Peerapan Tan-AriyaChariya R. BrockelmanMahidol University2018-10-122018-10-121983-01-01Experimental Parasitology. Vol.55, No.3 (1983), 364-37110902449001448942-s2.0-0020568104https://repository.li.mahidol.ac.th/handle/20.500.14594/30476Plasmodium falsiparum, Thai strain FCM-5S sensitive to sulfadoxine, was grown continuously for 1 year in a medium with a low concentration of p-aminobenzoic acid (PABA) without the emergence of a sulfadoxine-resistant line. The minimum PABA-requirement for growth of sulfadoxine-sensitive Thai strains in vitro was found to be 25.0 ng/ml, whereas resistant Burmese and Gambian strains completed their schizogony in the absence of PABA. Cultivation in dialyzed and nondialyzed human serum suggested that the sulfadoxine-resistant parasite might use another serum factor in place of PABA for folate biosynthesis, thus overcoming the effect of sulfadoxine, a PABA antagonist. The significantly lower rate of [14C]sulfadoxine incorporation into erythrocytes infected with sulfadoxine-resistant strains strongly supports this suggestion. © 1983.Mahidol UniversityImmunology and MicrobiologyMedicineArticleSCOPUS10.1016/0014-4894(83)90033-4