Beauveria bassiana Keratitis: A Case Series and Review of Literature

Abstract

Background: Beauveria bassiana is a filamentous fungus commonly used as an insecticide that rarely causes keratitis.

Methods: Patients affected by Beauveria bassiana keratitis were retrospectively recruited at San Raffaele Hospital (Milan, Italy) between 2020 and 2022. All subjects underwent comprehensive ophthalmic evaluation, including in vivo confocal microscopy (IVCM) and microbiologic examination of corneal scrapings. Beauveria bassiana was identified using 18S rDNA targeted PCR.

Results: Four eyes of four patients (51 ± 8.8 years old) were evaluated. The main risk factors were soft contact lens wear (75%) and trauma with vegetative matter (50%). A superficial infiltrate was displayed in the majority of patients. Three cases (75%) showed hyphae on IVCM. All patients showed clinical improvement after topical antifungal therapy, although mostly through a combination of two antifungals (75%). One patient with a deeper infection required a systemic antifungal agent after one month of topical therapy. All cases required debridement to reduce the microbial load and enhance drug penetration. All patients experienced keratitis resolution following medical treatment (average: 3.3 months).

Conclusions: The identification of risk factors and the early diagnosis of Beauveria bassiana keratitis are fundamental in order to avoid its penetration in the deeper corneal stromal layers. Topical antifungal drugs, possibly accompanied by ulcer debridement, may be a successful treatment if instilled from the early phases of the disease.

Keywords: Beauveria bassiana; cornea; fungal keratitis; in vivo confocal microscopy; infectious keratitis.

Figure 1

Clinical presentations and confocal microscopy of corneal infiltrate in Case 1 (A–C). (A) Initial presentation of the peripheral corneal infiltrate caused by Beauveria bassiana. (B) Resolution of the corneal infiltrate in Case 1 after three months of topical therapy with 1% voriconazole. (C) Confocal microscopy of the corneal infiltrate, revealing presence of hyperintense branching lines compatible with presence of hyphae in the anterior corneal stroma.

Figure 2

Clinical presentations and confocal microscopy of corneal infiltrate in Case 3 (A–C). (A) Initial presentation of corneal infiltrate caused by Beauveria bassiana. (B) Resolution of the corneal infiltrate in Case 3 after 2.5 months of therapy with two topical antifungal drugs (1% voriconazole and 5% natamycin). (C) Confocal microscopy of the corneal infiltrate. Structures compatible with hyphae can be identified in the anterior corneal stroma.

Figure 3

Cultural examination in Case 4 (A–C). (A) Typical white floccose colonies of Beauveria bassiana on Sabouraud dextrose agar. (B) LPCB slide mount showing sympodial development of conidiogenous cells forming dense clusters at 400× magnification. (C) Details of flask-shaped, geniculate conidiogenous cells with ovalar conidia (3.5× digital zoom on top of 400× magnification).