Investigation of Acid Proteinase and Phospholipase Activity as Virulence Factors in Clinical Aspergillus spp. Isolates

Aspergillus spp. are widespread in nature and cause severe infections especially in immunocompromised patients. Aspergillus fumigatus complex is the most common species that causes infections in humans; however Aspergillus niger complex and Aspergillus flavus complex are the emerging agents that are isolated frequently from clinical specimens more recently. Besides the host factors such as immunosuppression, hematologic malignancy and corticosteroid use, fungal virulence factors such as elastase, acid protease and phospholipase enzymes are considered among the factors that affect the development of invasive aspergillosis. The aim of this study was to detect the acid proteinase and phospholipase enzyme activities in 30 A.fumigatus complex, nine A.flavus complex and four A.niger complex strains isolated from clinical specimens. Acid proteinase and phospholipase activities of the isolates were investigated by using bovine serum albumin agar (BSA), and egg yolk agar plates, respectively. Acid proteinase and phospholipase activity was detected in 76.7% (23/30) and 93.3% (28/30) of A.fumigatus complex isolates, respectively. None of the nine A.flavus complex isolates exhibited acid proteinase or phospholipase activity. Acid proteinase activity was not detected in any of the A.niger complex isolates (n= 4), however phospholipase activity was detected in one (25%) isolate. All of the acid proteinase positive A.fumigatus complex strains (n= 23) were also positive for phospholipase activity. In conclusion, further larger scale multicenter studies supported by clinical data, are needed to enlighten the roles of acid proteinase and phospholipase in the pathogenesis of infections due to Aspergillus spp.