Characterisation of Antifungal Resistance to Azoles in Colombian Isolates of Malassezia spp.

Background: Malassezia genus includes lipodependent commensal yeasts of humans and animals' skin and mucous membranes. It can cause dermatological pathologies, and azoles are mainly used for treatment. However, in vitro susceptibility testing has shown decreased sensitivity to these antifungals. Some publications have suggested that resistance mechanisms to azoles include biofilm formation and efflux pump expression, which are proteins encoded by the ATM1 gene, among others.

Objective: This work aimed to characterise Colombian isolates of Malassezia spp. resistant to azoles.

Methods: Twenty-six Malassezia spp. isolates were identified via PCR, ribosomal gene sequencing and phylogenetic analyses. Susceptibility tests were performed on planktonic and sessile cells by microdilution against azoles and by adding efflux pump inhibitors. The relative expression levels of the ATM1 gene in fluconazole-resistant isolates were evaluated via RT-qPCR.

Results: It was observed that 42% of the isolates in their planktonic form were resistant to voriconazole, 31% to fluconazole, 23% to itraconazole and 15% to ketoconazole. The minimum inhibitory concentration (MIC) was higher in sessile cells than planktonic cells, especially for fluconazole. The MICs of itraconazole, ketoconazole and voriconazole decreased in the presence of haloperidol, promethazine and tacrolimus, while this effect did not occur with fluconazole. The expression of the ATM1 gene was markedly greater in Malassezia spp. isolates resistant to fluconazole than in those susceptible (p < 0.05), both in those exposed and not exposed to the antifungal agent.

Conclusions: We observed resistance of Colombian Malassezia spp. isolates to azoles, mainly fluconazole, through the expression of efflux pumps and biofilm formation.