Acridine Orange Staining and Fluorescence of Nucleic Acids in Plasmodia and Associated Host Erythrocytes

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Abstract
Acridine orange in daily doses of 1, 2 and 4 mg for 4 days was given to chicks averaging 50 gm in weight. Dosage was started 1, 2 and 3 days after infection with Plasmodium gallinaceum. Such doses were sufficient to stain the parasite in vivo, as shown by its bright fluorescence in UV light, but did not exhibit any antimalarial action. Staining of fresh blood samples from infected chicks with 0.01% acridine orange in Krebs–Ringer containing 0.1 M phosphate buffer (pH 6.0-6.2) resulted in differential fluorescence of the nucleic acids of the plasmodia, to show nuclear DNA bright green and cytoplasmic RNA orange-red. After optimum acid hydrolysis, as used for the Feulgen reaction, staining with 0.1% acridine orange produced intense red fluorescence of the nuclear DNA in the plasmodia. Nuclear DNA of the chick erythrocytes showed bright fluorescence both in vivo and in vitro.