Growth phenotypes of Δodc promastigotes and axenic amastigotes. Wild-type, Δodc1, Δodc1[pXG-BSD-ODC] (Δodc1[pODC]), Δodc2, and Δodc2[pXG-BSD-ODC] (Δodc2[pODC]) promastigotes (A) and axenic amastigotes (B) were each incubated in their respective growth media in the absence or presence of 200 μM putrescine. Parasites were enumerated after 5 days by using a hemocytometer. Promastigotes were maintained at pH 7.4 and 28°C, while axenic amastigotes were cultured at pH 5.5 and 37°C.