Intrinsic in vitro susceptibility of primary clinical isolates of Aspergillus fumigatus, Aspergillus terreus, Aspergillus nidulans, Candida albicans and Candida lusitaniae against amphotericin B

The Environmental Spread of Aspergillus terreus in Tyrol, Austria

Fungal infections due to Aspergillus species have become a major cause of morbidity and mortality among immunocompromised patients. At the Medical University of Innsbruck, A. terreus and related species are the second most common causative agents of aspergillosis. In this one-year study we collected environmental samples to investigate (i) the environmental distribution, (ii) the ecological niche of A. terreus in Tyrol, (iii) the genetic relatedness of environmental and clinical isolates and the correlation between those two groups of isolates, and (iv) the antifungal susceptibility patterns. A. terreus was present in 5.4% of 3845 environmental samples, with a significantly higher frequency during winter (6.8%) than summer (3.9%). An increased A. terreus abundance in Tyrol’s Eastern part was detected which is in agreement with the proof of clinical cases. In total, 92% of environmental and 98% of clinical A. terreus isolates were amphotericin B resistant; 22.6% and 9.8% were resistant against posaconazole. Overall, 3.9% of clinical isolates were resistant against voriconazole. Short tandem repeat analysis identified three major genotypes persisting in Tyrol. Soil from agricultural cornfields seems to be an important source; the environmental frequency of A. terreus correlates with the high incidence of A. terreus infections in certain geographical areas.

Genetic diversity and antifungal susceptibility patterns of Aspergillus nidulans complex obtained from clinical and environmental sources

The molecular epidemiology and antifungal susceptibility of Aspergillus nidulans species complex has not been well studied. To evaluate the genetic diversity and antifungal susceptibility patterns of clinical and environmental isolates of A. nidulans complex. Sixty clinical and environmental isolates of Aspergillus section Nidulantes were collected from five countries (Iran, The Netherlands, Spain, Portugal and Greece). The species were molecularly identified by sequencing of β-tubulin gene. The genetic diversity of A nidulans complex isolates (n = 54) was determined with a microsatellite genotyping assay. Antifungal susceptibility profile was determined using EUCAST method. The isolates were classified as A nidulans (46.7%), A spinulosporus (26.6%), A quadrilineatus (10%), A pachycristatus (3.3%), A rugulosus (3.3%), A unguis (5%), A creber, (1.7%), A olivicola (1.7%) and A sydowii (1.7%). Thirty-four sequence types (STs) were identified among the 54 A nidulans complex isolates. A high level of genetic diversity was found among A nidulans sensu stricto strains but low diversity was found among A spinulosporus strains. Amphotericin B showed high MICs to all species. The most active azole was posaconazole (GM = 0.64 mg/L), while itraconazole showed the highest MICs among azoles (GM = 2.95 mg/L). A spinulosporus showed higher MICs than A nidulans sensu stricto for all antifungals except for micafungin and anidulafungin. Interspecies variations may result in differences in antifungal susceptibility patterns and challenge antifungal therapy in infections caused by A nidulans. Differences in the distribution of STs or persistence of multiple STs might be related to the sources of isolation and niche specialisation.

A role for the unfolded protein response (UPR) in virulence and antifungal susceptibility in Aspergillus fumigatus

Filamentous fungi rely heavily on the secretory pathway, both for the delivery of cell wall components to the hyphal tip and the production and secretion of extracellular hydrolytic enzymes needed to support growth on polymeric substrates. Increased demand on the secretory system exerts stress on the endoplasmic reticulum (ER), which is countered by the activation of a coordinated stress response pathway termed the unfolded protein response (UPR). To determine the contribution of the UPR to the growth and virulence of the filamentous fungal pathogen Aspergillus fumigatus, we disrupted the hacA gene, encoding the major transcriptional regulator of the UPR. The ΔhacA mutant was unable to activate the UPR in response to ER stress and was hypersensitive to agents that disrupt ER homeostasis or the cell wall. Failure to induce the UPR did not affect radial growth on rich medium at 37°C, but cell wall integrity was disrupted at 45°C, resulting in a dramatic loss in viability. The ΔhacA mutant displayed a reduced capacity for protease secretion and was growth-impaired when challenged to assimilate nutrients from complex substrates. In addition, the ΔhacA mutant exhibited increased susceptibility to current antifungal agents that disrupt the membrane or cell wall and had attenuated virulence in multiple mouse models of invasive aspergillosis. These results demonstrate the importance of ER homeostasis to the growth and virulence of A. fumigatus and suggest that targeting the UPR, either alone or in combination with other antifungal drugs, would be an effective antifungal strategy.

The pathogenic mold Aspergillus fumigatus is the leading cause of airborne fungal infections in immunocompromised patients. The fungus normally resides in compost, an environment that challenges the organism to obtain nutrients by degrading complex organic polymers. This is accomplished by secreted enzymes, some of which may also contribute to nutrient acquisition during infection. Extracellular enzymes are folded in the endoplasmic reticulum (ER) prior to secretion. If the folding capacity of the ER is overwhelmed by increased secretory demand, the resulting ER stress triggers an adaptive response termed the unfolded protein response (UPR). In this study, we uncover a previously unknown function for the master transcriptional regulator of the UPR, HacA, in fungal virulence. In the absence of HacA, A. fumigatus was unable to secrete high levels of proteins and had reduced virulence in mice. In addition, loss of HacA caused a cell wall defect and increased susceptibility to two major classes of antifungal drugs used for the treatment of aspergillosis. These findings demonstrate that A. fumigatus relies on HacA for growth in the host environment and suggest that therapeutic targeting of the UPR could have merit against A. fumigatus, as well as other eukaryotic pathogens with highly developed secretory systems.

Proteomic and transcriptomic analysis of Aspergillus fumigatus on exposure to amphotericin B

Amphotericin B (AMB) is the most widely used polyene antifungal drug for the treatment of systemic fungal infections, including invasive aspergillosis. It has been our aim to understand the molecular targets of AMB in Aspergillus fumigatus by genomic and proteomic approaches. In transcriptomic analysis, a total of 295 genes were found to be differentially expressed (165 upregulated and 130 downregulated), including many involving the ergosterol pathway, cell stress proteins, cell wall proteins, transport proteins, and hypothetical proteins. Proteomic profiles of A. fumigatus alone or A. fumigatus treated with AMB showed differential expression levels for 85 proteins (76 upregulated and 9 downregulated). Forty-eight of them were identified with high confidence and belonged to the above-mentioned categories. Differential expression levels for Rho-GDP dissociation inhibitor (Rho-GDI), secretory-pathway GDI, clathrin, Sec 31 (a subunit of the exocyst complex), and RAB GTPase Ypt51 in response to an antifungal drug are reported here for the first time and may represent a specific response of A. fumigatus to AMB. The expression of some of these genes was validated by real-time reverse transcription-PCR. The AMB responsive genes/proteins observed to be differentially expressed in A. fumigatus may be further explored for novel drug development.

Emericella quadrilineata as cause of invasive aspergillosis

We noted a cluster of 4 cases of infection or colonization by Emericella spp., identified by sequence-based analysis as E. quadrilineata. Sequence-based analysis of an international collection of 33 Emericella isolates identified 12 as E. nidulans, all 12 of which had previously been identified by morphologic methods as E. nidulans. For 12 isolates classified as E. quadrilineata, only 6 had been previously identified accordingly. E. nidulans was less susceptible than E. quadrilineata to amphotericin B (median MICs 2.5 and 0.5 mg/L, respectively, p<0.05); E. quadrilineata was less susceptible than E. nidulans to caspofungin (median MICs, 1.83 and 0.32 mg/L, respectively, p<0.05). These data indicate that sequence-based identification is more accurate than morphologic examination for identifying Emericella spp. and that correct species demarcation and in vitro susceptibility testing may affect patient management.

Comparison of disk diffusion, E-test and broth microdilution test in determination of susceptibility of Aspergillus species to amphotericin B, itraconazole and voriconazole

In response to the recent increase in Aspergillus infections, new antifungal agents have become available accompanied by studies on antifungal susceptibility tests for epidemiological follow-up. The aim of this study was to compare the efficacy of Clinical Laboratory Standards Institute (CLSI) M 38-A broth microdilution test with the disk diffusion and E-test in determining the susceptibility of Aspergillus spp. to amphotericin B, itraconazole and voriconazole. The study was carried out on 18 A. fumigatus, 7 A. flavus, 5 A. niger and 2 A. versicolor strains isolated from clinical samples. The microdilution method was performed by following the instructions of CLSI M 38-A. The E-test and disk diffusion tests were performed according to the instructions of their manufacturers. The percent agreement between the E-test and CLSI M38-A broth microdilution test at 24 (48) h within +/- 2 dilutions was, respectively, 81% (69%) for amphotericin B, 75% (72%) for itraconazole and 85% (81%) for voriconazole. The disk diffusion test showed good correlation with the E-test but poor correlation with the broth microdilution test for the three antifungal agents we tested. In conclusion, E-test and disk diffusion test have their advantages such as ease of application and interpretation, but their correlation with the broth microdilution should be improved.

Meta-analysis of nebulized amphotericin B to prevent or treat pulmonary aspergillosis in immunosuppressed animals

OBJECTIVES

Pulmonary aspergillosis in immunosuppressed patients is associated with significant mortality and morbidity. We assessed the prophylactic and therapeutic effect of nebulized amphotericin B (AmB) on mortality of immunosuppressed animals with pulmonary aspergillosis in this meta-analysis.

METHODS

Literature search was based on MEDLINE (1966 to January 15, 2007), EMBASE, and Cochrane-Controlled Trials Register (2006 issue 4) databases. Only randomized-controlled studies comparing nebulized AmB with placebo on immunosuppressed animals were included. Two reviewers reviewed and extracted the data independently.

RESULTS

Eight studies including 839 immunosuppressed animals were considered. The overall mortality of the immunosuppressed animals with pulmonary aspergillosis treated with nebulized AmB was reduced (69.4% versus 87.7%, odds ratio [OR] 0.12, 95% confidence interval [CI]: 0.08-0.19; P < 0.0001). The effect of nebulized AmB on mortality was more significant when the drug was administered as prophylaxis before the inoculation of Aspergillus fumigatus (OR 0.07, 95% CI: 0.03-0.12, P = 0.0001; I(2) = 0) than as a therapeutic agent (OR 0.20, 95% CI: 0.11-0.36, P < 0.0001; I(2) = 0) (ratio of the 2 ORs = 2.86, 95% CI: 1.03-6.11; P = 0.04). The effectiveness of AmB desoxycholate (OR 0.16, 0.06-0.38, P < 0.0001; I(2) = 0) and lipid-associated (liposomal, or lipid complex or colloidal dispersion) amphotericin (OR 0.11, 95% CI: 0.06-0.20, P < 0.0001; I(2) = 0) was not significantly different (ratio of the 2 ORs = 1.46, 95% CI: 0.49-4.39; P = 0.50). Three studies evaluated the potential side effects of nebulized amphotericin and showed that there was no significant renal toxicity but the amphotericin desoxycholate had some detrimental effects on pulmonary surfactant function.

CONCLUSIONS

The use of nebulized amphotericin, either as a prophylactic or therapeutic agent, is effective in reducing mortality of immunosuppressed animals with pulmonary aspergillosis. A large randomized controlled trial is needed to confirm whether combining nebulized amphotericin with systemic antifungal agents will reduce mortality in immunosuppressed patients with suspected or proven pulmonary aspergillosis.

Safety of aerosolized liposomal versus deoxycholate amphotericin B formulations for prevention of invasive fungal infections following lung transplantation: a retrospective study

BACKGROUND

Nebulized amphotericin B deoxycholate (AmBd) has been used to prevent invasive pulmonary aspergillosis after lung transplantation.

METHODS

In this retrospective study we compared the safety and tolerability of nebulized AmBd and nebulized liposomal amphotericin B (L-AmB) in 38 consecutive lung transplant recipients. Progress notes, medication administration records, microbiology, and pulmonary function reports were reviewed. Histologic sections from lung tissue were examined. Plasma amphotericin B levels were measured.

RESULTS

A total of 1206 doses of AmBd and 1149 doses of L-AmB were administered. Eighteen patients received AmBd only, 11 received L-AmB only, and 9 received the medications sequentially. The total number of complaints vs. the number of doses administered was 1.0% for AmBd-treated patients and 1.2% for L-AmB-treated patients. No differences were observed between the treatment groups on lung biopsy specimens. Plasma amphotericin B levels were <0.2-0.9 microg/mL in AmBd-treated patients and <0.2 microg/mL in L-AmB-treated patients.

CONCLUSIONS

In lung transplant recipients, both inhaled AmBd and L-AmB were safe and well tolerated over a large number of medication exposures.

Is there a role for polyenes in treating invasive mycoses?

PURPOSE OF REVIEW

This is a clinical review on the current role of polyene antifungals in the treatment of invasive fungal infections. It is timely and relevant because the number of new antifungals being developed has never been greater than today. In addition to re-examining the landmark clinical trials of the past, the more recent findings are put into perspective. The past year has been particularly rich in clinical trials.

RECENT FINDINGS

The main topics of this review are invasive candidiasis, invasive aspergillosis, and the so-called rare fungal infections: zygomycosis, fusariosis, cryptococcosis and histoplasmosis.

SUMMARY

Practical implications of the recent developments are the almost complete replacement of amphotericin B deoxycholate by lipid-based formulations; antifungal efficacy without compromising safety; and treatment choices for infections previously considered untreatable.