Comparing in vitro antileishmanial activity of Scrophularia bavanatica hydroalcoholic extract against Leishmania major and Leishmania tropica promastigotes

Cutaneous leishmaniasis (CL), a neglected tropical disease, presents a significant therapeutic challenge due to the toxicity and emerging resistance of first-line drugs like Glucantime. Medicinal plants offer a promising reservoir for novel antileishmanial agents. Scrophularia bavanatica is a traditionally-used plant in Iran; yet, its efficacy against different Leishmania species remains unexplored. This study compared the in vitro antileishmanial efficacy of Scrophularia bavanatica hydroalcoholic extract (SBE) against promastigotes of Leishmania major and Leishmania tropica . Two parallel in vitro studies were conducted. Promastigotes of L. major [MRHO/IR/75/ER] and L. tropica [MHOM/IR/NADIM3] were exposed to various concentrations of SBE (0.01–100 mg/mL and 0.2–125 mg/mL, respectively) and standard Glucantime for 24, 48, and 72 hours. Parasite viability was assessed using the XTT cell proliferation assay. LC ₅₀ values and survival percentages were calculated and statistically compared. SBE exhibited a time- and concentration-dependent antileishmanial effect against both species. However, L. tropica demonstrated significantly higher resistance. The LC ₅₀ of SBE for L. major in the dynamic phase (47.1 µg/mL) was significantly lower than that for L. tropica , for which the LC ₅₀ exceeded the highest tested concentration (> 125 µg/mL). A significant reduction in L. tropica promastigote survival was only observed after 72 hours of exposure (P = 0.000), whereas L. major showed significant susceptibility at 24 and 48 hours. Glucantime was effective against both species by 72 hours, but required higher concentrations for L. tropica . Scrophularia bavanatica extract possesses potent antileishmanial activity, but its efficacy is highly species-specific. L. tropica is inherently more resistant to both SBE and Glucantime compared to L. major , necessitating longer exposure times and higher doses for effective treatment. This highlights the critical importance of species identification in CL management and puts SBE forward as a promising candidate for further development against L. major .