Genomic analysis of Isometamidium Chloride resistance in Trypanosoma congolense

BackgroundIsometamidium Chloride (ISM) is one of the principal drugs used to counteract Trypanosoma congolense infection in livestock, both as a prophylactic as well as a curative treatment. Numerous cases of ISM-resistance have been reported in different African regions, representing a significant constraint in the battle against Animal African Trypanosomiasis. Methodology/Principal findingsTo identify genetic signatures associated with ISM-resistance in T. congolense, the sensitive strain MSOROM7 was selected for induction of ISM-resistance in a murine host. Administered ISM-concentrations in immune-suppressed mice were gradually increased from 0.001 mg/kg to 1mg/kg, the maximal dose used in livestock. As a result, three independent MSOROM7 lines acquired full resistance to this concentration after five months of selection, and retained this full resistant phenotype following a six months period without drug pressure. In contrast, parasites did not acquire ISM-resistance in immune-competent animals, even after more than two years under ISM-pressure. Flow cytometry and ex vivo ISM-uptake assays revealed a decrease in the accumulation of ISM in the resistant parasites, and whole genome sequencing analysis comparing the ISM-resistant lines with the parental sensitive line identified allele frequency shifts in genes coding for different transporters and transmembrane products, as well as long gene deletions and gene amplifications. A whole genome analysis was also performed on 50 field-isolated strains of known ISM-susceptibility to further explore genomic signatures of ISM-resistance. Conclusion/significanceThe exact mechanisms underlying ISM-resistance in T. congolense remain to be further elucidated, but our findings suggest that genotype shifts and genomic structural variations due to an ISM-pressure result in a reduced intracellular accumulation of the drug and promote the acquisition of ISM-resistance. Moreover, the development of full ISM-resistance is strongly enhanced when the host immune response is compromised. Int J Parasitol Drugs Drug Resist. 2017 Dec;7(3):350-361. doi: 10.1016/j.ijpddr.2017.10.002. Epub 2017 Oct 6. Genomic analysis of Isometamidium Chloride resistance in Trypanosoma congolense. Tihon E, Imamura H et al.