Molecular characterization of fungal endophthalmitis and keratitis caused by yeasts

Abstract

Candida species are the most common causes of sight-threatening fungal ocular infections in temperate regions of the world. Despite their relevance, little is known about the emergence of novel species and the molecular epidemiology of these infections. Here, we molecularly characterized 38 yeast isolates collected from patients diagnosed with endophthalmitis or keratitis at Massachusetts Eye and Ear from 2014 to 2021. Sequencing of the ITS1-5.8S-/ITS2 regions demonstrated that this population of yeasts was dominated by Candida spp. (37 out of 38; 97%), with 58% of the cases caused by C. albicans (n = 22) and the remaining by emerging non-albicans species, predominantly by C. parapsilosis (n = 8) and C. dubliniensis (n = 6). One isolate each was identified as C. tropicalis and Clavispora lusitaniae. Interestingly, all C. dubliniensis were isolated from endophthalmitis and most C. parapsilosis from keratitis. Multilocus sequence typing analysis of C. albicans showed a prevalence of CC-1 isolates that has DST69 as the putative founder, with 64% of them belonging to this clonal complex (CC). Isolates grouped within this cluster were more predominant in endophthalmitis (10 out of 14; 71%). One C. albicans CC-1 isolate was multi-azole resistant. In conclusion, we observed that nearly half of the ocular infections caused by yeasts are associated with C. albicans, with evidence for the emergence of non-albicans species that are differentially enriched in distinct ocular niches. Candida albicans isolates clustered within the predominant CC-1 group were particularly more common in endophthalmitis, demonstrating a potential pattern of ocular disease enrichment within this clade.

Keywords: Candida; Endophthalmitis; keratitis; molecular typing; ocular surface disease.

Figure 1.

(A) Species distribution of isolates collected from Massachusetts Eye and Ear for cases of endophthalmitis and keratitis from 2014 to 2021. (B) A comparison between the number of Candida albicans and non-albicans species responsible for causing endophthalmitis and keratitis between the first and second halves of the isolate collection period.

Figure 2.

Multilocus sequence typing of the 22 C. albicans isolates from Massachusetts Eye and Ear. Red represents isolates collected from cases of endophthalmitis, and blue represents isolates collected from keratitis cases. The diploid sequence type (DST) is displayed above the circle, and the number of isolates for each DST is shown at the bottom of each circle. The CC-1 group is outlined.

Figure 3.

Presenting visual acuities (VA) and final best corrected visual acuities (BCVA) for the endophthalmitis patients and keratitis patients for cases caused by C. albicans and non-albicans species.