Use of voriconazole in a patient with aspergilloma caused by an itraconazole-resistant strain of Aspergillus fumigatus.

The case is reported of a patient with cavitary sarcoidosis complicated by an aspergilloma caused by an itraconazole-resistant strain of Aspergillus fumigatus, who was treated with voriconazole. The authors suggest that susceptibility testing of A. fumigatus strains is of value during long-term therapy with itraconazole, and that voriconazole may be a good option for treatment of patients infected with itraconazole-resistant strains of A. fumigatus.

Azole and fungicide resistance in clinical and environmental Aspergillus fumigatus isolates.

Aspergillus fumigatus is a human pathogen but it is also a widespread filamentous fungus in the environment. A. fumigatus can therefore be exposed to antifungals used in medical and agricultural environments. Only the class of azoles is used in both of these environments (i.e. voriconazole and itraconazole in medicine; prochloraz, propiconazole or imazalil in agriculture). Exposure to azoles provides the potential for the development of resistance. Several clinical itraconazole-resistant isolates have been reported in A. fumigatus and their resistance mechanisms have been partially resolved. Since limited data exist on the susceptibility of A. fumigatus to both medical and agricultural antifungals, we undertook a drug susceptibility study including clinical (400) and agricultural (150) A. fumigatus isolates (Swiss origin). We tested azoles and also compounds of major antifungal classes used in agriculture (i.e. azoxystrobin, iprodione, benalaxyl or cyprodinil). The results showed that all A. fumigatus isolates were intrinsically resistant to iprodione, benalaxyl or cyprodinil (MIC90 > 32 microg x ml(-1)) and that azoxystrobin minimal inhibitory concentrations (MICs) showed a wide range (0.06 to 32 microg x ml(-1)). MIC ranges of azoles were compound-dependent. MIC90 for voriconazole, itraconazole, imazalil and prochloraz were within a range of 0.13 to 1 microg x ml(-1) and similar between clinical and environmental isolates, whereas propiconazole was the least active compound (MIC90: 4-8 microg x ml(-1)). Ten clinical and 36 environmental isolates with high itraconazole MIC ( > or = 2 microg x ml(-1)) were detected. In clinical isolates, no cross-resistance was observed between itraconazole and all others azoles tested. Several patterns of azole MICs were, however, observed in the environmental isolates. Unexpectedly, a single environmental isolate was voriconazole-resistant (MIC of 16 microg x ml(-1)) but still susceptible to itraconazole (MIC of 2 microg x ml(-1)). Taken together, our results demonstrate the absence of susceptibility of A. fumigatus isolates to non-azole agricultural agents and that there is little impact of azole resistance in both clinical and environmental isolates. When detected, azole resistance was compound-specific.

Pneumocystis jiroveci dihydropteroate synthase polymorphisms confer resistance to sulfadoxine and sulfanilamide in Saccharomyces cerevisiae.

Failure of anti-Pneumocystis jiroveci prophylaxis with sulfa drugs is associated with mutations within the putative active site of the fungal dihydropteroate synthase (DHPS), an enzyme encoded by the multidomain FAS gene. This enzyme is involved in the essential biosynthesis of folic acid. The most frequent polymorphisms are two mutations leading to two amino acid changes ((55)Trp-Arg-(57)Pro to (55)Ala-Arg-(57)Ser), observed as a single or double mutation in the same P. jiroveci isolate. In the absence of a culture method for P. jiroveci, we studied potential resistance to sulfa drugs conferred by these polymorphisms by using Saccharomyces cerevisiae as a model. Single or double mutations identical to those observed in the DHPS domain of the P. jiroveci FAS gene were introduced by in vitro site-directed mutagenesis into alleles of the S. cerevisiae FOL1 gene, which is the orthologue of the P. jiroveci FAS gene. The mutated alleles were integrated at the genomic locus in S. cerevisiae and expressed by functional complementation in a strain with a disrupted FOL1 allele. The single mutation (55)Trp to (55)Ala conferred resistance to sulfanilamide, whereas the single mutation (57)Pro to (57)Ser conferred resistance to both sulfanilamide and sulfadoxine. Both single mutations also separately conferred hypersensitivity to sulfamethoxazole and dapsone. The resistance to sulfadoxine is consistent with epidemiological data on P. jiroveci. The double mutation (55)Trp-Arg-(57)Pro to (55)Ala-Arg-(57)Ser conferred on S. cerevisiae a requirement for p-aminobenzoate, suggesting reduced affinity of DHPS for this substrate. This characteristic is commonly observed in mutated DHPS enzymes conferring sulfa drug resistance from other organisms. However, the double mutation conferred hypersensitivity to sulfamethoxazole, which is not in agreement with epidemiological data on P. jiroveci. Taken together, our results suggest that the DHPS polymorphisms observed in P. jiroveci confer sulfa drug resistance on this pathogen.