In-vitro isolation and antifungal susceptibility of amphotericin B-resistant mutants of Aspergillus fumigatus.
Aspergillus fumigatus mutants resistant to amphotericin B were selected in the laboratory following UV irradiation. A total of 18 colonies (frequency 1.8 x 10(-7)) that grew in the presence of amphotericin B (8 mg/L and 16 mg/L) on peptone yeast extract glucose agar were tested for their susceptibility to amphotericin B, nystatin, azoles, and the echinocandin L-743872. Ten of the 18 isolates showed an eight-fold rise in amphotericin B MIC (4 mg/L) compared with the susceptible parent whereas the remaining isolates showed a 16 to 32-fold rise in amphotericin B MIC (8-16 mg/L). Subculturing of three representatives from each of the groups that had MIC values of 4 mg/L and 8-16 mg/L for six cycles revealed that the resistance trait was stably expressed. All amphotericin B-resistant isolates showed a significant level of cross-resistance to nystatin but not to azoles and L-743872. Kill-curve studies with amphotericin B revealed that the killing of the resistant isolates was significantly less than that of the susceptible parent strain. These results show that amphotericin B-resistant mutants of A. fumigatus can be isolated in the laboratory following a single-step UV-induced mutagenesis and suggest that similar mechanisms could operate in nature for the emergence of resistance in clinical isolates.
Manavathu
E K
EK
Department of Medicine, Wayne State University, Detroit, MI 48201, USA. emanavat@med.wayne.edu
Alangaden
G J
GJ
Chandrasekar
P H
PH
D000666:Amphotericin B / Q000494:pharmacology*; D000935:Antifungal Agents / Q000494:pharmacology*; D001232:Aspergillus fumigatus / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification*; D004352:Drug Resistance, Microbial / Q000235:genetics; D008826:Microbial Sensitivity Tests; D008828:Microbiological Techniques; D014466:Ultraviolet Rays
D000935:Antifungal Agents; D000666:Amphotericin B