ALS3 and Romidepsin HWP1 were also highly overexpressed in the in vivo model, which is not surprising as hyphae are the predominant form in biofilms grown in this model system [32]. Previous research demonstrated that members of the SAP gene family are expressed in biofilms associated with mucosal surfaces [24]. To investigate whether SAP genes are also highly expressed in biofilms associated with abiotic surfaces, the expression of each

SAP gene was quantified in the various biofilm model systems. All SAP genes (except SAP3) were upregulated in the vitro and in vivomodels, supporting recent findings that sessile C. albicans cells associated with abiotic surfaces secrete more aspartyl proteases than planktonic cells [39]. In the RHE model, we also observed an overexpression of all SAP genes, except SAP3. When comparing the fold expression of BTK inhibitor SAP genes between the various model systems, we found that the expression levels of SAP9 and SAP10 were similar in all model systems, while for other SAP genes model-dependent expression levels were observed. The expression levels of SAP1 were more pronounced in both in vitro models, while those of SAP2, SAP4 and SAP6 were higher in the in vivo model. The expression levels of SAP3 were rather erratic in both in vitro models, and no considerable overexpression of this gene

was found in the in vivo and RHE models. Furthermore, the expression ifenprodil levels of SAP5 were more pronounced in the in vivo model and also in the RHE model at later time points (from 12 h up to 48 h). In in vitro grown biofilms, SAP1, SAP2, SAP4 and SAP6 in particular are highly upregulated.

It is known that the main function of Saps is to degrade proteins [9], but they were also found to play a role in cell-cell adhesion [40]. Hence, it is possible that Saps are important for adhesion and nutrient acquisition in in vitro grown biofilms, although this hypothesis requires further investigation. Furthermore, SAP2, SAP4, SAP5 and SAP6 were highly overexpressed in in vivo grown biofilms, while only SAP5 was highly upregulated in the RHE model. Recently, it was shown that SAP5 is the only gene that is upregulated as infection of the RHE progressed [24], and our findings are in agreement with this observation. Like Naglik et al. [24], we found no correlation between the expression of other SAP genes and LDH activity, indicating that only SAP5 may contribute to tissue damage in the RHE model. However, it was recently demonstrated that aspartyl proteases (including Sap5) are not required for invasion of the RHE [41], and this questions the role of Sap proteins in biofilms grown in the RHE model. It would be interesting to investigate whether the high expression of SAP2, SAP4, SAP5 and SAP6 in the in vivo model is associated with tissue damage of rats.