Browsing by Author "Ko, Hui-Ching"

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Candida albicans ENO1 null mutants exhibit altered drug susceptibility, hyphal formation, and virulence
(2013-06-01)
Ko, Hui-Ching
;
Hsiao, Ting-Yin
;
Chen, Chiung-Tong
;
Yang, Yun-Liang
;
生物科技學系
We previously showed that the expression of ENO1 (enolase) in the fungal pathogen Candida albicans is critical for cell growth. In this study, we investigate the contribution of the ENO1 gene to virulence. We conducted our functional study of ENO1 in C. albicans by constructing an eno1/eno1 null mutant strain in which both ENO1 alleles in the genome were knockouted with the SAT1 flipper cassette that contains the nourseothricin-resistance marker. Although the null mutant failed to grow on synthetic media containing glucose, it was capable of growth on media containing yeast extract, peptone, and non-fermentable carbon sources. The null mutant was more susceptible to certain antifungal drugs. It also exhibited defective hyphal formation, and was avirulent in BALB/c mice.
Loss of Heterozygosity of FCY2 Leading to the Development of Flucytosine Resistance in Candida tropicalis
(2011-06-01)
Chen, Yen-Ning
;
Lo, Hsiu-Jung
;
Wu, Chia-Chen
;
Ko, Hui-Ching
;
Chang, Te-Pin
As fluconazole resistance becomes an emerging issue for treating infections caused by Candida tropicalis, searching for alternative becomes a prominent task. In the present study, 97 clinical isolates of C. tropicalis were tested for the susceptibilities to flucytosine (5FC) with the Etest method. Although only one isolate was resistant to 5FC, 30 susceptible isolates could produce resistant progeny after exposure to the drug. Interestingly, 22 of these 30 clinical isolates had a heterozygous G/T at the 145th position on FCY2, encoding purine-cytosine permease, whereas their progeny recovered from within the inhibitory ellipses had homozygous T/T, resulting in null alleles for both copies of the gene and produced only truncated proteins, effecting the 5FC resistance. Furthermore, we found that two major fluconazole-resistant clinical clones, diploid sequence type 98 (DST98) and DST140, had a homozygous G/G at the 145th position, and neither was able to produce 5FC-resistant progeny within the inhibitory ellipses. Hence, strains of C. tropicalis containing heterozygous alleles may develop 5FC resistance readily, whereas those with homozygous G/G wild-type alleles can be treated with 5FC. Subsequently, a combination of 5FC and another antifungal drug is applicable for treating infections of C. tropicalis.
Two Closely Related Fluconazole-Resistant Candida tropicalis Clones Circulating in Taiwan from 1999 to 2006
(2009-09-01)
Li, Shu-Ying
;
Yang, Yun-Liang
;
Lin, Yu-Hsin
;
Ko, Hui-Ching
;
Wang, An-Huei
Recently, we reported that diploid sequence type (DST) 140 was a predominant type of Candida tropicalis among isolates with fluconazole minimum inhibitory concentrations (MICs) >= 64 mu g/ml collected in the Taiwan Surveillance of Antimicrobial Resistance of Yeasts (TSARY) in 1999. To determine if DST140 persists in Taiwan, we have used multilocus sequence typing to characterize the genetic profiles of 31 resistant isolates (MICs >= 64 mu g/ml), together with 19 susceptible isolates (MICs <= 16 mu g/ml) collected in TSARY 2006. Among the 50 isolates, 33 distinct DSTs were detected. Of the 31 resistant isolates, 11 (35.5%) belonged to two closely related DSTs (140 and 98), whereas none of the 19 susceptible isolates did (p = 0.004). The isolates belonging to DST140 and 98 were from different geographic regions instead of a restricted area. Thus, our data show temporal and spatial transmission of C. tropicalis clones with high fluconazole MICs in Taiwan from 1999 to 2006.