Multi-drug tolerance in Leishmania persister-like cells

Persisters are a small fraction of non-proliferative cells with reduced metabolism that are adapted to withstand a variety of environmental assaults, including lethal doses of antibiotics. Here, we present evidence of existence of persister-like cells in protozoan parasite Leishmania, induced upon exposure to normally lethal doses of antimonials. We show that Leishmania promastigotes survive lethal doses of antimonials by adopting a quiescence phenotype characterised by reduced proliferation, diminished metabolism and a reduced mitochondrial membrane potential. Depending on the presence of genomic pre-adaption to antimonial resistance, two types of persister-like cells were observed for L. donovani field isolates. In non-preadapted lines, persister-like cells are transiently tolerant to antimonials and return to the sensitive state upon removal of drug pressure. In contrast, isolates with genetic changes associated with antimony-resistance, resume growth after just a short period of quiescent state and retain their reduced sensitivity to antimonials in drug-free conditions. Both types of persister-like cells display cross-tolerance to a selection of antileishmanial compounds, but the degree of tolerance is drug- and strain-dependent. Our results demonstrate extreme versatility of this eukaryotic pathogen in adaptation to drug pressure and highlight the need for the development of new antileishmanials targeting non-proliferative forms.