Nocardia sienata: a new causative species of infectious keratitis

Abstract

A 25-year-old man presented with a 2-month history of progressively worsening left eye pain and an atypical corneal ring infiltrate. His condition deteriorated despite topical antibiotic therapy. Cultures for bacteria, fungus and acanthamoeba, repeated twice, all demonstrated no growth. On third corneal scraping, culture on Middlebrook agar grew colonies after 3 weeks of incubation. Sixteen-second deep sequencing identified Nocardia sienata as the pathogen. This species of Nocardia has not previously been described as a causative pathogen for infectious keratitis. Sloughing and loose epithelium with recurrent filament formation are unusual in infectious keratitis and could be associated with this species. In culture-negative cases, clinicians should consider Nocardia as a cause of keratitis despite its rarity outside of south Asia and use steroids cautiously. Next generation sequencing technology may facilitate identification of the causate of keratitis and can be especially useful in culture-negative cases and with unexpected pathogens.

Keywords: anterior chamber; infectious diseases; ophthalmology.

Figure 1

Slit-lamp examination of Nocardia sienata keratitis. (A) Conjunctival injection and an irregular patchy ovoid infiltrate on presentation. White arrows annotate the ‘wreath-like’ patchy infiltrate. (B) Post corneal scraping with central corneal filaments (white arrow). (C) Worsening symptoms with epithelial breakdown. (D) A large peripheral filament after the second keratectomy (arrow) associated with prominent nasal limbal inflammation.

Figure 2

(A) Slit-lamp examination after 4 weeks of topical amikacin. (B) Complete resolution of infection and VA recuperating to 20/30.