Differential Expression Levels of Agglutinin-Like Sequence, Lipase, and Secreted Aspartyl Protease Genes in Candida tropicalis Treated with Fluconazole Alone and in Combination with Clotrimazole

Background: The frequency of opportunistic fungal infections in immunocompromised patients, especially by Candida species, has sharply increased in the last few decades. As the number of antifungal drugs available for the treatment of candidiasis is limited, combination therapy has been employed as one of the most commonly used techniques to alleviate this problem. 
Aims: The main aim of this study was to explore the antifungal activity of fluconazole in combination with clotrimazole on expression levels of virulence genes, agglutinin‑like sequences (ALS1 and ALS2), lipases (LIP1 and LIP4) and secreted aspartyl proteases (SAP2 and SAP4) in Candida tropicalis. 
Methods: Ten infected clinical isolates obtained from recurrent vulvovaginal candidiasis patients were used in this study. The broth microdilution assay was utilized to investigate antifungal susceptibilities to fluconazole alone and in combination with clotrimazole and the synergistic effects were interpreted with reference to the fractional inhibitory concentration (FIC) index model. The expression levels of ALS1, ALS2, LIP1, LIP4, SAP2 and SAP4 genes were quantified by real-time RT–PCR. 
Results: Antifungal susceptibility results showed that isolates were resistant to at least one type of azole antifungals. The combination of fluconazole with clotrimazole revealed synergistic effects against C. tropicalis isolates with FIC90 index ranging from 0.011 to 0.43. The results indicated that combination of fluconazole with clotrimazole could cause a down-regulation of gene expression of ALS1, SAP2, LIP4, SAP4, LIP1 and ALS2 genes, respectively. 
Conclusions: Fluconazole in combination with clotrimazole may diminish the virulence properties of C. tropicalis.