Antimalarial Drug Sensitivity Profile of Western Kenya Plasmodium falciparum Field Isolates Determined by a SYBR Green I in vitro Assay and Molecular Analysis

In vitro drug sensitivity and molecular analyses of Plasmodium falciparum track drug resistance. DNA-binding fluorescent dyes like SYBR Green I may allow field laboratories, proximal to P falciparum collection sites, to conduct drug assays. In 2007-2008, we assayed 121 P falciparum field isolates from western Kenya for 50% inhibitory concentrations (IC50) against 6 antimalarial drugs using a SYBR Green 1 in vitro assay: 91 immediate ex vivo (IEV) and 30 culture-adapted, along with P falciparum reference clones D6 (chloroquine [CQ] sensitive) and W2 (CO resistant). We also assessed P falciparum mdr1 (Pfmdr1) copy number and single nucleotide polymorphisms (SNPs) at four codons. The IC(50)s for IEV and culture-adapted P. falciparum isolates were similar, and approximated historical IC(50)s. For Pfmdr1, mean copy number was 1, with SNPs common at codons 86 and 184. The SYBR Green I assay adapted well to our field-based laboratory, for both IEV and culture-adapted P falciparum, warranting continued use.