Role of the inducible adhesin, CpAls7, in binding of Candida parapsilosis to extracellular matrix under fluid shear.

The yeast, Candida parapsilosis , is an increasingly common cause of systemic fungal infections among the immune compromised, including premature infants. Adhesion to host surfaces is an important step in pathogenesis, but this process has not been extensively studied in this organism. A microfluidics assay was developed to test the ability of C. parapsilosis to adhere to immobilized host extracellular matrix proteins under physiologic fluid shear conditions. Growth in mammalian tissue culture media at 37°C for 3-6 hours led to induction of an adhesive phenotype at shear forces of 1-5 dynes/cm2 in some isolates of C. parapsilosis Glutamic acid, proline and calcium appeared to be the minimally necessary requirements for increased adhesion in these assays. To determine whether genes homologous to the ALS gene family of C. albicans were important for the adhesive phenotype, expression of 5 homologous C. parapsilosis genes were quantified using qPCR under conditions leading to increased adhesion. CPAR2_404800 ( CpALS7 ) and CPAR2_404780 showed increased expression compared to control yeast. The extent of adhesion was variable among different isolates, and linear regression identified expression of CpALS7 but not CPAR2_404780 to have a strong positive correlation with adhesion. A homozygous CpALS7 deletion strain was deficient in adhesion, whereas expression of CpALS7 in S. cerevisiae resulted in increased adhesion. Together, these data provide strong evidence that CpAls7 aids in the adherence of C. parapsilosis to extracellular matrix under shear forces and support its previously reported role in virulence.