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X. Hua, X. Yuan, B. M. Mitchell, M. C. Lorenz, K. R. Wilhelmus; Fungal Genes Involved in Hyphal Filamentation May Explain the Difference in Human Corneal Virulence Among Candida albicans Strains. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5535.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the molecular differences responsible for fungal virulence between two wild-type strains of Candida albicans.
C.albicans strains SC5314 and VE175 were compared using filamentation assays and in vitro growth kinetics under pH 7.3 and pH 8.0 at 37ºC and 26ºC, respectively. C. albicans microarray analysis compared gene expression between SC5317 and VE175 at pH 8.0. To compare the hyphal invasion of these two strains, eye-bank donor corneas were inoculated with 105 colony-forming units of C. albicans after superficial scarification, maintained in an explant culture system at pH 7.3 or pH 8.0, then processed for histologic examination at 1 and 3 days post fungal exposure. On PAS-stained sections, overall average and maximal hyphal penetration ratios were determined for corneal penetration by SC5314 and VE175. A C. albicans homozygous deletion mutant of secreted aspartyl proteinases four, five and six (SAP4-6) was used in the in vitro and corneal culture assays to potentially define genetic factors responsible for the functional difference between SC5314 and VE175.
SC5314 was highly flamentous in vitro, but VE175 demonstrated only limited filamentation, with the difference more apparent at pH 8.0. Microarray analysis revealed that 7.4% of SC5314 genes were significantly changed compared to VE175 (≥2 fold, p<0.05). Thirty-two genes controlling filamentation or virulence were significantly upregulated, including SAP5 (10.1-fold, p<0.001) and SAP6 (9.5-fold, p<0.001). Human corneal explants showed that SC5314 was more invasive than VE175 at pH8.0 with mean±SD penetration ratios of 1.7%±0.8% for SC5314 and 0 for VE175 at day 1 p.i. and mean maximal ratios of 16.9%±6.6% and 0, respectively. The SAP4-6 deletion mutant had a similar growth-kinetic profile as the wild-type strains but showed intermediate in vitro filamentation and in vivo infiltration in human corneas.
Genes involved in fungal filamentation contribute to virulence differences between C. albicans strains. Fungal SAP5 and/or SAP6 may have a key role in the corneal pathogenicity of C. albicans keratitis and offer a unique target for new antifungal chemotherapy of keratomycosis.
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