Study of Pathogens of Fungal Keratitis and the Sensitivity of Pathogenic Fungi to Therapeutic Agents with the Disk Diffusion Method

Evaluation of antifungal susceptibility and clinical characteristics in fungal keratitis in a tertiary care center in North India

Purpose

To study the antifungal susceptibility of common corneal pathogenic fungi to antifungal agents in the North Indian population.

Methods

Prospective study of the antifungal sensitivity testing (natamycin, amphotericin B, voriconazole, itraconazole, fluconazole, posaconazole, caspofungin, micafungin) of fungal isolates from 50 cases of culture positive fungal keratitis by using E test method. Details noted included demographic data, visual acuity, clinical details, grade of keratitis, healing time, and success in medical management.

Results

Of 50 patients with fungal keratitis (mean age: 40.28 ± 16.77 years), 12 eyes healed within 3 weeks, 14 had a delayed healing response, and 24 had chronic keratitis. Among the 15 cases of Fusarium isolates, 93.3% were sensitive to natamycin, while 40% to amphotericin B; 66.6% to voriconazole, 13.4% to itraconazole and fluconazole each. 80% of Fusarium cases (n = 12) showed susceptibility to posaconazole. Among Aspergillus flavus isolates, 53.4% (n = 8) were sensitive to natamycin, with only 40% (n = 7) showing sensitivity to amphotericin B and good susceptibility to azoles. MIC against susceptible Fusarium spp. for natamycin was 3-16 μg/mL, amphotericin B: 1-8 μg/mL, voriconazole: 0.5-1.5 μg/mL, itraconazole: 0.5-12 μg/mL, posaconazole: 0.094-1.5 μg/mL. MIC against Aspergillus flavus was natamycin: 8-32 μg/mL, amphotericin B: 0.5-16 μg/mL, voriconazole: 0.025-4 μg/mL, itraconazole: 0.125-8 μg/mL, posaconazole: 0.047-0.25 μg/mL; against Aspergillus niger isolates, to natamycin was 6 μg/mL (n=1), amphotericin B 8-12 μg/mL (n = 3), voriconazole: 0.125-0.19 μg/mL (n = 3), itraconazole: 0.38-0.75 μg/mL, posaconazole: 0.064-0.19 μg/mL and against Aspergillus fumigatus (n = 1), was natamycin4 μg/mL, amphotericin B - 8 μg/mL, voriconazole 0.25 μg/mL, itraconazole 1 μg/mL, and posaconazole 0.19 μg/mL. MIC against susceptible Acremonium spp. for natamycin was 1.5-16 μg/mL, amphotericin B: 0.5-8 μg/mL, voriconazole: 0.19-3 μg/mL, itraconazole: 0.125 μg/mL, posaconazole: 0.125-0.5 μg/mL and against susceptible Curvularia was natamycin 0.75-4 μg/mL, amphotericin B 0.5-1 μg/mL, voriconazole 0.125-0.19 μg/mL, itraconazole 0.047-0.094 μg/mL, posaconazole 0.047-0.094 μg/mL. MIC against Mucor spp.+ Rhizopus spp. (n = 1) was natamycin: 8 μg/mL, amphotericin B: 0.75 μg/mL, posaconazole: 1.5 μg/mL. MIC against of Alternaria (n = 1) was voriconazole: 0.19 μg/mL, posaconazole: 0.094 μg/mL. MIC against Penicillium (n=1) was natamycin: 8 μg/mL, voriconazole: 0.25 μg/mL, itraconazole: 0.5 μg/mL, and Posaconazole: 0.125 μg/mL.

Conclusion

Our observations highlight the variations in susceptibility to antifungal agents. Posaconazole seems to be effective with low MIC against common corneal pathogenic fungal isolates.

Fusarium Keratitis-Review of Current Treatment Possibilities

In many parts of the world, fungi are the predominant cause of infectious keratitis; among which, Fusarium is the most commonly isolated pathogen. The clinical management of this ophthalmic emergency is challenging. Due to the retardation of the first symptoms from an injury and the inability to differentiate fungal from bacterial infections based on clinical symptoms and difficult microbial diagnostics, proper treatment, in many cases, is postponed. Moreover, therapeutical options of Fusarium keratitis remain limited. This paper summarizes the available treatment modalities of Fusarium keratitis, including antifungals and their routes of administration, antiseptics, and surgical interventions.

Clinical Characteristics and Outcomes of Fungal Keratitis in the United Kingdom 2011-2020: A 10-Year Study

Fungal keratitis (FK) is a serious ocular infection that often poses significant diagnostic and therapeutic dilemmas. This study aimed to examine the causes, clinical characteristics, outcomes, and prognostic factors of FK in the UK. All culture-positive and culture-negative presumed FK (with complete data) that presented to Queen’s Medical Centre, Nottingham, and the Queen Victoria Hospital, East Grinstead, between 2011 and 2020 were included. We included 117 patients (n = 117 eyes) with FK in this study. The mean age was 59.0 ± 19.6 years (range, 4–92 years) and 51.3% of patients were female. Fifty-three fungal isolates were identified from 52 (44.4%) culture-positive cases, with Candida spp. (33, 62.3%), Fusarium spp. (9, 17.0%), and Aspergillus spp. (5, 9.4%) being the most common organisms. Ocular surface disease (60, 51.3%), prior corneal surgery (44, 37.6%), and systemic immunosuppression (42, 35.9%) were the three most common risk factors. Hospitalisation for intensive treatment was required for 95 (81.2%) patients, with a duration of 18.9 ± 16.3 days. Sixty-six (56.4%) patients required additional surgical interventions for eradicating the infection. Emergency therapeutic/tectonic keratoplasty was performed in 29 (24.8%) cases, though 13 (44.8%) of them failed at final follow-up. The final corrected-distance-visual-acuity (CDVA) was 1.67 ± 1.08 logMAR. Multivariable logistic regression analyses demonstrated increased age, large infiltrate size (>3 mm), and poor presenting CDVA (<1.0 logMAR) as significant negative predictive factors for poor visual outcome (CDVA of <1.0 logMAR) and poor corneal healing (>60 days of healing time or occurrence of corneal perforation requiring emergency keratoplasty; all p < 0.05). In conclusion, FK represents a difficult-to-treat ocular infection that often results in poor visual outcomes, with a high need for surgical interventions. Innovative treatment strategies are urgently required to tackle this unmet need.

Infectious keratitis: an update on epidemiology, causative microorganisms, risk factors, and antimicrobial resistance

Corneal opacity is the 5th leading cause of blindness and visual impairment globally, affecting ~6 million of the world population. In addition, it is responsible for 1.5-2.0 million new cases of monocular blindness per year, highlighting an ongoing uncurbed burden on human health. Among all aetiologies such as infection, trauma, inflammation, degeneration and nutritional deficiency, infectious keratitis (IK) represents the leading cause of corneal blindness in both developed and developing countries, with an estimated incidence ranging from 2.5 to 799 per 100,000 population-year. IK can be caused by a wide range of microorganisms, including bacteria, fungi, virus, parasites and polymicrobial infection. Subject to the geographical and temporal variations, bacteria and fungi have been shown to be the most common causative microorganisms for corneal infection. Although viral and Acanthamoeba keratitis are less common, they represent important causes for corneal blindness in the developed countries. Contact lens wear, trauma, ocular surface diseases, lid diseases, and post-ocular surgery have been shown to be the major risk factors for IK. Broad-spectrum topical antimicrobial treatment is the current mainstay of treatment for IK, though its effectiveness is being challenged by the emergence of antimicrobial resistance, including multidrug resistance, in some parts of the world. In this review, we aim to provide an updated review on IK, encompassing the epidemiology, causative microorganisms, major risk factors and the impact of antimicrobial resistance.

The Spectrum of Microbial Keratitis: An Updated Review

Background:

In microbial keratitis, infection of the cornea can threaten vision through permanent corneal scarring and even perforation resulting in the loss of the eye. A literature review was conducted by Karsten, Watson and Foster (2012) to determine the spectrum of microbial keratitis. Since this publication, there have been over 2600 articles published investigating the causative pathogens of microbial keratitis.

Objective:

To determine the current spectrum of possible pathogens implicated in microbial keratitis relative to the 2012 study.

Methods:

An exhaustive literature review was conducted of all the peer-reviewed articles reporting on microbial pathogens implicated in keratitis. Databases including MEDLINE, EMBASE, Scopus and Web of Science were searched utilising their entire year limits (1950-2019).

Results:

Six-hundred and eighty-eight species representing 271 genera from 145 families were implicated in microbial keratitis. Fungal pathogens, though less frequent than bacteria, demonstrated the greatest diversity with 393 species from 169 genera that were found to cause microbial keratitis. There were 254 species of bacteria from 82 genera, 27 species of amoeba from 11 genera, and 14 species of virus from 9 genera, which were also identified as pathogens of microbial keratitis.

Conclusion:

The spectrum of pathogens implicated in microbial keratitis is extremely diverse. Bacteria were most commonly encountered and in comparison, to the review published in 2012, further 456 pathogens have been identified as causative pathogens of microbial keratitis. Therefore, the current review provides an important update on the potential spectrum of microbes, to assist clinicians in the diagnosis and treatment of microbial keratitis.

Fungal keratitis: An overview of clinical and laboratory aspects

Mycotic keratitis or keratomycosis is a fungal infection with global distribution. The dominant aetiology of this disease varies based on geographical origin, socioeconomic status, and climatic condition. Generally, Aspergillus spp. and Fusarium spp. are common in tropical and subtropical regions and Candida spp. are dominant in temperate areas. Demonstration of fungal elements in microscopic examination besides the isolation of fungi in culture is the gold standard of laboratory diagnosis. As the culture is a time-consuming procedure, other approaches such as in vivo confocal microscopy which produces real-time imaging of corneal tissue and molecular techniques have been developed to facilitate rapid diagnosis of fungal keratitis. The first choice of treatment is topical natamycin, although topical amphotericin B is the best choice for Aspergillus and Candida keratitis. Regarding the diversity of fungal aetiology and the emergence of drug resistance in some genera and species, proper identification using molecular methods and antifungal susceptibility testing could provide useful data. Furthermore, as the better efficacy of combination therapy in comparison to monotherapy is reported, in vitro determination of interactions between various drugs seem informative. This review aims to provide a general and updated view on the aetiology, risk factors, epidemiology, clinical and laboratory diagnosis, and management of fungal keratitis.

Identification and Characterization of Fusarium proliferatum, a New Species of Fungi that Cause Fungal Keratitis

Fusarium proliferatum (F. proliferatum) is known as a pathogen of corn and other crops, but its role in fungal keratitis has not been well investigated. Among 877 Fusarium isolates, we identified 155 (17.7%) stains as F. proliferatum according to their morphological features and partial DNA sequencing of translation elongation factor-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1\alpha $$\end{document}1α (EF-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1\alpha $$\end{document}1α) in this study. In vitro antifungal susceptibility tests showed that the F. proliferatum strains were sensitive to natamycin and vorionazole but resistant to amphotericin B, fluconazol, ketoconazole and itaconazole. Most of the F. proliferatum-positive keratitis patients (44/155,28.4%) were aged 51–60 years old. The main cause of infection was injury by a plant (51/155, 32.9%). A combination of 1% amphotericin B and 3% ketoconazole cured 45.2% (14/31) and a combination of 0.5% natamycin and 0.5% voriconazole cured 59.1% (13/22) of F. proliferatum-positive patients. The date suggests that F. proliferatum identified through EF-1ɑ DNA sequencing is an important new species that causes fungal keratitis. Based on antifungal susceptibility, treatment with a combination of 0.5% natamycin and 0.5% voriconazole improves the therapeutic efficacy in F. prolifertum-positive patients.

[Fungal keratitis]

Fungal keratitis, or keratomycoses, are corneal infections which must be considered in cases of corneal trauma, prior corneal surgery, chronic ocular surface disease, topical corticosteroids or contact lens wear. Filamentous fungi or yeasts may be involved. Presenting clinical features such as corneal infiltrates with feathery edges and/or raised surface, intact epithelium with deep stromal involvement, satellite lesions, endothelial plaques, lack of improvement with antibiotics and worsening with steroids are suggestive of fungal keratitis. Corneal scraping for laboratory examination is mandatory. Medical management with antifungal eye drops and systemic agents should be started as soon as possible. Surgical interventions are required in a significant number of cases to control the infection. The prognosis of fungal keratitis is worse than that of bacterial keratitis.