Use of Morphology Index Histograms to Quantify Populations of the Fungal Pathogen Paracoccidioides Brasiliensis

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Abstract
To quantify the dimorphic process in wild and mutant strains of Paracoccidioides brasiliensis, we defined a morphology index (Mi) in terms of the maximum cell length (I), maximum cell diameter (d), and septal diameter (s), according to the equation Mi = 2.13 + 1.13 log10(Is/d 2), whose intercept and slope were such that Mi was around 1 for yeast (spherical) cells or 4 for hyphal (elongated) cells. This discriminatory power was used to quantify morphological population mixtures through Mi histograms. During the temperature-induced dimorphic transition (either way), mean Mi (Mi) varied linearly with time, suggesting a continuity in the process. Also, in wild strains and mutants thereof we found an inverse relationship between Mi and content of both cell wall chitin and 1,3-a-glucan.