I. Extracellular Cultivation and Morphological Characterization of Amastigote‐Like Forms of Leishmania panamensis and L. braziliensis

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Abstract
Two strains of the Leishmania braziliensis complex have been adapted to grow extracellularly at elevated temperature as amastigote-like forms in a cell-free medium. The parasites can be serially cultivated and maintained at 32.degree.C for L. panamensis (WR442: L. braziliensis panamensis) and at 28.degree.C for L. braziliensis (M5052; L. braziliensis braziliensis). Several observations are presented that the forms adapted at elevated temperature are amastigote-like. Morphologically, the amastigote-like organisms appear rounded to ovoid and are immotile and smaller than promastigotes; the flagellum of the amastigote-like forms does nt extend beyond the flagelluar pocket. In comparsion, the promastigotes are very elongated, with a nucleus at mid-cell length and a very long flagellum. By electron microscopy, the short flagellum of the amastigote-like form is within a distended flagellar pocket; the 9 + 2 axonemal configuation is present but the paraxial rod is not observed. By contrast, the flagellum of the promastigote has a paraxial rod which extends from the axosome level. In addition, these amastigote-like forms of Leishmania are able to infect, to survive and to divide within the macrophage cell line J774.