Comparison of the Etest and the sensititre colorimetric methods with the NCCLS proposed standard for antifungal susceptibility testing of Aspergillus species

A novel procedure for the quantification of antifungal activity against filamentous fungi, mycelial invasion distance (MID) method

A novel method for the quantification of antifungal activity of fungicides and painted surfaces, mycelial invasion distance (MID) method, was developed and applied to the quantification of activities of parabens and an antifungal paint. In this method, the MID of aerial mycelia on a test paper or a panel placed on a nutrient agar plate was measured with a stereoscopic microscope and a micro-ruler. The antifungal activities of the parabens and painted surfaces were expressed as the MID. The higher the hydrophobicity of parabens, the longer the MID, that is the lower the antifungal activity, were observed. Conversely, relatively polar parabens, such as methyl and ethyl parabens, exhibited stronger antifungal activity, that is shorter MID. The most hydrophobic paraben, benzyl paraben, showed the weakest antifungal activity. Furthermore, it was confirmed that the MID method was effective for the evaluation of the painted surfaces.

Invasive aspergillosis in adult patients in Australia and New Zealand: 2017-2020

Background

New and emerging risks for invasive aspergillosis (IA) bring the need for contemporary analyses of the epidemiology and outcomes of IA, in order to improve clinical practice.

Methods

The study was a retrospective, multicenter, cohort design of proven and probable IA in adults from 10 Australasian tertiary centres (January 2017-December 2020). Descriptive analyses were used to report patients' demographics, predisposing factors, mycological characteristics, diagnosis and management. Accelerated failure-time model was employed to determine factor(s) associated with 90-day all-cause mortality (ACM).

Findings

Of 382 IA episodes, 221 (in 221 patients) fulfilled inclusion criteria - 53 proven and 168 probable IA. Median patient age was 61 years (IQR 51-69). Patients with haematologic malignancies (HM) comprised 49.8% of cases. Fifteen patients (6.8%) had no pre-specified immunosuppression and eleven patients (5.0%) had no documented comorbidity. Only 30% of patients had neutropenia. Of 170 isolates identified, 40 (23.5%) were identified as non-Aspergillus fumigatus species complex. Azole-resistance was present in 3/46 (6.5%) of A. fumigatus sensu stricto isolates. Ninety-day ACM was 30.3%. HM (HR 1.90; 95% CI 1.04-3.46, p = 0.036) and ICU admission (HR 4.89; 95% CI 2.93-8.17, p < 0.001) but not neutropenia (HR 1.45; 95% CI 0.88-2.39, p = 0.135) were associated with mortality. Chronic kidney disease was also a significant predictor of death in the HM subgroup (HR 3.94; 95% CI 1.15-13.44, p = 0.028).

Interpretation

IA is identified in high number of patients with mild/no immunosuppression in our study. The relatively high proportion of non-A. fumigatus species complex isolates and 6.5% azole-resistance rate amongst A. fumigatus sensu stricto necessitates accurate species identification and susceptibility testing for optimal patient outcomes.

Funding

This work is unfunded. All authors' financial disclosures are listed in detail at the end of the manuscript.

Evaluation of the Sensititre YeastOne and Etest in Comparison with CLSI M38-A2 for Antifungal Susceptibility Testing of Three Azoles, Amphotericin B, Caspofungin, and Anidulafungin, against Aspergillusfumigatus and Other Species, Using New Clinical Breakpoints and Epidemiological Cutoff Values

Aspergillosis is an invasive fungal disease associated with high mortality. Antifungal susceptibility testing (AFST) is receiving increasing consideration for managing patients, as well as for surveilling emerging drug resistance, despite having time-consuming and technically complex reference methodologies. The Sensititre YeastOne (SYO) and Etest methods are widely utilized for yeasts but have not been extensively evaluated for Aspergillus isolates. We obtained Posaconazole (POS), Voriconazole (VCZ), Itraconazole (ITC), Amphotericin B (AMB), Caspofungin (CAS), and Anidulafungin (AND) minimum inhibitory concentrations (MICs) for both the Etest (n = 330) and SYO (n = 339) methods for 106 sequenced clinical strains. For 84 A. fumigatus, we analyzed the performance of both commercial methods in comparison with the CLSI-AFST, using available cutoff values. An excellent correlation could be demonstrated for Etest-AMB and Etest-VCZ (p < 0.01). SYO-MICs of AMB, VCZ, and POS resulted in excellent essential agreement (>93%), and >80% for AMB, VCZ, and ITC Etest-MICs. High categoric agreement was found for AMB, ITC, and CAS Etest-MICs (>85%) and AMB SYO-MICs (>90%). The considerable number of major/very major errors found using Etest and SYO, possibly related to the proposed cutoffs and associated with the less time-consuming processes, support the need for the improvement of commercial methods for Aspergillus strains.

Antifungal Susceptibility Testing: A Primer for Clinicians

Clinicians treating patients with fungal infections may turn to susceptibility testing to obtain information regarding the activity of different antifungals against a specific fungus that has been cultured. These results may then be used to make decisions regarding a patient's therapy. However, for many fungal species that are capable of causing invasive infections, clinical breakpoints have not been established. Thus, interpretations of susceptible or resistant cannot be provided by clinical laboratories, and this is especially true for many molds capable of causing severe mycoses. The purpose of this review is to provide an overview of susceptibility testing for clinicians, including the methods used to perform these assays, their limitations, how clinical breakpoints are established, and how the results may be put into context in the absence of interpretive criteria. Examples of when susceptibility testing is not warranted are also provided.

Development and multicentre validation of an agar-based screening method for echinocandin susceptibility testing of Aspergillus species

BACKGROUND

Reference antifungal susceptibility testing of echinocandins against Aspergillus spp. relies on the determination of the minimal effective concentration, which is difficult to perform, time-consuming and subjective. We developed and evaluated in a multicentre study an agar-based screening method for echinocandin susceptibility testing of Aspergillus spp.

METHODS

Forty WT isolates [10 Aspergillus fumigatus species complex (SC), 10 Aspergillus flavus SC, 10 Aspergillus terreus SC and 10 Aspergillus niger SC] and 4 non-WT A. fumigatus isolates with or without known fks alterations were used. The optimal test conditions and stability over time were evaluated in preliminary studies monitoring colony growth. Twenty-microlitre aliquots of 1-2 McFarland inocula in 0.1% Tween 20 aqueous solution were added to each well and plates were incubated for 24/48 h at 35 ± 2°C. Subsequently, all isolates were tested blindly at three centres using four-well screening plates, containing anidulafungin, caspofungin, micafungin or no antifungal in each of the four wells, respectively.

RESULTS

WT isolates produced fluffy colonies on drug-free agar wells only. The non-WT isolates produced fluffy colonies on echinocandin-containing and control agar wells. Using the echinocandin concentrations of 0.25 mg/L anidulafungin, 1 mg/L caspofungin and 0.125 mg/L micafungin, and the compact (non-fluffy) versus fluffy colony morphology endpoint, all centres successfully discriminated non-WT and WT strains even after 24 h. Among the three echinocandins, anidulafungin produced the clearest endpoints.

CONCLUSIONS

The four-well plate agar method is suitable for echinocandin susceptibility screening of Aspergillus spp. and can be used to detect echinocandin non-WT isolates.

Comparative Evaluation of MIRONAUT-AM and CLSI broth microdilution method for antifungal susceptibility testing of Aspergillus species against four commonly used antifungals

The aim of this study was to evaluate a colorimetric method, MIRONAUT-AM, for determining susceptibility testing of anidulafungin, amphotericin, voriconazole, and itraconazole by comparing the minimum inhibitory (effective) concentrations (MICs/MECs) obtained by this method to those generated by the reference Clinical Laboratory Standard Institute (CLSI) broth microdilution method. In sum, 78 clinical isolates of Aspergillus species, nine of them non-wild type (non-WT) with itraconazole MIC ranging from 2 mg/l to &gt;16 mg/l, were tested against above antifungals. A. fumigatus ATCC 204305 was used as a reference strain, and test was performed in accordance with slightly modified yeast susceptibility testing instruction of the manufacture; conidia suspension inoculum and alamarBlue concentration were optimized. These same isolates were referred to Bristol Mycology reference laboratory and tested by CLSI method. The MICs and MECs generated by the two methods were compared using concordance analysis. MIRONAUT-AM showed significant concordance (P &lt; .0001) with CLSI method, and overall agreement was high (≥90%). In addition, MIRONAUT-AM produced echinocandin MECs results within 18–24 hours incubation time and correctly detected all non-WT isolates except one isolate. This colorimetric method is very promising and appears to be a suitable alternative susceptibility testing method to labor intensive broth microdilution reference method for Aspergillus species.

Antifungal Susceptibly Testing by Concentration Gradient Strip Etest Method for Fungal Isolates: A Review

Antifungal susceptibility testing is an important tool for managing patients with invasive fungal infections, as well as for epidemiological surveillance of emerging resistance. For routine testing in clinical microbiology laboratories, ready-to-use commercial methods are more practical than homemade reference techniques. Among commercially available methods, the concentration gradient Etest strip technique is widely used. It combines an agar-based diffusion method with a dilution method that determinates a minimal inhibitory concentration (MIC) in µg/mL. Many studies have evaluated the agreement between the gradient strip method and the reference methods for both yeasts and filamentous fungi. This agreement has been variable depending on the antifungal, the species, and the incubation time. It has also been shown that the gradient strip method could be a valuable alternative for detection of emerging resistance (non-wild-type isolates) as Etest epidemiological cutoff values have been recently defined for several drug-species combinations. Furthermore, the Etest could be useful for direct antifungal susceptibility testing on blood samples and basic research studies (e.g., the evaluation of the in vitro activity of antifungal combinations). This review summarizes the available data on the performance and potential use of the gradient strip method.

Multicentre validation of 4-well azole agar plates as a screening method for detection of clinically relevant azole-resistant Aspergillus fumigatus

Objectives

Azole-resistant Aspergillus fumigatus is emerging worldwide. Reference susceptibility testing methods are technically demanding and no validated commercial susceptibility tests for moulds currently exist. In this multicentre study a 4-well azole-containing screening agar method was evaluated using clinically relevant isolates.

Methods

Forty WT and 39 cyp51A mutant A. fumigatus [G54 (n = 10), M220 (n = 10), TR34/L98H (n = 9) and TR46/Y121F/T289A (n = 10)] were tested individually and as simulated mixed samples (sampling 4 WT and 1 mutant colonies). EUCAST MICs were determined following E.Def 9.3. In-house and commercial 4-well plates containing agars supplemented with 4 mg/L itraconazole, 1 mg/L voriconazole, 0.5 mg/L posaconazole and no antifungal, respectively, were evaluated. Growth was scored (0-3) by two independent observers in three laboratories. Inter-plate, inter-observer, essential and categorical agreement, sensitivity and specificity were calculated.

Results

CYP51A genotype and antifungal compound-specific MICs and growth patterns were documented. The inter-observer agreement was excellent with 86%-99% identical scores (range 80%-100%) for both plates. The qualitative agreement (no growth versus growth) was excellent (median 95%-100%, range 87%-100%, overall). The overall sensitivity and specificity for the 4-well plate (no growth versus growth) was 99% (range 97%-100%) and 99% (95%-100%), respectively. The sensitivity for simulated WT/mutant specimens was 94% (range 83%-100%) for the WT-TR34/L98H combination, but 100% for the WT/G54W combination. The performance remained unchanged using only itraconazole- and voriconazole-containing agars, but was lower for the other combinations.

Conclusions

Implementation of the 4-well screening plate in routine laboratories will allow easy and reliable detection of the most common azole-resistant A. fumigatus.

Monitoring H2O2 inside Aspergillus fumigatus with an Integrated Microelectrode: The Role of Peroxiredoxin Protein Prx1

Peroxiredoxins (Prx) are important proteins involved in hydroperoxide degradation and are related to virulence in several pathogens, including Aspergillus fumigatus. In this work, in vivo studies on the degradation of hydrogen peroxide (H₂O₂) in the microenvironment of A. fumigatus fungus were performed by using an integrated Pt microelectrode. Three A. fumigatus strains were used to confirm the role of the cytosolic protein Prx1 in the defense mechanism of this microorganism: a wild-type strain, capable to expressing the protein Prx1; a Δprx strain, whose gene prx1 was removed; and a genetically complemented Δprx1::prx1⁺ strain generated from the Δprx1 and in which the gene prx1 was reintroduced. The fabricated microelectrode was shown to be a reliable inert probe tip for in situ and real-time measurements of H₂O₂ in such microenvironments, with potential applications in investigations involving the mechanism of oxidative stress.

Comparative evaluation of different gradient diffusion tests for detection of azole resistance in Aspergillus fumigatus

Gradient diffusion assays Etest and MIC Test Strip for itraconazole, posaconazole and voriconazole as well as isavuconazole (MIC Test Strip) were evaluated for Aspergillus fumigatus against EUCAST broth microdilution. Both assays demonstrated generally good performance; however, posaconazole MIC Test Strip showed low agreement with broth microdilution due to MIC overestimation.

Comparative Evaluation of Sensititre YeastOne and CLSI M38-A2 Reference Method for Antifungal Susceptibility Testing of Aspergillus spp. against Echinocandins

Sensititre YeastOne (YO) panels were assessed for in vitro susceptibility testing of echinocandins against 39 isolates of Aspergillus fumigatus, A. flavus, and A. terreus, including two echinocandin-resistant A. fumigatus strains, using different inocula (103, 104, and 105 CFU/ml), incubation times (16 to 48 h), and endpoints (first blue or purple well) and compared to CLSI M38-A2. The best agreement was found with an inoculum of 104 CFU/ml, incubation times of 20 h for A. flavus and of 30 h for A. fumigatus and A. terreus, and reading the first purple well. The reproducibility within ±1 2-fold dilutions was 100% for all three echinocandins. YO color endpoints were 2 to 3 2-fold dilutions lower than CLSI minimum effective concentrations (MECs) of caspofungin and 1 to 2 2-fold dilutions higher than CLSI MECs of micafungin. For anidulafungin, off-scale YO color endpoints were observed. Nevertheless, A. fumigatus echinocandin-resistant isolates were detected after 24 h of incubation.

Antifungal Susceptibility Testing of Malassezia spp. with an Optimized Colorimetric Broth Microdilution Method

Malassezia is a genus of lipid-dependent yeasts. It is associated with common skin diseases such as pityriasis versicolor and atopic dermatitis and can cause systemic infections in immunocompromised individuals. Owing to the slow growth and lipid requirements of these fastidious yeasts, convenient and reliable antifungal drug susceptibility testing assays for Malassezia spp. are not widely available. Therefore, we optimized a broth microdilution assay for the testing of Malassezia that is based on the CLSI and EUCAST assays for Candida and other yeasts. The addition of ingredients such as lipids and esculin provided a broth medium formulation that enabled the growth of all Malassezia spp. and could be read, with the colorimetric indicator resazurin, by visual and fluorescence readings. We tested the susceptibility of 52 strains of 13 Malassezia species to 11 commonly used antifungals. MIC values determined by visual readings were in good agreement with MIC values determined by fluorescence readings. The lowest MICs were found for the azoles itraconazole, posaconazole, and voriconazole, with MIC₉₀ values of 0.03 to 1.0 μg/ml, 0.06 to 0.5 μg/ml, and 0.03 to 2.0 μg/ml, respectively. All Malassezia spp. were resistant to echinocandins and griseofulvin. Some Malassezia spp. also showed high MIC values for ketoconazole, which is the most widely recommended topical antifungal to treat Malassezia skin infections. In summary, our assay enables the fast and reliable susceptibility testing of Malassezia spp. with a large panel of different antifungals.

Molecular identification and amphotericin B susceptibility testing of clinical isolates of Aspergillus from 11 hospitals in Korea

BACKGROUND

We investigated the species distribution and amphotericin B (AMB) susceptibility of Korean clinical Aspergillus isolates by using two Etests and the CLSI broth microdilution method.

METHODS

A total of 136 Aspergillus isolates obtained from 11 university hospitals were identified by sequencing the internal transcribed spacer (ITS) and β-tubulin genomic regions. Minimal inhibitory concentrations (MICs) of AMB were determined in Etests using Mueller-Hinton agar (Etest-MH) and RPMI agar (Etest-RPG), and categorical agreement with the CLSI method was assessed by using epidemiological cutoff values.

RESULTS

ITS sequencing identified the following six Aspergillus species complexes: Aspergillus fumigatus (42.6% of the isolates), A. niger (23.5%), A. flavus (17.6%), A. terreus (11.0%), A. versicolor (4.4%), and A. ustus (0.7%). Cryptic species identifiable by β-tubulin sequencing accounted for 25.7% (35/136) of the isolates. Of all 136 isolates, 36 (26.5%) had AMB MICs of ≥2 μg/mL by the CLSI method. The categorical agreement of Etest-RPG with the CLSI method was 98% for the A. fumigatus, A. niger, and A. versicolor complexes, 87% for the A. terreus complex, and 37.5% for the A. flavus complex. That of Etest-MH was ≤75% for the A. niger, A. flavus, A. terreus, and A. versicolor complexes but was higher for the A. fumigatus complex (98.3%).

CONCLUSIONS

Aspergillus species other than A. fumigatus constitute about 60% of clinical Aspergillus isolates, and reduced AMB susceptibility is common among clinical isolates of Aspergillus in Korea. Molecular identification and AMB susceptibility testing by Etest-RPG may be useful for characterizing Aspergillus isolates of clinical relevance.

Antifungal Activity of Amphotericin B and Itraconazole against Filamentous Fungi: Comparison of the Sensititre Yeast OneŴ and NCCLS M38-A Reference Methods

The susceptibilities of 81 clinical isolates of Aspergillus spp., Fusarium spp., and Scedosporium spp., to amphotericin B and itraconazole were determined by the colorimetric microdilution method Sensititre and the reference microdilution method of NCCLS standard M38-A for filamentous fungi. No major discrepancies were found and agreement ranged between 86.4% to 84% and 69.1% to 86.4% for amphotericin B and itraconazole respectively at 48 h and 72 h of incubation by using the recommended endpoints. Within two two-fold dilutions, high levels of agreement were found in general for amphotericin B at 48 or 72 h (86.4 to 87.7%) and itraconazole (91.4 to 93.8%). Relatively better agreement was found for itraconazole at 72 h of incubation and 48 for amphotericin B.

Differential Responses of Colletotrichum gloeosporioides and C. truncatum Isolates from Different Hosts to Multiple Fungicides Based on Two Assays

Anthracnose is one of the most important postharvest diseases of many economically important crops worldwide. This study was conducted with the objective of investigating the sensitivity of Colletotrichum gloeosporioides and C. truncatum isolates to multiple fungicides with different modes of action. The study analyzed quantitative sensitivity data derived from conventional amended agar (AA) assays and qualitative spore responses obtained from a novel microtiter bioassay that is based on reduction of a viability dye, Alamar blue (AB). Generally, for AA assays, the percent growth inhibition (%RGI) increased with increasing concentration for all isolates and all fungicides, except for copper hydroxide. C. truncatum isolates reacted differently to increasing concentrations of the various fungicides depending on whether the isolates originated from pepper or papaya. C. truncatum from pepper had generally less %RGI than C. truncatum isolates from papaya. C. gloeosporioides isolates from papaya had generally higher %RGI than C. truncatum isolates for all concentrations tested for pyraclostrobin, chlorothalonil, and fosetyl-aluminum. C. gloeosporioides isolates from pepper had generally higher %RGI than C. truncatum isolates for all concentrations tested for most fungicides. In all cases, Colletotrichum sp. and fungicide had significant (P ≤ 0.001) effects on the log concentration of fungicide for which relative growth was inhibited by 50 and 90% (log EC50 and log EC90, respectively) calculated for all isolates, regardless of whether values were compared for only C. gloeosporioides isolates or only C. truncatum isolates. Correlation analyses of log EC50 and log EC90 values of all the isolates revealed a nonsignificant association for pyraclostrobin. In AB assays, all fungicides had an equivalent effect at inhibiting spore germination at the lower concentrations. According to binary logistic regression analyses, species, isolate, and fungicide concentration had significant predictive value in determining whether an AB test would be positive. Sequence alignments between C. gloeosporioides isolates and C. gloeosporioides f. sp. aeschynomene revealed no base substitutions at codons 198, 199, 200, and 240; however, sequence comparisons between C. truncatum isolates and C. gloeosporioides f. sp. aeschynomene revealed two codon changes located outside of the identified codon 198 or 200 associated with the benzimidazole-resistant phenotype of C. gloeosporioides isolates.

Multiple applications of Alamar Blue as an indicator of metabolic function and cellular health in cell viability bioassays

Accurate prediction of the adverse effects of test compounds on living systems, detection of toxic thresholds, and expansion of experimental data sets to include multiple toxicity end-point analysis are required for any robust screening regime. Alamar Blue is an important redox indicator that is used to evaluate metabolic function and cellular health. The Alamar Blue bioassay has been utilized over the past 50 years to assess cell viability and cytotoxicity in a range of biological and environmental systems and in a number of cell types including bacteria, yeast, fungi, protozoa and cultured mammalian and piscine cells. It offers several advantages over other metabolic indicators and other cytotoxicity assays. However, as with any bioassay, suitability must be determined for each application and cell model. This review seeks to highlight many of the important considerations involved in assay use and design in addition to the potential pitfalls.

A Rapid Resazurin-Based Microtiter Assay to Evaluate QoI Sensitivity for Alternaria alternata Isolates and Their Molecular Characterization

Chemical management of Alternaria brown spot of citrus is based upon the timely application of site-specific fungicides, many of which are vulnerable to the development of fungicide resistance. A rapid microtiter bioassay based on the colorimetric changes of resazurin (RZ) dye was developed to evaluate the sensitivity of Alternaria alternata to quinone outside inhibitor (QoI) fungicides. Four liquid media (complete medium, minimal medium, potato dextrose broth, and yeast peptone dextrose broth), five conidia concentrations (from 10¹ to 10⁵ conidia/ ml), and five RZ concentrations (10, 20, 30, 40, and 50 μM) were evaluated. Complete medium at 10⁵ conidia/ml and 40 μM RZ were identified as optimal for measuring RZ reduction. The effective concentration of two QoI fungicides (azoxystrobin and pyraclostrobin) needed to reduce RZ by 50% (EC₅₀) was calculated and compared with those obtained from conidia germination tests on fungicide-amended media. Concordant EC₅₀ values were observed (R² = 0.923; P < 0.0001) from both methods. Resistant phenotypes were further characterized by the partial sequencing of the cytochrome b gene. Genetic variability associated with the presence or absence of two introns was observed among isolates. The identified resistant isolates had the amino acid substitution G143A, typical of QoI resistance in other fungi.

Rapid susceptibility testing and microcolony analysis of Candida spp. cultured and imaged on porous aluminum oxide

BACKGROUND

Acquired resistance to antifungal agents now supports the introduction of susceptibility testing for species-drug combinations for which this was previously thought unnecessary. For pathogenic yeasts, conventional phenotypic testing needs at least 24 h. Culture on a porous aluminum oxide (PAO) support combined with microscopy offers a route to more rapid results.

METHODS

Microcolonies of Candida species grown on PAO were stained with the fluorogenic dyes Fun-1 and Calcofluor White and then imaged by fluorescence microscopy. Images were captured by a charge-coupled device camera and processed by publicly available software. By this method, the growth of yeasts could be detected and quantified within 2 h. Microcolony imaging was then used to assess the susceptibility of the yeasts to amphotericin B, anidulafungin and caspofungin (3.5 h culture), and voriconazole and itraconazole (7 h culture).

SIGNIFICANCE

Overall, the results showed good agreement with EUCAST (86.5% agreement; n = 170) and E-test (85.9% agreement; n = 170). The closest agreement to standard tests was found when testing susceptibility to amphotericin B and echinocandins (88.2 to 91.2%) and the least good for the triazoles (79.4 to 82.4%). Furthermore, large datasets on population variation could be rapidly obtained. An analysis of microcolonies revealed subtle effects of antimycotics on resistant strains and below the MIC of sensitive strains, particularly an increase in population heterogeneity and cell density-dependent effects of triazoles. Additionally, the method could be adapted to strain identification via germ tube extension. We suggest PAO culture is a rapid and versatile method that may be usefully adapted to clinical mycology and has research applications.

A Rapid Colorimetric Microtiter Bioassay to Evaluate Fungicide Sensitivity Among Verticillium dahliae Isolates

Management of Verticillium wilt relies on the adoption of integrated control strategies. The effects of long-term chemical use may be negated by the development of fungicide resistance. A rapid colorimetric bioassay was developed to evaluate sensitivity of V. dahliae isolates to differently acting fungicides. This assay capitalizes on the advantages of a 96-well microtiter plate format and the nontoxic cell viability dye, Alamar Blue (AB). Analysis of variance revealed that incubation time, spore density, and media type were important parameters that must be optimized for the AB assay. The effective linear range of the assay was dependent on incubation time and spore density. Survival of 10⁷ spores/ml of each of 10 isolates in the presence of a range of serial dilutions of nine commercial fungicides was assessed. Effective concentrations at 50 and 90% inhibition of growth were calculated for each fungicide. A comparison of the percent growth inhibition for each fungicide at 0.6 mg/ml, as determined by AB and amended-agar assays, revealed a strong positive correlation for six of the fungicides. The optimized AB assay proved to be a rapid and reproducible method of testing the efficacy of fungicides with the option of deriving quantitative or qualitative data.

Antifungal activity of bis-azasqualenes, inhibitors of oxidosqualene cyclase

The antifungal activity and in vitro toxicity toward animal cells of two inhibitors of oxidosqualene cyclase, squalene bis-diethylamine (SBD) and squalene bis-diethylmethylammonium iodide (SBDI) were studied. Minimum inhibitory concentration (MIC) against dermatophytes and other fungi involved in cutaneous and systemic infections (12 isolates from seven species) were determined by the broth microdilution method based on the reference documents M38-A and M27-A2 of Clinical and Laboratory Standards Institute (CLSI). Both compounds exerted fungistatic activities, although with different action. SBDI was the more active compound and displayed low MIC values (in the 3.12-12.5 μg ml(-1) range) against Microsporum canis, Trichophyton mentagrophytes and one isolate of Scopulariopsis brevicaulis, while SBD showed MIC values against these species in the 3.12-25 μg ml(-1) range. Toxicity was tested on Madin-Darby canine kidney (MDCK) epithelial cells and human microvascular endothelial cells (HMEC). SBDI proved the less toxic compound: it inhibited M. canis, T. mentagrophytes and S. brevicaulis at concentrations below those found toxic for MDCK cells. HMEC were the more sensitive cells.

In vitro susceptibility testing in Aspergillus species: an update

Aspergillus species are the most common causes of invasive mold infections in immunocompromised patients. The introduction of new antifungal agents and recent reports of resistance emerging during treatment of Aspergillus infections have highlighted the need for in vitro susceptibility testing. Various testing procedures have been proposed, including macro- and micro-dilution, disk diffusion, Etest (AB Biodisk, Sweden) and other commercial tests. Although Aspergillus species are generally susceptible to various compounds, intrinsic and acquired resistance has been documented. Amphotericin B has limited activity against Aspergillus terreus and Aspergillus nidulans. Not surprisingly, continued use of azole-based drugs has the undesirable consequence of elevating the resistance of subsequent isolates from these patients. Several species in the Aspergillus fumigatus complex appear to be resistant to azoles; there is evidence of in vitro and in vivo correlation. Each in vitro susceptibility testing method has its own advantages and disadvantages. Etest is easy to perform and use on a daily basis, yet it is expensive. Disk diffusion is the most attractive alternative method to date, yet we lack sufficient data for aspergilli. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) and the Clinical Laboratory Standard Institute (CLSI) have produced reproducible reference testing methods. This article reviews the available methods for antifungal susceptibility testing in Aspergillus spp. as well as the scant data regarding the clinical implications of in vitro testing.

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.

Voriconazole: a broad spectrum triazole for the treatment of serious and invasive fungal infections

For many years, serious systemic fungal infections have been treated with amphotericin B or narrow-spectrum azole antifungals. These treatments have been effective in many patients, but are associated with tolerability or pharmacokinetic concerns, or suboptimal antifungal activity in some patient groups. Voriconazole is a second-generation triazole with an extended spectrum of activity offering the potential to treat life-threatening fungal infections. The drug is available for intravenous or oral administration and has been shown to be effective in invasive aspergillosis, fluconazole-susceptible and -resistant candidiasis, and infections caused by various other fungal pathogens, including some formerly refractory organisms. Voriconazole is generally well tolerated with transient visual disturbances, liver enzyme abnormalities and skin rashes being the most common adverse events reported, but these rarely lead to treatment discontinuation.

Correlation between the E test and the CLSI M-38 A microdilution method to determine the activity of amphotericin B, voriconazole, and itraconazole against clinical isolates of Aspergillus fumigatus

The in vitro activities of amphotericin B, itraconazole, and voriconazole against 283 clinical isolates of Aspergillus fumigatus were studied by comparing the E test method with the reference procedure NCCLS (CLSI) M-38A. The methods were considered to agree when the results of the MICs by E test were within +/-2 dilutions of the MICs obtained by CLSI M-38 A. Agreement of readings at 24, 48, and 72 h of incubation was as follows: amphotericin B: 4.2%, 98%, and 40.6%; itraconazole: 92.5%, 100%, and 89.9%; and voriconazole: 98.9%, 100%, and 99.7%. The correlation between methods to classify the strains as "susceptible" or "resistant" was very good for itraconazole and voriconazole after 48 h of incubation, but 23% of the strains were incorrectly classified by E test for amphotericin B. The E test is an efficacious method for antifungal susceptibility testing in A. fumigatus for itraconazole and voriconazole when the plates are read after 48 h of incubation. The use of the E test to study the activity of amphotericin B should be avoided.

In vitro methods for antifungal susceptibility testing of Trichophyton spp

In general, methods to test the susceptibility of fungi to antifungal drugs require standardized techniques, but so far there is no methodology that is widely applicable to dermatophytes. Here we introduced modifications to the protocols from documents of the National Committee for Clinical Laboratory Standards (CLSI) M38-A and the Antifungal Susceptibility Testing Subcommittee of the European Committee on Antimicrobial Susceptibility Testing (EUCAST) that are usually applied to moulds and fermentative yeasts, in order to adjust the conditions for the growth of dermatophytes. The modifications included: growth on potato dextrose agar supplemented with 2% in-house rice flour to encourage sporulation, the addition of 2% glucose to the culture media (RPMI-1640), and an incubation temperature of 28 degrees C. In addition, the incubation period was 7d, the minimum inhibitory concentration (MIC) was defined as 80% growth inhibition endpoints for azole agents, and the inocula only contained microconidia. Results obtained by both tested methodologies were very similar to the ones reported by other researchers. MIC90 (MIC at which 90% of isolates tested were inhibited) values were identical for four out of five antifungal drugs tested and there was only a difference of one or two dilutions when MIC50 values were compared. Although the modifications introduced did not interfere with the results, more studies are necessary to establish a standard technique to test susceptibility of dermatophytes to antifungal drugs.

Comparison of three commercial assays and a modified disk diffusion assay with two broth microdilution reference assays for testing zygomycetes, Aspergillus spp., Candida spp., and Cryptococcus neoformans with posaconazole and amphotericin B

We compared posaconazole M27-A2 and M38-A MICs to Etest and YeastOne MICs for 92 zygomycetes, 126 Aspergillus isolates, 110 Candida isolates, and Cryptococcus neoformans. Reference MICs were also correlated with inhibition zone diameters in millimeters (modified M44-A disk and Neo-Sensitabs tablet methods). Etest MICs were obtained on solidified (1.5% agar) RPMI 1640 (2% dextrose), and zone diameters were obtained on supplemented (2% glucose and 0.5 microg/ml methylene blue [for all isolates]) and nonsupplemented Mueller-Hinton (MH; molds only) agar. MICs and zone diameters were obtained between 16 and 72 h. The overall agreement (% MIC pairs within a three-dilution range) between reference posaconazole and YeastOne MICs was 98 to 100% at 16 to 24 h for zygomycetes and yeasts and 99% at 24 to 48 h for Aspergillus. The overall agreement was lower between reference posaconazole and Etest MICs (94 to 97%) and by both methods with amphotericin B for all species (95 to 99.3%). For yeasts, the correlation coefficient was similar between reference posaconazole MICs and either disk (R, 0.810) or tablet (R, 0.769) zone diameter at 24 h and was superior on MH agar for molds at 16 to 48 h (R, 0.804 and 0.799 for disk and tablet, respectively). For amphotericin B, the best correlation between reference MICs and zone diameters was observed at 16 to 48 h for molds on MH agar (R, 0.736 to 0.812 and 0.765 to 0.749 for disk and tablet, respectively) and at 48 h for yeasts (R, 0.681 and 0.503 for disk and tablet, respectively). These data suggest the potential value of these alternative broth dilution and agar diffusion methods for testing posaconazole and amphotericin B in the clinical laboratory against the species evaluated.

Antifungal susceptibility testing by flow cytometry: is it the future?

The current increase in the number and significance of fungal infections, the expanding armamentarium of antifungal agents, and the emergence of the problem of antifungal drug resistance have been intensifying the importance of antifungal susceptibility testing (AST). The Clinical and Laboratory Standards Institute (CLSI, formerly NCCLS) in the United States and the Antifungal Susceptibility Testing Subcommittee of the European Committee on Antimicrobial Susceptibility Testing (AFST-EUCAST) published standard methodologies in order to achieve higher reproducibility and allow direct inter-laboratory comparison of the susceptibility results. Nevertheless, several problems remain unresolved and the methods depend on long incubation periods of a minimum of 24 h (EUCAST) or even 48 h (CLSI). Over the last 15 years, successful applications of flow cytometric techniques to AST of both yeast and moulds have been reported. These techniques are based on the analysis of a great number of fungal cells individually and frequently rely on short incubation times of no more than a few hours. Considering these attributes, flow cytometry (FC) seems to have the potential to achieve clinical usefulness in the near future. The collection of data on the reproducibility of the results and on the correlation with clinical outcomes has barely started, however. Practical validation of the experimental methodologies is not granted before a significant amount of data addressing those questions is available.

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

A total of 60 clinical fungal isolates from patients without prior amphotericin B treatment and three control strains were evaluated for their intrinsic susceptibility to amphotericin B (AmB) using microdilution, Etest and disc diffusion assays, on three media each, Roswell Park Memorial Institute (RPMI) 1640, Antibiotic Medium 3 (AM3) and High Resolution Medium. The fungal strains included isolates of Aspergillus fumigatus (n = 10), Aspergillus terreus (n = 12), Aspergillus nidulans (n = 9), Candida albicans (n = 6) and Candida lusitaniae (n = 23). The A. terreus strains were significantly less susceptible to AmB than the A. fumigatus strains in all nine experimental settings (P-values ranging from 0.009 to <0.00001). The A. nidulans strains were equally susceptible to AmB as the A. fumigatus strains in seven of nine experimental settings and less susceptible in two (microdilution performed on RPMI and AM3, P = 0.01 and 0.007). The C. lusitaniae strains were equally susceptible to AmB as the C. albicans strains in seven of nine experimental settings and more susceptible in two (microdilution and Etest, both performed on AM3, P = 0.01 and 0.0002). Thus, we confirmed that A. terreus is intrinsically less susceptible to AmB than A. fumigatus. In contrast, nine German clinical isolates of Aspergillus nidulans were found equally susceptible to AmB as 10 isolates of A. fumigatus. Furthermore, we found 23 German clinical isolates of C. lusitaniae from patients without prior treatment with AmB equally susceptible to AmB as C. albicans.

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.

[In vitro susceptibility of fungal and yeast clinical isolates to itraconazole and voriconazole]

The interest on the in vitro susceptibility to itraconazole has recently increased due the availability of the intravenous formulation. In this study, comparative MICs of this antifungal with voriconazole were carried out in 62 clinical isolates of filamentous fungi and 100 yeasts isolates using the NCCLS microbroth methods described in M38-A and M27-A2 documents. A MIC90 of 0.125 micrograms per ml was observed for itraconazole and voriconazole against Aspergillus fumigatus. Higher susceptibility to itraconazole was found for the filamentous form of Sporotrhix schenckii (p = 0.001). Voriconazole was more effective against Scedosporium apiospermium while Scedosporium prolificans isolates were resistant to both azoles. Some isolates of Rhizopus stolonifer were susceptible to itraconazole and resistant to voriconazole, but without statistical significance. Susceptibility of nine species of Candida was similar for both triazoles used in this study. However, Candida glabrata was more susceptible to voriconazole. Some fluconazole-resistant Candida albicans isolates were susceptible to itraconazole and / or voriconazole. Cryptococcus neoformans was more susceptible to itraconazole than to voriconazole. Itraconazole and voriconazole showed very close in vitro activity against the tested fungal isolated, except against S. schenckii. In spite of this, there were some differences in susceptibility among isolates within the same fungal species.

Sensititre YeastOne caspofungin susceptibility testing of Candida clinical isolates: correlation with results of NCCLS M27-A2 multicenter study

The ability of Sensititre YeastOne to discriminate isolates with reduced caspofungin susceptibility was determined against 36 Candida spp. (6 with a known FKS1 mutation). Results were compared with those of M27-A2. The MIC endpoint was 100% growth inhibition. Overall agreement (+/-2 log2) was 87.16%. Sensititre YeastOne detected strains with reduced caspofungin susceptibility.

Testing of the in vitro susceptibilities of Madurella mycetomatis to six antifungal agents by using the Sensititre system in comparison with a viability-based 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5- [(phenylamino)carbonyl]-2H-tetrazolium hydroxide (XTT) assay and a modified NCCLS method

The in vitro susceptibilities of 36 clinical isolates of Madurella mycetomatis, the prime agent of eumycetoma in Africa, to ketoconazole, itraconazole, fluconazole, voriconazole, amphotericin B, and flucytosine were determined by the Sensititre YeastOne system. This system appeared to be a rapid and easy test, and by use of hyphal suspensions it generated results comparable to those of a modified NCCLS method. After 10 days of incubation, the antifungal activities of ketoconazole (MIC at which 90% of isolates were inhibited [MIC90], 0.125 microg/ml), itraconazole (MIC90, 0.064 microg/ml), and voriconazole (MIC90, 0.125 microg/ml) appeared superior to those of fluconazole (MIC90, 128 microg/ml) and amphotericin B (MIC90, 1 microg/ml), with MICs in the clinically relevant range. All isolates were resistant to flucytosine (all MICs above 64 microg/ml). Based on the relatively broad range of MICs obtained for the antifungal agents, routine testing of M. mycetomatis isolates for susceptibility to antifungal agents seems to be relevant to adequate therapeutic management.

Increased frequency of non-fumigatus Aspergillus species in amphotericin B– or triazole–pre-exposed cancer patients with positive cultures for aspergilli

Invasive aspergillosis (IA) can occur despite prior prophylactic or empiric use of triazoles or amphotericin B (AMB). Although profound immunosuppression may account for breakthrough IA, resistance of Aspergillus to antifungals may also play a role. To examine this question, we measured the minimal inhibitory concentration of 105 Aspergillus isolates recovered from 105 cancer patients (64 with IA, 41 with Aspergillus colonization) to AMB, itraconazole (ITC), and voriconazole (VRC) using the National Committee for Clinical Laboratory Standards (NCCLS) M38-A microdilution and E-test methods. We also determined the minimal fungicidal concentration (MFC) of these agents and the minimal effective concentration (MEC) of caspofungin (CAS) using standardized methods. We then collected information regarding pre-exposure to AMB or triazoles (fluconazole, ITC, VRC) within 3 months before Aspergillus isolation. Pre-exposure of cancer patients to AMB or triazoles was associated with increased frequency of non-fumigatus Aspergillus species. Aspergillus isolates recovered from patients who previously received AMB exhibited higher E-test AMB MICs compared with isolates from patients without prior AMB exposure (P = 0.01). In addition, the AMB MICs by E-test were higher in triazole-pre-exposed patients compared with those not exposed to triazoles (P = 0.001). The ITC and VRC MICs by E-test were not affected by prior AMB or triazole exposure. Finally, neither the AMB, ITC, and VRC MICs and MFCs by NCCLS method nor CAS MECs showed such changes. In conclusion, cancer patients with positive Aspergillus cultures who are pre-exposed to AMB or triazoles have high frequency of non-fumigatus Aspergillus species. These Aspergillus isolates were found to be AMB-resistant by the more sensitive E-test method.

[In vitro activity of amphotericin B, itraconazole and voriconazole against 20 species of Aspergillus using the Sensititre microdilution method]

BACKGROUND

The in vitro activity of antifungal agents against Aspergillus has been recently investigated. We studied the susceptibility to amphotericin B, itraconazole and voriconazole of 68 strains belonging to 20 different Aspergillus species.

METHODS

The minimum inhibitory concentrations (MICs) for 10 strains of A. fumigatus, 9 A. flavus, 8 A. niger, 5 A. tamarii, 5 A. versicolor, 4 A. terreus, 3 A. glaucus, 3 A. ochraceus, 3 A. oryzae, 2 A. candidus, 2 A. chevalieri, 2 A. rubrobrunneus, 2 A. sclerotiorum, 2 A. sydowii, 2 A. unguis, 2 A. ustus, 1 A. clavatus, 1 A. nidulans, 1 A. pseudofischeri y 1 A. reptans, were determined using the Sensititre Yeast One microdilution method.

RESULTS

Voriconazole was more active in vitro than amphotericin B and itraconazole, with 95.6% (65/68) of strains exhibiting MICs of < or = 2 mg/l. A. flavus, A. versicolor, A. terreus, A. ochraceus, A. sclerotiorum, A. ustus and A. reptans species presented reduced susceptibility to amphotericin B (MIC > or = 2 mg/l); A. niger, A. versicolor, A. sclerotiorum and A. ustus showed in vitro resistance to itraconazole (MIC > or = 1 mg/l); and A. sclerotiorum and A. ustus displayed poor susceptibility to voriconazole (MIC > or = 2 mg/l).

CONCLUSIONS

The susceptibility of Aspergillus species to itraconazole and voriconazole was generally good; nevertheless, susceptibility to amphotericin B was low. These results suggest that Aspergillus susceptibility testing to this antifungal agent would be advisable to guide treatment.

Susceptibility of filamentous fungi to voriconazole tested by two microdilution methods

The growing number of fungal infections, coupled with emerging resistance to classical antifungal agents, has led to the development of new agents, among them voriconazole. Susceptibility to voriconazole was tested by two microdilution techniques: the National Committee for Clinical Laboratory Standards reference method M38-A and a colorimetric method, Sensititre YeastOne. The study tested a total of 244 isolates: 223 Aspergillus (136 Aspergillus fumigatus, 37 A. niger, 26 A. terreus, 16 A. flavus, 7 A. nidulans, and 1 A. ustus), 14 Fusarium (8 Fusarium moniliformis, and 6 F. oxysporum), 6 Scedosporium apiospermum, and 1 Rhizomucor pusillus strain and four control strains (Candida parapsilosis ATCC 22019, C. krusei ATCC 6258, A. fumigatus ATCC 204305, and A. flavus ATCC 204304). For all tested species except one F. moniliforme strain and R. pusillus, the MIC, the MIC at which 50% of the isolates are inhibited (MIC(50)), and MIC(90) ranges of Collapse

Key Words Collapse

MESH Headings

• Antifungal Agents/pharmacology
• Fungi/classification
• Fungi/drug effects
• Humans
• Microbial Sensitivity Tests/methods
• Microbial Sensitivity Tests/standards
• Pyrimidines/pharmacology
• Quality Control
• Reference Standards
• Triazoles/pharmacology
• Voriconazole

Collapse

Grants Collapse

Affiliation(s)

Maria José Linares Departamento de Microbiología, Facultad de Medicina, University of Córdoba, Spain
Guadalupe Charriel
Francisco Solís
Fernando Rodriguez
Ana Ibarra
M Casal

Collapse

Comparison of the Sensititre YeastOne colorimetric antifungal panel with a modified NCCLS M38-A method to determine the activity of voriconazole against clinical isolates of Aspergillus spp

The susceptibilities of 63 isolates of Aspergillus spp. to voriconazole were evaluated by a modified NCCLS M38-A method and the Sensititre YeastOne method. The overall agreement was 82.5%, ranging from 100% for Aspergillus niger and Aspergillus terreus to 62.5% for Aspergillus flavus. Discrepancies between the methods were due to higher Sensititre MICs. The Sensititre YeastOne method could have potential value for susceptibility testing of Aspergillus spp. to voriconazole.

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.

Differentiation between isolates of Aspergillus fumigatus from breeding turkeys and their environment by genotyping with microsatellite markers

To elucidate the epidemiology of the different forms of avian aspergillosis, 114 Aspergillus fumigatus isolates from sacrificed turkeys and 134 A. fumigatus isolates from air samples were collected and genotyped by microsatellite polymorphism marker analysis. Air sampling confirmed the huge diversity of A. fumigatus populations. Whereas older animals harbored several combinations of genotypes, 1-day-old chicks carried a unique genotype, suggesting a unique source of contamination.

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.

In vitro susceptibility testing of Aspergillus spp.: comparison of Etest and reference microdilution methods for determining voriconazole and itraconazole MICs

The performance of the Etest for voriconazole and for itraconazole susceptibility testing of 376 isolates of Aspergillus spp. was assessed in comparison with the National Committee for Clinical Laboratory Standards (NCCLS) proposed standard microdilution broth method. The NCCLS method employed RPMI 1640 broth medium, and MICs were read after incubation for 48 h at 35 degrees C. Etest MICs were determined with RPMI agar containing 2% glucose and were read after incubation for 48 h at 35 degrees C. The isolates included A. fumigatus, A. flavus, A. niger, A. terreus, A. versicolor, A. glaucus, A. nidulans, A. ustus, and A. sydowii. Overall agreement percentages between the Etest and microdilution MICs were 97.6% for voriconazole and 95.8% for itraconazole. Where a discrepancy was observed between Etest and the reference method, the Etest tended to give lower values with voriconazole and higher values with itraconazole. The Etest method using RPMI agar appears to be a useful method for determining the voriconazole and itraconazole susceptibilities of Aspergillus spp.