Molecular analysis of DHFR and DHPS genes in P. falciparum clinical isolates from the Haut--Ogooué region in Gabon.

The main objective of this work was to determine the prevalence of mutations in genes coding for the dihydropteroate synthase (DHPS) and the dihydrofolate reductase (DHFR) enzymes which are implicated in resistance of P. falciparum to antifolate (pyrimethamine-sulfadoxine (P/S)). In this study, 117 human blood samples were collected at Franceville located in the region of Haut-Ogooué (South-eastern Gabon). In this area, a relatively low level of sensitivity of Plasmodium falciparum to P/S has been reported with 18.2% of RII and 12.1% of RI resistance. A nested polymerase chain reaction was used to amplify a fragment of the DHFR gene containing codon 108, where a point mutation causing a Serine (wild type) to Asparagine or to a Threonine (resistant types) change occurs in pyrimethamine resistant parasites. Eleven DHFR fragments were sequenced and mutations occurring at codons 51, 59 and 108 were analysed. The DHPS gene was amplified by polymerase chain reaction (PCR) and sequenced directly or after cloning. Variant amino acid residues 436, 437, 540, 581, 613 associated with sulfadoxine resistance were analysed. The analysis of codon 108 of the DHFR gene was undertaken for 81 isolates. More than one DHFR P. falciparum genotype was present in 64% of the samples. We showed that 47% of 141 DHFR gene PCR products had Serine (wild phenotype), and 52% had Asparagine. We found one isolate with the Thr-108 confirmed by sequencing of the PCR product. Triple, double and single DHFR mutant at positions 51, 59 and 108 were found. Only codons 436 and 437 of the 38 analysed sequences of the DHPS gene revealed point mutations. These results have been compared with those reported from different sites in Africa, Asia or South-America.