TY - JOUR
T1 - Isolation and in vitro susceptibility to amphoterecin B, itraconazole and posaconazole of voriconazole-resistant laboratory isolates of Aspergillus fumigatus
AU - Manavathu, E. K.
AU - Abraham, O. C.
AU - Chandrasekar, P. H.
PY - 2001/3
Y1 - 2001/3
N2 - Objectives. To select voriconazole-resistant mutants of Aspergillus fumigatus in the laboratory from drug-susceptible clinical isolates and examine their in vitro susceptibility to amphotericin B and investigational azoles, and to compare the intramycelial accumulation of voriconazole in the resistant isolates with that in the susceptible parent. Methods. Voriconazole-resistant Aspergillus fumigatus isolates were selected in the laboratory from three highly susceptible (MIC ≤ 0.5 mg/L) clinical isolates by stepwise selection on peptone yeast extract glucose (PYG) agar containing 0.5 mg and 4 mg voriconazole/L. Twenty-three colonies that grew in the presence of 4 mg voriconazole/L on PYG agar (frequency 1.9 × 10-8) were tested for their in vitro susceptibility to amphotericin B, itraconazole, voriconazole and posaconazole by a broth macrodilution technique. The accumulation of voriconazole in the mycelia of two representative resistant isolates (VCZ-W42 and VCZ-W45) was determined by a previously described bioassay. Results. The geometric mean MICs (mg/L) of amphotericin B, itraconazole, voriconazole and posaconazole for these isolates were 0.45 ± 0.19, 0.69 ± 0.45, 5.24 ± 3.74 and 0.27 ± 0.18, respectively. A comparison of the geometric mean MICs of the antifungals obtained for the resistant isolates to those of the susceptible parents showed 1.15-, 2.76-, 16.90- and 1.42-fold increases, respectively, for amphotericin B, itraconazole, voriconazole and posaconazole, suggesting that low-level cross-resistance exists between the azole antifungals. The susceptible parent and the resistant isolates accumulated similar amounts of voriconazole. Conclusions. These results suggest that spontaneous mutants of Aspergillus fumigatus resistant to voriconazole could emerge among clinical isolates under selection pressure and that the observed reduced in vitro susceptibility to voriconazole may not be due to reduced accumulation of the drug in the mycelia.
AB - Objectives. To select voriconazole-resistant mutants of Aspergillus fumigatus in the laboratory from drug-susceptible clinical isolates and examine their in vitro susceptibility to amphotericin B and investigational azoles, and to compare the intramycelial accumulation of voriconazole in the resistant isolates with that in the susceptible parent. Methods. Voriconazole-resistant Aspergillus fumigatus isolates were selected in the laboratory from three highly susceptible (MIC ≤ 0.5 mg/L) clinical isolates by stepwise selection on peptone yeast extract glucose (PYG) agar containing 0.5 mg and 4 mg voriconazole/L. Twenty-three colonies that grew in the presence of 4 mg voriconazole/L on PYG agar (frequency 1.9 × 10-8) were tested for their in vitro susceptibility to amphotericin B, itraconazole, voriconazole and posaconazole by a broth macrodilution technique. The accumulation of voriconazole in the mycelia of two representative resistant isolates (VCZ-W42 and VCZ-W45) was determined by a previously described bioassay. Results. The geometric mean MICs (mg/L) of amphotericin B, itraconazole, voriconazole and posaconazole for these isolates were 0.45 ± 0.19, 0.69 ± 0.45, 5.24 ± 3.74 and 0.27 ± 0.18, respectively. A comparison of the geometric mean MICs of the antifungals obtained for the resistant isolates to those of the susceptible parents showed 1.15-, 2.76-, 16.90- and 1.42-fold increases, respectively, for amphotericin B, itraconazole, voriconazole and posaconazole, suggesting that low-level cross-resistance exists between the azole antifungals. The susceptible parent and the resistant isolates accumulated similar amounts of voriconazole. Conclusions. These results suggest that spontaneous mutants of Aspergillus fumigatus resistant to voriconazole could emerge among clinical isolates under selection pressure and that the observed reduced in vitro susceptibility to voriconazole may not be due to reduced accumulation of the drug in the mycelia.
KW - Antifungal resistance
KW - Aspergillus fumigatus
KW - Posaconazole
KW - Susceptibility studies
KW - Vorioconazole
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U2 - 10.1046/j.1469-0691.2001.00220.x
DO - 10.1046/j.1469-0691.2001.00220.x
M3 - Article
C2 - 11318811
AN - SCOPUS:0035295450
SN - 1198-743X
VL - 7
SP - 130
EP - 137
JO - Clinical Microbiology and Infection
JF - Clinical Microbiology and Infection
IS - 3
ER -