Keratitis by Fusarium temperatum, a novel opportunist

Abstract

Background: Fusarium species are among the most common fungi present in the environment and some species have emerged as major opportunistic fungal infection in human. However, in immunocompromised hosts they can be virulent pathogens and can cause death. The pathogenesis of this infection relies on three factors: colonization, tissue damage, and immunosuppression. A novel Fusarium species is reported for the first time from keratitis in an agriculture worker who acquired the infection from plant material of maize. Maize plants are the natural host of this fungus where it causes stalk rot and seeding malformation under temperate and humid climatic conditions. The clinical manifestation, microbiological morphology, physiological features and molecular data are described.

Methods: Diagnosis was established by using polymerase chain reaction of fungal DNA followed by sequencing portions of translation elongation factor 1 alpha (TEF1 α) and beta-tubulin (BT2) genes. Susceptibility profiles of this fungus were evaluated using CLSI broth microdilution method.

Results: The analyses of these two genes sequences support a novel opportunist with the designation Fusarium temperatum. Phylogenetic analyses showed that the reported clinical isolate was nested within the Fusarium fujikuroi species complex. Antifungal susceptibility testing demonstrated that the fungus had low MICs of micafungin (0.031 μg/ml), posaconazole (0.25 μg/ml) and amphotericin B (0.5 μg/ml).

Conclusion: The present case extends the significance of the genus Fusarium as agents of keratitis and underscores the utility of molecular verification of these emerging fungi in the human host.

Figure 1

Morphological description of Fusarium temperatum. (A) Slit lamp photograph showing infected cornea involving regions of sclera; (B) KOH mount of the scraping material showing fungal hyaline and nonseptate hyphae (magnification, ×40); (C) Sporodochia present in yellowish orange on CLA; (D) Growth of the isolate F. temperatum on OA, agar pigmentation ranges from colorless to dark purple on; reverse pigmentations in light pink; (E) Growth of isolates on PDA at 25°C; (F) In situ conidiophores with false heads; (G) Microconidia on CLA; (H-I) Macroconida; (J) Coild hyphae; (K-L) Monophialidic and polyphialidic conidiogenous cells. All scale bars, 10 μm.

Figure 2

Average growth of Fusarium temperatum . Colony diameters (mm) at different temperatures ranging from 25°C to 40°C, measured after 5 days of incubation on 2% MEA, were calculated for F. temperatum, CBS135540.

Figure 3

Phylogenetic analysis of Fusarium temperatum. Phylogenetic tree resulting from Bayesian analysis for the TEF-1α and β-tubulin genes (values of 0.8 for Bayesian probability are shown). Fusarium oxysporum (NRRL 22902) was used as the outgroup.