Detection of Plasmodium falciparum DNA using repetitive DNA clones as species specific probes

Repetitive sequences were identified in genomic libraries of Plasmodium falciparum and analyzed for their potential use as specific DNA probes. Nucleotide sequencing revealed inserts composed of 21 base pair tandem repeats. Clone 26 containing an insert of 147 base pairs in M13mp18 was used in three different approaches as a probe to detect P. falciparum DNA: the replicative form of clone 26 was labeled by nick translation; the single strand DNA of clone 26 was labeled by primer extension and a two step sandwich assay was employed hybridizing single strand unlabeled clone 26 DNA to the target DNA (first step) and using nick translated M13 DNA in a second step to detect the vector part of clone 26. The most sensitive probes detected 25 pg of P. falciparum DNA after 2 h of film exposure, 3 pg after 14 h and 0.78 pg after 40 h. Hybridization to genomic blots of Plasmodium vivax and human DNA using clone 26 as a probe revealed that the 21 base pair repeats specifically hybridized with P. falciparum DNA while failing to react with either human or P. vivax DNA.