In vitro antimalarial susceptibility profile of Plasmodium falciparum isolates in the BEI Resources repository.

BEI Resources, a National Institute of Allergy and Infectious Diseases-funded program managed by the American Type Culture Collection, serves researchers worldwide through the provision of a centralized repository for the acquisition, production, characterization, preservation, storage, and distribution of standardized biological resources targeting National Institutes of Health priority pathogens including bacteria, viruses, pathogenic fungi, and parasitic protozoa. These reference materials are critical for the development of diagnostics, vaccines, and therapeutics and are available to qualified registered investigators and institutions worldwide. Bioresources within BEI include well-characterized malaria isolates as part of the Malaria Research and Reference Reagent Resource Center (MR4). These isolates are critical for screening antimalarial compounds, conducting drug resistance studies, and for resistance surveillance and management. In our efforts to enhance the characterization of MR4 P. falciparum isolates, we measured antimalarial susceptibility of >100 isolates against a panel of standard antimalarial compounds. Our results provide valuable information to assist current and prospective users of the BEI Resources repository in making data-driven requests of isolates to meet their research needs.

Dissection of haplotype-specific drug response phenotypes in multiclonal malaria isolates.

Natural infections of Plasmodium falciparum, the parasite responsible for the deadliest form of human malaria, often comprise multiple parasite lineages (haplotypes). Multiclonal parasite isolates may exhibit variable phenotypes including different drug susceptibility profiles over time due to the presence of multiple haplotypes. To test this hypothesis, three P. falciparum Cambodian isolates IPC_3445 (MRA-1236), IPC_5202 (MRA-1240) and IPC_6403 (MRA-1285) suspected to be multiclonal were cloned by limiting dilution, and the resulting clones genotyped at 24 highly polymorphic single nucleotide polymorphisms (SNPs). Isolates harbored up to three constituent haplotypes, and exhibited significant variability (p < 0.05) in susceptibility to chloroquine, mefloquine, artemisinin and piperaquine as measured by half maximal drug inhibitory concentration (IC50) assays and parasite survival assays, which measure viability following exposure to pharmacologically relevant concentrations of antimalarial drugs. The IC50 of the most abundant haplotype frequently reflected that of the uncloned parental isolate, suggesting that a single haplotype dominates the antimalarial susceptibility profile and masks the effect of minor frequency haplotypes. These results indicate that phenotypic variability in parasite isolates is often due to the presence of multiple haplotypes. Depending on intended end-use, clinical isolates should be cloned to yield single parasite lineages with well-defined phenotypes and genotypes. The availability of such standardized clonal parasite lineages through NIAID's BEI Resources program will aid research directed towards the development of diagnostics and interventions including drugs against malaria.