Drug resistance genes and trailing growth in Candida albicans isolates

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.

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.

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.

Trailing isolates, although susceptible to fluconazole, express the same molecular mechanisms as SDD and R isolates following fluconazole exposure but regulate them differently.