Investigation on the Association between In Vitro Sensitivity of Plasmodium falciparum isolates in Thailand to Antimalarial Drugs and Polymorphisms of Molecular Markers of Antimalarial Drug Resistance

Abstract

The emergence and spreading of multidrug resistance Plasmodium falciparum throughout is a major problem of malaria control in Thailand. The aim of this study was to assess the in vitro susceptibility of 25 P. falciparum isolates in Thailand to the four standard antimalarial drugs, i.e., chloroquine (CQ), quinine (QN), mefloquine (MQ) and artesunate (AS) including their relationships with polymorphisms (gene mutation of pfcrt, pfmdr1 and copy number of pfmdr1). In vitro sensitivity test was performed using SYBR green I assay. The mutations of pfcrt and pfmdr1 were analyzed by PCR-RFLP and copy number of pfmdr1was determined by SYBR green I real-time PCR. The median IC₅₀ (95%CI) of CQ, QN, MQ and AS were 96.02 (67.72-132.29), 226.95 (163.88-299.66), 23.88 (19.40-31.29) and 1.73(1.30-2.04) nM, respectively. All isolates (100%) carried mutation of pfcrt at codons 76, 220, 271, 326, 356, 371. No mutation of pfmdr1at codon 86 was detected; 19 isolates (76%) carried 1 pfmdr1 copy number while 6 isolates (24%) carried more than 1 pfmdr1 copy number. MQ resistant phenotype correlated well with the increase in pfmdr1 copy number. Further investigation should focus on confirmation of these observations in a larger sample size.