Development of reference procedures for broth microdilution antifungal susceptibility testing of yeasts with standardized endpoint determination

Comparative Evaluation of Standard Dilution Method and Commercial Kit for Frozen Plate Antifungal Susceptibility Testing of Yeasts Using 200 Clinical Isolates

A comparative evaluation of standard microdilution methods and a commercial kit for frozen plate antifungal susceptibility testing of yeasts was performed using amphotericin B, flucytosine, fluconazole, miconazole, and itraconazole on 200 yeast isolates. The isolates included 100 strains of Candida albicans, eight of C. tropicalis, twelve of C. parapsilosis, eight of C. glabrata, five of Cryptococcus neoformans, thirteen of Trichosporon asahii, and 54 other strains of seven other species of ascomycotic yeasts. Microdilution testing was performed according to the standard method for antifungal susceptibility testing published by the Japanese Society for Medical Mycology (JSMM), which are a modification of the method developed by the National Committee for Clinical Laboratory Standards (NCCLS) M27-P. The commercial kit was prepared according to the manufacturer's instructions. The degree of agreement within +/-1 dilution for 200 clinical isolates against five antifungal agents was excellent with values for amphotericin B, flucytosine, fluconazole, miconazole, and itraconazole of 100%, 99.0%, 97.5%, 97.0%, and 97.0%, respectively. Overall, the frozen plate antifungal susceptibility testing kit provided convenient and reproducible results comparable to those obtained with the JSMM standard method.

Multicenter Evaluation of Commercial Frozen Plates for Microdilution Broth Antifungal Susceptibility Testing of Yeasts and Comparison of MIC Limits Recommended in NCCLS M27-A2

A commercial kit, Frozen Plate for Antifungal Susceptibility Testing of Yeasts, Eiken (Eiken Chemical Co., Ltd., Tokyo), was tested in a multi-institute study to evaluate the agreement between interinstitute MICs and National Committee for Clinical Laboratory Standards (NCCLS) M27-A2 recommendation limits of MIC value. The kit was reported as a method equivalent to the standardized guidelines for antifungal susceptibility testing by the Committee for Clinical Laboratory Standards-1994, the Japanese Society for Medical Mycology, and which is widely used in Japan for amphotericin B, flucytosine, fluconazole, miconazole, and itraconazole. The degrees of inter-institute and NCCLS agreements were good to excellent especially with 48-hr incubation for all antifungal agents. However, the percent agreements to NCCLS recommendations against itraconazole were poor. Overall, MIC values obtained using the frozen plate antifungal susceptibility testing kit, with 48-hr incubation, were thought to be reliable and convenient alternatives to the data obtained by the NCCLS M27-A2 reference macrodilution and microdilution method. This kit will allow matching of results between international laboratories. However, the MIC value for itraconazole requires careful interpretation.

In vitro and in vivo activities of HQQ-3, a new triazole antifungal agent

The activity of HQQ-3, a new triazole antifungal agent, was evaluated and compared with those of fluconazole, ketoconazole and terbinafine in vitro and with fluconazole in vivo. HQQ-3 exhibited potent in vitro activity against clinically important fungi. The activity of HQQ-3 against Candida spp. was superior to those of fluconazole and terbinafine and comparable or superior to that of ketoconazole. HQQ-3 retained potent activity against Candida albicans strains with low levels of susceptibility to fluconazole (fluconazole MIC80s range, 4 to >64 microg/ml). Against Cryptococcus neoformans and filamentous fungi, the activity of HQQ-3 was superior to that of fluconazole. HQQ-3 also exhibited potent in vivo activity against murine systemic infections caused by C. albicns and C. krusei. The 50% effective doses against these infections were 0.12 to 1.9 mg/kg of body weight. These result suggest that HQQ-3 may be useful in the treatment of candidiasis.

In Vitro Antifungal Activity of ZJ-522, a New Triazole Restructured from Fluconazole and Butenafine, against Clinically Important Fungi in Comparison with Fluconazole and Butenafine

The antifungal activity of ZJ-522, a new triazole antifungal agent restructured from fluconazole and butenafine, was compared to that of fluconazole and butenafine against 43 strains of fungi representing 13 fungal species. MICs were determined by using the National Committee for Clinical Laboratory Standards (NCCLS)-recommended broth microdilution method for yeasts, which was modified for filamentous fungi. ZJ-522 was about 50-fold and 2 to 16-fold more potent than fluconazole against yeasts and filamentous fungi respectively, but it was less active than butenafine against filamentous fungi, although butenafine was inactive against most yeasts. Thus, the fashion of ZJ-522 antifungal activity more similar to that of fluconazole than that of butenafine indicates that ZJ-522 should be an inhibitor of lanosterol 14alpha-demethylase but not of squalene epoxidase, and should be a candidate for clinical development.

In vitro and in vivo activities of CS-758 (R-120758), a new triazole antifungal agent

The activity of CS-758 (R-120758), a new triazole antifungal agent, was evaluated and compared with those of fluconazole, itraconazole, and amphotericin B in vitro and with those of fluconazole and itraconazole in vivo. CS-758 exhibited potent in vitro activity against clinically important fungi. The activity of CS-758 against Candida spp. was superior to that of fluconazole and comparable or superior to those of itraconazole and amphotericin B. CS-758 retained potent activity against Candida albicans strains with low levels of susceptibility to fluconazole (fluconazole MIC, 4 to 32 microg/ml). Against Aspergillus spp. and Cryptococcus neoformans, the activity of CS-758 was at least fourfold superior to those of the other drugs tested. CS-758 also exhibited potent in vivo activity against murine systemic infections caused by C. albicans, C. neoformans, Aspergillus fumigatus, and Aspergillus flavus. The 50% effective doses against these infections were 0.41 to 5.0 mg/kg of body weight. These results suggest that CS-758 may be useful in the treatment of candidiasis, cryptococcosis, and aspergillosis.

Effect of sealing and Tween 80 on the antifungal susceptibility testing of essential oils

Concentrations of essential oils showing high volatility decreased substantially in broth and agar media when incubated under open conditions. The decrease in the half life was from 0.7 to 38 hr in broth medium at 27 C. When evaporation was prevented by sealing, MIC values against Aspergillus fumigatus, Candida albicans and Trichophyton mentagrophytes by broth or agar dilution assay were lowered two to eight-fold, as compared with those obtained under open conditions. Addition of Tween 80 caused a rise of the MICs against A. fumigatus by two to four-fold in broth dilution assay, but little affected the MICs in agar dilution assay.

Blood lysate staining, a new microscopic method for diagnosis of fungemia using peripheral blood

We developed a microscopy method for the detection of fungal cells in peripheral blood, termed blood lysate staining, using an approximately 5x5 mm dotted blood lysate. This method was able to detect the emerging fungal pathogen Trichosporon asahii in murine models of systemic fungal infection and fungemia in patients quickly and at minimal cost. Pathogenic yeasts were successfully detected in 6 of 8 blood samples which were taken from feverish immunocompromised patients who were clinically suspected of having fungal infections. Fungal cells were observed as ovoid to elongated, 3x3 to 7x10 microm, and occurred singly, budding, and in short chains and clusters in a periodic acid-Schiff-stained blood smear. The yeast cells were easily distinguished from blood-cell debris by their size, shape and smooth yet rigid outline.

Inhibitory effect of essential oils on apical growth of Aspergillus fumigatus by vapour contact

The inhibitory effect of seven essential oils on the apical growth of hyphae of Aspergillus fumigatus was studied using a bio cell tracer by vapour contact in a sealed vessel. Based on the inhibitory pattern, these essential oils were classified into three groups. The first group, composed of citron, lavender and tea tree oils, stopped the apical growth in a loading dose of 63 micrograms ml-1 air, but allowed the regrowth of the hyphae after removal of the vapour, indicating fungistatic action. The second group, consisting of perilla and lemon-grass oils, stopped the apical growth in a loading dose of 6.3 micrograms ml-1 air, and did not allow the regrowth after gaseous contact at 63 micrograms ml-1 air, indicative of fungicidal action. The third group, consisting of cinnamon bark and thyme oils, retarded the growth in a dose of 6.3 micrograms ml-1 air, stopped it in a dose of 63 micrograms ml-1 air, and incompletely suppressed regrowth of the hyphae. Gas chromatographic analysis revealed that vapours of essential oils were absorbed on fungal mycelia and agar medium most abundantly by the first group, followed by the second and third groups, reflecting the volatility of the respective groups. Suppression of the apical growth by vapour contact was ascribed to the direct deposition of essential oils on fungal mycelia, together with an indirect effect via the agar medium absorbed.

Quantitation of ergosterol content: novel method for determination of fluconazole susceptibility of Candida albicans

MIC end points for the most commonly prescribed azole antifungal drug, fluconazole, can be difficult to determine because its fungistatic nature can lead to excessive "trailing" of growth during susceptibility testing by National Committee for Clinical Laboratory Standards broth macrodilution and microdilution methods. To overcome this ambiguity, and because fluconazole acts by inhibiting ergosterol biosynthesis, we developed a novel method to differentiate fluconazole-susceptible from fluconazole-resistant isolates by quantitating ergosterol production in cells grown in 0, 1, 4, 16, or 64 microg of fluconazole per ml. Ergosterol was isolated from whole yeast cells by saponification, followed by extraction of nonsaponifiable lipids with heptane. Ergosterol was identified by its unique spectrophotometric absorbance profile between 240 and 300 nm. We used this sterol quantitation method (SQM) to test 38 isolates with broth microdilution end points of </=8 microg/ml (susceptible), 16 to 32 microg/ml (susceptible dose-dependent [SDD]), or >/=64 microg/ml (resistant) and 10 isolates with trailing end points by the broth microdilution method. No significant differences in mean ergosterol content were observed between any of the isolates grown in the absence of fluconazole. However, 18 susceptible isolates showed a mean reduction in ergosterol content of 72% after exposure to 1 microg of fluconazole/ml, an 84% reduction after exposure to 4 microg/ml, and 95 and 100% reductions after exposure to 16 and 64 microg of fluconazole/ml, respectively. Ten SDD isolates showed mean ergosterol reductions of 38, 57, 73, and 99% after exposure to 1, 4, 16, and 64 microg of fluconazole/ml, respectively. In contrast, 10 resistant isolates showed mean reductions in ergosterol content of only 25, 38, 53, and 84% after exposure to the same concentrations of fluconazole. The MIC of fluconazole, by using the SQM, was defined as the lowest concentration of the drug which resulted in 80% or greater inhibition of overall mean ergosterol biosynthesis compared to that in the drug-free control. Of 38 isolates which gave clear end points by the broth microdilution method, the SQM MIC was within 2 dilutions of the broth microdilution MIC for 33 (87%). The SQM also discriminated between resistant and highly resistant isolates and was particularly useful for discerning the fluconazole susceptibilities of 10 additional isolates which gave equivocal end points by the broth microdilution method due to trailing growth. In contrast to the broth microdilution method, the SQM determined trailing isolates to be susceptible rather than resistant, indicating that the SQM may predict clinical outcome more accurately. The SQM may provide a means to enhance current methods of fluconazole susceptibility testing and may provide a better correlation of in vitro with in vivo results, particularly for isolates with trailing end points.