1338. Cryptococcus neoformans cell wall integrity provides defense to superoxide and photo generated ROS but not hydrogen peroxide
Session: Oral Abstract Session: Fungal Pathogenesis, Virulence, and Anti-fungal Therapy
Saturday, October 22, 2011: 2:45 PM
Room: 151AB
Background: Within a human host, Cryptococcus neoformans is subjected to host defenses that pose a threat to fungal survival. Reactive oxygen and nitrogen species are part of the host-defense arsenal against C. neoformans. Oxidative stress is caused by reactive oxygen species (ROS), produced by phagocytic cells and as a product of normal cell metabolism. Particularly in the brain, C. neoformans encounters nitrosative stress in the form of reactive nitrogen species produced by various nitric oxide isoforms. The fungal cell maintains integrity in the presence of stressors via the cell wall, a structure unique to fungi among eukaryotes. The cell wall integrity (CWI) pathway reacts to environmental stresses and strengthens the cell wall. An important part of the CWI pathway is the Rho1 guanyl nucleotide exchange factor, Rom2.

Methods: Using a C. neoformans rom2 mutant strain we were able to evaluate the requirement for the cell wall integrity in defense to various oxidative and nitrosative stresses by observing growth in the presence of oxidative stressors. We also exposed cells to a photoactivatable dye to determine if the rom2 mutant was susceptible to ROS.

Results: We found that ROM2 is required for defense to superoxide but not hydrogen peroxide. Further, we found that ROM2 is required for defense against nitrosative stress. When the defense to oxidative stress is damaged, as with the rom2 mutant, C. neoformans is susceptible to photodynamic activation using a polycationic conjugate between polyethylenimine and the PS chlorin(e6). 

Conclusion: Photoactivated dyes produce either singlet oxygen or other ROS such as superoxide and hydroxyl radicals, but in either case it is thought that ROS primarily react with the microbial cell wall leading to membrane permeabilization and cell death. Our findings indicate that permeabilization of the cell wall can allow ROS to gain entry and kill fungi, suggesting a potential therapy development in the future whereby drugs are designed to weaken the cell wall, making fungi susceptible to host defenses; or for added effect, could be used in combination with direct delivery of ROS at the infection site.

Subject Category: M. Mycology including clinical and basic studies of fungal infections

Beth Fuchs, Ph.D., Infectious Diseases, Massachusetts General Hospital, Boston, MA, George Tegos, Ph.D., University of New Mexico, Albuquerque, NM, Michael Hamblin, Ph.D., Massachusetts General Hospital, Boston, MA and Eleftherios Mylonakis, M.D., Ph. D., Massachusetts General Hospital, Harvard Medical School, BOSTON, MA


B. Fuchs, None

G. Tegos, None

M. Hamblin, None

E. Mylonakis, Astella: Grant Investigator and Research Contractor, Consulting fee and Research grant
T2 Biosystems: Grant Investigator, Grant recipient

Findings in the abstracts are embargoed until 12:01 a.m. EST Thursday, Oct. 20 with the exception of research findings presented at IDSA press conferences.