Keratitis With Prototheca wickerhamii, a Rare and Atypical Pathogen

Purpose: The aim of this study was to describe the diagnostic and therapeutic challenges of infectious keratitis caused by Prototheca wickerhamii , a rare and atypical pathogen. Methods: This study is a case report. Results: A 70-year-old man with a complex oculoplastic history and recent penetrating keratoplasty for a perforated neurotrophic ulcer developed infectious keratitis in the graft 10 weeks after surgery. The initial culture grew pansensitive Corynebacterium species, but despite treatment with broad-spectrum antibiotics, clinical findings worsened. Repeat corneal cultures ultimately identified P. wickerhamii , an achlorophyllic alga that can mimic fungal infections. The patient subsequently underwent therapeutic penetrating keratoplasty for infection control. Histopathologic examination revealed PAS-positive, morula-like spherules in the corneal stroma, consistent with P. wickerhamii infection. Postoperatively, antifungal therapy was tailored, and corticosteroids were initially withheld to minimize the risk of recurrent infection. No recurrence was observed during the 10-week postoperative period. Conclusions: This case underscores the importance of considering rare, atypical pathogens, such as algal species in recalcitrant infectious keratitis, and emphasizes the need for careful surgical planning when medical therapy proves ineffective.