Enuo Chen

Correlation between E-Test, Disk Diffusion, and Microdilution Methods for Antifungal Susceptibility Testing of Fluconazole and Voriconazole

ABSTRACT The activities of fluconazole and voriconazole against isolates of Candida spp. (n = 400) were tested by the E-test, disk diffusion, and the National Committee for Clinical Laboratory Standards (NCCLS) M27-A2 broth microdilution-based reference methods. More than 96% of isolates found to be susceptible to fluconazole by the reference method were identified as susceptible by the agar-based methods. Lesser degrees of correlation with the reference method were seen for isolates identified as resistant by the agar-based methods. Interpretive categories are not available for voriconazole, but results qualitatively similar to those for fluconazole were seen. The agar-based E-test and disk diffusion methods are reliable alternatives to the NCCLS M27-A2 reference microdilution method for isolates that test susceptible to fluconazole.

In Vitro Antifungal Susceptibilities of Trichosporon Species

ABSTRACT The in vitro activities of amphotericin B, itraconazole, fluconazole, voriconazole, posaconazole, and ravuconazole against 39 isolates of Trichosporon spp. were determined by the NCCLS M27-A microdilution method. The azoles tested appeared to be more potent than amphotericin B. Low minimal fungicidal concentration/MIC ratios were observed for voriconazole, posaconazole, and ravuconazole, suggesting fungicidal activity.

Differences in beta-glucan levels in culture supernatants of a variety of fungi.

(1-->3)-beta-d-glucan is a well known cell wall constituent of fungal isolates that can be detected by assays in vivo and in vitro. Previous studies have shown that different fungal isolates may show different levels of reactivity with an assay for beta glucan. In this study we evaluated the in vitro reactivity of 127 clinical fungal isolates belonging to 40 different genera, with the Glucatell assay. The majority of the fungal isolates released high levels of beta glucan. Beta glucan test reactivity appears to be species-specific and this may reflect the beta glucan content of the organism.

In Vitro Synergy Testing of Anidulafungin with Itraconazole, Voriconazole, and Amphotericin B against Aspergillus spp. and Fusarium spp

ABSTRACT The in vitro interactions of anidulafungin with itraconazole, voriconazole, and amphotericin B were evaluated by using the checkerboard method. For Aspergillus spp., anidulafungin with amphotericin B showed indifference for 16/26 isolates, while anidulafungin with either azole showed a synergy trend for 18/26 isolates. All drug combinations showed indifference for 7/7 Fusarium sp. isolates.

In Vitro Activity of Anidulafungin against Selected Clinically Important Mold Isolates

ABSTRACT In this study, we evaluated the in vitro activity of anidulafungin against selected mold isolates. Anidulafungin showed promising activity against Bipolaris spicifera, Exophiala jeanselmei, Fonsecaea pedrosoi, Madurella mycetomatis, Penicillium marneffei, Phialophora verrucosa, Pseudallescheria boydii, Sporothrix schenckii, and Wangiella dermatitidis.

In Vitro Activities of Investigational Triazoles against Fusarium Species: Effects of Inoculum Size and Incubation Time on Broth Microdilution Susceptibility Test Results

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

Correlation between Microdilution, E-test, and Disk Diffusion Methods for Antifungal Susceptibility Testing of Posaconazole against Candida spp.

ABSTRACT Agar-based antifungal susceptibility testing is an attractive alternative to the microdilution method. We examined the correlation between the microdilution, E-test, and disk diffusion methods for posaconazole against Candida spp. A total of 270 bloodstream isolates of Candida spp. with a broad range of posaconazole MICs were tested using the CLSI M27-A2 method for microdilution, as well as the M-44A method and E-test methods for agar-based testing on Mueller-Hinton agar supplemented with 2% glucose and 0.5 μg of methylene blue. MICs and inhibitory zone diameters at the prominent growth reduction endpoint were recorded at 24 and 48 h. The Candida isolates included Candida albicans (n = 124), C. parapsilosis (n = 44), C. tropicalis (n = 41), C. glabrata (n = 36), C. krusei (n = 20), C. lusitaniae (n = 3), and C. dubliniensis (n = 2). The overall concordance (i.e., the percentage of isolates within two dilutions) between the E-test and microdilution was 64.8% at 24 h and 82.6% at 48 h. When we considered an arbitrary breakpoint of ≤1 μg/ml, the agreement between the E-test and microdilution methods was 87.8% at 24 h and 93.0% at 48 h. The correlation of MICs with disk diffusion zone diameters was better for the E-test than the microdilution method. Zone correlation for diameters produced by the disks of two manufacturers was high, with a Pearson test value of 0.941 at 24 h. The E-test and microdilution MICs show good concordance and interpretative agreement. The disk diffusion zone diameters are highly reproducible and correlate well with both the E-test and the microdilution method, making agar-based methods a viable alternative to microdilution for posaconazole susceptibility testing.

Evaluation of a method for identification of Candida dubliniensis bloodstream isolates

ABSTRACT To evaluate methods for differentiating Candida albicans and Candida dubliniensis, 772 putative C. albicans bloodstream isolates were tested for growth at 37 and 42°C. Isolates showing no growth at 42°C, abundant chlamydospore production, and the sugar assimilation pattern of the type strain were confirmed by DNA-based procedures to be C. dubliniensis.

Differential Antifungal Activity of Isomeric Forms of Nystatin

ABSTRACT When nystatin is placed in RPMI and other biological fluids, there is loss of pure nystatin, with the development of two distinguishable chromatographic peaks, 1 and 2. Peak 1 appears identical to commercially prepared nystatin. By nuclear magnetic resonance (NMR) and mass spectral analysis, peak 2 appears to be an isomer of peak 1. The isomers are quantitatively and fully interconvertible. Formation of peak 2 is accelerated at a pH of >7.0 and ultimately reaches a near 55:45 (peak 1/peak 2 ratio) mixture. We sought to determine the relative activities of peaks 1 and 2 against Candidaspp. Peak 2 consistently showed higher MICs when it was the predominant form during the experiment. Time-kill analyses showed that peak 2 required ≥8× the concentration of peak 1 to produce a modest and delayed killing effect, which was never of the same magnitude as that produced by peak 1. In both types of assays, the activity of peak 2 corresponded with intra-assay formation of peak 1. Both MIC measurements and time-kill analysis suggest that peak 2 has considerably less activity, if any at all, againstCandida spp. Peak 2 may serve as a reservoir for peak 1.

Activity of Anidulafungin in a Murine Model of Candida krusei Infection: Evaluation of Mortality and Disease Burden by Quantitative Tissue Cultures and Measurement of Serum (1,3)-β-d-Glucan Levels

ABSTRACT Experience with anidulafungin against Candida krusei is limited. Immunosuppressed mice were injected with 1.3 × 107 to 1.5 × 107 CFU of C. krusei. Animals were treated with saline, 40 mg/kg fluconazole, 1 mg/kg amphotericin B, or 10 and 20 mg/kg anidulafungin for 5 days. Anidulafungin improved survival and significantly reduced the number of CFU/g in kidneys and serum β-glucan levels.