Franzot S P, Mukherjee J, Cherniak R, Chen L C, Hamdan J S, Casadevall A
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Infect Immun. 1998 Jan;66(1):89-97. doi: 10.1128/IAI.66.1.89-97.1998.
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.
新型隐球菌是免疫系统衰弱患者的主要真菌病原体。然而，关于新型隐球菌实验室菌株的毒力稳定性或与毒力相关的表型稳定性，尚无相关信息。我们实验室偶然观察到，一株新型隐球菌ATCC 24067（菌株52D）在连续体外培养后毒力减弱，这促使我们对从六个不同研究实验室获得的九株24067菌株进行了比较研究。对每株菌株进行了DNA分型、对小鼠的毒力、蛋白酶产生、细胞外蛋白合成、黑色素合成、碳同化模式、抗真菌药物敏感性、菌落形态、生长速率、凝集效价、被小鼠巨噬细胞吞噬情况、荚膜大小和荚膜多糖结构等特征分析。所有菌株具有相似的DNA分型模式，与其属于同一菌株的分类一致，尽管在两株菌株的电泳核型中观察到了微小的染色体大小多态性。几株菌株在可能与毒力相关的表型上存在重大差异，包括生长速率、荚膜大小、蛋白酶产生和黑色素化。这些发现表明，新型隐球菌能够在体外迅速发生变化，可能是适应实验室条件的结果，并提示需要仔细关注储存和保存条件。总之，我们的结果表明，新型隐球菌（i）可因体外培养而减毒，（ii）能够在体外发生微进化，出现表现出新基因型和表型特征的变体。
