Intraspecies differences in natural susceptibility to amphotericine B of clinical isolates of Leishmania subgenus Viannia.

Amphotericin B (AmB) is a recommended medication for the treatment of cutaneous and mucosal leishmaniasis in cases of therapeutic failure with first-line medications; however, little is known about the in vitro susceptibility to AmB of clinical isolates of the subgenus Viannia, which is most prevalent in South America. This work aimed to determine the in vitro susceptibility profiles to AmB of clinical isolates of the species L. (V.) panamensis, L. (V.) guyanensis and L. (V.) braziliensis. In vitro susceptibility to AmB was evaluated for 65 isolates. Macrophages derived from the U937 cell line were infected with promastigotes and exposed to different AmB concentrations. After 96 hours, the number of intracellular amastigotes was quantified by qPCR, and median effective concentration (EC50) was determined using the PROBIT model. The controls included sensitive strains and experimentally derived less sensitive strains generated in vitro, which presented EC50 values up to 7.57-fold higher than the values of the sensitive strains. The isolates were classified into groups according to their in vitro susceptibility profiles using Ward's hierarchical method. The susceptibility to AmB differed in an intraspecies-specific manner as follows: 28.21% (11/39) of L. (V.) panamensis strains, 50% (3/6) of L. (V.) guyanensis strains and 34.61% (9/26) of L. (V.) braziliensis strains were classified as less sensitive. The latter subset featured three susceptibility groups. We identified Colombian isolates with different AmB susceptibility profiles. In addition, the capacity of species of subgenus Viannia to develop lower susceptibility to AmB was demonstrated in vitro. These new findings should be considered in the pharmacovigilance of AmB in Colombia and South America.