Mechanisms of Azole Resistance in a Clinical Isolate of Candida tropicalis

Abstract

Azole resistance has been insufficiently investigated in the yeast Candida tropicalis. Here we determined the molecular mechanisms responsible for azole resistance in a clinical isolate of this pathogenic yeast. Antifungal susceptibility testing performed by a disk diffusion method showed resistance or markedly decreased susceptibility to azoles, which was confirmed by determination of MICs. Considering the relationship between azole susceptibility and the respiration reported for other yeast species, the respiratory activity of this isolate was investigated. Flow cytometry using rhodamine 123 and oxygraphy demonstrated an increased respiratory activity, which was not linked to an overexpression or increased number of copies of the mitochondrial genome. Among previously described resistance mechanisms, an increased activity of efflux pumps was investigated by flow cytometry using rhodamine 6G. However, the efflux of rhodamine 6G was lower in the resistant isolate than in susceptible ones. Likewise, real-time reverse transcription-PCR quantification of the expression of C. tropicalis MDR1 (CtMDR1), which encodes an efflux protein belonging to the major facilitator superfamily, did not show overexpression of this gene. In contrast, the resistant isolate overexpressed the CtERG11 gene coding for lanosterol 14␣-demethylase. This was in agreement with the larger amount of ergosterol found in this isolate. Moreover, sequencing of CtERG11 showed a point mutation leading to a tyrosine substitution in the protein sequence, which might lead to decreased binding affinity for azoles. In conclusion, overexpression of CtERG11 associated with a missense mutation in this gene seemed to be responsible for the acquired azole resistance of this clinical isolate.

Candida tropicalis Antifungal Cross-Resistance Is Related to Different Azole Target (Erg11p) Modifications

“…Candida tropicalis is usually susceptible to all antifungal agents, although several cases of fluconazole and azole cross-resistance in clinical isolates have been reported (5,13,14), especially in the Asia-Pacific region (1,15). On the other hand, C. tropicalis resistance to amphotericin B is rare, and very few strains have reliably demonstrated high-level resistance to this agent (16,17).…”

Candidose na medicina veterinária: um enfoque micológico, clínico e terapêutico

“…A resistência in vitro pode ser subdividida ainda em resistência in vitro primária, chamada também de intrínseca ou inata, que se apresenta naturalmente no microrganismo; e resistência in vitro secundária, que aparece quando o microrganismo inicialmente sensível se faz resistente (BALKIS et al, 2002;SANGLARD & ODSS, 2002;VANDEPUTTE et al, 2005). A resistência in vivo ocorre em virtude de fatores diferentes, como: farmacocinética da droga antifúngica, fatores dependentes do hospedeiro (estado imune, doenças de base, dentre outros) e fatores relacionados ao microrganismo, como virulência e resistência (BALKIS et al, 2002).…”

“…VANDEPUTTE et al (2005) detectaram a superexpressão de gens responsáveis pelas bombas de efluxo em cepas de C. tropicalis, e segundo os autores, a resistência nessa espécie pode ser induzida facilmente.…”

“…Diferentes drogas antifúngicas são utilizadas para o tratamento de candidoses em animais, mas a atividade dessas drogas vai dependerá da sensibilidade da cepa, tendo sido relatados alguns casos de cepas pouco sensíveis ou até resistentes a derivados azólicos (ROCHETTE et al, 2003;OZAWA et al, 2005;VANDEPUTTE et al, 2005;BRITO et al, 2007;LASSA & MALINOWSKI, 2007).…”

Mechanisms of Antifungal Drug Resistance

“…Overexpression of ERG11 has also been reported for azole-resistant isolates of C. glabrata, Candida parapsilosis, Candida tropicalis, and Candida krusei (Barchiesi et al 2000;Redding et al 2002;Vandeputte et al 2005;Rogers et al 2006;Jiang et al 2013). The mechanism for this overexpression or its contribution to azole resistance in these species remains largely unknown.…”