To investigate the role and relationship of virulence factor SAP2 and transcription factor STP1 in itraconazole (ITR) resistance of Candida albicans in free state and biofilm state.

The experimental strains were 10 itraconazole-resistant Candida albicans and 10 sensitive strains. Firstly, the SAP2 and STP1 of itraconazole-resistant and sensitive strains of Candida albicans isolated in free state were sequenced by PCR method, and the relationship between gene mutation and drug resistance was analyzed. Then, the biofilm of Candida albicans was constructed by 96-well plate. The mRNA expression levels of SAP2, STP1 and STP1Δ/Δ of Candida albicans in free state and biofilm state were detected by RT-PCR method, and the differences and correlation of SAP2, STP1 and STP1Δ/Δ expression in different states were compared and analyzed. The growth morphology of Candida albicans biofilm at different time points and the effects of SAP2, STP1 and STP1Δ/Δ on its formation ability were observed by crystal violet staining and laser confocal microscope.

SAP2 sequencing showed that there were no missense mutations with three synonymous mutations (T276A, G543A and A675C), two missense mutations N394S (20) and D71I (2) and two synonymous mutations C453T (4) and A799G (1) were found in STP1 gene sequencing, among which N394S existed in all drug resistant and sensitive strains, while D71I only existed in two sensitive strains. Compared with sensitive strains, Candida albicans resistant strains and STP1 gene deficient strains (STP1Δ/Δ) had stronger biofilm forming ability, and the expressions of SAP2 and STP1 were up-regulated in free state and biofilm state, and the expression levels of SAP2 and STP1 in biofilm state were significantly higher in resistant and sensitive strains than in free state. However, there was a significant positive correlation between the mRNA expression levels of SAP2 and STP1 under any condition. In addition, compared with the standard strain ATCC11006, the expression of SAP2 in the STP1 gene deficient strain (STP1Δ/Δ) was also significantly up-regulated under the two states, and the difference was statistically significant.

The formation of biofilm can increase the itraconazole resistance of Candida albicans, but the mutations of SAP2 and STP1 genes may not be related to the drug resistance of Candida albicans. In free state, the high expression of SAP2 is related to the drug resistance of Candida albicans ITR, while in both free state and biofilm state, the increase of ITR resistance of Candida albicans is related to STP1. In addition, STP1 can regulate and control SAP2, and its mechanism needs to be studied urgently.