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Fungicidal properties of defensin NP-1 and activity against Cryptococcus neoformans in vitro
M S Alcouloumre1, M A Ghannoum, A S Ibrahim
1Division of Infectious Diseases, St. John's Cardiovascular Research Center, LAC-Harbor UCLA Medical Center, University of California-Los Angeles School of Medicine, Torrance 90509.
Abstract:
Defensin NP-1, derived from the neutrophils of rabbits, was tested for its fungistatic and fungicidal activity against strains of Cryptococcus neoformans. The MICs for the encapsulated strains tested ranged from 3.75 to 15.0 micrograms of NP-1 per ml. The minimum fungicidal concentrations for these strains were similar to the MICs. An acapsular strain, however, had a lower MIC of 0.93 and minimum fungicidal concentration of 1.88 micrograms/ml. NP-1 demonstrated time-dependent and concentration-dependent killing of C. neoformans. Killing occurred rapidly in the first 20 min of exposure to NP-1 and was maximum at 90 to 120 min. Killing of C. neoformans by NP-1 was concentration dependent with 31% +/- 9% survival at 25 micrograms/ml, 13% +/- 4% survival at 50 micrograms/ml, 9% +/- 5% survival at 75 micrograms/ml, and 5% +/- 3% survival at 100 micrograms/ml. NP-1's fungicidal effect on C. neoformans was also inoculum dependent, with increased activity observed at 10(4) versus 10(5) or 10(6) cells per ml. In addition, stationary-phase C. neoformans was less susceptible to NP-1 killing than yeast cells in the logarithmic phase. Subinhibitory concentrations of both NP-1 (0.25 x MIC) and fluconazole (0.25 x MIC) acted synergistically in inhibiting growth of C. neoformans. Similar combinations of NP-1 and amphotericin B, however, did not yield synergy.
Insights
Rabbit defensin NP-1 shows fungicidal activity against Cryptococcus neoformans, with enhanced efficacy at lower cell concentrations and synergistic effects with fluconazole. This research highlights NP-1
Area of Science:
- Antimicrobial Peptides
- Mycology
- Infectious Diseases
Background:
- Cryptococcus neoformans is a significant fungal pathogen causing life-threatening infections, particularly in immunocompromised individuals.
- Defensins are a class of antimicrobial peptides with broad-spectrum activity, including against fungi.
- Rabbit defensin NP-1 is a neutrophil-derived peptide with potential antifungal properties that warrant investigation.
Purpose of the Study:
- To evaluate the fungistatic and fungicidal activity of rabbit defensin NP-1 against Cryptococcus neoformans.
- To determine the influence of inoculum size, growth phase, and drug combinations on NP-1's efficacy.
- To assess the synergistic potential of NP-1 with established antifungal agents like fluconazole and amphotericin B.
Main Methods:
- Minimum Inhibitory Concentrations (MICs) and Minimum Fungicidal Concentrations (MFCs) were determined for NP-1 against encapsulated and acapsular C. neoformans strains.
- Time-kill kinetics, concentration-dependent killing, inoculum-dependent activity, and growth phase susceptibility were assessed.
- Checkerboard assays were employed to evaluate the synergistic effects of NP-1 in combination with fluconazole and amphotericin B.
Main Results:
- NP-1 exhibited fungistatic and fungicidal activity against C. neoformans, with MICs ranging from 3.75 to 15.0 µg/ml for encapsulated strains and 0.93 µg/ml for an acapsular strain.
- Killing was time-dependent, rapid within 20 minutes, and maximal at 90-120 minutes, showing concentration-dependent efficacy.
- NP-1 demonstrated increased activity against lower inoculums (10^4 cells/ml) and logarithmic-phase yeast cells; NP-1 and fluconazole showed synergistic inhibition, unlike NP-1 and amphotericin B.
Conclusions:
- Rabbit defensin NP-1 possesses significant fungicidal activity against Cryptococcus neoformans.
- NP-1's efficacy is influenced by factors such as fungal strain characteristics, inoculum size, and growth phase.
- The combination of NP-1 with fluconazole shows promise for synergistic antifungal therapy against C. neoformans.