Introduction: Candida glabrata is one of the commensal fungal species in human. In immune compromised individuals, it becomes one of the second major causes of candidiasis in mucosal, blood stream, and genito-urinary tract. The high incidences of C. glabrata infections have increased significantly in the last two decades, mainly due to its abilities to resist various antifungal drugs (MDR) and form biofilm. The ability of membrane transport to actively efflux the drug out of the cell is mediated mainly by ATP-Binding Cassette (ABC) and MFS (Major Facilitator Superfamily) transporters. In this study, we focus on one of C. glabrata genes belong to MFS-DHA1 family, namely C. glabrata QDR2. This gene was identified as one of the genes related to the biofilm formation in our previous study. By forming the biofilm on implanted medical devices, C. glabrata limits drug penetration and further cause drug resistance with persistent infection. In an attempt to clarify the mechanism of C. glabrata biofilm formation, we investigated the role of CgQDR2 in the virulence traits of C. glabrata.

Methods: The difference of biofilm formation between C. glabrata qdr2 mutant and its wild type strain (CBS138) was found out by XTT and crystal violet assay on the surface of 96-well polystyrene plate. The biofilm cells were further examined under SEM and also several gene expressions were checked by qRT-PCR. In addition, we used antifungal drug fluconazole to determine MIC of C. glabrata qdr2 mutant. To detect the adherent cells during the initial step of biofilm formation, we used CFDA-SE as a fluorescent dye that only label viable cells. Furthermore, we analyzed C. glabrata qdr2 mutant growth under certain pH conditions.

Results: There was a significant difference of the biofilm formation between C. glabrata ∆qdr2 mutant and the wild type strain (CBS138). We found that the relative qdr2 mRNA expression level during biofilm phase of the wild type increased significantly as compared to the free-floating (planktonic) cells. Moreover, QDR2 deletion affected C. glabrata susceptibility to fluconazole that might interrupt the drug efflux mechanism in C. glabrata biofilm. In further examination, we discovered a decrease in the adherent cells of the ∆qdr2 mutant at the initial step (90 minutes) of the biofilm formation process. Additionally, CgRIM101 (CAGL0E03762g), a pH responsive transcription factor, was upregulated in the mutant during planktonic phase and the qdr2 mutant was unable to grow vigorously under neutral pH conditions compared to the wild type.

Conclusion: Based on our results, we suggested that QDR2 deletion might cause an impaired ability of C. glabrata to maintain pH homeostasis, then might lead to the reduction of cell growth, adherent cells numbers, the amount of biofilm formed, and eventually affect C. glabrata biofilm susceptibility and drug efflux towards antifungal drugs.

Role of MFS Transporter QDR2 in a Pathogen Candida glabrata