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In vitro activities of polyene and imidazole antifungal agents against unusual opportunistic fungal pathogens
N A Rotowa1, H J Shadomy, S Shadomy
1Department of Microbiology and Immunology, Medical College of Virginia, Virginia Commonwealth University, Richmond.
Abstract:
Guidelines for the treatment of infections caused by unusual opportunistic fungi are limited and available in vitro data are scanty. In vitro susceptibility tests, employing an agar dilution procedure, were performed with amphotericin B (AMB), natamycin (NTC), itraconazole (ICZ), and ketoconazole (KTZ). Two media were used: Kimmig's agar (KA) and Yeast Morphology Agar (YMA). Fungi tested included isolates (n) of Acremonium spp. (10), Cunninghamella spp. (6), Fusarium spp. (18), Pseudallescheria boydii (14), and Trichosporon beigelii (5). All Acremonium and Cunninghamella isolates were susceptible to NTC (MIC less than or equal to 4 micrograms/ml) but many appeared to be resistant to AMB, (MIC greater than or equal to 32 micrograms/ml), KTZ and ICZ (MIC greater than or equal to 128 micrograms/ml). Most isolates of Fusarium spp. were susceptible to both AMB and NTC (MIC90 = 4 micrograms/ml); one isolate was cross-resistant to both polyenes (MIC greater than 32 micrograms/ml). Only two of 18 Fusarium isolates appeared susceptible to the imidazoles (MIC less than or equal to 4 micrograms/ml); the remaining isolates exhibited high MICs (greater than or equal to 64 micrograms/ml). All 14 isolates of P. boydii were susceptible to NTC (MIC less than or equal to 4 micrograms/ml) but four appeared to be resistant to AMB (MIC greater than or equal to 32 micrograms/ml). Most isolates of P. boydii were susceptible to both KTZ (MIC less than or equal to 4 micrograms/ml) and ICZ (MIC less than or equal to 16 micrograms/ml) but two isolates appeared to be resistant (MIC greater than or equal to 16 micrograms/ml).(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
This study evaluated antifungal drug susceptibility for unusual opportunistic fungi. Natamycin (NTC) showed broad-spectrum activity, while resistance varied for amphotericin B (AMB), ketoconazole (KTZ), and itraconazole (ICZ).
Area of Science:
- Medical Mycology
- Antimicrobial Susceptibility Testing
- Opportunistic Fungal Infections
Background:
- Limited treatment guidelines exist for infections caused by unusual opportunistic fungi.
- In vitro antifungal susceptibility data for these fungi are scarce.
- This study addresses the need for more comprehensive in vitro data.
Purpose of the Study:
- To determine the in vitro susceptibility of various unusual opportunistic fungi to four antifungal agents.
- To compare the efficacy of amphotericin B (AMB), natamycin (NTC), itraconazole (ICZ), and ketoconazole (KTZ) against specific fungal isolates.
Main Methods:
- Agar dilution method was employed for in vitro susceptibility testing.
- Two media, Kimmig's agar (KA) and Yeast Morphology Agar (YMA), were utilized.
- Tested fungal isolates included Acremonium spp., Cunninghamella spp., Fusarium spp., Pseudallescheria boydii, and Trichosporon beigelii.
Main Results:
- Natamycin (NTC) demonstrated susceptibility across all tested Acremonium and Cunninghamella isolates.
- Fusarium spp. showed susceptibility to AMB and NTC, but resistance to ketoconazole (KTZ) and itraconazole (ICZ).
- Pseudallescheria boydii isolates were susceptible to NTC and generally to KTZ and ICZ, with some resistance noted to AMB.
Conclusions:
- Natamycin (NTC) appears to be a promising agent against Acremonium, Cunninghamella, and Pseudallescheria boydii.
- Significant resistance to azoles (KTZ, ICZ) was observed in Fusarium spp.
- Further in vitro and clinical studies are warranted to guide treatment strategies for these challenging infections.