DETERMINATION OF PLOIDY IN CRYPTOCOCCUS-NEOFORMANS BY FLOW-CYTOMETRY

We determined the ploidy of Cryptococcus neoformans (28 strains) isola ted from patients and nature. The cellular DNA content of these strain s, which stained with propidium iodide in comparison to that of two au thentic haploid strains, was determined by flow cytometry. All the str ains exhibited diphasic histograms. In case of the authentic haploid s trains, the first peak was centred around channel 9, and the second pe ak around channel 18. Most strains exhibited this type of histogram. S ome strains exhibited another type of histogram: the first peak was ce ntred around channel 18, and the second one around channel 35. In flow cytometry, the channel number is correlated with the intensity of flu orescence, namely, in proportion to the channel number the DNA content in the cells increases. The cellular DNA content of the second type o f histograms showed twice that of the authentic haploid strains, and t hus, five of 28 isolates were concluded to be diploid, and the others haploid.