Chymotrypsin- and trypsin-like activities secreted by the multidrug-resistant yeasts forming the Candida haemulonii complex.

Candida haemulonii complex (C. haemulonii, C. haemulonii var. vulnera and C. duobushaemulonii) consists of emergent multidrug-resistant pathogens that cause bloodstream and deep-seated infections. However, little is known about their virulence factors. Herein, we evaluated the presence of extracellular serine peptidases in this fungal complex. Serine peptidase activity was measured by spectrophotometry using chromogenic peptide substrates to the S1 family. Chymotrypsin-, trypsin- and elastase-like activities were detected in all fungal isolates. Since higher chymotrypsin- and trypsin-like activities were observed from the cleavage of N-succinyl-Ala-Ala-Pro-Phe-pNa and N-benzoyl-Phe-Val-Arg-pNa, respectively, these substrates were selected for further experiments. Overall, pHs 7.0 and 9.0 were those in which higher chymotrypsin- and trypsin-like activities were observed, respectively, displaying higher hydrolytic activities at 37-45°C. Additionally, the serine peptidases produced by C. haemulonii complex were inhibited by PMSF and AEBSF in a typically concentration-dependent manner. Although the Michaelis constant (Km) values obtained for chymotrypsin-like peptidases were similar, greater differences were observed for trypsin-like enzymes secreted by the different fungal isolates. This is the first time that peptidases belonging to the S1 family are described in the C. haemulonii species complex. Thus, these data open the doors for more detailed studies into potential roles of these peptidases in fungal virulence.