Improving Leishmania isolation in field conditions: Efficacy of caspofungin against yeasts contamination

Cutaneous leishmaniasis (CL), a neglected disease prevalent in 88 countries, is commonly caused by Leishmania (L.) major in the Old World, posing significant public health concerns. Isolation from sand flies or infected mammals and in vitro cultivation of Leishmania parasites are critical for epidemiological studies, but these cultures are often compromised by bacterial and fungal contamination, especially when outsourced from vector digestive tracts. While the Leishmania parasite's natural resistance to antibiotics simplifies bacterial control, most antifungals also inhibit the parasites growth, complicating efforts to manage fungal contamination. This study aimed to identify antifungal agents that could protect Leishmania cultures from yeast contamination with minimal impact on parasite growth. Five antifungal drugs: griseofulvin (GRF), caspofungin diacetate (CSF), 5-fluorocytosine (5-FC), po(ly)vidone-iodine (PVI), and undecylenic acid (UCA) were assessed in vitro for their effects on promastigote forms of L. major. The IC50 values indicated strong antileishmanial activity for 5-FC, GRF, UCA, and PVI (50 value (17 µM), suggesting relatively lower toxicity to the parasites. Under continuous CSF exposure, L. major promastigotes demonstrated substantial survival, with only a modest reduction in maximum parasite growth curves (peak of 2.65 × 10⁶ parasites/mL) compared to untreated controls (4.31 × 10⁶ parasites/mL maximum growth). These findings suggest that caspofungin diacetate could be used in the field to decontaminate Leishmania cultures from yeasts without significant parasite loss, facilitating L. major isolation and epidemiological investigations in endemic regions.