Thomas Edlind Professor, Microbiology and Immunology Ph.D., 1979, State University of New York, Upstate Medical Center, Syracuse, N.Y. 2900 Queen Lane Philadelphia, PA 19129 Tel :(215) 991-8377 Fax: (215) 848-2271 Email: tedlind@drexelmed.edu

Research Staff: Santosh Katiyar, Ph.D
Graduate Students: Shriya Raj, Michael Johnson

Keywords:

Molecular microbiology; Yeast genetics; Opportunistic fungi; Candida; Saccharomyces; Aspergillus; Antifungals; Azole; Echinocandins; Flucytosine; Multidrug resistance; Signal transduction; Gene regulation

Research Interests

Mycoses caused by opportunistic fungi, in particular the yeast Candida albicans and Candida glabrata and molds such as Aspergillus fumigatus, are life-threatening problems in immunocompromised individuals, primarly because of deficiencies in antifungal therapy. To address these needs, our research is aimed at understanding the molecular mechanisms of antifungal action, resistance, and toxicity. Current efforts exploit the powerful genetic and genomic tools available for the model yeast Saccharomyces cerevisiae.

With respect to sterol synthesis-inhibiting azole antifungals, we have shown that their activity is modulated by three distinct signal transduction pathways: calcium-calmodulin-calcineurin, cyclic AMP-protein kinase A, and protein kinase C-MAP kinase. Importantly, our genetic studies have identified new ways to enhance azole activity by combining them with signaling inhibitors, such as calmodulin antagonists. The downstream targets of these signaling pathways include genes encoding multidrug transporters, which confer resistance by pumping antifungals out of the cell. These genes are induced in response to antifungal treatment, and upregulated in many resistant mutants. We are working hard to characterize the transcription factor Pdr1 responsible for this upregulation. Recent studies have implicated MAP kinase Slt2 as activator and protein kinase A Tpk3 as repressor of Pdr1 activity.

We are also studying resistance to cell wall synthesis-inhibiting echinocandins, the newest group of  antifungals. Mutational analysis of echinocandin target Fks1 suggests a novel interaction in which the echinocandin is anchored in the membrane where it binds to both transmembrane and cytoplasmic regions of Fks1. Further studies will facilitate the design of new echinocandins with activity against multidrug-resistant fungi such as Fusarium and Scedosporium.

Finally, we are characterizing mechanisms of resistance to the antifungal flucytosine, and the mechanism of flucytosine-azole antagonism. This knowledge should lead to a more rational use of flucytosine, once a mainstay of antifungal therapy but now rarely used due to problems of resistance and toxicity. All of these projects are greatly aided by the development in our laboratory of novel PCR-based methods for genetic analysis, including gene disruption and site-directed mutagenesis.

Selected Publications

1. Henry, K.W., J.T. Nickels, and T.D. Edlind. Upregulation of ERG genes in Candida species by azoles and other sterol biosynthesis inhibitors. Antimicrob. Agents Chemother. 44:2693-2700, 2000.
   
   
2. Katiyar, S.K. and T.D. Edlind. Identification and expression of multidrug resistance-related ABC transporter genes in Candida krusei. Med. Mycol. 39:109-116, 2001.
   
   
3. Edlind, T., L. Smith, K. Henry, S. Katiyar, and J. Nickels. Antifungal activity in Saccharomyces cerevisiae is modulated by calcium signalling. Mol. Microbiol. 46:257-268, 2002.
   
   
4. Jain, P., I. Akula, and T. Edlind. The cyclic AMP signalling pathway modulates susceptibility of Candida species and Saccharomyces cerevisiae to antifungal azoles and other sterol biosynthesis inhibitors. Antimicrob. Agents Chemother. 47:3195-3201, 2003.
   
   
5. Edlind, T.D. Molecular detection of antifungal resistance. In: Molecular Microbiology: Diagnostic Principles and Practice (eds., D.H. Persing et al.), ASM Press, Washington D.C., 2003.
   
   
6. Vermitsky, J. P., and T. D. Edlind. Azole resistance in Candida glabrata: coordinate upregulation of multidrug transporters and evidence for a Pdr1-like transcription factor. Antimicrob. Agents Chemother., 48: 3773-3781, 2004.
   
   
7. Edlind, T. D., Henry, K. W., Vermitsky, J. -P., Edlind, M. P., Raj, S., and S. K. Katiyar. Promoter-dependent disruption of genes: simple, rapid, and specific PCR-based method with application to three different yeast. Curr. Gen., 48: 117-125, 2005.
   
   
8. Vermitsky, J. -P., Earhart, K. D., Smith, W. L., Homayouni, R., Edlind, T. D., and P. D. Rogers.  Pdr1 regulates multidrug resistance in Candida glabrata: gene disruption and genome-wide expression studies. Mol. Microbiol., 61: 704-722, 2006.
   
   
9. Katiyar, S., Pfaller, M., and T. Edlind. Characterization of Candida albicans and Candida glabrata clinical isolates exhibiting reduced echinocandin susceptibility. Antimicrob. Agents Chemother., 50: 2892-2894, 2006.
   
   
10. T. D. Edlind.  Emergence and evolution of antifungal resistance. In: Evolutionary Biology of Bacterial and Fungal Pathogens (eds., F. Baquero, C. Nombela, G.H. Cassell, and J.A. Gutierrez). ASM Press, Washington, DC, 2007.


11. Guillermo, G. E., Katiyar, S. K., Park, S., Edlind, T. D., and D. S. Perlin. A naturally-occurring Fks1p proline to alanine amino acid change in Candida parapsilosis, Candida orthopsilosis and Candida metapsilosis acounts for reduced echinocandin susceptibility. Antimicrob. Agents Chemother., in press, 2008.