A unique amino acid substitution in the ERG11 gene mediated azole cross-resistance in Candida tropicalis bloodstream isolates

Ref ID: 17756

Author:

E. Borghi*, R. Iatta, R. Sciota, D. Cirasola, M.T. Montagna, G.
Morace

Author address:

Milan, Bari, IT)

Full conference title:

22nd European Congress of Clinical Microbiology and Infectious Diseases

Abstract:

Objectives: Compared with C. albicans there are relatively few studies
examining the virulence factors of C. tropicalis, and its mechanisms of
drug-resistance.
C. tropicalis accounts for a significant proportion of Candida
bloodstream infection, and traditionally is considered as second to C.
albicans in terms of virulence and clinical importance. Here we
investigated the molecular mechanism responsible for cross-resistance
to fluconazole and voriconazole in C. tropicalis clinical strains isolated
from bloodstream infections.
Materials and methods: During a 10-year retrospective surveillance
of candidemia we collected ten C. tropicalis isolates, showing
resistance to fluconazole and voriconazole. For comparative purpose
an equal number of azole-susceptible strains were studied. Isogenicity
of the isolates was investigated by RAPD (primers OPE03, GC70 and
UBC703) and Maldi-TOF analysis.
Antifungal susceptibility testing was performed by Sensititre procedure
and broth microdilution method. Quantification of the expression of the
CtMDR1, CtCDR1 and CtERG11 genes was performed by real-time
PCR, using SYBR Green chemistry. To stimulate the espression of
efflux pumps genes, all the isolates were cultured in presence and
absence of various fluconazole concentrations. The primers have been
designed with the primer express 3.0 software (Applied Biosystems).
For ERG11 sequencing, five pairs of oligonucleotide primers (Bouchara
et al., 2005) were used.
Results: The resistant isolates, coming from four different hospitals,
clustered in three groups. No significant differences were found in the
expression levels of the resistant isolates compared to the susceptible
ones, even if cultured in the presence of sub-MIC concentration of
fluconazole.
Comparison of the CtERG11 gene sequences of the ten C. tropicalis
resistant isolates with the available corresponding sequence in the
GenBank database (accession number M23673) revealed the point
mutation Y132F in the coding region. This mutation is located in the
region between the B’ and C helices that have been postulated to be
involved in inhibitor- or substrate-induced structural changes.
Conclusions: In contrast to what observed in C. albicans, where azole
resistance is usually the result of a combination of different
mechanisms, in C. tropicalis we found a unique single point mutation
sufficient to induce a decreased affinity of fluconazole and its derivative
voriconazole.

Abstract Number: NULL

Conference Year: 2012

Link to conference website: NULL

New link: NULL

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