Discussion

In a previous phylogenomic study of L. donovani in the Indian subcontinent (ISC), we identified molecular events likely involved in SSG resistance, like an intra-chromosomal amplification (ICA) of the H- and MAPK1-loci and a 2-nt indel in AQP1 gene. We experimentally selected here Sb3-resistance in 3 ISC reference strains (A, ICA-neg, B and C, ICA-pos and respectively SSG-resistant and -sensitive). Initial Sb3 sensitivity of B-C promastigotes was 10 times lower than A. Time-to-resistance was shorter for B-C (4 cycles) than A (7 cycles). All quadruplicates of B-C reached the last cycle but only 1 replicate of A was recovered at the final concentration. At genomic level there were no local CNV, no indel and very few SNPs (only in A); in contrast, chromosomal copy number increased (noteworthy in chr 23, carrying H-locus), aneuploidy being more pronounced in A. Metabolomic results are currently integrated and will be presented.  B-C parasites (main ISC population) are likely pre-adapted to antimonials and the gene dosage effect of ICA is multiplied by aneuploidy, while resistance seems harder to acquire for A (highland genotype).