Abstract: In this invention, cell lines are created for enzyme inhibitory testing of inhibitors against Plasmodium falciparum DHFR-TS and HPPK-DHPS. Provided the complementing DHFR-TS and HPPK-DHPS have sufficient activities to support growth of the surrogates in un-supplemented medium, the same surrogates could be used for screening inhibitors of targets against other parasite and pathogen species e.g. Plasmodium vivax, Trypanosoma brucei, Trypanosoma cruzi, Toxoplasma gondii or Mycobacterium tuberculosis. The cell lines in this invention are Escherichia coli strain whose thyA, folA, folK, and folP genes were disrupted using genetic knockout coupled with elimination of antibiotic resistance markers. The thyA KO, folP KO, folK KO, thyAfolA KO, folKfolP KO, thyAfolAfolP KO, thyAfolAfolK KO and thyAfolAfolKfolP KO E.

Abstract: The objective of this invention is to create a double thyA folA knockout Escherichia coli (E. coli) strain for antifolate screening against DHFR of malaria and other parasites. This strain is used together with a plasmid expressing DHFR-TS from the desired pathogenic organism, which constitutes an anti-DHFR assay against the pathogenic organism of interest. The benefit of this invention is that there is no interference from either host DHFR or trimethoprim, a bacterial DHFR inhibitor. This tool is easy to use and maintain. It provides quick and reliable results as compared with conventional anti-malarial and anti-parasitic assays. This invention should facilitate discovery of new anti-DHFR compounds against malaria and other parasitic diseases.

Abstract: In this invention, cell lines are created for enzyme inhibitory testing of inhibitors against Plasmodium falciparum DHFR-TS and HPPK-DHPS. Provided the complementing DHFR-TS and HPPK-DHPS have sufficient activities to support growth of the surrogates in un-supplemented medium, the same surrogates could be used for screening inhibitors of targets against other parasite and pathogen species e.g. Plasmodium vivax, Trypanosoma brucei, Trypanosoma cruzi, Toxoplasma gondii or Mycobacterium tuberculosis. The cell lines in this invention are Escherichia coli strain whose thyA, folA, folK, and folP genes were disrupted using genetic knockout coupled with elimination of antibiotic resistance markers. The thyA KO, folP KO, folK KO, thyAfolA KO, folKfolP KO, thyAfolAfolP KO, thyAfolAfolK KO and thyAfolAfolKfolP KO E.