Objectives: To investigate possible molecular mechanisms of azole resistance among fluconazole-susceptible bloodstream isolates of Candida albicans that displayed the trailing growth phenomenon, and to compare these isolates with bloodstream and mucosal isolates that showed reduced susceptibilities to fluconazole.
Methods: Twelve C. albicans isolates-seven trailing and five susceptible dose dependent (SDD) or resistant (R)-were screened for ERG11 mutations by DNA sequencing and quantification of ERG11, CDR1 and MDR1 expression by RT-PCR using the LightCycler high-speed PCR system.
Results: SDD and R isolates possessed more homozygous ERG11 mutations than did the trailing isolates. Two of these, V404I and V509M, have not been described previously and were found exclusively in fluconazole SDD and R isolates. Quantification of ERG11 expression revealed that both trailing and SDD and R isolates were capable of ERG11 up-regulation in response to fluconazole, although the SDD and R isolates showed maximal up-regulation at higher fluconazole concentrations. Quantification of CDR1 and MDR1 revealed that all isolates, regardless of in vitro fluconazole response, were capable of CDR1 and MDR1 up-regulation following fluconazole exposure. Furthermore, the SDD and R isolates expressed higher constitutive levels of CDR1 and MDR1 or CDR1, respectively, in the absence of drug compared with trailing isolates.
Conclusions: Trailing isolates, although susceptible to fluconazole, express the same molecular mechanisms as SDD and R isolates following fluconazole exposure but regulate them differently.