Comparison study of broth macrodilution and microdilution antifungal susceptibility tests

Aldgamycins Q1 and Q2, two novel 16-membered macrolides from the rare actinomycete Saccharothrix sp. 16Sb2-4

Two novel 16-membered macrolides, named aldgamycin Q1 (1) and Q2 (2), were isolated from the culture broth of the rare actinomycete Saccharothrix sp. 16Sb2-4. The structures of 1 and 2 were elucidated as new aldgamycin analogs with a demethylated mycinose residue by spectroscopic analyses and comparison with data of aldgamycin K. Compounds 1 and 2 showed moderate to weak antibacterial activities against Enterococcus faecalis, Bacillus subtilis, Staphylococcus aureus and Acinetobacter baumannii, with MIC values ranging from 16 to 64 μg mL-1.

Miniaturised broth microdilution for simplified antibiotic susceptibility testing of Gram negative clinical isolates using microcapillary devices

Miniaturised antibiotic susceptibility testing: 100 times smaller microcapillary broth microdilution gives equivalent result to standard microplate broth microdilution.

The type isolate of a rare Phaeoacremonium species as a cause of human eumycetoma

An isolate of unknown identity that had been identified as causing eumycetoma was retained in an international culture collection, and eventually became the nomenclatural type isolate of the rarely encountered Phaeoacremonium sphinctrophorum. The case featured an indurated, painless, swollen lesion on the dorsum of the foot that had developed in a Canadian resident who had previously been a farmer in Laos. Resection alone was curative.

Postbiotic and Anti-aflatoxigenic Capabilities of Lactobacillus kunkeei as the Potential Probiotic LAB Isolated from the Natural Honey

The use of probiotic, postbiotic, and anti-aflatoxigenic capabilities of the lactic acid bacteria (LAB) isolated from stressful niches is a major strategy to prepare functional cultures and bio-preservatives for food industries. In the present study, abundant LAB strains isolated from natural honey were screened based on their tolerance to continuous pH and bile salt treatments. Then, the pro-functional properties of the selected LAB were investigated. In accordance with the screening data, a bacilli isolate was selected for further characterization. Sequencing results led to the identification of Lactobacillus kunkeei as the selected LAB isolate. In vitro antibacterial and antifungal activities of the LAB and in situ antifungal activity of the isolate cell-free supernatant (CFS) were verified against food-borne indicators. Accordingly, in vitro antibacterial and antifungal effects of Lact. kunkeei ENH01 on respective Escherichia coli and Aspergillus niger were significantly (P < 0.05) higher than the other indicators. Furthermore, in situ inhibitory effect of Lact. kunkeei CFS on Candida albicans (as the highest in situ effect) was equal to 76.36%. The presence of three antibacterial peptides was also verified in the Lact. kunkeei CFS according to the results of liquid chromatography mass spectrometry (LC/MS) assay. Antibiotic susceptibility profile and auto-aggregation ability of the isolate were noticeable. Anti-mycotoxigenic capabilities of Lact. kunkeei ENH01 as viable and heat-killed cells were also revealed against total aflatoxins according to the HPLC-based analysis. In vivo safety of the isolate was also attested through the evaluation of blood biochemistry and hematological parameters in the Lact. kunkeei ENH01 fed-mice compared with the control. Based on the findings, probiotic properties of Lact. kunkeei ENH01 and postbiotic capabilities of the isolate CFS and its heat-killed cells were approved.

Antibacterial activity against Staphylococcus aureus of chitosan/chondroitin sulfate nanocomplex aerogels alone and enriched with erythromycin and elephant garlic (Allium ampeloprasum L. var. ampeloprasum) extract

The antibacterial activity against Staphylococcus aureus of aerogels fabricated from colloidal suspensions of chitosan/chondroitin sulfate nanocomplexes is analyzed. Upon freeze-drying the colloidal suspensions, the aerogels presented a porous structure made of microsheets and microfibers. The aerogels could, in addition, be loaded with antimicrobial agents. Loaded with the antibiotic erythromycin, the aerogels showed crystalline deposits, affecting the topography of the samples as well as their mechanical properties, showing a decrease on the apparent Young’s modulus and hardness at 40% deformation. Loaded with elephant garlic (Allium ampeloprasum L. var. ampeloprasum) extract, the aerogels showed texturization of the microsheets and microfibers, and the higher relative mass allowed an increase on the apparent Young’s modulus and hardness at 40% deformation with respect to pristine aerogels. Unloaded aerogels showed activity against Staphylococcus aureus, including a methicillin-resistant strain. The release of erythromycin from the aerogels to an agar environment is governed by equilibrium forces with the polysaccharides, which allow modulating the load of antibiotic and its concomitant diffusion from the material. The diffusion of the active components of the elephant garlic extract did not show a dependence on the polysaccharide content, revealing a week interaction. The elephant garlic extract resulted active against the methicillin-resistant Staphylococcus aureus strain, while resistance was found for the antibiotic, revealing the therapeutic potential of the natural extract. The antimicrobial aerogels may be used for several therapeutic purposes, such as healing of infected chronic wounds.

Synergistic combination of marine oligosaccharides and azithromycin against Pseudomonas aeruginosa

In this paper we describe how utilization of low molecular weight alginate-derived oligosaccharide (ADO) and chito-oligosaccharide (COS) in conjunction with antibiotics, could more effectively inhibit the growth of wild-type and resistant Pseudomonas aeruginosa. Inhibition is effected by modulating the bacteria's quorum sensing (QS) system, thus regulating biofilm formation and reducing resistance to antibiotic treatment. This can be demonstrated by using conventional MIC screening. COS showed synergistic effects with azithromycin, whereas ADO indicated additive effects against wild-type P. aeruginosa. Using electrospray-ionization mass spectroscopy (ESI-MS), matrix-assisted laser desorption/ionization-time of flightmass spectroscopy (MALDI-TOF-MS) and nuclear magnetic resonance (NMR), the chemical structure of ADO and of COS was characterized. The wild-type and resistant strains were identified by 16S rRNA sequence analysis. This report demonstrates the feasibility of attenuating the tolerance of P. aeruginosa to azithromycin by using specific marine oligosaccharides.

The potential inhibitory effect of cuminum cyminum, ziziphora clinopodioides and nigella sativa essential oils on the growth of Aspergillus fumigatus and Aspergillus

The goals of this study were to evaluate the effectiveness of Cuminum cyminum, Ziziphora clinopodioides and Nigella sativa essential oils to inhibit the growth of Aspergillus fumigatus and A.flavus and to evoke ultrastructural changes. The fungi were cultured into RPMI 1640 media in the presence of oils at concentrations of 8, 6, 5, 4, 3, 2, 1.5, 1.25, 1, 0.75 and 0.5 mg/ml in broth microdilution and 2, 1.5, 1 and 0.5 mg/ml in broth macrodilution methods with shaking for 48 h at 28^oC. Conidial and mycelial samples exposed to 0.25, 0.5, 1, 1.5 and 2 mg essential oils/ml for 5 days in 2% yeast extract granulated plus 15% Saccharose media were processed for transmission electron microscopy (TEM). Based on broth dilution methods, C. cyminum and to a lesser extent Z. clinopodioides oils exhibited the strongest activity against A. fumigatus and A.flavus with MIC₉₀ ranging from 0.25 to 1.5 mg/ml, while the oil from N. sativa exhibited relatively moderate activity against two above fungi with MIC₉₀ ranging from 1.5 to 2 mg/ml. The main changes observed by TEM were in the cell wall, plasma membrane and membranous organelles; in particular, in the nuclei and mitochondria. These modifications in fungal structure were associated with the interference of the essential oils with the enzymes responsible for cell wall synthesis, which disturbed normal growth. Moreover, the essential oils caused high vacuolation of the cytoplasm, detachment of fibrillar layer of cell wall, plasma membrane disruption and disorganization of the nuclear and mitochondrial structures. Aspergillus fumigatus and A. flavus growth inhibition induced by these oils were found to be well-correlated with subsequent morphological changes of the fungi exposed to different fungistatic concentrations of the oils. Our results show the anti-Aspergillus activities of C. cyminum, Z. clinopodioides and N. sativa essential oils, which strengthens the potential use of these substances as anti-mould in the future.

Synthesis and antifungal activity of C-21 steroids with an aromatic D ring

Six analogues of salpichrolides with a simplified side chain (6-11) were synthesized using a new methodology to obtain steroids with an aromatic D-ring. The key step was the elimination of HBr in a vicinal dibromo D-homosteroid by treatment with 1,4-diazabicyclo[2.2.2]octane (DABCO). All new compounds were completely characterized by 2D NMR techniques and tested on two fungal pathogenic species, Fusarium virguliforme and Fusarium solani.

Lack of correlation of 24- vs. 48-h itraconazole minimum inhibitory concentrations with microbiological and survival outcomes in a guinea pig model of disseminated candidiasis

A 'trailing' effect has been commonly observed when azole antifungals are tested against Candida spp. Previous experience with fluconazole indicates that 24-h minimum inhibitory concentration (MIC) values are more compatible endpoints when compared with clinical outcomes. We evaluated the trailing effect of Candida isolates tested with itraconazole in a guinea pig model of systemic candidiasis. Survival and organ burden were only significantly affected by using a higher dose of itraconazole, irrespective of the MIC differences at 24 and 48 h. A fluconazole-resistant strain with susceptible dose-dependent MICs to itraconazole was successfully treated with high-dose itraconazole. Our data suggests that survival and microbiological response depend more on drug dosing than on the trailing phenotype of the isolates.

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.

In vitro susceptibility testing of dermatophytes: comparison of disk diffusion and reference broth dilution methods

A total of 56 strains belonging to 4 species of dermatophytes were tested against 10 antifungal drugs by using a modification of the NCCLS (M38-P) standard for filamentous fungi. The minimum inhibitory concentration (MIC) values obtained using the dilution method were compared with the diameters of growth inhibition zones using the disk diffusion method. The antifungals used were itraconazole, fluconazole, ketoconazole, miconazole, sulconazole, oxiconazole, bifonazole, griseofulvin, ciclopiroxolamine, and terbinafine. Relative to the other agents tested, terbinafine possessed the highest antifungal activity against all of the dermatophytes. In contrast, fluconazole was the least active drug. An increase of MIC values was accompanied by a decrease of growth inhibition zone diameter. The disk diffusion method of fungal susceptibility assessment yields data consistent with results obtained from the dilution method. The study suggests the potential value of the disk diffusion method as a convenient alternative method for testing the susceptibilities of dermatophytes.

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 comparison of activities of terbinafine and itraconazole against Paracoccidioides brasiliensis

In vitro, terbinafine is highly active against a broad spectrum of pathogenic fungi. We evaluated the activities of terbinafine and itraconazole against 31 isolates of Paracoccidioides brasiliensis. The tests were conducted by using a broth macrodilution procedure. MICs, in micrograms per milliliter, were as follows: terbinafine, 0.015 to 1.0 (geometric mean, 0.1188); itraconazole, 0.007 to 0.5 (geometric mean, 0.03165). The usual therapy for paracoccidioidomycosis is sulfonamides, amphotericin B, and azole derivatives (ketoconazole, itraconazole, and fluconazole). In comparison to amphotericin B, azole derivatives allow shorter treatment courses, can be administered orally, and are equally effective. Itraconazole has as high efficacy as ketoconazole, but with superior tolerance. It is the current drug of choice for treatment of paracoccidioidomycosis. The data obtained in this study indicate that terbinafine is active against P. brasiliensis in vitro and suggest that this allylamine can be considered a new option as drug therapy for paracoccidioidomycosis.

Candida: a causative agent of an emerging infection

Incidences of infections due to Candida have increased over the last 15-20 y. This increase in the incidence and the high associated mortality rate despite therapy has focused the attention on this disease and prompted investigators to undertake research aimed at understanding the pathogenesis of this disease as well as methods to treat it. This paper discusses recent developments in the Candida field and the impact they have on patient management.

In vitro antifungal susceptibility testing

With the rising frequency of fungal infections, as well as increasing reports of resistance to antifungal agents, it is imperative that clinically applicable antifungal susceptibility testing be available. In 1997 the National Committee for Clinical Laboratory Standards published standard guidelines for antifungal susceptibility testing of Candida sp and Cryptococcus neoformans with amphotericin B, flucytosine, fluconazole, itraconazole, and ketoconazole. Although the methods are standard, they are time consuming, can be difficult to interpret, and are approved only for testing limited organisms and drugs. Modifications to the methods and alternative approaches have been proposed to make these tests more convenient and efficient, applicable to a greater number of species, and appropriate for performing in the clinical laboratory.

Comparison of Etest with the broth microdilution method in susceptibility testing of yeast isolates against four antifungals

A comparative evaluation of the Etest and the broth microdilution methods for antifungal susceptibility testing of 102 clinical yeast isolates against amphotericin B, fluconazole, itraconazole, and ketoconazole was conducted. The agreements between the Etest and the broth microdilution methods were 93.1% for amphotericin B 85.2% for ketoconazole, 82.3% for itraconazole and 79.4% for fluconazole. These results suggest that the Etest approach to antifungal susceptibility testing may be a viable alternative to the NCCLS reference methods for testing yeasts, but that further evaluations are needed.

Effects of amphotericin B and three azole derivatives on the lipids of yeast cells of Paracoccidioides brasiliensis

Yeast cells of five different strains of Paracoccidioides brasiliensis were obtained for partial analysis of lipid composition, and sterol content was determined quantitatively and qualitatively. The determinations were conducted with cells cultured in the presence and absence of amphotericin B and azole derivatives at levels below the MIC.

In vitro antifungal susceptibility of clinical isolates of Candida spp. from hospitalized patients

A total of 122 Candida spp. strains, isolated from a group of 100 patients hospitalized in the Santa Casa de Misericordia of Belo Horizonte were assayed for in vitro susceptibility to amphotericin B, fluconazole, itraconazole, ketoconazole and flucytosine using a microbroth technique proposed by the National Committee for Clinical Laboratory Standards. In this study large variations were observed among minimum inhibitory concentration values depending on the species tested. The statistical analysis (Kruskal-Wallis test) showed that itraconazole and flucytosine were the more efficient antifungal drugs for most of species, and amphotericin B and fluconazole were the least efficient.

Fluorometric assessment of In vitro antidermatophytic activities of antimycotics based on their keratin-penetrating power

Keratin particles impregnated with amorolfine or clotrimazole in serial doubling dilutions (64 to 0.125 microg/ml) were used to evaluate the activities of these agents against 20 isolates each of Trichophyton mentagrophytes and Trichophyton rubrum in a yeast carbon broth medium incorporating Alamar Blue dye. The proposed MIC with keratin impregnation (MIC(K)) is defined as the lowest concentration of an agent used to impregnate keratin particles that effects a fluorescence-based fungal growth quotient of 0.05 or less. The conventional colorimetric and visual MICs of amorolfine for the dermatophytes, </=0.03 microg/ml for T. mentagrophytes and </=0.063 microg/ml for T. rubrum, were approximately half of those of clotrimazole for the same isolates. The superiority of the MIC(K)s of amorolfine for isolates of T. mentagrophytes (2.0 microg/ml; range, 0.5 to 8.0 microg/ml) and T. rubrum (4.0 microg/ml; range, 2. 0 to 8.0 microg/ml) over those of clotrimazole (32 microg/ml [range, 8.0 to >64 microg/ml] and 64 microg/ml [range, 16 to >64 microg], respectively) may indicate the strong in vivo antidermatophytic activity of amorolfine as a topical agent. The new antidermatophytic susceptibility testing procedure has potential clinical utility for the in vitro screening of agents for use in the topical treatment of superficial mycoses.

Antifungal susceptibility testing of yeasts: uses and limitations

With recent developments in the field of mycology, such as increased incidence of fungal infections, the introduction of newer, safer antifungals, and the emergence of resistance, the need for clinically relevant antifungal susceptibility testing methods is obvious. Studies performed over the past decade have allowed the National Committee for Clinical Laboratory Standards Subcommittee on Antifungal Testing to achieve consensus on a new standardized broth dilution method for in vitro susceptibility testing of yeasts (NCCLS M27-A). Once the reproducibility of the M27-A document was established, tentative breakpoints for fluconazole and itraconazole were derived. The availability of a standardized procedure for determining the minimum inhibitory concentrations (MICs) of antifungal agents is an important tool in drug discovery and development. In addition, it provides means for detection of resistant strains and, in the case of oropharyngeal candidiasis, means for patient management. Copyright 2000 Harcourt Publishers Ltd.

Antifungal susceptibilities of Paecilomyces species

The MICs and minimum fungicidal concentrations (MFCs) of amphotericin B, miconazole, itraconazole, ketoconazole, fluconazole, and flucytosine for 52 isolates of Paecilomyces species were evaluated by the broth microdilution method, largely based on the recommendations of the National Committee for Clinical Laboratory Standards (document M27-A). The fungal isolates tested included 16 P. variotii, 11 P. lilacinus, 9 P. marquandii, 6 P. fumosoroseus, 4 P. javanicus, and 2 P. viridis isolates and 1 isolate of each of the following species: P. carneus, P. farinosus, P. fulvus, and P. niveus. The MFCs and the MICs at which 90% of isolates were inhibited (MIC90s) for the six antifungal agents were remarkably high; the MIC50s indicated that amphotericin B, miconazole, itraconazole, and ketoconazole had good activities, while fluconazole and flucytosine demonstrated poor efficacy. The ranges of the MICs were generally wider and lower than those of the MFCs. There were significant susceptibility differences among the species. All species with the exception of P. variotii were highly resistant to fluconazole and flucytosine; P. variotii was susceptible to flucytosine. Amphotericin B and the rest of the azoles showed good activity against P. variotii, while all the antifungal agents assayed showed low efficacy against P. lilacinus.

Comparative evaluation of FUNGITEST and broth microdilution methods for antifungal drug susceptibility testing of Candida species and Cryptococcus neoformans

The FUNGITEST method (Sanofi Diagnostics Pasteur, Paris, France) is a microplate-based procedure for the breakpoint testing of six antifungal agents (amphotericin B, flucytosine, fluconazole, itraconazole, ketoconazole, and miconazole). We compared the FUNGITEST method with a broth microdilution test, performed according to National Committee for Clinical Laboratory Standards document M27-A guidelines, for determining the in vitro susceptibilities of 180 isolates of Candida spp. (50 C. albicans, 50 C. glabrata, 10 C. kefyr, 20 C. krusei, 10 C. lusitaniae, 20 C. parapsilosis, and 20 C. tropicalis isolates) and 20 isolates of Cryptococcus neoformans. Overall, there was 100% agreement between the methods for amphotericin B, 95% agreement for flucytosine, 84% agreement for miconazole, 83% agreement for itraconazole, 77% agreement for ketoconazole, and 76% agreement for fluconazole. The overall agreement between the methods exceeded 80% for all species tested with the exception of C. glabrata (71% agreement). The poorest agreement between the results for individual agents was seen with C. glabrata (38% for fluconazole, 44% for ketoconazole, and 56% for itraconazole) and C. tropicalis (50% for miconazole). The FUNGITEST method misclassified as susceptible 2 of 12 (16.6%) fluconazole-resistant isolates, 2 of 10 (20%) itraconazole-resistant isolates, and 4 of 8 (50%) ketoconazole-resistant isolates of several Candida spp. Further development of the FUNGITEST procedure will be required before it can be recommended as an alternative method for the susceptibility testing of Candida spp. or C. neoformans.

Inhibition of RNA synthesis as a therapeutic strategy against Aspergillus and Fusarium: demonstration of in vitro synergy between rifabutin and amphotericin B

We investigated the in vitro antifungal activity of amphotericin B, alone and in combination with rifabutin, an inhibitor of bacterial RNA polymerase, against 26 clinical isolates of Aspergillus and 25 clinical isolates of Fusarium. Synergy or additivism between these drugs was demonstrated against all isolates tested. Amphotericin B MICs were reduced upon combination with rifabutin from a mean of 0.65 microg/ml to a mean of 0.16 microg/ml against Aspergillus, and from a mean of 0.97 microg/ml to a mean of 0.39 microLg/ml against Fusarium (P < 0.000001 for both). Similarly, the MICs of rifabutin were reduced upon combination with amphotericin B from a mean of >32 microg/ml to a mean of 1.1 microg/ml against both fungi (P < 0.000001 for both). These positive interactions were corroborated by a colony count study with two Fusarium isolates, for which treatment with the combination of subinhibitory concentrations of amphotericin B (at concentrations 2- and 4-fold less than the MIC) and rifabutin (at concentrations ranging from 4- to 64-fold less than the MIC) resulted in 3.2-log reductions in colony counts compared to those after treatment with either drug alone. Inhibition of RNA synthesis was shown to be the mechanism of antifungal activity. These results suggest that inhibition of fungal RNA synthesis might be a potential target for antifungal therapy.

Effects of three azole derivatives on the lipids of different strains of Sporothrix schenckii

The comparative effects of ketoconazole, itraconazole, and fluconazole on the lipids of five Sporothrix schenckii strains were investigated. Quantitative analysis of lipids and sterols was completed, as well as qualitative analysis of sterols, by thin-layer chromatography and ultraviolet spectrophotometry. Growth of the S. schenckii isolates in the presence of azole derivative concentrations below the minimum inhibitory concentration (MIC) resulted in significant alterations in the lipid and sterol contents as compared with the control values. Furthermore, lanosterol was detected in these azole-treated cells. These results were in complete agreement with the proposed mechanism of action of azoles, which act by inhibiting ergosterol biosynthesis with a consequent accumulation of lanosterol. Concerning the MIC values, fluconazole was found to be the least effective drug. On the other hand, as determined from a comparison of the effects of the three azoles on the sterol content of the strains studied, no significant differences in efficacy were found among the tested drugs.

Comparison of a photometric method with standardized methods of antifungal susceptibility testing of yeasts

We determined the fluconazole MICs for 101 clinical isolates of Candida and Cryptococcus neoformans using the macro- and microdilution methods recommended by the National Committee for Clinical Laboratory Standards. We compared the MICs obtained by these methods with those obtained by a photometric assay that quantified the reduction of 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) by viable fungi. The MIC determined by this method was defined as the highest fluconazole concentration associated with the first precipitous drop in optical density. For Candida, both the MTT and the microdilution methods demonstrated excellent agreement with the standard macrodilution method. The MTT method, however, generated MICs at 24 h that were comparable to those generated by the standard macrodilution method, whereas the microdilution method required 48 h. For C. neoformans, the levels of agreement between the MICs determined by the MTT and microdilution methods after 48 h and those determined by the standard 72-h macrodilution method were 94% (29 of 31) and 94% (29 of 31), respectively. The MTT method therefore provided results comparable to those of currently recommended methods and had the advantages of a more rapid turnaround time and potential adaptability to use as an automated system. Furthermore, the MICs determined by the MTT method were determined photometrically, thereby eliminating reader bias.

Azole resistance in Candida

Resistance of Candida to azoles is an increasing problem. Susceptibility testing of Candida against fluconazole and ketoconazole is now feasible and desirable. Good correlation of resistance in vitro with clinical failure of fluconazole therapy has now been shown in mucosal candidiasis. The relationship, if any, between resistance and clinical failure in the context of invasive candidiasis is not clear at present and additional correlative work needs to be done. Monitoring of resistance trends in Candida is clearly important now.

Evaluation of the E test for fluconazole susceptibility testing of Candida albicans isolates from oropharyngeal candidiasis

The aim of the present study was to evaluate the utility of the E test in determining the antifungal susceptibility of Candida albicans. Reproducibility of the E test was determined for amphotericin B, fluconazole, and itraconazole using three different solid media: RPMI 1640, Casitone, and yeast nitrogen base agar. Minimum inhibitory concentrations (MICs) were comparable (results at +/- 2 dilutions) in 92% of the tests for amphotericin B and in 100% for fluconazole and itraconazole. Determination of MIC endpoints was easiest on Casitone agar. Candida albicans isolates from 23 patients undergoing fluconazole therapy for oropharyngeal candidiasis were tested for fluconazole susceptibility. Good correlation was obtained between the MICs of fluconazole and clinical outcome. Clinical failure was associated with strains for which MICs were > or = 48 micrograms/ml. These results suggest that the E test has potential utility for fluconazole susceptibility testing of clinical yeast isolates.

Comparison study of broth macrodilution and microdilution antifungal susceptibility tests for the filamentous fungi

An evaluation of broth dilution antifungal susceptibility tests was performed by determining both the micro- and macrodilution MICs of amphotericin B, fluconazole, ketoconazole, 5-fluorocytosine, miconazole, and itraconazole against representative species of opportunistic hyphomycetes (Fusarium spp. and Cladosporium [Cladophialophora] spp.) and ascomycetes (Chaetomium spp.). A total of 78 strains were tested, the majority of them twice and some three times on different days. Both methods were performed according to the recommendations of the National Committee for Clinical Laboratory Standards (Document M27-P), with the exception of the temperature of incubation, which was 25 degrees C in our case. A spectrophotometric method for inoculum preparation, RPMI 1640 medium buffered with morpholinepropanesulfonic acid (pH 7.0), and an additive drug dilution procedure were used. The MICs obtained by the two methods were read after 48, 72, and 96 h of incubation for Fusarium spp. and after 72, 96, and 120 h for the remaining isolates. The kappa test was used to calculate the degree of agreement. Considering the three fungal groups together, a good agreement between the results of both tests was observed with almost all the drugs at the different incubation times. There were no cases of poor agreement. The highest level (kappa index = 1) was observed with ketoconazole at the second-day reading. These results support the further evaluation of the broth microdilution test as an alternative to the reference broth macrodilution susceptibility test.

A comparative study of the broth micro- and macro-dilution techniques for the determination of the in vitro susceptibility of Aspergillus fumigatus

The effects of inoculum size, medium, temperature, and duration of growth on the in vitro susceptibility testing of Aspergillus fumigatus were investigated using broth micro- and macro-dilution techniques. The minimum inhibitory concentrations (MICs) of ketoconazole, miconazole, itraconazole, fluconazole, and amphotericin B were significantly influenced by the inoculum size, regardless of the techniques used. Two- to four-fold higher MIC values were obtained when the inoculum size was increased 100-fold. The use of peptone yeast extract glucose and RPMI 1640 media provided essentially identical MIC values at 30 and 35 degrees C after incubation for 48 h or longer. A comparison of broth micro- and macro-dilution techniques revealed that, under equivalent conditions, the latter with an inoculum size between 1 x 10(3) and 1 x 10(4) conidia (strain W73355)/mL consistently provided the lowest MICs of fluconazole (256 micrograms/mL), ketoconazole (8 micrograms/mL), miconazole (2 micrograms/mL), itraconazole (0.25 micrograms/mL), and amphotericin B (0.25 micrograms/mL). Using the broth macrodilution technique we screened 24 clinical isolates of A. fumigatus obtained from the Detroit Medical Center in 1994. The MIC values of fluconazole, ketoconazole, miconazole, itraconazole and amphotericin B for all the isolates were 128-256, 8-16, 1-2, 0.25-0.5, and 0.25-1.0 micrograms/mL, respectively, indicating that none of the clinical isolates that we tested shows acquired resistance to the antifungals used.

Comparison of a spectrophotometric microdilution method with RPMI-2% glucose with the National Committee for Clinical Laboratory Standards reference macrodilution method M27-P for in vitro susceptibility testing of amphotericin B, flucytosine, and fluconazole against Candida albicans

The National Committee for Clinical Laboratory Standards has proposed a reference broth macrodilution method for in vitro antifungal susceptibility testing of yeasts (the M27-P method). This method is cumbersome and time-consuming and includes MIC endpoint determination by visual and subjective inspection of growth inhibition after 48 h of incubation. An alternative microdilution procedure was compared with the M27-P method for determination of the amphotericin B, flucytosine, and fluconazole susceptibilities of 8 American Type Culture Collection strains (6 of them were quality control or reference strains) and 50 clinical isolates of candida albicans. This microdilution method uses as culture medium RPMI 1640 supplemented with 18 g of glucose per liter (RPMI-2% glucose). Preparation of drugs, basal medium, and inocula was done by following the recommendations of the National Committee for Clinical Laboratory Standards. The MIC endpoint was calculated objectively from the turbidimetric data read at 24 h. Increased growth of C. albicans in RPMI-2% glucose and its spectrophotometric reading allowed for the rapid (24 h) and objective calculation of MIC endpoints compared with previous microdilution methods with standard RPMI 1640. Nevertheless, good agreement was shown between the M27-P method and this microdilution test. The MICs obtained for the quality control or reference strains by the microdilution method were in the ranges published for those strains. For clinical isolates, the percentages of agreement were 100% for amphotericin B and fluconazole and 98.1% for flucytosine. These data suggest that this microdilution method may serve as a less subjective and more rapid alternative to the M27-P method for antifungal susceptibility testing of yeasts.

Interlaboratory evaluation of Etest method for testing antifungal susceptibilities of pathogenic yeasts to five antifungal agents by using Casitone agar and solidified RPMI 1640 medium with 2% glucose

An interlaboratory evaluation (two centers) of the Etest method was conducted for testing the antifungal susceptibilities of yeasts. The MICs of amphotericin B, fluconazole, flucytosine, itraconazole, and ketoconazole were determined for 83 isolates of Candida spp., Cryptococcus neoformans, and Torulopsis glabrata. Two buffered (phosphate buffer) culture media were evaluated: solidified RPMI 1640 medium with 2% glucose and Casitone agar. MIC endpoints were determined after both 24 and 48 h of incubation at 35 degrees C. Analysis of 3,420 MICs demonstrated higher interlaboratory agreement (percentage of MIC pairs within a 2-dilution range) with Casitone medium than with RPMI 1640 medium when testing amphotericin B (84 to 90% versus 1 to 4%), itraconazole (87% versus 63 to 74%), and ketoconazole (94 to 96% versus 88 to 90%). In contrast, better interlaboratory reproducibility was determined between fluconazole MIC pairs when RPMI 1640 medium rather than Casitone medium was used (96 to 98% versus 77 to 90%). Comparison of the flucytosine MICs obtained with RPMI 1640 medium revealed greater than 80% reproducibility. The study suggests the potential value of the Etest as a convenient alternative method for testing the susceptibilities of yeasts. It also indicates the need for further optimization of medium formulations and MIC endpoint criteria to improve interlaboratory agreement.

Factors affecting the results of a broth microdilution antifungal susceptibility testing in vitro

In experiments involving 10 antifungal drugs and 46 strains of potentially pathogenic fungi, the factors affecting the results of in vitro susceptibility testing were studied. The composition of the test medium, inoculum size, temperature and length of incubation were the most pronounced effects influencing the results of testing in vitro. Minimal inhibitory concentrations (MIC) of the antimycotics tested were lowest in complex media (Brain Heart Infusion, Antibiotic Medium 3, Sabouraud broth) except for 5-fluorocytosine which was most effective in Yeast Nitrogen Base medium. Inoculum sizes of 10(3) to 10(4) cfu* mL(-1) had no marked effect on MIC but starting from a final concentration of 10(5) cfu*mL(-1), an abrupt increase in MIC in azole derivatives and 5-fluorocytosine was observed. There was a direct relationship between the duration of incubation and MIC of fungistatic antimycotics. The influence of the incubation temperature became generally manifest primarily in fungi with retarded growth at elevated temperature (>35 degrees C). In these fungal species, a tendency towards a decrease in MIC with increasing temperature was apparent. The other factors studied (medium pH, buffer, solvent) had no substantial influence on the antifungal activity of the drugs tested.

Susceptibility testing of fungi: current status of correlation of in vitro data with clinical outcome

In summary, it is clear that in vitro susceptibility testing can predict outcome in selected clinical situations. The clearest data are from the fluconazole-treated AIDS patients with oropharyngeal candidiasis. In this setting, the homogeneity of the underlying immune defect, combined with the ease of identification and monitoring of the infection, creates a near-perfect test situation. In more complex scenarios, such as the heterogeneous population of patients enrolled in a recent study of candidemia, no such clear-cut correlation was present. The importance of host factors in the correlation of the MIC with outcome cannot be overemphasized. Examples of these parameters include patient status (underlying disease, the presence of intravascular catheters, and CD4+ T-cell number), drug pharmacokinetics (absorption and distribution), patient compliance, and drug-drug interactions. Identification of relevant factors can substantially improve the degree of the MIC-outcome correlation and thus improve the clinical utility of in vitro testing. An important feature in this entire process is the role of standardized susceptibility testing procedures. While not without flaws, the proposed NCCLS reference method has been invaluable in allowing multiple investigators to contribute data that can be used to clarify the correlation between the fluconazole MIC and outcome. While the development of simplified second-generation methods is eagerly anticipated, the role of the reference method as a common touchstone is critical. Only by use of either the reference method itself or methods with a known relationship to the reference method can this broad collaborative process really proceed. Current work is focusing on defining interpretive breakpoints for fluconazole and Candida species, refinement of the in vitro procedures used to measure susceptibility to amphotericin B, ketoconazole, and itraconazole, and the acquisition of a broad base of data on the relationship between the MIC and outcome for these three drugs. Although considerable work remains to be done, the available data suggest that solutions to each of these problems are possible and that routine susceptibility testing of fungi will become meaningful for clinical decision making in the foreseeable future.

In vitro susceptibilities of clinical and environmental isolates of Cryptococcus neoformans to five antifungal drugs

A total of 53 Cryptococcus neoformans strains, including clinical and environmental Brazilian isolates, were tested for their susceptibilities to amphotericin B, 5-flucytosine, ketoconazole, fluconazole, and itraconazole. The tests were performed according to the National Committee of Clinical Laboratory Standards recommendations (document M27-P). In general, there was a remarkable homogeneity of results for all strains, and comparable MICs were found for environmental and clinical isolates. This paper represents the first contribution in which susceptibility data for Brazilian C. neoformans isolates are provided.

Molecular karyotyping of multiple yeast species isolated from nine patients with AIDS during prolonged fluconazole therapy

Variations in molecular karyotype and fluconazole susceptibility of serial yeast isolates from the oral cavities of nine patients with AIDS receiving fluconazole for single or multiple episodes of oropharyngeal candidiasis were monitored. Multiple yeast species were isolated from the initial oral specimens in six patients. Molecular karyotyping identified at least eight different DNA subtypes of C. albicans, at least eight of T. glabrata and only one DNA subtype each of C. krusei, C. tropicalis and C. parapsilosis. Among isolates of T. glabrata, fluconazole MICs in each patient were consistently within one or two dilutions, regardless of strain variations. Similarly, among five patients monitored during one course of therapy, the MICs of fluconazole of C. albicans isolates of either the same or different DNA subtypes remained within two dilutions. However, increases in MICs of fluconazole of C. albicans were observed in four patients who received two or more courses of fluconazole, three of whom had the same DNA subtype and one of whom changed from one DNA subtype to another.

Effect of amphotericin B on the lipids of yeast cells of Sporothrix schenckii

Yeast cells of five strains of Sporothrix schenckii were obtained for partial analysis of lipid composition. Quantitative analysis of lipids and sterols were completed, as well as qualitative analysis of sterols by thin layer chromatography and by ultraviolet spectra. These determinations were made on cells cultured in the absence and presence of amphotericin B at sub-MIC (minimum inhibitory concentration) levels. Marked alterations in lipid content were observed in the amphotericin B-treated cells. The major alterations were the reduction of total lipid (18.7-57.6%) and sterols (48.5-96.7%) after exposure to the polyenic antibiotic. It is concluded that amphotericin B altered the lipid profiles, especially sterols of S. schenckii.

Comparison of two alternative microdilution procedures with the National Committee for Clinical Laboratory Standards reference macrodilution method M27-P for in vitro testing of fluconazole-resistant and -susceptible isolates of Candida albicans

The National Committee for Clinical Laboratory Standards has proposed a reference broth macrodilution method for in vitro antifungal susceptibility testing of yeasts (the M27-P method). This method is cumbersome and time-consuming and includes MIC endpoint determination by the visual and subjective inspection of growth inhibition after 48 h of incubation. Two alternative microdilution procedures for MIC endpoint determination, a spectrophotometric MIC endpoint test that evaluates 80% growth inhibition by the drug and a colorimetric method with an oxidation-reduction indicator (Alamar Blue), were compared with the M27-P method for fluconazole susceptibility testing of 45 susceptible and resistant isolates of Candida albicans. The spectrophotometric method was performed with RPMI 1640 medium with 2% glucose, and the other two tests were performed with plain RPMI 1640 medium. All tests were incubated at 35 degrees C. Excellent agreement was demonstrated between the M27-P method and both 24-h microdilution tests (97.7%) as well as between the two microdilution tests (95.5%). Also, there was agreement in the detection in vivo of fluconazole resistance by the three methods. These preliminary data indicate that both microdilution methods may serve as less subjective alternatives to the M27-P method for the determination of fluconazole MIC endpoints.

Comparative evaluation of macrodilution and alamar colorimetric microdilution broth methods for antifungal susceptibility testing of yeast isolates

A comparative evaluation of the macrodilution method and the Alamar colorimetric method for the susceptibility testing of amphotericin B, fluconazole, and flucytosine was conducted with 134 pathogenic yeasts. The clinical isolates included 28 Candida albicans, 17 Candida tropicalis, 15 Candida parapsilosis, 12 Candida krusei, 10 Candida lusitaniae, 9 Candida guilliermondii, 18 Torulopsis glabrata, and 25 Cryptococcus neoformans isolates. The macrodilution method was performed and interpreted according to the recommendations of the National Committee for Clinical Laboratory Standards (document M27-P), and the Alamar colorimetric method was performed according to the manufacturer's instructions. For the Alamar colorimetric method, MICs were determined at 24 and 48 h of incubation for Candida species and T. glabrata and at 48 and 72 h of incubation for C. neoformans. The overall agreement within +/- 1 dilution for Candida species and T. glabrata against the three antifungal agents was generally good, with the values for amphotericin B, fluconazole, and flucytosine being 85.3, 77.9, and 86.2%, respectively, at the 24-h readings and 69.3, 65.2, and 97.2%, respectively, at the 48-h readings. Most disagreement was noted with fluconazole against C. tropicalis and T. glabrata. Our studies indicate that determination of MICs at 24 h by the Alamar colorimetric method is a valid alternate method for testing amphotericin B, fluconazole, and flucytosine against Candida species but not for testing fluconazole against C. tropicalis and T. glabrata. For flucytosine, much better agreement can be demonstrated against Candida species and T. glabrata at the 48-h readings by the Alamar method. Excellent agreement within +/- dilution can also be observed for amphotericin B, fluconazole, and flucytosine (80, 96, and 96%, respectively) against c. neoformans when the MICs were determined at 72 h by the Alamar method.

Fatal meningoencephalitis caused by Scedosporium inflatum (Scedosporium prolificans) in a child with lymphoblastic leukemia

A fatal case of meningoencephalitis caused by Scedosporium inflatum (Scedosporium prolificans) in a 5-year-old boy with acute myeloblastic leukemia who was given intrathecal treatment is reported. Itraconazole treatment was ineffective. The fungus was identified on brain sections at autopsy and was not observed in any other organ. As no other portal of entry was detected, meningoencephalitis may have originated via direct introduction of the fungus at therapeutic lumbar puncture.

Effects of three azole derivatives on the lipids of different strains of Cryptococcus neoformans

The comparative effects of ketoconazole, itraconazole and fluconazole on the lipids of four Cryptococcus neoformans strains were investigated. Quantitative analysis of lipids and sterols was completed, as well as qualitative analysis of sterols by thin-layer chromatography and by the ultraviolet spectrum. Growth of the cryptococcal isolates in the presence of the azoles derivatives concentrations below the minimum inhibitory concentration resulted in significant alterations in the lipid and sterol contents as compared with the control values. Furthermore, lanosterol was detected in these azole-treated cells. These results were in complete agreement with the proposed mechanism of action of azoles, which act through the inhibition of ergosterol biosynthesis, with resultant accumulation of lanosterol. Ketoconazole was found to be the least effective drug, as determined from a comparison of the effect of the three azoles on the sterol content of the four strains. Itraconazole showed to be the most effective drug, probably because of its high lipophilicity, which allows the drug to penetrate into fungi cells more efficiently.

Comparison of visual and spectrophotometric methods of MIC endpoint determinations by using broth microdilution methods to test five antifungal agents, including the new triazole D0870

A study to compare three different methods for reading MIC endpoints tested by the broth microdilution modification of the National Committee for Clinical Laboratory Standards (Villanova, Pa.) reference method was conducted. MICs of amphotericin B, flucytosine, fluconazole, itraconazole, and a new triazole, D0870, were determined for five reference yeast strains and 100 clinical isolates of Candida spp. MICs were read visually according to National Committee for Clinical Laboratory Standards guidelines from microdilution trays that had been (VS) and had not been (V) shaken. MICs were also determined spectrophotometrically (SP) at 492 nm. SP endpoints were determined as the concentrations resulting in a > or = 50% inhibition of growth (flucytosine and azoles) and a > or = 90% inhibition of growth (amphotericin B) relative to control growth. The five reference strains were tested nine times each against all five antifungal agents, and the MIC results for each reading method were compared with a 3-log2 dilution reference range determined by the macrodilution (M27-P) method. Overall, 84 to 100% of the MICs determined by V, 93 to 100% of those determined by VS, and 89 to 100% of those determined by SP fell within the 3-log2 dilution reference range for each reference strain and antifungal agent. Reproducibility was 99% for V and SP and 98% for VS. Agreement among the three methods of reading ranged from 97 to 99%. Excellent agreement among reading methods was also observed for all antifungal agents when tested against 100 clinical isolates. Agreement between the standard V method (no agitation) and VS ranged from 99 to 100%, and that between V and SP ranged from 89 to 99%. The VS and SP reading methods provided more definitive endpoints than the V method, which does not involve shaking.

Detection of amphotericin B-resistant Candida isolates in a broth-based system

Because of the limited ability of the National Committee for Clinical Laboratory Standards proposed M27P methodology to detect resistance to amphotericin B by Candida isolates, we sought to identify alternative media and pH conditions that could reliably identify resistant isolates. Antibiotic Medium 3 broth (also known as Penassay broth) buffered to pH 5 or pH 7 produced superior results and readily identified a series of resistant isolates.

In vitro susceptibilities of clinical yeast isolates to three antifungal agents determined by the microdilution method

A comparative evaluation of the in vitro susceptibilities of 597 clinical yeast isolates to amphotericin B, fluconazole, and 5-fluorocytosine (5FC) was conducted. The broth macrodilution reference method of the National Committee for Clinical Laboratory Standards (NCCLS, M27-P) was adapted to the microdilution method. Microdilution endpoints for amphotericin B were scored as the lowest concentration in which a score of 0 (complete absence of growth) was observed and for 5FC and fluconazole as the lowest concentration in which a score of 2 (prominent decrease in turbidity; MIC-2) was observed compared to the growth control. The MIC values were read after 24 and 48 h incubation. A broad range of MIC values was observed with each antifungal agent. Amphotericin B was very active (MIC90 < or = 1.0 microgram/ml) against all of the yeast isolates with the exception of C. lusitaniae (MIC90 > or = 2.0 micrograms/ml). Fluconazole was most active against C. parapsilosis (MIC90 of 1.0 microgram/ml) and least active against C. krusei (MIC90 of 32 micrograms/ml). 5FC was most active against C. albicans, C. parapsilosis, C. tropicalis, and T. glabrata (MIC90 < or = 1.0 microgram/ml) and was least active against C. krusei and C. lusitaniae (MIC90 > or = 16 micrograms/ml). These data indicate that the microdilution method, performed in accordance with M27-P, provides a means of testing larger numbers of yeast isolates against an array of antifungal agents and allows this to be accomplished in a reproducible and standardized manner. Given these results, it appears that the microdilution method may be a useful alternative to the macrodilution reference method for susceptibility testing of yeasts.

Comparative and collaborative evaluation of standardization of antifungal susceptibility testing for filamentous fungi

The purpose of the study was to evaluate the interlaboratory agreement of broth dilution susceptibility methods for five species of conidium-forming (size range, 2 to 7 microns) filamentous fungi. The methods used included both macro- and microdilution methods that were adaptations of the proposed reference method of the National Committee for Clinical Laboratory Standards for yeasts (m27-P). The MICs of amphotericin B, fluconazole, itraconazole, miconazole, and ketoconazole were determined in six centers by both macro- and microdilution tests for 25 isolates of Aspergillus flavus, Aspergillus fumigatus, Pseudallescheria boydii, Rhizopus arrhizus, and Sporothrix schenckii. All isolates produced clearly detectable growth within 1 to 4 days at 35 degrees C in the RPMI 1640 medium. Colony counts of 0.4 x 10(6) to 3.3 x 10(6) CFU/ml (mean, 1.4 x 10(6) CFU/ml) were demonstrated in 90% of the 148 inoculum preparations. Overall, good intralaboratory agreement was demonstrated with amphotericin B, fluconazole, and ketoconazole MICs (90 to 97%). The agreement was lower with itraconazole MICs (59 to 79% median). Interlaboratory reproducibility demonstrated similar results: 90 to 100% agreement with amphotericin B, fluconazole, miconazole, and ketoconazole MICs and 59 to 91% with itraconazole MICs. Among the species tested, the MICs for S. schenckii showed the highest variability. The results of the study imply that it may be possible to develop a reference method for antifungal susceptibility testing of filamentous fungi.

Oral Candida albicans isolates with reduced susceptibility to fluconazole in Swedish HIV-infected patients

A total of 62 patients with HIV-related conditions were examined for clinical and mycological oral findings. Cultures from 51 patients were positive for yeasts and included 49 Candida albicans and 8 non-albicans isolates. Of patients with positive culture, 35% had pseudomembranous thrush. In vitro susceptibility testing of 49 C. albicans isolates revealed that the minimal inhibitory concentration for 50% of the strains (MIC50) was 2.0 mg/l for fluconazole, and the MIC50 was < or = 0.125 mg/l for both ketoconazole and itraconazole. Fluconazole resistance (MIC > or = 32.0 mg/l) was found for 14% of the C. albicans isolates tested. Two C. albicans isolates showed cross-resistance to ketoconazole and itraconazole. Associations between reduced susceptibility to fluconazole and low CD4+ cell counts, the length of time since the first AIDS-defining illness and the interval from the first fluconazole treatment, indirectly reflecting the total fluconazole exposure, were observed.