Resistant mechanisms of fluconazole resistant Candida albicans

Abstract

The purpose of this study was to investigate the evolution of fluconazole resistant in susceptible C.albicans under the condition of high drug concentrations. Four difference higher concentrations, 8, 16, 24 and 32 µg/m1, than its original MIC (8 µg/ml by Etest and 2 µg/m1 by broth microdilution test) were prepared to induced each single yeast cell. Five repeats were tested in each concentration. The continuous induction with the same concentration for 60-day period was performed by changing fresh medium, RPMI-1640 broth, with the same drug concentration everyday and then inoculating the certain amount of the previous day's culture to obtain 5 ml. To reveal the objective of this study, MICs, hot spot of ERG11 gene, and expression of four putative gene CDR1, CDR2, MDR and ERG11, of the cultures at day 0, 14, 29, 50 and 60 were determined. Regarding the MICs result, it was found that the increasing level of MIC from its original level to 32 µg/m1 was demonstrated in all fluconazole induced cultures at day 14 through day 60 whereas the MIC of the all cultures from free-fluconazole broth remianed the same through day 60. It is of interested that the MIC of two cultures from day 29 was to 64 µg/ml and down to 32 µg/m1 in day 50. C. albicans in other remain group MIC were not changed. C. albicans strain 22 and 23 showed MIC increased to 64 µg/ml and stable until day 60. To determine the base sequences of ERG 11 and the expression of the four putative genes, the cultures at all the 5 time-points of any cultures which demonstrated the changing of MIC at any time point were recruited. Although the resistant induction was revealed by the increasing of the MICs, only silent position or no amino acid change was found in the hot spot area. The study of base sequence showed that this gene was not involved in fluconazole resistant mechanism because amino acid were not changed. The putative resistant gene CDR1, CDR2, MDR1 and ERG11 were expressed in all tested strain except CDR2 was not detected in the drug absence media groups from all time point of study.