Opportunistic fungal infections have increased dramatically over the last few decades due to the increased number of individuals who are immunocompromised in association with AIDS, organ and tissue transplantation, and long term treatments for cancer patients. In recent years, Candida glabrata has emerged as the second most common cause of mucosal and invasive fungal infection. Most C. glabrata isolates display intrinsically low susceptibility and capacity for acquired resistance to sterol synthesis-inhibiting azoles, the major antifungal group. As in C. albicans, azole resistance is most commonly mediated by upregulated expression of multidrug transporters, a mechanism that is the most important problem facing antimicrobial chemotherapy.
Project 1: The primary limitation of the azoles is their lack of fungicidal activity, necessitating long-term treatments in immunocompromised individuals. This frequently selects for azole-resistance, which can be either intrinsic or acquired. We are characterizing the transcription factor Pdr1 responsible for the upregulation of multidrug transporter, hence the azole resistance. Our recent studies have implicated Pdr1 as the “master regulator” in C. glabrata azole and multidrug resistance. The long-term goal is to use this information to develop new approaches to prevent antifungal resistance.
Project 2: The new class of antifungals are Echinocandins (ECs), inhibitor of glucan synthase. ECs are fungicidal especially for Candida albicans and Aspergillus fumigatus, other fungi have variable or poor susceptibility for reasons which are unclear. Furthermore, acquired resistance of ECs has been documented in other Candida species and will increase as their use expands. In Saccharomyces cerevisiae and related yeast, mutations that confer acquired EC resistance have been mapped to the Fks1 gene encoding glucan synthase.
Since acquired EC resistance in susceptible fungi is associated with specific mutations in the integral membrane protein Fks1 or its paralog. We focused our study on EC target, Fks1 using site-directed mutagenesis, and deletion strategy in S. cerevisiae as a model fungi by the development of novel PCR-based methods. Recently, we have identified the Fks1 residue (hot spot 1 region) from Candida parapsilosis, Scedosporium prolificans, S. apiospermum and Fusarium solani and propose that Fks1 sequences represent the primary determinants of intrinsic EC resistance of these fungi. To test the role of Fks1 in intrinsic EC resistance, we constructed Fks1 hybrids in S. cerevisiae by incorporating Fusarium solani hot spot 1 region of Fks1 residues. The hybrid conferred significantly reduced EC susceptibility to further support our hypothesis.
C. glabrata is closely related to S. cerevisiae, and encodes Fks1/2/3 orthologs, but their function, regulation and role in reduced ECs susceptibility (RES) is unclear. We are characterizing Fks1/2/3 in C. glabrata by gene disruption, expression and site-directed mutagenesis to understand the basis for EC resistance/susceptibility.
Selected publications: (See all Santosh Katiyar's publications in PubMed.)
Role for FKS1 in the intrinsic echinocandin resistance of Fusarium solani as evidenced by hybrid expression in Saccharomyces cerevisiae.
Katiyar SK, and TD Edlind.
Antimicrobial Agents and Chemotherapy, 53: 1772-1778, 2009.
"A naturally-occurring Fks1p proline to alanine amino acid change in Candida parapsilosis, Candida orthopsilosis and Candida metapsilosis accounts for reduced echinocandin susceptibility."
Garcia-Effron G, Katiyar SK, Park S, Edlind TD, and DS Perlin.
Antimicrobial Agents and Chemotherapy, 52(7):2305-2312, 2008.
"Candida albicans and Candida glabrata clinical isolates exhibiting reduced echinocandin susceptibility."
Katiyar SK, Pfaller M, and T Edlind.
Antimicrobial Agents and Chemotherapy, 50(8): 2892-2894, 2006.
"Promoter-dependent disruption of genes: simple, rapid, and specific PCR-based method with application to three different yeast."
Edlind TD, Henry KW, Vermitsky JP, Raj S, Edlind MP, and SK Katiyar
Current Genetics, 48: 117-125, 2005.
"Candida albicans echinocandin “target” identified by crosslinking is homolog of Pil1 and Lsp1, sphingolipid-dependent regulators of cell wall integrity signaling."
Edlind T, and SK Katiyar.
Antimicrobial Agents and Chemotherapy, 48: 4491, 2004.
"Antifungal activity in Saccharomyces cerevisiae is modulated by calcium signalling."
Edlind T, Smith L, Henry K, Katiyar SK, and J Nickels.
Molecular Microbiology, 46, 257-268, 2002.
"Aspergillus fumigatus CYP51 sequence: potential basis for fluconazole resistance."
Edlind TD, Henry KW, Metera K, and SK Katiyar.
Molecular Microbiology, 39(3): 299-302, 2001.
"Identification and expression of multidrug resistance-related ABC transporter genes in Candida krusei."
Katiyar SK, and TD Edlind.
Molecular Microbiology, 39: 109-116, 2000.
"Antagonism of azole activity against Candida albicans following induction of multidrug resistance genes by selected antimicrobial agents."
Henry KW, Cruz MC, Katiyar SK, and TD Edlind.
Antimicrobial Agents and Chemotherapy, 43, 1968-1974, 1999.
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