Rare Kodamaea ohmeri keratitis following a trivial vegetative trauma

Abstract

Kodamaea ohmeri keratitis is an opportunistic pathogen seen in patients who have undergone invasive procedures and immunocompromised state. It has been identified in septicemia patients, resulting in mortality. To the best of our knowledge, we identified the first case of K. ohmeri keratitis following an injury with vegetative material. A 57-year-old woman with underlying, poorly controlled diabetes mellitus was gardening when a tree leaf accidentally poked her in the eye. Two weeks later, the patient presented with right eye pain, redness and progressive blurring of vision due to a traumatised right cornea. Slit-lamp examination showed a small inferior paracentral corneal stromal infiltrate with overlying epithelial defect. A corneal scraping sample yielded K. ohmeri from Analytical Profile Index (API) 20C yeast identification system. She was treated with intensive topical amphotericin B and fluconazole. After 6 weeks of treatment, the keratitis resolved with faint scar tissue, and her visual acuity improved.

Background

Kodamaea ohmeri is an unusual pathogenic fungus commonly encountered with septicemia in compromised hosts. To the best of our knowledge, there are no previously reported cases of K. ohmeri keratitis. This is the first case occurring in a patient with low host immunity following a trivial vegetative trauma.

Case presentation

A 57-year-old woman with underlying poorly controlled diabetes mellitus presented with 2 weeks of right eye pain, redness and progressive blurring of vision. She also reported photophobia and tearing. The patient’s symptoms began after a tree leaf accidentally injured her right eye while she was gardening. She also noticed a whitish net of fungal growth on the leaf after the accident.

Ocular examination of the patient showed best corrected visual acuity (BCVA) of 20/60 in the affected eye and 20/20 in the left eye. Slit-lamp biomicroscopy examination of the right eye showed that the conjunctiva was infected. There was an inferior paracentral corneal stromal ulcer measuring 1.2 mm vertically and 2.6 mm horizontally (figure 1). The ulcer margin was well defined, and a fluorescein staining test showed an overlying epithelial defect (figure 2). The surrounding cornea was edematous. There was an absence of anterior chamber activity, and the intraocular pressure was normal. Posterior segment examination was unremarkable.

Figure 1.

A slit-lamp examination image demonstrating a small, inferior paracentral corneal ulcer with regular margin and absence of satellite lesion.

Figure 2.

A slit-lamp examination image demonstrating overlying epithelial defect stained with fluorescence strip upon examined under cobalt-blue light.

Investigations

Immediate corneal scrapings were taken, and the samples were sent for Gram staining to look for Gram-positive or Gram-negative bacteria in view of clinical resemblance of bacterial keratitis. The sample was also sent for potassium hydroxide staining for identification of fungal hyphae. Another sample was sent for microbiological cultures and antibiotic susceptibility. Initial Gram stain results showed Gram-positive yeast, but absence of fungal colonies in Sabouraud Dextrose Agar (SDA), which normally shows typical fungus growth such as Candida spp. Based on the Gram-positive finding and history of vegetative trauma in an immunocompromised host, we investigated further. Using API 20C, a commercial kit available for the detection of rare yeast, we isolated K. ohmeri in our patient.

Differential diagnosis

A typical fungal corneal infection may mimic bacterial keratitis. In our case, we had difficulty in differentiating a causative organism. Clinically, the ulcer was small and demonstrated a well-defined margin with the absence of a satellite lesion, endothelial plaque and hypopyon. Our initial diagnosis was bacterial keratitis; however, based on the Gram-positive finding and culture result for K. ohmeri, we changed our diagnosis to fungal keratitis, a rare fungal infection that was not reported in any literature review.

Treatment

The patient was treated empirically with a topical broad-spectrum antibiotic based on presumed bacterial keratitis. The antibiotic was then substituted with intensive topical amphotericin B 0.15% and topical fluconazole 0.3%, on receiving the Gram stain and culture results. The ulcer responded dramatically to topical antifungal over a week as the eye became less painful and red. Clinically, the corneal stromal infiltrate reduced in size with re-epithelisation.

Outcome and follow-up

During subsequent follow-up, the epithelial defect healed. The corneal stromal infiltration appeared less dense and decreased in size, with resolution of surrounding corneal oedema. At 6 weeks of follow-up, the area where the corneal stromal infiltrate was located showed scar tissue. Topical antifungals were tapered down in frequency with resolution of the ulcer. The patient’s BCVA returned to 20/20.

Discussion

K. ohmeri, formerly known as Pichia ohmeri or Yamadazyma ohmeri, belongs to a yeast-like fungus with characteristic budding colonies on culture agar.¹ It was initially found as a facultative fungus for fermentations and is widely used in the food industry.² K. ohmeri can also be found in pools, in sand, and on floors.² In our case, the patient was poked in the eye by a tree leaf, on which she noted a whitish colony of fungus after the incident. Presumably, K.ohmeri also grow on plants in environments with high humidity.

The first isolation of K. ohmeri species in humans occurred in 1984, when it was cultured from a patient’s pleural fluid and assumed to be a contaminated sample. However, K. ohmeri was again cultured from the blood of a septicaemia patient who succumbed to K. ohmeri fungaemia infection.³ Since then, K. ohmeri has been recognised as a true opportunistic pathogen in immunosuppressed humans.

Emergence of this unusual fungal species has led to the identification of several risk factors in humans. One risk factor reported in the literature includes patients with a history of invasive procedures; for example, this fungal species was inoculated in central venous catheters, prosthetic valves and peritoneal dialysis catheters.^4–6 It was also cultured on the skin of patients with burns.⁷ Another well-known risk factor includes immunosuppressed patients, including those with uncontrolled diabetes mellitus, malignancy, and HIV.^{8 9} In the paediatric age group, premature babies are at high risk for invasive infections.¹⁰

To date, this is the first reported case of K. ohmeri keratitis in a patient with a significant risk factor. Another important point to be highlighted in this case is that our patient had an additional risk factor of uncontrolled diabetes mellitus.

Clinically, K. ohmeri keratitis is presumed to be a slow-growing, less invasive pathogen on the corneal tissue. Ocular trauma with vegetative materials is an important predisposing factor to fungal keratitis.¹¹ As it invades the corneal tissue, inflammatory cascade initiated and ultimately lead to tissue necrosis. Further deeper invasion can occur through penetration of the Descemet’s membrane.¹¹ Typically, fungal keratitis exhibits characteristics such as an ulcer with a feathery edge, a moderate to large corneal infiltrate, presence of a satellite lesion and endothelial plaque with hypopyon. Furthermore, untreated fungal ulcer over a long period inevitably leads to deeper penetration and corneal perforation. In our case, with a subacute onset of 2 weeks, the level of corneal tissue infected with this fungus was shallow, at the stromal level. There was no evidence, such as endothelial plaque, corneal melting, hypopyon and posterior segment involvement, of deeper penetration. In the literature, this organism was isolated from a burn patient’s skin on disruption of skin barrier.⁷ A similar concept was applied to corneal tissue whereby corneal epithelial tissue breakdown as result of trauma caused this organism to invade the corneal tissue.

Isolation of K. ohmeri in a routine culture on SDA may yield false-negative results. K. ohmeri resembles Candida spp., which appear as white fluffy colonies on SDA, and this may falsely report as other Candida spp. API 20C has been considered a gold standard for rare yeast species identification since 2002.¹² The increasing number of human infections has resulted in the development of commercial kits for the identification of rare fungal species.¹² Furthermore, the increase in immunosuppressed patients has led to an increase in the isolation of rare yeast species. As in our case, K.ohmeri yielded Gram-positive fungus on Gram stain slide, a result similar to other yeast group species. However, with negative growth on typical SDA, further tests were given to rule out the presence of other types of fungal infection in our patient. Besides, the patient’s underlying uncontrolled diabetes mellitus and history of trauma with vegetative material were important risk factors for K. ohmeri infection.

The patient responded well to treatment with topical amphotericin B and fluconazole, similar to Candida spp. keratitis cases, possibly because this organism is a similar yeast-like fungus. As in patients with systemic K. ohmeri infection, topical amphotericin B is the treatment of choice.¹³ Amphotericin B is a broad-spectrum fungicidal with good ocular penetration and high bioavailability. It can penetrate deep corneal stroma following topical application.¹¹ In systemic infection, K. ohmeri is commonly resistant to fluconazole and is avoided in empirical treatment.¹³ In contrast, the application of topical fluconazole in our case, complemented with amphotericin B, exhibited synergistic effects with good response. Fluconazole is also a broad-spectrum antifungal with high bioavailability and low toxicity.¹¹ K. ohmeri is also susceptible to voriconazole and micafungin.¹¹

Patient’s perspective.

I was surprised that being poked by a tree leaf in the right eye would lead to a fungal infection in my right eye. The trauma to the eye seemed trivial. Since then, I am quite cautious because I have frequently observed the same fungus growing around me, especially on food due to my country’s high humidity. However, I was happy I was treated well and regained my normal vision.

Learning points.

• Kodamaea ohmeri is a potential causative agent of keratitis in an immunocompromised patient with a trivial vegetative injury.

• K. ohmeri keratitis is an atypical fungal infection that can mimic bacterial keratitis.

• K. ohmeri appears as a slow-growing, less invasive pathogen on corneal tissue.

• K. ohmeri keratitis responds well to amphotericin B, which has similarity in patients with systemic K. ohmeri infection.