Antifungal drug resistance in Aspergillus

Analysis of glycosylinositol phosphorylceramides expressed by the opportunistic mycopathogen Aspergillus fumigatus

Acidic glycosphingolipid components were extracted from the opportunistic mycopathogen Aspergillus fumigatus and identified as inositol phosphorylceramide and glycosylinositol phosphorylceramides (GIPCs). Using nuclear magnetic resonance sppectroscopy, mass spectrometry, and other techniques, the structures of six major components were elucidated as Ins-P-Cer (Af-0), Manp(alpha1-->3)Manp(alpha1-->2)Ins-P-Cer (Af-2), Manp(alpha1-->2)Manp(alpha1-->3)Manp(alpha1-->2)Ins-P-Cer (Af-3a), Manp(alpha1-->3)[Galf(beta1-->6)]Manp(alpha1-->2)-Ins-P-Cer (Af-3b), Manp(alpha1-->2)-Manp(alpha1-->3)[Galf(beta1-->6)]Manp(alpha1-->2)Ins-P-Cer (Af-4), and Manp(alpha1-->3)Manp(alpha1-->6)GlcpN(alpha1-->2)Ins-P-Cer (Af-3c) (where Ins = myo-inositol and P = phosphodiester). A minor A. fumigatus GIPC was also identified as the N-acetylated version of Af-3c (Af-3c*), which suggests that formation of the GlcNalpha1-->2Ins linkage may proceed by a two-step process, similar to the GlcNalpha1-->6Ins linkage in glycosylphosphatidylinositol (GPI) anchors (transfer of GlcNAc, followed by enzymatic de-N-acetylation). The glycosylinositol of Af-3b, which bears a distinctive branching Galf(beta1-->6) residue, is identical to that of a GIPC isolated previously from the dimorphic mycopathogen Paracoccidioides brasiliensis (designated Pb-3), but components Af-3a and Af-4 have novel structures. Overlay immunostaining of A. fumigatus GIPCs separated on thin-layer chromatograms was used to assess their reactivity against sera from a patient with aspergillosis and against a murine monoclonal antibody (MEST-1) shown previously to react with the Galf(beta1-->6) residue in Pb-3. These results are discussed in relation to pathogenicity and potential approaches to the immunodiagnosis of A. fumigatus.

Economic evaluation of voriconazole versus caspofungin for the treatment of invasive aspergillosis in Spain

BACKGROUND AND OBJECTIVE

Invasive fungal infections are becoming increasingly prevalent and are more frequently the aetiological agents responsible for nosocomial infections. Since mid-2002, two new antifungal drugs - voriconazole, a third-generation azole, and caspofungin, a member of a new class of drugs called echinocandins - have been marketed in Spain. Both drugs have proven [corrected] efficacy in the treatment of aspergillosis, are better tolerated than amphotericin B and are cheaper [corrected] than liposomal amphotericin B. The objective of this study was to conduct an economic evaluation of voriconazole versus caspofungin for the treatment of invasive aspergillosis in Spain.

METHODS

This was a cost-minimisation analysis (2006 costs) from the hospital perspective. Duration of treatment and bodyweight of patients were obtained from the Fungcost study and the incidence of adverse events was obtained from different published sources. Only direct costs were considered. Mean expected cost and incremental cost were calculated, and univariate and bivariate (bodyweight/treatment duration) sensitivity analyses were conducted.

RESULTS

The mean expected cost per episode was 6041.93 euro (intravenous treatment acquisition cost 5524.75 euro) for voriconazole and 7174.05 euro (intravenous treatment acquisition cost 6672.80 euro) for caspofungin in invasive aspergillosis; the incremental cost was 1132.18 euro. Results were robust for any treatment duration and sensitive to bodyweights <103.42 kg.

CONCLUSION

Voriconazole is a more cost-effective option than caspofungin in invasive aspergillosis in patients with a bodyweight <103.42 kg.

Enhancement of fludioxonil fungicidal activity by disrupting cellular glutathione homeostasis with 2,5-dihydroxybenzoic acid

The activity of fludioxonil, a phenylpyrrole fungicide, is elevated by coapplication of the aspirin/salicylic acid metabolite, 2,5-dihydroxybenzoic acid (2,5-DHBA). Fludioxonil activity is potentiated through a mitogen-activated protein kinase (MAPK) pathway that regulates osmotic/oxidative stress-responses. 2,5-DHBA disrupts cellular GSH (reduced glutathione)/GSSG (oxidized glutathione) homeostasis, further stressing the oxidative stress-response system. This stress enhances fludioxonil activity. 2,5-DHBA treatment also prevents tolerance of MAPK mutants resistant to fludioxonil.

Filamentous fungi in a tertiary care hospital: environmental surveillance and susceptibility to antifungal drugs

OBJECTIVE

To evaluate filamentous fungi with respect to environmental load and potential drug resistance in a tertiary care teaching hospital.

DESIGN

Monthly survey in 2 buildings of the hospital during a 12-month period.

SETTING

Hippokration Hospital in Thessaloniki, Greece.

METHODS

Air, surface, and tap water sampling was performed in 4 departments with high-risk patients. As sampling sites, the solid-organ transplantation department and the hematology department (in the older building) and the pediatric oncology department and the pediatric intensive care unit (in the newer building) were selected.

RESULTS

From January to May of 2000, the fungal load in air (FLA) was low, ranging from 0 to 12 colony-forming units (cfu) per m(3) in both buildings. During the summer months, when high temperature and humidity predominate, the FLA increased to 4-56 cfu/m(3). The fungi commonly recovered from culture of air specimens were Aspergillus niger (25.9%), Aspergillus flavus (17.7%), and Aspergillus fumigatus (12.4%). Non-Aspergillus filamentous fungi, such as Zygomycetes and Dematiaceous species, were also recovered. The pediatric intensive care unit had the lowest mean FLA (7.7 cfu/m(3)), compared with the pediatric oncology department (8.7 cfu/m(3)), the solid-organ transplantation department (16.1 cfu/m(3)), and the hematology department (22.6 cfu/m(3)). Environmental surfaces were swabbed, and 62.7% of the swab samples cultured yielded filamentous fungi similar to the fungi recovered from air but with low numbers of colony-forming units. Despite vigorous sampling, culture of tap water yielded no fungi. The increase in FLA observed during the summer coincided with renovation in the building that housed the solid-organ transplantation and hematology departments. All 54 Aspergillus air isolates randomly selected exhibited relatively low minimum inhibitory or effective concentrations for amphotericin B, itraconazole, voriconazole, posaconazole, micafungin, and anidulafungin.

CONCLUSION

Air and surface fungal loads may vary in different departments of the same hospital, especially during months when the temperature and humidity are high. Environmental Aspergillus isolates are characterized by lack of resistance to clinically important antifungal agents.

Role of antifungal susceptibility testing in patient management

PURPOSE OF REVIEW

The review focuses on the evolving role of antifungal susceptibility testing in the clinical management of patients with invasive fungal infections. It will clarify how to clinically interpret available susceptibility testing methods.

RECENT FINDINGS

Fluconazole susceptibility testing for yeasts has now shown a relationship between fluconazole resistance and therapeutic failure. Of increasing concern are the reported cases of fluconazole cross-resistance to the newer triazoles. The correlation between amphotericin B and echinocandin susceptibility testing for yeasts, resistance, and outcomes is unknown. Although there are reports of clinical failures with echinocandins, resistance is uncommon and susceptibility testing is unhelpful. There are standardized methods of testing for the triazoles and amphotericin B against molds; however, resistance has not been correlated with outcomes due to host and laboratory factors. Knowing the intrinsic resistance of molds to particular antifungals is of greater importance. Posaconazole is a potent new antifungal agent against many difficult-to-treat molds including fusariosis and zygomycosis.

SUMMARY

Antifungal susceptibility testing of yeasts can assist in treating patients with prior antifungal exposure in determining resistance or cross-resistance. Mold susceptibility testing is of limited clinical benefit, while posconazole is an exciting new agent for treating difficult invasive fungal infections.

The concentration-dependent nature of in vitro amphotericin B–itraconazole interaction against Aspergillus fumigatus: isobolographic and response surface analysis of complex pharmacodynamic interactions

The interaction between polyenes and azoles is not well understood. We therefore explored the in vitro combination of amphotericin B with itraconazole against 14 clinical Aspergillus fumigatus isolates (9 itraconazole susceptible and 5 itraconazole resistant) with a colorimetric broth microdilution checkerboard technique using two drug interaction models able to explore complicated patterns of interactions: the response surface analysis of Bliss independence and the isobolographic analysis of Loewe additivity zero interaction theories. Synergy was found at combinations with low concentrations of amphotericin B (<0.125 mg/L), whereas antagonism was found at combinations with higher concentrations of amphotericin B. For itraconazole-resistant isolates, synergistic interactions were observed at high concentrations of itraconazole (>0.5 mg/L). Synergy was more frequently observed for the itraconazole-resistant isolates than for the itraconazole-susceptible isolates.

Multi-azole resistance in Aspergillus fumigatus

Azole resistance in Aspergillus spp. is unusual. We report a patient who received long-term treatment with itraconazole and voriconazole for bilateral chronic cavitary aspergillosis with aspergillomas whose isolates of Aspergillus fumigatus developed simultaneous resistance to itraconazole and voriconazole. A novel mutation (G138C) in the target gene (cyp51A) encoding 14alpha-demethylase was detected. The patient had some response to intravenous caspofungin, which he received six times weekly, without the development of resistance over 9 months.

The echinocandins: comparison of their pharmacokinetics, pharmacodynamics and clinical applications

Caspofungin, micafungin and anidulafungin are three drugs of the echinocandin class of antifungals available for intravenous treatment of invasive candidiasis and aspergillosis. They exhibit high in vitro and in vivo activities against Candida spp. and Aspergillus spp. In various clinical studies investigating candidemia and invasive candidiasis, Candida esophagitis, and fever in neutropenia, the clinical efficacy of the echinocandin tested was similar to that of established antifungals. Antifungal activity against strains no longer susceptible to conventional antifungal agents, such as fluconazole and amphotericin B suggests that echinocandins can be used as salvage therapy in life-threatening fungal infections. There is no cross-resistance to other antifungals. Excellent safety and tolerability of treatment with caspofungin has been documented over a total of 4.3 million patient days. Echinocandins are poor substrates of the cytochrome P450 enzyme family and can be safely co-administered with most drugs without the need for dosage adaptation. No dose reduction is required in renal impairment. A reduction in the daily maintenance dose has been recommended for caspofungin, but not for micafungin and anidulafungin in patients presenting with mild to moderate hepatic failure.

Use of Posaconazole in the Management of Invasive Orbital Aspergillosis in a Cat

Orbital infection with Aspergillus fumigatus was diagnosed in a Persian cat that was presented with chronic third eyelid protrusion and exophthalmos. Evidence of nasal, sinus, or disseminated aspergillosis was not detected in this cat. Complete surgical excision of diseased tissues was not possible during orbital exenteration, and infection subsequently extended into the tissues of the oral cavity. Oral therapy with itraconazole and parenteral therapy with amphotericin B were ineffective in resolving the infection. Oral therapy with a novel triazole, posaconazole, was curative.

Reducing the cost of resistance; experimental evolution in the filamentous fungus Aspergillus nidulans

We have studied compensatory evolution in a fludioxonil resistant mutant of the filamentous fungus Aspergillus nidulans. In an evolution experiment lasting for 27 weeks (about 3000 cell cycles) 35 parallel strains of this mutant evolved in three different environmental conditions. Our results show a severe cost of resistance (56%) in the absence of fludioxonil and in all conditions the mutant strain was able to restore fitness without loss of the resistance. In several cases, the evolved strain reached a higher fitness than the original sensitive ancestor. Fitness compensation occurred in one, two or three discrete steps. Genetic analysis of crosses between different evolved strains and between evolved and ancestral strains revealed interaction between compensatory mutations and provided information on the number of loci involved in fitness compensation. In addition, we discuss the opportunities for the experimental study of evolutionary processes provided by the filamentous fungus A. nidulans.

Infectious Disease Update: New Anti-Microbials

Effective antimicrobials are critical in controlling one of the most common conditions encountered in medicine, namely, skin and skin structure infections. Unfortunately, the identification of appropriate and novel antimicrobials is continually challenged by the emergence of antimicrobial resistance among bacteria, fungi, and parasites. This work will focus on describing novel antibacterials and antifungals approved by the United States Food and Drug Administration in the past 4 years.

Voriconazole treatment for subacute invasive and chronic pulmonary aspergillosis

BACKGROUND

Voriconazole is a novel triazole antifungal with a broad spectrum including Aspergillus species. We conducted an open, noncomparative multicenter study to evaluate the efficacy and safety of voriconazole in subacute invasive and chronic pulmonary aspergillosis (CPA).

METHODS

Patients without profound neutropenia and a proven or probable diagnosis of subacute invasive aspergillosis (IA) or CPA received voriconazole 200 mg twice daily for a period of 4-24 weeks as primary or salvage therapy. Dose escalation was allowed if efficacy was suboptimal, and toleration and safety were satisfactory. Response was assessed by clinical, radiological and mycological changes. A complete or partial response in subacute IA and improved or stable in CPA were assessed as favorable responses.

RESULTS

Of 39 patients treated, 36 were assessable. The majority of patients had subacute IA (n = 21), proven in all 11 extra-pulmonary and in 23/25 (92%) of the pulmonary cases. Voriconazole was given as primary therapy in 22 (61%). All patients receiving salvage therapy (n = 14) had refractory IA, having failed itraconazole or amphotericin B (AmB) or both. Overall, a complete or partial response was seen in 9/21(43%) of subacute IA and improved or stable in 12/15 (80%) of those with CPA. Adverse events, mainly liver function test abnormalities, skin reactions, and visual disturbances were mild and transient, leading to early discontinuation of treatment in 5 cases.

CONCLUSIONS

In patients with subacute IA and CPA, voriconazole was efficacious as salvage or primary therapy.

Update on antifungal drug resistance mechanisms of Aspergillus fumigatus

Although the arsenal of agents with anti-Aspergillus activity has expanded over the last decade, mortality due to invasive aspergillosis (IA) remains unacceptably high. Aspergillus fumigatus still accounts for the majority of cases of IA; however less susceptible to antifungals non-fumigatus aspergilli began to emerge. Antifungal drug resistance of Aspergillus might partially account for treatment failures. Recent advances in our understanding of mechanisms of antifungal drug action in Aspergillus, along with the standardization of in vitro susceptibility testing methods, has brought resistance testing to the forefront of clinical mycology. In addition, molecular biology has started to shed light on the mechanisms of resistance of A. fumigatus to azoles and the echinocandins, while genome-based assays show promise for high-throughput screening for genotypic antifungal resistance. Several problems remain, however, in the study of this complex area. Large multicenter clinical studies--point prevalence or longitudinal--to capture the incidence and prevalence of antifungal resistance in A. fumigatus isolates are lacking. Correlation of in vitro susceptibility with clinical outcome and susceptibility breakpoints has not been established. In addition, the issue of cross-resistance between the newer triazoles is of concern. Furthermore, in vitro resistance testing for polyenes and echinocandins is difficult, and their mechanisms of resistance are largely unknown. This review examines challenges in the diagnosis, epidemiology, and mechanisms of antifungal drug resistance in A. fumigatus.

Antifungal susceptibility testing in Aspergillus spp. according to EUCAST methodology

The availability of new antifungal agents has multiplied the demand for in vitro antifungal susceptibility testing for Aspergillus spp. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) has charged its Antifungal Susceptibility Testing Subcommittee (AFST-EUCAST) with the preparation of new guidelines for in vitro susceptibility testing of antifungals against Aspergillus spp (EUCAST-AST-ASPERGILLUS). This committee has modified the reference method for broth dilution antifungal susceptibility testing of filamentous fungi (M38-A) as follows: (i) RPMI 1640 supplemented with 2% glucose (RPMI 2%G) as assay medium, (ii) inoculum preparation by conidium counting in a haemocytometer and (iii) an inoculum size of 2×105-5×105 CFU/ml. The incubation time is about 48 h at 35°C and MIC is read visually. The MIC value is a no-growth visual endpoint. The standard method described herein is intended to provide a valid and economic method for testing the susceptibility to antifungal agents of Aspergillus spp., to identify resistance, and to facilitate an acceptable degree of conformity, e.g. agreement within specified ranges and between laboratories in measuring the susceptibility.

The ergosterol biosynthesis pathway, transporter genes, and azole resistance in Aspergillus fumigatus

The continuous use of triazoles can result in the development of drug resistance. Azole-resistant clinical isolates, spontaneous and induced mutants of Aspergillus fumigatus have been documented. The azoles block the ergosterol biosynthesis pathway by inhibiting the enzyme 14-alpha-demethylase, product of the CYP51. Fungal azole resistance involves both amino acid changes in the target site that alter drug-target interactions and those that decrease net azole accumulation. The reduced intracellular accumulation has also been correlated with overexpression of multidrug resistance (MDR) efflux transporter genes of the ATP-binding cassette (ABC) and the major facilitator superfamily (MFS) classes. About 20 genes are involved in the A. fumigatus ergosterol biosynthesis pathway. There are several duplicated genes in this pathway. Interestingly, erg3 and erg11 showed two copies in A. fumigatus. In general, Aspergillus spp. have proportionally more MFS transporter encoding genes than Saccharomyces cerevisiae, S. pombe, and Neurospora crassa. The drug H+ (12 and 14 spanners) sub-families are also proportionally greater than in the other species. Although the numbers of ABC transporter encoding genes are comparable, again the Aspergillus spp. have more ABC transporters related to multidrug permease than the other fungal species.

Actividad in vitro de las equinocandinas ¿Cómo debe evaluarse?

Echinocandins are a novel class of antifungal drugs. They have good activity against Candida spp and Aspergillus spp. Their low selective toxicity allows their administration at high doses with few secondary side effects. We have reviewed the available data on the endpoints for these drugs in their in vitro susceptibility testing on yeasts and moulds. The microdilution broth method is the most commonly used technique and MIC-1 (80% of growth inhibition) seems to be the most reliable endpoint when yeasts are tested. This endpoint also seems to be the most appropriate for the different drugs when they are combined with echinocandins using the checkerboard method for testing yeasts. By contrast, in the case of moulds, the minimum effective concentration (MEC) correlates better with the in vivo activity than the MIC when echinocandins are tested, and when these drugs are combined with other antifungals, MIC-2 (50% of growth inhibition) seems the most appropriate endpoint. Criteria based on drug pharmacodynamics is the most useful to define the echinocandin endpoints that best correlate with their in vivo efficacy.

Amino acid substitution in Trichophyton rubrum squalene epoxidase associated with resistance to terbinafine

There has only been one clinically confirmed case of terbinafine resistance in dermatophytes, where six sequential Trichophyton rubrum isolates from the same patient were found to be resistant to terbinafine and cross-resistant to other squalene epoxidase (SE) inhibitors. Microsomal SE activity from these resistant isolates was insensitive to terbinafine, suggesting a target-based mechanism of resistance (B. Favre, M. Ghannoum, and N. S. Ryder, Med. Mycol. 42:525-529, 2004). In this study, we have characterized at the molecular level the cause of the resistant phenotype of these clinical isolates. Cloning and sequencing of the SE gene and cDNA from T. rubrum revealed the presence of an intron in the gene and an open reading frame encoding a protein of 489 residues, with an equivalent similarity (57%) to both yeast and mammalian SEs. The nucleotide sequences of SE from two terbinafine-susceptible strains were identical whereas those of terbinafine-resistant strains, serially isolated from the same patient, each contained the same single missense introducing the amino acid substitution L393F. Introduction of the corresponding substitution in the Candida albicans SE gene (L398F) and expression of this gene in Saccharomyces cerevisiae conferred a resistant phenotype to the transformants when compared to those expressing the wild-type sequence. Terbinafine resistance in these T. rubrum clinical isolates appears to be due to a single amino acid substitution in SE.

Antifungal protein PAF severely affects the integrity of the plasma membrane of Aspergillus nidulans and induces an apoptosis-like phenotype

The small, basic, and cysteine-rich antifungal protein PAF is abundantly secreted into the supernatant by the beta-lactam producer Penicillium chrysogenum. PAF inhibits the growth of various important plant and zoopathogenic filamentous fungi. Previous studies revealed the active internalization of the antifungal protein and the induction of multifactorial detrimental effects, which finally resulted in morphological changes and growth inhibition in target fungi. In the present study, we offer detailed insights into the mechanism of action of PAF and give evidence for the induction of a programmed cell death-like phenotype. We proved the hyperpolarization of the plasma membrane in PAF-treated Aspergillus nidulans hyphae by using the aminonaphtylethenylpyridinium dye di-8-ANEPPS. The exposure of phosphatidylserine on the surface of A. nidulans protoplasts by Annexin V staining and the detection of DNA strand breaks by TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) gave evidence for a PAF-induced apoptotic-like mechanism in A. nidulans. The localization of reactive oxygen species (ROS) by dichlorodihydrofluorescein diacetate and the abnormal cellular ultrastructure analyzed by transmission electron microscopy suggested that ROS-elicited membrane damage and the disintegration of mitochondria played a major role in the cytotoxicity of PAF. Finally, the reduced PAF sensitivity of A. nidulans strain FGSC1053, which carries a dominant-interfering mutation in fadA, supported our assumption that G-protein signaling was involved in PAF-mediated toxicity.

Combined activity in vitro of caspofungin, amphotericin B, and azole agents against itraconazole-resistant clinical isolates of Aspergillus fumigatus

Interactions in vitro between amphotericin B, itraconazole, voriconazole, and caspofungin against itraconazole-resistant Aspergillus fumigatus clinical strains were determined. Differential results were obtained depending on the criteria (MIC or minimal effective concentration) used. Caspofungin and voriconazole exhibited the most potent interactions, with synergy against at least 50% of isolates, and the average fractional concentration index was 0.38. Antagonism was not found for any combination.

Cholesterol import by Aspergillus fumigatus and its influence on antifungal potency of sterol biosynthesis inhibitors

High mortality rates from invasive aspergillosis in immunocompromised patients are prompting research toward improved antifungal therapy and better understanding of fungal physiology. Herein we show that Aspergillus fumigatus, the major pathogen in aspergillosis, imports exogenous cholesterol under aerobic conditions and thus compromises the antifungal potency of sterol biosynthesis inhibitors. Adding serum to RPMI medium led to enhanced growth of A. fumigatus and extensive import of cholesterol, most of which was stored as ester. Growth enhancement and sterol import also occurred when the medium was supplemented with purified cholesterol instead of serum. Cells cultured in RPMI medium with the sterol biosynthesis inhibitors itraconazole or voriconazole showed retarded growth, a dose-dependent decrease in ergosterol levels, and accumulation of aberrant sterol intermediates. Adding serum or cholesterol to the medium partially rescued the cells from the drug-induced growth inhibition. We conclude that cholesterol import attenuates the potency of sterol biosynthesis inhibitors, perhaps in part by providing a substitute for membrane ergosterol. Our findings establish significant differences in sterol homeostasis between filamentous fungi and yeast. These differences indicate the potential value of screening aspergillosis antifungal agents in serum or other cholesterol-containing medium. Our results also suggest an explanation for the antagonism between itraconazole and amphotericin B, the potential use of Aspergillus as a model for sterol trafficking, and new insights for antifungal drug development.

Antifungal susceptibilities of clinical isolates of Candida species, Cryptococcus neoformans, and Aspergillus species from Taiwan: surveillance of multicenter antimicrobial resistance in Taiwan program data from 2003

The susceptibilities of nonduplicate isolates to six antifungal agents were determined for 391 blood isolates of seven Candida species, 70 clinical isolates (from blood or cerebrospinal fluid) of Cryptococcus neoformans, and 96 clinical isolates of four Aspergillus species, which were collected in seven different hospitals in Taiwan (as part of the 2003 program of the study group Surveillance of Multicenter Antimicrobial Resistance in Taiwan). All isolates of Candida species other than C. glabrata and C. krusei were susceptible to fluconazole. Among the 59 C. glabrata isolates, 16 (27%) were not susceptible to fluconazole, and all were dose-dependently susceptible or resistant to itraconazole. For three (5.1%) C. glabrata isolates, voriconazole MICs were 2 to 4 microg/ml, and for all other Candida species isolates, voriconazole MICs were </=0.5 microg/ml. The proportions of isolates for which amphotericin B MICs were >/=2 microg/ml were 100% (3 isolates) for C. krusei, 11% (23 of 207 isolates) for Candida albicans, 3.0% (2 of 67 isolates) for Candida tropicalis, 20% (12 of 59 isolates) for C. glabrata, and 0% for both Candida parapsilosis and Candida lusitaniae. For three (4%) Cryptococcus neoformans isolates, fluconazole MICs were >/=16 microg/ml, and two (3%) isolates were not inhibited by 1 mug of amphotericin B/ml. For four (4.2%) of the Aspergillus isolates, itraconazole MICs were 8 microg/ml. Aspergillus flavus was less susceptible to amphotericin B, with the MICs at which 50% (1 microg/ml) and 90% (2 microg/ml) nsrsid417869\delrsid7301351 of isolates were inhibited being twofold greater than those for Aspergillus fumigatus and Aspergillus niger. All Aspergillus isolates were inhibited by </=1 microg of voriconazole/ml, including isolates with increased resistance to amphotericin B and itraconazole. This study revealed the emergence in Taiwan of decreased susceptibilities of Candida species to amphotericin B and of C. neoformans to fluconazole and amphotericin B. Voriconazole was the most potent agent against the fungal isolates tested, including fluconazole- and amphotericin B-nonsusceptible strains.

Rapid, high-throughput, multiplex, real-time PCR for identification of mutations in the cyp51A gene of Aspergillus fumigatus that confer resistance to itraconazole

Aspergillus fumigatus is an important cause of life-threatening invasive fungal disease in patients with compromised immune systems. Resistance to itraconazole in A. fumigatus is closely linked to amino acid substitutions in Cyp51A that replace Gly54. In an effort to develop a new class of molecular diagnostic assay that can rapidly assess drug resistance, a multiplexed assay was established. This assay uses molecular beacons corresponding to the wild-type cyp51A gene and seven mutant alleles encoding either Arg54, Lys54, Val54, Trp54, or Glu54. Molecular beacon structure design and real-time PCR conditions were optimized to increase the assay specificity. The multiplex assay was applied to the analysis of chromosomal DNA samples from a collection of 48 A. fumigatus clinical and laboratory-derived isolates, most with reduced susceptibility to itraconazole. The cyp51A allelic identities for codon 54 were established for all of the strains tested, and mutations altering Gly54 in 23 strains were revealed. These mutations included G(54)W (n = 1), G(54)E (n = 12), G(54)K (n = 3), G(54)R (n = 3), and G(54)V (n = 4). Molecular beacon assay results were confirmed by DNA sequencing. Multiplex real-time PCR with molecular beacons is a powerful technique for allele differentiation and analysis of resistance mutations that is dynamic and suitable for rapid high-throughput assessment of drug resistance.

Emerging fungal resistance

There has been an increase in systemic fungal infections over the past several decades, partially because of an increasing number of critically ill patients, surgical procedures, and immunosuppressive therapies, as well as the use of more invasive diagnostic and therapeutic medical procedures. Concomitant with this increase in infections has been the increase in azole-resistant Candida species and opportunistic molds with intrinsic resistance to many of the currently available antifungal agents. This review focuses on antifungal resistance, with emphasis on emerging resistance patterns and emerging fungi that are intrinsically resistant to antifungal agents.

Emerging fungal diseases: the importance of the host

More yeasts and molds are now recognized to cause more human disease than ever before. This development is not due to a change in the virulence of these fungi, but rather to changes in the human host. These changes include immunosuppression secondary to the pandemic of HIV, the use of life-saving advances in chemotherapy and organ transplantation, and the use of corticosteroids and other immunosuppressive agents to treat a variety of diseases. Fungi that were once considered common saprophytes are now recognized as potential pathogens in these patients. This situation necessitates better communication than ever between the clinician, pathologist, and clinical mycologist to ensure the prompt and accurate determination of the cause of fungal diseases.

Extra copies of the Aspergillus fumigatus squalene epoxidase gene confer resistance to terbinafine: genetic approach to studying gene dose-dependent resistance to antifungals in A. fumigatus

With the increasing use of antifungals such as amphotericin B, itraconazole, voriconazole, caspofungin, and terbinafine (TRB) in patients at high risk for invasive aspergillosis, resistance of Aspergillus fumigatus to these agents will ultimately emerge. Due to the limited availability of molecular genetics for A. fumigatus, few studies have addressed its mechanisms of resistance to antifungals. We transformed A. fumigatus protoplasts with a pyrG-based A. fumigatus genomic DNA library (constructed in the multicopy nonintegrating vector pRG3-AMA1-NotI, which also has the pyr-4 gene for selection). We obtained one pyrG(+) transformant that grew in medium containing a fungicidal concentration (0.625 microg/ml) of TRB. To determine whether TRB resistance in that transformant was plasmid dependent, we evicted the plasmid and found concomitant loss of uracil prototrophy and TRB resistance. DNA sequence analysis identified the gene responsible for TRB resistance as the A. fumigatus squalene epoxidase gene (ERG1), which encodes the target enzyme of TRB. Authentic A. fumigatus ERG1, amplified from the genome and cloned into pRG3-AMA1-NotI, also conferred TRB-specific resistance. This molecular approach has the potential to enhance our knowledge of the mechanisms of A. fumigatus resistance to modern antifungals.

Insight into the genome of Aspergillus fumigatus: analysis of a 922 kb region encompassing the nitrate assimilation gene cluster

Aspergillus fumigatus is the most ubiquitous opportunistic filamentous fungal pathogen of human. As an initial step toward sequencing the entire genome of A. fumigatus, which is estimated to be approximately 30 Mb in size, we have sequenced a 922 kb region, contained within 16 overlapping bacterial artificial chromosome (BAC) clones. Fifty-four percent of the DNA is predicted to be coding with 341 putative protein coding genes. Functional classification of the proteins showed the presence of a higher proportion of enzymes and membrane transporters when compared to those of Saccharomyces cerevisiae. In addition to the nitrate assimilation gene cluster, the quinate utilisation gene cluster is also present on this 922 kb genomic sequence. We observed large scale synteny between A. fumigatus and Aspergillus nidulans by comparing this sequence to the A. nidulans genetic map of linkage group VIII.

Potent synergistic in vitro interaction between nonantimicrobial membrane-active compounds and itraconazole against clinical isolates of Aspergillus fumigatus resistant to itraconazole

To develop new approaches for the treatment of invasive infections caused by Aspergillus fumigatus, the in vitro interactions between itraconazole (ITZ) and seven different nonantimicrobial membrane-active compounds--amiodarone (AMD), amiloride, lidocaine, lansoprazole (LAN), nifedipine (NIF), verapamil, and fluphenazine--against seven ITZ-susceptible and seven ITZ-resistant (ITZ-R) strains were evaluated by the checkerboard microdilution method based on National Committee for Clinical Laboratory Standards M-38A guidelines. The nature and the intensity of the interactions were assessed by a nonparametric approach (fractional inhibitory concentration [FIC] index model), a fully parametric response surface approach (Greco model) of the Loewe additivity no-interaction theory, and the nonparametric (Prichard model) and semiparametric response surface approaches of the Bliss independence (BI) no-interaction theory. Statistically significant synergy was found for the combination of ITZ and AMD and the combination of LAN and NIF, although with different intensities against ITZ-R strains. The FIC index values ranged from 1 to 0.02 for ITZ-AMD, 0.53 to 0.04 for ITZ-LAN, and 0.28 to 0.06 for ITZ-NIF. By use of the BI-based model, the strongest synergy was found for the combination of ITZ with AMD, followed by the combination of ITZ and NIF. The parametric models could not be fit adequately because most of the drugs alone did not show any effect and, thus, no sigmoid dose-response. In general, the combination of ITZ with calcium pump blockers displayed in vitro synergistic activity, primarily against ITZ-R strains, and warrants further investigation.

Invasive aspergillosis in patients with hematologic malignancies

Invasive aspergillosis is an increasingly common and often fatal opportunistic fungal infection in patients with hematologic malignancies. Prolonged and profound neutropenia remains a key risk factor for the development of invasive aspergillosis. However, qualitative deficiencies in host immune responses resulting from prolonged corticosteroid therapy, graft-versus-host disease, and cytomegalovirus infection are important risk factors for the recurrence and progression of Aspergillus infections after bone marrow recovery. Early diagnosis of invasive aspergillosis remains a challenge, and few tools are available for monitoring its course once the diagnosis is established. Even with the recent introduction of new antifungal therapies, mortality in patients with invasive aspergillosis remains high, and uniformly effective prophylaxis or preemptive therapeutic strategies are lacking. Strategies such as combination antifungal therapy and immunotherapy often are used as first-line treatment approaches in patients with documented invasive aspergillosis despite a paucity of clinical trial data. Recent advances in our understanding of the epidemiology, pathogenesis, and treatment of invasive aspergillosis in patients with hematologic malignancies are reviewed. The problems and controversies associated with defining optimal treatment strategies for invasive aspergillosis in this heavily immunocompromised population are highlighted.

In vitro activities of three licensed antifungal agents against spanish clinical isolates of Aspergillus spp

The aim of the present study was to identify retrospectively trends in the species distributions and the susceptibility patterns of Aspergillus species causing fungal infections in Spanish medical centers from 2000 to 2002. The susceptibilities of 338 isolates to amphotericin B, itraconazole, and voriconazole were tested. Aspergillus fumigatus was the most common species (54.7%), followed by Aspergillus terreus (14.8%) and Aspergillus flavus (13.9%). Non-A. fumigatus species were encountered in 45.3% of the samples studied. The majority of Aspergillus isolates were obtained from respiratory tract specimens, followed by ear and skin samples. The geometric mean (GM) MIC of amphotericin B was 0.56 micro g/ml, and the amphotericin B MIC was >2 micro g/ml for 16 isolates (4.7%). Nine of them were A. terreus. The GM MIC of itraconazole was 0.37, and the itraconazole MIC was >4 micro g/ml for 12 (3.5%) isolates. The voriconazole MICs were also high for 8 of the 12 strains for which itraconazole MICs were high (voriconazole MIC range, 2 to 8 micro g/ml).

Interlaboratory evaluation of hematocytometer method of inoculum preparation for testing antifungal susceptibilities of filamentous fungi

A three-laboratory study was performed to evaluate conidium counting in a hematocytometer as a technique of inoculum preparation for susceptibility testing of Aspergillus spp. In addition, inocula were quantified by colony counting and optical density determination. The agreement and correlation coefficient between conidium and colony quantifications were 89.2% and 0.73 (P < 0.01). Correlations with optical density determination were not significant.

Use of turbidimetric growth curves for early determination of antifungal drug resistance of filamentous fungi

A previously described microbroth kinetic system (J. Meletiadis, J. F. Meis, J. W. Mouton, and P. E. Verweij, J. Clin. Microbiol. 39:478-484, 2001) based on continuous monitoring of changes in the optical density of fungal growth was used to describe turbidimetric growth curves of different filamentous fungi in the presence of increasing concentrations of antifungal drugs. Therefore, 24 clinical mold isolates, including Rhizopus oryzae, Aspergillus fumigatus, Aspergillus flavus, and Scedosporium prolificans, were tested against itraconazole, terbinafine, and amphotericin B according to NCCLS guidelines. Among various parameters of the growth curves, the duration of the lag phase was strongly affected by the presence of antifungal drugs. Exposure to increasing drug concentrations resulted in prolonged lag phases of the turbidimetric growth curves. The lag phases of the growth curves at drug concentrations which resulted in more than 50% growth (for itraconazole and terbinafine) and more than 75% growth (for amphotericin B) after 24 h of incubation for R. oryzae, 48 h for Aspergillus spp., and 72 h for S. prolificans were 4 h longer than the lag phases of the growth curves at the corresponding drug-free growth controls which varied from 4.4 h for R. oryzae, 6.5 h for A. flavus, 7.9 h for A. fumigatus, and 11.6 h for S. prolificans. The duration of the lag phases showed small experimental and interstrain variability, with differences of less than 2 h in most of the cases. Using this system, itraconazole and terbinafine resistance (presence of >50% growth) as well as amphotericin B resistance (presence of >75% growth) was determined within incubation periods of 5.0 to 7.7 h for R. oryzae (for amphotericin B resistance incubation for up to 12 h was required), 8.8 to 11.4 h for A. fumigatus, 6.7 to 8.5 h for A. flavus, and 13 to 15.6 h for S. prolificans while awaiting formal MIC determination by the NCCLS reference method.

Glycosphingolipids of the model fungus Aspergillus nidulans: characterization of GIPCs with oligo-alpha-mannose-type glycans

Aspergillus nidulans is a well-established nonpathogenic laboratory model for the opportunistic mycopathogen, A. fumigatus. Some recent studies have focused on possible functional roles of glycosphingolipids (GSLs) in these fungi. It has been demonstrated that biosynthesis of glycosylinositol phosphorylceramides (GIPCs) is required for normal cell cycle progression and polarized growth in A. nidulans (Cheng, J., T.-S. Park, A. S. Fischl, and X. S. Ye. 2001. Mol. Cell Biol. 21: 6198-6209); however, the structures of A. nidulans GIPCs were not addressed in that study, nor were the functional significance of individual structural variants and the downstream steps in their biosynthesis. To initiate such studies, acidic GSL components (designated An-2, -3, and -5) were isolated from A. nidulans and subjected to structural characterization by a combination of one-dimensional (1-D) and 2-D NMR spectroscopy, electrospray ionization-mass spectrometry (ESI-MS), ESI-MS/collision-induced decomposition-MS (MS/CID-MS), ESI-pseudo-[CID-MS]2, and gas chromatography-MS methods. All three were determined to be GIPCs, with mannose as the only monosaccharide present in the headgroup glycans; An-2 and An-3 were identified as di- and trimannosyl inositol phosphorylceramides (IPCs) with the structures Man alpha 1-->3Man alpha 1-->2Ins1-P-1Cer and Man alpha 1-->3(Man alpha 1-->6)Man alpha 1-->2Ins1-P-1Cer, respectively (where Ins = myo-inositol, P = phosphodiester, and Cer = ceramide). An-5 was partially characterized, and is proposed to be a pentamannosyl IPC, based on the trimannosyl core structure of An-3.

Echinocandin antifungal drugs

The echinocandins are large lipopeptide molecules that are inhibitors of beta-(1,3)-glucan synthesis, an action that damages fungal cell walls. In vitro and in vivo, the echinocandins are rapidly fungicidal against most Candida spp and fungistatic against Aspergillus spp. They are not active at clinically relevant concentrations against Zygomycetes, Cryptococcus neoformans, or Fusarium spp. No drug target is present in mammalian cells. The first of the class to be licensed was caspofungin, for refractory invasive aspergillosis (about 40% response rate) and the second was micafungin. Adverse events are generally mild, including (for caspofungin) local phlebitis, fever, abnormal liver function tests, and mild haemolysis. Poor absorption after oral administration limits use to the intravenous route. Dosing is once daily and drug interactions are few. The echinocandins are widely distributed in the body, and are metabolised by the liver. Results of studies of caspofungin in candidaemia and invasive candidiasis suggest equivalent efficacy to amphotericin B, with substantially fewer toxic effects. Absence of antagonism in combination with other antifungal drugs suggests that combination antifungal therapy could become a general feature of the echinocandins, particularly for invasive aspergillosis.

Modification of rapid susceptibility assay for antifungal susceptibility testing of Aspergillus fumigatus

To improve objectivity and speed of current antifungal mold susceptibility testing, the yeast Rapid Susceptibility Assay (RSA) was adapted for Aspergillus species. The RSA is based on glucose utilization in the presence of an antifungal drug. Aspergillus fumigatus conidia were incubated in 0.2% glucose RPMI 1640 containing 0.03 to 16 micro g of amphotericin B or itraconazole/ml. Drug-related inhibition of glucose utilization correlated with suppression of conidial germination. Following incubation of conidia with various concentrations of antifungal drug, the percentage of residual glucose in the growth medium was determined colorimetrically and plotted against drug concentration to determine the MIC (MIC(RSA)). National Committee for Clinical Laboratory Standards (NCCLS) M38-P testing was also performed to obtain NCCLS MICs (MIC(NCCLS)) for direct comparison with MIC(RSA)s. Conidial inocula of an optical density at 530 nm (OD(530)) of 0.11 facilitated determination of amphotericin B and itraconazole MIC(RSA)s at 16 h equal to or within a single twofold dilution of MIC(NCCLS)s obtained at 48 h. Preliminary testing with a 0.11-OD(530) conidial inoculum of the slower-growing Aspergillus terreus resulted in itraconazole and amphotericin B MIC(RSA)s at 16 h equal to or within a single twofold dilution of MIC(NCCLS)s obtained at 48 h. These data indicate that the mold RSA provides a more objective and rapid method for Aspergillus spp. susceptibility testing than the NCCLS M38-P assay.

Entry into the stationary phase is associated with a rapid loss of viability and an apoptotic-like phenotype in the opportunistic pathogen Aspergillus fumigatus

When the opportunistic pathogen Aspergillus fumigatus entered the stationary phase, there was a rapid loss in cell viability which was associated with the appearance of markers characteristic of apoptosis, namely annexin V-FITC binding to the cytoplasmic membrane, demonstrating exposure of phosphatidylserine to the outer leaflet of the membrane; and TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) staining of the nuclei, indicating DNA fragmentation. This was followed later by a loss of membrane integrity as revealed by propidium iodide staining. The development of the apoptotic phenotype was blocked when the protein synthesis inhibitor cycloheximide was added to the culture 1h prior to the onset of the stationary phase, demonstrating active participation of the cell. In addition, intracellular activity against substrates specific for caspase-1 and -8 also increased on stationary phase entry and the development of the apoptotic phenotype was blocked when the cell permeant caspase inhibitor Z-FAD-fmk was present in the medium. Cell death in A. fumigatus during the stationary phase therefore appears to share similarities to apoptotic cell death in higher eukaryotes and to be dependent on a caspase-like activity.

Susceptibility testing of fungi--current status and open questions

The increase of fungal infections and the improvement of therapeutical options demand reliable antifungal susceptibility testing. In vitro susceptibility testing of fungi--in contrast to bacteria--is not yet established as a routine method. The NCCIS (National Committee for Clinical Laboratory Standards) guidelines for susceptibility testing of yeasts (and proposed for hyphomycetes) are most important for standardization. Meanwhile, essential parts of this test procedure are accepted, but it should still be improved. The concept of using only one test medium for all drugs and test organisms is not realized so far. There are also some test situations that prevent the NCCLS standard from being applied. Based on our experience, this article describes the NCCLS methods and their modifications. It places emphasis on lipophilic drugs showing controversies despite standardization. Furthermore, the prediction of MICs on the clinical outcome is discussed. Since there are some pitfalls in testing antifungals, this should be done in experienced laboratories only. The MIC has to be regarded as only one, but an important, factor in the management of fungal diseases. Host-, drug-, and pathogen-specific data should be considered simultaneously.

In vitro susceptibility testing of filamentous fungi: comparison of Etest and reference M38-A microdilution methods for determining posaconazole MICs

The performance of the Etest for posaconazole susceptibility testing of 72 isolates of filamentous fungi was assessed in comparison with the National Committee for Clinical Laboratory Standards (NCCLS) approved standard broth microdilution method (M38-A). The NCCLS method employed RPMI 1640 broth medium, and MICs were read after incubation for 48h at 35 degrees C. Etest MICs were determined with RPMI agar containing 2% glucose and were read after incubation for 48h at 35 degrees C. The isolates included Aspergillus fumigatus, A. flavus, A. nidulans, A. niger, A. versicolor, A. oryzae, A. terreus, Cladosporium spp., Curvularia sp., Exophiala sp., Fusarium spp., Paecilomyces spp., Pithomyces sp., Penicillium spp. and Scedosporium apiospermum. Overall agreement between Etest and microdilution MICs was 84% for Aspergillus spp. and 100% for the less common opportunistic molds, with the exception of Penicillium spp. (67%). Where a discrepancy was observed between Etest and the reference method, the Etest tended to give lower values. The Etest method using RPMI agar appears to be a useful method for determining posaconazole susceptibilities of filamentous fungi.

British Society for Medical Mycology proposed standards of care for patients with invasive fungal infections

Outcomes for invasive fungal infections have greatly improved in the past decade, and several new antifungal drugs have been or will be licensed in the next few years. Early accurate diagnosis and appropriate treatment have major impact on survival. In a 1995 survey of laboratory practice in the UK for mycology, major disparities were seen, with many laboratories not undertaking even simple diagnostic procedures. Delays in processing and inadequate procedures for handling samples, incomplete or delayed reporting of results, or a combination of these, compromise the care of patients. In randomised trials of antifungal chemotherapy, optimum treatments and good alternatives for others have been defined for some infections. High-quality care requires a multidisciplinary approach to diagnosis and management. In this review, we propose microbiology, histopathology, radiology, and clinical auditing standards, with the evidence base for each reviewed. The standards are absolutes, and, therefore, provide a straightforward basis for improving services to patients if they are all implemented.

Mutations in Aspergillus fumigatus resulting in reduced susceptibility to posaconazole appear to be restricted to a single amino acid in the cytochrome P450 14alpha-demethylase

To better understand the molecular basis of posaconazole (POS) resistance in Aspergillus fumigatus, resistant laboratory isolates were selected. Spontaneous mutants arose at a frequency of 1 in 10(8) and fell into two susceptibility groups, moderately resistant and highly resistant. Azole resistance in A. fumigatus was previously associated with decreased drug accumulation. We therefore analyzed the mutants for changes in levels of transcripts of genes encoding efflux pumps (mdr1 and mdr2) and/or alterations in accumulation of [(14)C]POS. No changes in either pump expression or drug accumulation were detected. Similarly, there was no change in expression of cyp51A or cyp51B, which encode the presumed target site for POS, cytochrome P450 14alpha-demethylase. DNA sequencing revealed that each resistant isolate carried a single point mutation in residue 54 of cyp51A. Mutations at the same locus were identified in three clinical A. fumigatus isolates exhibiting reduced POS susceptibility but not in susceptible clinical strains. To verify that these mutations were responsible for the resistance phenotype, we introduced them into the chromosome of a POS-susceptible A. fumigatus strain under the control of the glyceraldehyde phosphate dehydrogenase promoter. The transformants exhibited reductions in susceptibility to POS comparable to those exhibited by the original mutants, confirming that point mutations in the cyp51A gene in A. fumigatus can confer reduced susceptibility to POS.

Aspergillosis. Pathogenesis, clinical manifestations, and therapy

Diseases caused by Aspergillus species are increasing in importance, especially among immunocompromised hosts. Clinical manifestations are variable, ranging from allergic to invasive disease, largely depending on the status of the host's immune system. This article focuses on the pathogenesis and clinical manifestations of diseases caused by Aspergillus species, with more detailed discussion on therapy of the most morbid manifestation, invasive aspergillosis.

Fungal ABC transporters and microbial interactions in natural environments

In natural environments, microorganisms are exposed to a wide variety of antibiotic compounds produced by competing organisms. Target organisms have evolved various mechanisms of natural resistance to these metabolites. In this study, the role of ATP-binding cassette (ABC) transporters in interactions between the plant-pathogenic fungus Botrytis cinerea and antibiotic-producing Pseudomonas bacteria was investigated in detail. We discovered that 2,4-diacetylphloroglucinol, phenazine-1-carboxylic acid and phenazine-1-carboxamide (PCN), broad-spectrum antibiotics produced by Pseudomonas spp., induced expression of several ABC transporter genes in B. cinerea. Phenazines strongly induced expression of BcatrB, and deltaBcatrB mutants were significantly more sensitive to these antibiotics than their parental strain. Treatment of B. cinerea germlings with PCN strongly affected the accumulation of [14C]fludioxonil, a phenylpyrrole fungicide known to be transported by BcatrB, indicating that phenazines also are transported by BcatrB. Pseudomonas strains producing phenazines displayed a stronger antagonistic activity in vitro toward ABcatrB mutants than to the parental B. cinerea strain. On tomato leaves, phenazine-producing Pseudomonas strains were significantly more effective in reducing gray mold symptoms incited by a ABcatrB mutant than by the parental strain. We conclude that the ABC transporter BcatrB provides protection to B. cinerea in phenazine-mediated interactions with Pseudomonas spp. Collectively, these results indicate that fungal ABC transporters can play an important role in antibiotic-mediated interactions between bacteria and fungi in plant-associated environments. The implications of these findings for the implementation and sustainability of crop protection by antagonistic microorganisms are discussed.

Has antifungal susceptibility testing come of age?

The in vitro susceptibility of an infecting organism to the antimicrobial agent selected for therapy is one of several factors that influence the likelihood that therapy for an infection will be successful. To appreciate the value of antifungal susceptibility testing, it is helpful to review the overall predictive utility of antibacterial susceptibility testing. After >30 years of study, in vitro susceptibility can be said to predict the response of bacterial infections with an accuracy that is well summarized as the "90-60 rule": infections due to susceptible isolates respond to therapy approximately 90% of the time, whereas infections due to resistant isolates respond approximately 60% of the time. On the basis of a growing body of knowledge, standardized susceptibility testing for selected organism-drug combinations (most notably, Candida species and the azole antifungal agents) has been shown to have similar predictive utility. Antifungal susceptibility testing is now increasingly and appropriately used as a routine adjunct to the treatment of fungal infections.

In vitro activities of investigational triazoles against Fusarium species: effects of inoculum size and incubation time on broth microdilution susceptibility test results

We studied the effects of inoculum size and incubation time on the susceptibility testing results for various antifungal agents against 22 Fusarium isolates by the NCCLS microdilution method. Increased inoculum size and extended incubation time resulted in elevated MICs. Posaconazole and voriconazole exhibited promising antifungal activities.