Sterol composition of itraconazole-resistant and itraconazole-susceptible isolates of Aspergillus fumigatus Eric Dannaoui, Florence Persat, Elisabeth Borel, Marie-Antoinette Piens, and Stéphane Picot Abstract: Sterol composition of four clinical isolates of Aspergillus fumigatus resistant to itraconazole was determined by gas chromatography – mass spectrometry and compared with that of four susceptible strains. For all strains, the ma- jor sterol was ergosterol. Sterol compositions were qualitatively and quantitatively similar for the resistant and suscepti- ble strains. These results suggest that itraconazole resistance is not related, for the strains studied, to alterations in the ergosterol synthesis pathway. Key words: Aspergillus fumigatus, itraconazole resistance, sterol composition. Résumé : La composition en stérols de quatre souches d’Aspergillus fumigatus, d’origine clinique, résistantes à l’itraconazole a été déterminée par chromatographie gazeuse couplée à la spectrométrie de masse et comparée avec celle de quatre souches sensibles. Chez toutes les souches, le principal stérol était l’ergostérol. Les compositions en stérols étaient qualitativement et quantitativement similaires chez les souches sensibles et chez les souches résistantes. Ces résultats suggèrent que la résistance à l’itraconazole n’est pas liée, pour les souches étudiées, à des modifications de la voie de synthèse de l’ergostérol. Mots clés : Aspergillus fumigatus, résistance à l’itraconazole, composition en stérol. 710 Dannaoui et al. Introduction The incidence of invasive infections caused by Aspergillus spp. has risen dramatically in recent years (Denning 1998). This partly reflects the increasing number of patients with neutropenia resulting from cancer treatment and transplant procedures. Invasive aspergillosis remains a life-threatening infection, and amphotericin B and itraconazole are currently the only two antifungal drugs available for treatment (Georgopapadakou and Walsh 1994). Nevertheless, the over- all success rate with either amphotericin B or itraconazole therapy is 34% (Denning 1998). Although azole drug resis- tance in yeasts has markedly increased in the last years (Johnson and Warnock 1995), it is only recently that resis- tance of Aspergillus fumigatus to itraconazole in vitro has been reported (Chryssanthou 1997; Dannaoui et al. 1999b; Denning et al. 1997). The in vitro detected resistance has been confirmed in vivo in animal models for some strains (Dannaoui et al. 1999a, 2001; Denning et al. 1997). Itraconazole is an azole antifungal agent that prevents the synthesis of ergosterol, the main sterol in fungi. This effect originates from selective inhibition of the 14- α-demethylase system (Vanden Bossche 1987). The consequences of 14- α- demethylase inhibition are depletion of ergosterol and accu- mulation of 14- α-methyl sterols, which cause alterations in membrane fluidity and growth arrest. Azole resistance in fungi can be related to different mechanisms (Vanden Bossche et al. 1998). One of these is inactivation of sterol C5-6 desaturase, which leads to the accumulation of inter- mediate sterols (White et al. 1998). To determine if itra- conazole resistance in A. fumigatus is mediated by an alteration of the sterol C5-6 desaturase, we compared the sterol composition of several clinical isolates of A. fumigatus that were susceptible and resistant to itraconazole. Materials and methods Organisms All strains were isolated in our laboratory. Four isolates (AF 1112, AF 1119, AF 1237, and AF 1290) were recovered from the same patient in whom an aspergilloma with subsequent evolution to chronic necrotizing aspergillosis was diagnosed. AF 1112 and AF 1119 were isolated from sputum before any antifungal treat- ment, and AF 1237 and AF 1290 were cultured after 4–5 months of itraconazole therapy. Molecular typing has shown the common identity of these four isolates (Dannaoui et al. 2001). AF 1412, AF 1422, and AF 1979 were cultured from three different patients with Can. J. Microbiol. 47: 706–710 (2001) © 2001 NRC Canada 706 DOI: 10.1139/cjm-47-8-706 Received November 20, 2000. Revision received May 14, 2001. Accepted May 16, 2001. Published on the NRC Research Press Web site at http://cjm.nrc.ca on August 2, 2001. E. Dannaoui, 1,2 F. Persat, E. Borel, M.-A. Piens, and S. Picot. Laboratoire de parasitologie, Mycologie médicale et pathologie exotique, Université Claude-Bernard Lyon I, 8, avenue Rockefeller, 69373 Lyon CEDEX, France. 1 Corresponding author (e-mail: e.dannaoui@mmb.azn.nl). 2 Present address: The Department of Medical Microbiology, Division of Mycology, University Medical Center St. Radboud, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.