Candida albicans Strain-Dependent Virulence and Rim13p-Mediated Filamentation in Experimental Keratomycosis

Baylor College of Medicine, Houston, Texas, United States
Investigative Ophthalmology &amp Visual Science (Impact Factor: 3.4). 03/2007; 48(2):774-80. DOI: 10.1167/iovs.06-0793
Source: PubMed


To compare the virulence of wild-type Candida albicans strains in a murine model of corneal candidiasis and to investigate the role of fungal filamentation in disease progression.
Scarified corneas of immunocompetent or cyclophosphamide-treated BALB/c mice were topically inoculated with one of three human isolates of C. albicans, a homozygous mutant of the pH-dependent filamentation gene rim13 or a mutant reference strain control. Mock-inoculated eyes served as negative controls. Corneal disease was categorized daily for 8 days with quantitative fungal culturing of eyes at 6 hours, 1 day, 4 days, and 8 days after infection and histopathologic examination at 1 day and 4 days after infection.
Corneal disease severity differed significantly among wild-type strains (P < or = 0.02). The rim13(-/-) mutant Tn7-rim13 was fully attenuated, whereas the mutant control DAY286 was fully virulent. Pretreatment of mice with cyclophosphamide increased susceptibility to wild-type C. albicans and partially rescued the attenuated phenotype of the genetically deficient rim13(-/-) fungal mutant. All strains replicated with similar kinetics in vitro, and wild-type strains had similar clearance from infected eyes. Histopathologic findings correlated with disease severity.
Wild-type strains of C. albicans that differ significantly in ocular pathogenicity correlate with the ability of yeast to produce pseudohyphae and hyphae and to invade corneal tissue. Full attenuation of the fungal rim13(-/-) mutant is the first direct demonstration of a hyphal morphogenesis-related gene as a specific virulence factor for C. albicans during corneal infection.

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    • "The OD values were converted into concentration of cells measured in CFU per milliliter (1.0 OD corresponded to 2.16×108 CFU/mL). In vitro growth kinetics of fungal strains were determined following the protocol described by Mitchell et al. [17]. In brief, fungal strains (103 CFU) were inoculated into 2 mL Sabouraud dextrose broth supplemented with different doses of complex 3a (0.25 to 4.0 µM), and incubated at 30°C with continuous rocking at 180 rpm. "
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    PLoS ONE 03/2013; 8(3):e58346. DOI:10.1371/journal.pone.0058346 · 3.23 Impact Factor
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    Molecular Microbiology 06/2012; 85(4):700-15. DOI:10.1111/j.1365-2958.2012.08134.x · 4.42 Impact Factor
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    • "Therefore, Snf7 is predicted to facilitate interaction between the protease Rim13 and its substrate Rim101 via Rim20. Rim101 activation is required for growth in neutral-alkaline environments and is required for C. albicans virulence in animal models of both systemic and mucosal disease (Porta et al. 1999; Ramon et al. 1999; Davis et al. 2000a,b; Mitchell et al. 2007; Villar et al. 2007). Thus, the sensing and adaptation to environmental pH through the Rim101 pathway is essential for C. albicans pathogenesis. "
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    ABSTRACT: The opportunistic pathogen Candida albicans can grow over a wide pH range, which is associated with its ability to colonize and infect distinct host niches. C. albicans growth in neutral-alkaline environments requires proteolytic activation of the transcription factor Rim101. Rim101 activation requires Snf7, a member of the endosomal sorting complex required for transport (ESCRT) pathway. We hypothesized that Snf7 has distinct functions in the Rim101 and ESCRT pathways, which we tested by alanine-scanning mutagenesis. While some snf7 alleles conferred no defects, we identified alleles with solely ESCRT-dependent, solely Rim101-dependent, or both Rim101- and ESCRT-dependent defects. Thus, Snf7 function in these two pathways is at least partially separable. Both Rim101- and ESCRT-dependent functions require Snf7 recruitment to the endosomal membrane and alleles that disrupted both pathways were found to localize normally, suggesting a downstream defect. Most alleles that conferred solely Rim101-dependent defects were still able to process Rim101 normally under steady-state conditions. However, these same strains did display a kinetic defect in Rim101 processing. Several alleles with solely Rim101-dependent defects mapped to the C-terminal end of Snf7. Further analyses suggested that these mutations disrupted interactions with bro-domain proteins, Rim20 and Bro1, in overlapping but slightly divergent Snf7 domains.
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