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Estimation of minimum sterol 14alpha-demethylation-inhibitory concentration of azoles in Candida yeasts using acetate-mediated growth inhibition: potential utility in susceptibility testing.

ABSTRACT: We have recently shown that 14alpha-demethylation-deficient cells of Candida albicans are subject to growth arrest by 0.24 M acetate in a yeast extract-peptone-glucose medium and that the minimum concentration of an azole antifungal agent required for total inhibition of sterol 14alpha-demethylation (MDIC for minimum demethylation-inhibitory concentration) is practically identical to its MIC determined in the acetate-supplemented medium (O. Shimokawa and H. Nakayama, Antimicrob. Agents Chemother. 43:100-105, 1999). In the present study we estimated the MDICs of three different azoles (fluconazole, ketoconazole, and itraconazole) for strains of various Candida species using this method and compared them with the MICs determined in the corresponding acetate-free medium. The results demonstrated that the test strains were divided into two classes. One class of strains was characterized by tolerance to 14alpha-demethylation deficiency (MIC > MDIC) and consisted of strains of C. albicans, C. guilliermondii, C. kefyr, and C. tropicalis. The other class was intolerant to 14alpha-demethylation deficiency (MIC approximately MDIC) and comprised strains of C. glabrata, C. krusei, and C. parapsilosis. We also showed that replacement of the yeast extract-peptone-glucose medium with RPMI 1640 medium did not affect the results substantially. Furthermore, the 80% inhibitory concentration (IC(80)) in RPMI 1640 medium, recommended as a substitute for the conventional MIC in susceptibility testing, was found to be close to the MDIC.

SUBMITTER: Shimokawa O

PROVIDER: S-EPMC87139 | biostudies-literature | 2000 Aug

REPOSITORIES: biostudies-literature

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Estimation of minimum sterol 14alpha-demethylation-inhibitory concentration of azoles in Candida yeasts using acetate-mediated growth inhibition: potential utility in susceptibility testing.

Shimokawa O O Nakayama H H

Journal of clinical microbiology 20000801 8

We have recently shown that 14alpha-demethylation-deficient cells of Candida albicans are subject to growth arrest by 0.24 M acetate in a yeast extract-peptone-glucose medium and that the minimum concentration of an azole antifungal agent required for total inhibition of sterol 14alpha-demethylation (MDIC for minimum demethylation-inhibitory concentration) is practically identical to its MIC determined in the acetate-supplemented medium (O. Shimokawa and H. Nakayama, Antimicrob. Agents Chemother ...[more]

PMID: 10921946

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Project description:BACKGROUND: In the fungal pathogen Candida albicans, amino acid substitutions of 14alpha-demethylase (CaErg11p, CaCYP51) are associated with azole antifungals resistance. This is an area of research which is very dynamic, since the stakes concern the screening of new antifungals which circumvent resistance. The impact of amino acid substitutions on azole interaction has been postulated by homology modeling in comparison to the crystal structure of Mycobacterium tuberculosis (MT-CYP51). Modeling of amino acid residues situated between positions 428 to 459 remains difficult to explain to date, because they are in a major insertion loop specifically present in fungal species. METHODOLOGY/PRINCIPAL FINDING: Fluconazole resistance of clinical isolates displaying Y447H and V456I novel CaErg11p substitutions confirmed in vivo in a murine model of disseminated candidiasis. Y447H and V456I implication into fluconazole resistance was then studied by site-directed mutagenesis of wild-type CaErg11p and by heterogeneously expression into the Pichia pastoris model. CLSI modified tests showed that V447H and V456I are responsible for an 8-fold increase in fluconazole MICs of P. pastoris mutants compared to the wild-type controls. Moreover, mutants showed a sustained capacity for producing ergosterol, even in the presence of fluconazole. Based on these biological results, we are the first to propose a hybrid homology structure-function model of Ca-CYP51 using 3 different homology modeling programs. The variable position of the protein insertion loop, using different liganded or non-liganded templates of recently solved CYP51 structures, suggests its inherent flexibility. Mapping of recognized azole-resistant substitutions indicated that the flexibility of this region is probably enhanced by the relatively high glycine content of the consensus. CONCLUSIONS/SIGNIFICANCE: The results highlight the potential role of the insertion loop in azole resistance in the human pathogen C. albicans. This new data should be taken into consideration for future studies aimed at designing new antifungal agents, which circumvent azole resistance.

Dataset Information

Estimation of minimum sterol 14alpha-demethylation-inhibitory concentration of azoles in Candida yeasts using acetate-mediated growth inhibition: potential utility in susceptibility testing.

Publications

Estimation of minimum sterol 14alpha-demethylation-inhibitory concentration of azoles in Candida yeasts using acetate-mediated growth inhibition: potential utility in susceptibility testing.

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