title: Cytometric measurement of in vitro inhibition of Plasmodium falciparum field isolates by drugs: a new approach for re-invasion inhibition study.
abstract: BACKGROUND
  A flow cytometric method is proposed to study in vitro drug sensitivity of Plasmodium falciparum. Standard [(3)H]-hypoxanthine incorporation assay gives only information on inhibition of maturation by drugs. This method is usable on field isolates and provides data on both inhibition of maturation and re-invasion.
  
  
  METHODS
  The method is based on the staining of parasites with hydroethidine (HE) and thiazole orange (TO) which allow differential identification of early, trophozoite and late stage of the parasite by flow cytometry. Late stages of the parasites are obtained by incubation in culture for 24 hours. Reinvasion is followed by culturing parasitized red blood cells for 24 h more.
  
  
  RESULTS
  Compared to the standard [(3)H]-hypoxanthine incorporation assay, it gave similar results as expressed by 50% inhibitory concentrations for chloroquine of laboratory strains and "field" isolates. The effect of quinine on the schizont-ring transition was also explored using this method. First data on the inhibition of re-invasion induced by quinine are presented for both P. falciparum-cultured strains and field isolates.
  
  
  CONCLUSIONS
  This method is simple to use event for field isolate study. It is suitable to analyse effect of drugs on steps of the parasite life cycle different for the maturation one. Using this method quinine was found to have a inhibitory effect on re-invasion of red cells by Plasmodium.
authors.forename: Marie Louise
authors.initials: ML
authors.lastname: Varela
authors.forename: Romy
authors.initials: R
authors.lastname: Razakandrainibe
authors.forename: Delphine
authors.initials: D
authors.lastname: Aldebert
authors.forename: Jean Christophe
authors.initials: JC
authors.lastname: Barale
authors.affiliation: Unité d'immunologie Institut Pasteur de Madagascar, Antananarivo BP1274, Madagascar. rjambou@pasteur.mg.
authors.forename: Ronan
authors.initials: R
authors.lastname: Jambou
mesh_terms: D000962:Antimalarials / Q000494:pharmacology*; D052160:Benzothiazoles; D002738:Chloroquine / Q000494:pharmacology; D004351:Drug Resistance; D005434:Flow Cytometry / Q000379:methods*; D005456:Fluorescent Dyes; D020128:Inhibitory Concentration 50; D010617:Phenanthridines; D010963:Plasmodium falciparum / Q000187:drug effects*; D011803:Quinine / Q000494:pharmacology; D011804:Quinolines
chemical_list: D000962:Antimalarials; D052160:Benzothiazoles; D005456:Fluorescent Dyes; D010617:Phenanthridines; D011804:Quinolines; C051000:thiazole orange; C058428:hydroethidine; D002738:Chloroquine; D011803:Quinine