Itraconazole resistance in Aspergillus fumigatus

Abstract

Invasive aspergillosis is an increasingly frequent opportunistic infection in immunocompromised patients. Only two agents, amphotericin B and itraconazole, are licensed for therapy. Itraconazole acts through inhibition of a P-450 enzyme undertaking sterol 14alpha demethylation. In vitro resistance in Aspergillus fumigatus to itraconazole correlated with in vivo outcome has not been previously described. For three isolates (AF72, AF90, and AF91) of A. fumigatus from two patients with invasive aspergillosis itraconazole MICs were elevated. A neutropenic murine model was used to establish the validity of the MICs. The isolates were typed by random amplification of polymorphic DNA. Analysis of sterols, inhibition of cell-free sterol biosynthesis from [14C] mevalonate, quantitation of P-450 content, and [3H]itraconazole concentration in mycelial pellets were used to determine the mechanisms of resistance. The MICs for the three resistant isolates were >16 microg/ml. In vitro resistance was confirmed in vivo for all three isolates. Molecular typing showed the isolates from the two patients to be genetically distinct. Compared to the susceptible isolate from patient 1, AF72 had a reduced ergosterol content, greater quantities of sterol intermediates, a similar susceptibility to itraconazole in cell-free ergosterol biosynthesis, and a reduced intracellular [3H]itraconazole concentration. In contrast, AF91 and AF92 had slightly higher ergosterol and lower intermediate sterol concentrations, fivefold increased resistance in cell-free systems to the effect of itraconazole on sterol 14alpha demethylation, and intracellular [3H] itraconazole concentrations found in susceptible isolates. Resistance to itraconazole in A. fumigatus is detectable in vitro and is present in wild-type isolates, and at least two mechanisms of resistance are responsible.

Antifungal drug resistance in molds: Clinical and microbiological factors

“…Ever since A. fumigatus isolates showing high MICs to azoles were described [32], subsequent reports has shown that this issue deserves permanent surveillance [15]. The rate of itraconazole resistance in vitro (MIC > 8 mg/L) is about 2% among clinical strains of A. fumigatus [22].…”

Tagging of genes involved in multidrug resistance in Aspergillus nidulans

“…Little work has been published concerning drug resistance in pathogenic Aspergillus species. Denning et al (1997a) have reported the occurrence of itraconazole resistance in A. fumigatus and provided evidence for two dierent resistance mechanisms: drug eux and target modi®ca-tion. In A. nidulans, resistance to the azole fungicide imazalil can be determined by mutations in at least eight dierent genes (van Tuyl 1977).…”

“…It is now clear that antifungals can create clinical and epidemiological situations that are analogous to those found with antibiotic-resistant bacteria (Rex et al 1995;Albertson et al 1996;Kelly et al 1996;Denning et al 1997aDenning et al , 1997bJoseph-Horne and Hollomon 1997;Nolte et al 1997). The typical determinants of multiple drug resistance, i.e.…”

Arzneimitteltherapie invasiver Candida- und Aspergillusinfektionen

“…Caillot et al konnten zeigen, dass beispielsweise die Ausdehnung pulmonaler Infiltrate in der Computertomographie der Lungen während der ersten 2 Behandlungswochen im Median um das Vierfache zunimmt und bei konsequenter Weiterbehandlung erst danach langsam aber sicher zurückgeht [11]. Eine Resistenz von Aspergillus fumigatus gegen Itraconazol kann bereits bei Wildtypstämmen vorliegen [17] und ist damit auch unter Therapie mit einem aspergilluswirksamen Azolderivat mög-lich. Die dazu geeigneten Resistenzmechanismen wie MDR1-Expression (Multidrug Resistance Effluxpumpe an der Zellmembran), Amplifikation der C14-Demethylase oder der Austausch von Basenpaaren im Bereich der Zielgene sind hinreichend identifiziert [67].…”