Exploration of the Antifungal Activity of Parotid Secretion

When local or general predisposing factors are present, Candida species, which are oral opportunistic pathogens, can cause acute or chronic oral infections. In healthy subjects, saliva may play a crucial role in maintaining oral fungal homeostasis. Components of human salivary secretions so far identified to display antifungal activity in vitro include lysozyme, lactoferrin and histatins. Aim: To explore more systematically the antifungal spectrum of parotid secretion (PS) using various treatment and fractionation approaches. Methods: PS was collected from two orally healthy individuals and subjected to three different treatments: 1) incubation of native PS with cation-exchange resin, 2) boiling; 3) boiling followed by filtration over 10 kD, 30 kD, and 50 kD MWCO filters. The composition of all PS fractions was verified by cationic and SDS-PAGE. Antifungal activity was evaluated in a fungal growth inhibition assay with C. kefyr as the test organism. Results: Native and boiled PS displayed IC₅₀ values of 24.5 ± 9.0 µg/ml and 20.2 ± 7.6 µg/ml, respectively. Incubation of PS with cation-exchange resin removed the positively charged proteins and increased the IC₅₀ value to 41.7 ± 11.2 µg/ml. Antifungal susceptibility testing of the various PS filtrates containing proteins <10 kD, <30 kD, and < 50 kD and of the retentates (>10 kD, >30 kD and >50 kD) yielded IC₅₀ values of >940 µg/ml, >492 µg/ml, >564µg/ml, and 59 µg/ml, 42 µg/ml, and 51 µg/ml, respectively. Conclusions: The antifungal activity in PS is heat-stable and thus likely conferred by non-enzymatic components that are conformation-independent. The size fractionation of PS suggested that the molecular weight of the active component(s) is/are > 50 kD. Supported by NIH/NIDCR grants DE05672, DE07652 and DE16699.