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Infect. Immun., Jan 1998, 89-97, Vol 66, No. 1
SP Franzot, J Mukherjee, R Cherniak, LC Chen, JS Hamdan and A Casadevall
Cryptococcus neoformans is a major fungal pathogen for patients with
debilitated immune systems. However, no information is available on the
stability of virulence or of phenotypes associated with virulence for C.
neoformans laboratory strains. A serendipitous observation in our
laboratory that one isolate of C. neoformans ATCC 24067 (strain 52D) became
attenuated after continuous in vitro culture prompted us to perform a
comparative study of nine strain 24067 isolates obtained from six different
research laboratories. Each isolate was characterized by DNA typing,
virulence for mice, proteinase production, extracellular protein synthesis,
melanin synthesis, carbon assimilation pattern, antifungal drug
susceptibility, colony morphology, growth rate, agglutination titers,
phagocytosis by murine macrophages, capsule size, and capsular
polysaccharide structure. All isolates had similar DNA typing patterns
consistent with their assignment to the same strain, although minor
chromosome size polymorphisms were observed in the electrophoretic
karyotypes of two isolates. Several isolates had major differences in
phenotypes that may be associated with virulence, including growth rate,
capsule size, proteinase production, and melanization. These findings imply
that C. neoformans is able to undergo rapid changes in vitro, probably as a
result of adaptation to laboratory conditions, and suggest the need for
careful attention to storage and maintenance conditions. In summary, our
results indicate that C. neoformans (i) can become attenuated by in vitro
culture and (ii) is capable of microevolution in vitro with the emergence
of variants exhibiting new genotypic and phenotypic characteristics.
Copyright © 1998, American Society for Microbiology
Microevolution of a standard strain of Cryptococcus neoformans resulting in differences in virulence and other phenotypes
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
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