Initial Characterization of Occidiofungin's Activity and Toxicity

D. Ellis, J. L. Smith, D. Gordon, S-E. Lu, F. Austin

Author address: 

Mississippi State Univ., Mississippi State, MS.


Background: Occidiofungin, a product of Burkholderia contaminans MS14, is a cyclic glycol-lipopeptide (1200.6 Da). We hypothesize that occidiofungin has a typical lipopeptide toxicity profile and is potent against Candida spp. Methods: Temperature stability and antifungal activity against isolates of Candida, according to the CLSI method, were determined using a microtiter plate assay. Two clinical isolates of C. albicans and one clinical isolate of C. glabrata were tested along with three quality control strains; C. albicans (ATCC 66027), C. tropicalis (ATCC 66029), and C. parapsilosis (ATCC 90018). An in vitro toxicity screen was performed using a rat hepatoma (H4IIE) cell line. Occidiofungin was added to the plates at concentrations of 0 to 10 μM, with equivalent concentrations of rotenone used as a control. After 24 hour exposure, the cells and cell supernatant were harvested for analysis. α -Glutathione, S-transferase, Tetrazolium Dye Reduction, and Cellular Adenosine Triphosphate (ATP) assays were used to determine the TC50 value. Results: Heating to 50°C for 30 min and 100°C for 30 min resulted in no loss and a 4-fold loss in activity, respectively. MIC values of all the Candida isolates were either 1.0 or 0.5 μg/mL. Toxicity was observed in all variables at 5 μM concentration, with a predicted TC50 value of 3 μM. The natural products used to synthesize the clinically used antifungals micafungin, caspofungin, and anidulafungin are toxic lipopeptides. These lipopeptides are modified to reduce toxicity and presumably the same results can be achieved with occidiofungin. The toxicity profile of occidiofungin is typical of membrane disruption. The cells remain viable, until a critical threshold is reached causing a loss of membrane integrity. This is unlike the rotenone control that is toxic due to inhibition of mitochondrial electron transport, where a dose dependent response is observed. Conclusion: Occidiofungin is heat stable and is a potent antifungal against Candida spp. Its toxicity profile is similar to other lipopeptides used clinically. The peptide nucleus of occidiofungin may be useful for synthesizing derivatives with less toxicity.

abstract No: 


Full conference title: 

110th General Meeting American Society for Microbiology
    • ASM 110th (2010)