Rhodamine 6G efflux for the detection of CDR1-overexpressing azole-resistant Candidaalbicans strains

Abstract

We investigated the drug efflux mechanism in azole-resistant strains of Candida albicans using rhodamine 6G (R6G). No significant differences in R6G uptake were observed between azole-sensitive B2630 (9.02 ± 0.02 nmol/10⁸ cells) and azole-resistant B67081 (8.86 ± 0.03 nmol/10⁸ cells) strains incubated in glucose-free phosphate buffered saline. A significantly higher R6G efflux (2.0 ± 0.21 nmol/10⁸ cells) was noted in the azole-resistant strain (B67081) when glucose was added, compared with that in the sensitive strain B2630 (0.23 ± 0.14 nmol/10⁸ cells). A fluconazole-resistant strain C40 that expressed the benomyl resistance gene (CaMDR) also showed a low R6G efflux (0.16 ± 0.06 nmol/10⁸ cells) as did the sensitive strains. Accumulation of R6G in growing C. albicans cells was inversely correlated with the level of CDR1 mRNA expression. Our data also suggest that measurement of intracellular accumulation of R6G is a useful method for identification of azole-resistant strains due to CDR1-expressed drug efflux pump.