Quantitation of Leishmania tropica major by its ability to form distinct colonies on agar-based media

The growth of the pathogen Leishmania tropica major on agar-based media was studied to further develop techniques that can be used to quantitate the number of viable organisms in infected tissues. Individual, intact amastigotes formed distinct, countable colonies on four different agar-based media. However, the largest colonies (0.35 mm) and highest plating efficiency (greater than 90%) were found on media formulated with a heart-infusion agar base. Use of this media in the quantitation of the organism should increase the sensitivity of the quantitation technique and allow one to collect more interpretable data on host-parasite interactions in experimental cutaneous leishmaniasis.