Fungal Keratitis: Update for 2014

Roles of pattern recognition receptors in response to fungal keratitis

Fungal keratitis is one of the leading causes of blindness worldwide, which has become an increasingly serious threat to public ocular health, but no effective treatment strategies are available now. Pattern recognition receptors (PRRs) of the innate immune system are the first line of host defense against fungal infections. They could recognize pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs) and trigger an array of inflammatory responses. Over the last decades, research has resulted in significant progress regarding the roles of PRRs in fungal keratitis. This review will highlight the importance of several pattern recognition receptors (C-type lectin-like receptors, Toll-like receptors, and NOD-like receptors) in regulating the innate immunity under fungal keratitis and describe the crosstalk and collaboration in PRRs contributing to disease pathology. Meanwhile, some potential therapy-based PRRs against corneal fungal infections are discussed.

Purpureocillium roseum sp. nov. A new ocular pathogen for humans and mice resistant to antifungals

BACKGROUND

Infectious keratitis is the main cause of preventable blindness worldwide, with about 1.5-2.0 million new cases occurring per year. This inflammatory response may be due to infections caused by bacteria, fungi, viruses or parasites. Fungal keratitis is a poorly studied health problem.

OBJECTIVES

This study aimed to identify a new fungal species by molecular methods and to explore the possible efficacy of the three most common antifungals used in human keratitis in Mexico by performing in vitro analysis. The capacity of this pathogen to cause corneal infection in a murine model was also evaluated.

METHODS

The fungal strain was isolated from a patient with a corneal ulcer. To identify the fungus, taxonomic and phylogenetic analyses (nrDNA ITS and LSU data set) were performed. An antifungal susceptibility assay for amphotericin B, itraconazole and voriconazole was carried out. The fungal isolate was used to develop a keratitis model in BALB/c mice; entire eyes and ocular tissues were preserved and processed for histopathologic examination.

RESULTS AND CONCLUSION

This fungal genus has hitherto not been reported with human keratitis in Mexico. We described a new species Purpurecillium roseum isolated from corneal infection. P roseum showed resistance to amphotericin B and itraconazole and was sensitive to voriconazole. In vivo study demonstrated that P roseum had capacity to developed corneal infection and to penetrate deeper corneal tissue. The global change in fungal infections has emphasised the need to develop better diagnostic mycology laboratories and to recognise the group of potential fungal pathogens.

Antimycotic Activity of Ozonized Oil in Liposome Eye Drops against Candida spp

Purpose

This study aims to investigate the antifungal activity and mechanism of action of ozonized oil eye drops in liposomes (Ozodrop), commercialized as eye lubricant for the treatment of dry eye syndrome and eye inflammation. The activity was tested against four clinical Candida species: C albicans, C glabrata, C krusei, and C orthopsilosis.

Methods

The antifungal activity of the eye drop solution was ascertained by microdilution method in accordance with EUCAST obtaining the minimum inhibitory concentration for Ozodrop. The mechanism of action was further investigated in C albicans by measuring cell vitality, intracellular reactive oxygen species production, levels of cellular and mitochondrial (∆Ψ_m) membrane potential, and the extent of membrane lipid peroxidation.

Results

All Candida isolates were susceptible to Ozodrop with minimum inhibitory concentration values ranging from 0.195% (v/v) for C glabrata to 6.25% (v/v) for C orthopsilosis. After 1 hour of exposure at the minimum inhibitory concentration value about 30% of cells were killed, reaching about 70% at the highest Ozodrop value. After Ozodrop exposure, C albicans showed cell membrane depolarization, increased levels of lipid peroxidation, depolarized ∆Ψ_m, and increased reactive oxygen species generation.

Conclusions

The significant increases in reactive oxygen species production cause the accumulation of reactive oxygen species-associated damages leading to progressive Candida cell dysfunction.

Translational Relevance

The antifungal activity of Ozodrop was demonstrated at concentrations several times lower than the concentration that can be retrieved in ocular surface after its application. The antifungal activity of the eye drops Ozodrop would represent an interesting off-label indication for a product basically conceived as an eye lubricant.

Magnetic hyperthermia adjunctive therapy for fungi: in vitro studies against Candida albicans

The poor penetration of anti-fungal agents into the cornea through the intact epithelium layer makes it difficult to treat acute fungal corneal infections. Herein, we developed Amphotret (amphotericin B) antifungal drug contained polycaprolactone-Fe₃O₄ (PCL-FO) magnetic nanofibers (MNFs) using the electrospinning technique. These MNFs generate heat in the presence of AC magnetic field (AMF) and release drug upon heating. MNFs were compatible with human mesenchymal stem cells (hMSCs) and HeLa cells, which exhibited unaltered proliferation, ruling out any toxicity from the systems. Hyperthermia induced via MNFs from 42 °C to 50 °C compromised the viability of Candida albicans cells. Further, the efficacy of the systems was increased in the presence of both heat and drug simultaneously in vitro, leading to near 100% loss in viability of C. albicans cells at 50 °C with simultaneous drug release from MNFs. Thus, we propose magnetic hyperthermia as adjunctive therapy for fungal keratitis.

A novel, tomographic imaging probe for rapid diagnosis of fungal keratitis

Fungal keratitis is a leading cause of ocular morbidity and blindness in developing countries. Diagnosing fungal keratitis currently relies on a comparative evaluation of corneal biopsy or scraping using a direct microscopy and culture results. These methods not only carry the risk of developing complications due to the invasive tissue sampling but also are largely limited by diagnostic speed and accuracy, making it difficult to initiate timely appropriate antifungal therapy. Therefore, rapid and noninvasive diagnostic tools are a pressing need for improved outcomes for fungal keratitis. Taking advantage of the highly specific fungal cell targeting properties of caspofungin, we have developed a fluorescent chemical probe with high selectivity against fungal pathogens. Utilizing fluorescence imaging technology, we have demonstrated a highly specific and sensitive detection of Aspergillus in a fungal keratitis model in mice as early as 5 min post-topical application of the probe. Our results indicate that a fluorescence-mediated platform can be used as a rapid (<10 min) alternative to conventional methods for detecting Aspergillus, and potentially other fungi, in fungal infections of the cornea.