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Development and comparison of quantitative assays for the dihydropteroate synthetase codon 540 mutation associated with sulfadoxine resistance in Plasmodium falciparum

  • M.-F. SHAIO (a1) (a2), P. WANG (a1), C.-S. LEE (a1), P. F. G. SIMS (a1) and J. E. HYDE (a1)...

Abstract

A point mutation in codon 540 of the dihydropteroate synthetase (dhps) gene affecting sulfadoxine resistance has previously been found in parasites from patients with Plasmodium falciparum infection. Here, we investigated 4 methods of identifying this mutation in clinical specimens and established a reliable quantitative assay to estimate the percentage of resistant type in mixed infections. A diagnostic PCR assay based on allele-specific amplification was developed, which clearly typed the clinical specimens examined. The mutation in codon 540 introduces an additional FokI cleavage site which provided a second method to differentiate mutant from wild type, where the former gives rise to 2 characteristic fragments of 538 and 326 bp that are absent from the latter. To calibrate quantitatively the ratio of alleles in mixed samples, we constructed artificial mixes containing 2 plasmid DNAs, one carrying the mutation and the other a wild-type insert. When 32P-labelling was employed, the allele-specific PCR assay could detect the level of resistant type in a mixture down to 0·1–1%, while for the restriction enzyme/PCR analysis, the figure was approximately 10%. Furthermore, neither fluorescent dye-labelled terminator nor dye-labelled primer cycle sequencing was able to detect the mutant allele if it was present at less than 20–30%. We conclude that the allele-specific PCR assay is the most sensitive method of detecting the codon 540 mutation in P. falciparum dhps, and the method of choice for estimating the composition of mixed samples.

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Corresponding author: Tel: +44 161 200 4185. Fax: +44 161 236 0409. E-mail: john.hyde@umist.ac.uk

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Development and comparison of quantitative assays for the dihydropteroate synthetase codon 540 mutation associated with sulfadoxine resistance in Plasmodium falciparum

  • M.-F. SHAIO (a1) (a2), P. WANG (a1), C.-S. LEE (a1), P. F. G. SIMS (a1) and J. E. HYDE (a1)...

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