90%, 95% CI 24.01-81.78), dust (48.60%, 95% CI 43.00-54.19), and sewage sludge (40.19%, 95% CI 30.68-49.70). In aerosols it was comparatively lower (17.21%, 95% CI 12.76-21.66). Acanthamoeba spp. (52.23%) and Hartmanella/Vermamoeba spp. (36.06%) were found to be more prevalent, whereas Naegleria spp. (34.98%) and Balamuthia spp. (27.32%) were less prevalent. The distribution of the highest global prevalence values for species of Acanthamoeba spp., considering different publication periods of the studies, is as follows: A. hatchetti (51.46%), A. rhysodes (47.49%), A. polyphaga (36.37%), A. culbertsoni (34.31%), A. castellanii (34.21%), and A. lenticulata (32.82%). For other FLA species, the distribution is: Hartmannella/Vermamoeba vermiformis (91.57%), Naegleria fowleri (42.32%), Naegleria gruberi (32.39%), and Balamuthia mandrillaris (25%). The most prevalent Acanthamoeba genotypes were T4 (33.38%) and T3 (23.94%). Overall, the global prevalence of FLA in solid matrices is as high as or greater than that reported in water by previous systematic reviews. Thus, actions aimed at reducing exposure to FLA or exploring their ecological dynamics should consider not only water but also the various solid matrices. The finding outlined here can provide valuable insights for such actions, e.g., informing on the level of exposure to FLA, or on the microbial biodiversity of specific environmental compartments.

Opportunistic free-living amoebal pathogens

Pathogenic free-living amoebae affecting the central nervous system are known to cause granulomatous amoebic encephalitis (GAE) or primary amoebic meningoencephalitis (PAM). Although hosts with impaired immunity are generally at a higher risk of severe disease, amoebae such as Naegleria fowleri and Balamuthia mandrillaris can instigate disease in otherwise immunocompetent individuals, whereas Acanthamoeba species mostly infect immunocompromised people. Acanthamoeba also cause a sight-threatening eye infection, mostly in contact lens wearers. Although infections due to pathogenic amoebae are considered rare, recently, these deadly amoebae were detected in water supplies in the USA. This is of particular concern, especially with global warming further exacerbating the problem. Herein, we describe the epidemiology, presentation, diagnosis, and management of free-living amoeba infections.

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.

Excisional keratectomy combined with focal cryotherapy and amniotic membrane inlay for recalcitrant filamentary fungal keratitis: A retrospective comparative clinical data analysis

The aim of the present study was to investigate the efficacy of a novel surgical intervention, excisional keratectomy combined with focal cryotherapy and amniotic membrane inlay (EKCAI), for the treatment of recalcitrant filamentary fungal keratitis. A retrospective analysis was performed of patients who underwent excisional keratectomy combined with conjunctival flap inlay (EKCFI), EKCAI or therapeutic penetrating keratoplasty (TPK) from January 2006 to January 2011. Recalcitrance was determined as being unresponsive to standard medical antifungal therapy for at ≥1 week. Outcome measures among the three intervention modalities were compared. A total of 128 patients had a follow-up of ≥1 year after the primary intervention. The success rates of interventions at 1-year follow-up were 58.33% in the EKCFI group, 88.37% in the EKCAI group and 93.44% in the TPK group (P<0.0002). The preoperative visual acuity of the three groups were similar (P=0.6458), while the postoperative best-corrected visual acuity (BCVA) of patients without recurrence was significantly different among the three groups 3 months after surgery. The best postoperative BCVA was found in the TPK group, while the worst was in the EKCFI group. In conclusion, EKCAI does not require donor cornea, is straightforward surgically, and has a favorable success rate compared with EKCFI.

Established and emerging ancillary techniques in management of microbial keratitis: a review

Microbial keratitis is a sight-threatening condition and an ocular emergency, because of the potential for rapid progression. Intensive topical antimicrobials are the mainstay and the gold standard of treatment for microbial keratitis. However, despite appropriate diagnosis and therapy, treatment failure is still common, and can result in significant morbidity due to corneal perforation and/or scarring. For this reason, clinicians continue to seek novel treatment techniques in order to expand the armamentarium of tools available to manage microbial keratitis, and in doing so improve clinical outcomes. In this review, we examine the evidence for some established, as well as a few emerging ancillary techniques used to manage microbial keratitis. These include topical corticosteroids, corneal collagen cross-linking, intrastromal antimicrobials, amniotic membrane transplantation and miscellaneous other techniques. Of these, collagen cross-linking shows some promise for selected cases of infectious keratitis, although more research in the area is required before it is accepted as mainstream treatment for this potentially blinding condition.

Medical interventions for acanthamoeba keratitis

BACKGROUND

Acanthamoeba are microscopic, free-living, single-celled organisms which can infect the eye and lead to Acanthamoeba keratitis (AK). AK can result in loss of vision in the infected eye or loss of eye itself; however, there are no formal guidelines or standards of care for the treatment of AK.

OBJECTIVES

To evaluate the relative effectiveness and safety of medical therapy for the treatment of AK.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (2015, Issue 1), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to January 2015), EMBASE (January 1980 to January 2015), PubMed (1948 to January 2015), Latin American and Caribbean Health Sciences Literature Database (LILACS) (1982 to January 2015), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic search for trials. We last searched the electronic databases on 9 January 2015.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of medical therapy for AK, regardless of the participants' age, sex, or etiology of disease. We included studies that compared either anti-amoeba therapy (drugs used alone or in combination with other medical therapies) with no anti-amoeba therapy or one anti-amoeba therapy with another anti-amoeba therapy.

DATA COLLECTION AND ANALYSIS

Two authors independently screened search results and full-text reports, assessed risk of bias, and abstracted data. We used standard methodological procedures as set forth by the Cochrane Collaboration.

MAIN RESULTS

We included one RCT (56 eyes of 55 participants) in this review. The study compared two types of topical biguanides for the treatment of AK: chlorhexidine 0.02% and polyhexamethylene biguanide (PHMB) 0.02%. All participants were contact lens wearers with a median age of 31 years. Treatment duration ranged from 51 to 145 days. The study, conducted in the UK, was well-designed and had low risk of bias overall.Outcome data were available for 51 (91%) of 56 eyes. Follow-up times for outcome measurements in the study were not reported. Resolution of infection, defined as control of ocular inflammation, relief of pain and photosensitivity, and recovery of vision, was 86% in the chlorhexidine group compared with 78% in the PHMB group (relative risk (RR) 1.10, 95% confidence intervals (CI) 0.84 to 1.42). In the chlorhexidine group, 20 of 28 eyes (71%) had better visual acuity compared with 13 of 23 eyes (57%) in the PHMB group at final follow-up (RR 1.26, 95% CI 0.82 to 1.94). Five participants required therapeutic keratoplasty: 2 in the chlorhexidine group compared with 3 in the PHMB group (RR 0.55, 95% CI 0.10 to 3.00). No serious adverse event related to drug toxicity was observed in the study.

AUTHORS' CONCLUSIONS

There is insufficient evidence to evaluate the relative effectiveness and safety of medical therapy for the treatment of AK. Results from the one included study yielded no difference with respect to outcomes reported between chlorhexidine and PHMB. However, the sample size was inadequate to detect clinically meaningful differences between the two groups as indicated by the wide confidence intervals of effect estimates.

Acanthamoeba keratitis: diagnosis and treatment update 2009

PURPOSE

To describe the current management of Acanthamoeba keratitis (AK).

DESIGN

A perspective based on the literature and author experience.

RESULTS

Early diagnosis and appropriate therapy are key to a good prognosis. A provisional diagnosis of AK can be made using the clinical features and confocal microscopy, although a definitive diagnosis requires culture, histology, or identification of Acanthamoeba deoxyribonucleic acid by polymerase chain reaction. Routine use of tissue diagnosis is recommended, particularly for patients unresponsive to treatment for AK. Topical biguanides are the only effective therapy for the resistant encysted form of the organism in vitro, if not always in vivo. None of the other drugs that have been used meet the requirements of consistent cysticidal activity and may have no therapeutic role. The use of topical steroids is controversial, but probably beneficial, for the management of severe corneal inflammatory complications that have not responded to topical biguanides alone. The scleritis associated with AK is rarely associated with extracorneal invasion and usually responds to systemic anti-inflammatory treatment combined with topical biguanides. Therapeutic keratoplasty retains a role for therapy of some severe complications of AK but not for initial treatment. With modern management, 90% of patients can expect to retain visual acuity of 6/12 or better and fewer than 2% become blind, although treatment may take 6 months or more.

CONCLUSIONS

Better understanding of the pathogenesis of the extracorneal complications, the availability of polymerase chain reaction for tissue diagnosis, and effective licensed topical anti-amoebics would substantially benefit patients with AK.

Acanthamoeba sclerokeratitis

BACKGROUND

Acanthamoeba scleritis is an uncommon but severe complication of acanthamoeba keratitis. We report the clinical and histopathologic features of a patient with acanthamoeba sclerokeratitis.

METHODS

Review of the patient's clinical records and histopathologic examination of the globe including light microscopy and transmission electron microscopy.

RESULTS

Review of the clinical record of the patient revealed a past ocular history of penetrating keratoplasty for persistent acanthamoeba keratitis. Later in the course of treatment, the patient developed nodular necrotizing scleritis with culture-proven viable acanthamoeba in this area. She underwent enucleation of the eye for persistent acanthamoeba sclerokeratitis. Histopathologic examination of the globe revealed no acanthamoeba cysts or trophozoites at the site of crotherapy.

CONCLUSION

Our study provides evidence for the invasion of acanthamoeba organisms into the sclera in a case of acanthamoeba keratitis. The presence of trophozites in scleral tissue may exacerbate the immune response leading to nodular scleritis.

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.

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.