| Summary: | The <i>Candida haemulonii</i> complex (<i>C. duobushaemulonii</i>, <i>C. haemulonii</i>, and <i>C. haemulonii</i> var. <i>vulnera</i>) is composed of emerging, opportunistic human fungal pathogens able to cause invasive infections with high rates of clinical treatment failure. This fungal complex typically demonstrates resistance to first-line antifungals, including fluconazole. In the present work, we have investigated the azole resistance mechanisms expressed in Brazilian clinical isolates forming the <i>C. haemulonii</i> complex. Initially, 12 isolates were subjected to an antifungal susceptibility test, and azole cross-resistance was detected in almost all isolates (91.7%). In order to understand the azole resistance mechanistic basis, the efflux pump activity was assessed by rhodamine-6G. The <i>C. haemulonii</i> complex exhibited a significantly higher rhodamine-6G efflux than the other non-<i>albicans Candida</i> species tested (<i>C. tropicalis</i>, <i>C. krusei</i>, and <i>C. lusitaneae</i>). Notably, the efflux pump inhibitors (Phe-Arg and FK506) reversed the fluconazole and voricolazole resistance phenotypes in the <i>C. haemulonii</i> species complex. Expression analysis indicated that the efflux pump (<i>ChCDR1</i>, <i>ChCDR2</i>, and <i>ChMDR1</i>) and <i>ERG11</i> genes were not modulated by either fluconazole or voriconazole treatments. Further, <i>ERG11</i> gene sequencing revealed several mutations, some of which culminated in amino acid polymorphisms, as previously reported in azole-resistant <i>Candida</i> spp. Collectively, these data point out the relevance of drug efflux pumps in mediating azole resistance in the <i>C. haemulonii</i> complex, and mutations in ERG11p may contribute to this resistance profile.
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