较高浓度的二氧化碳和 37°C 使白色念珠菌毒力较弱的不透明细胞稳定。

Higher concentration of CO₂ and 37°C stabilize the less virulent opaque cell of Candida albicans.

机构信息

Department of Medical Mycology, Institute of Dermatology, Chinese Academy of Medical Sciences and Peking Union Medical College, Nanjing, Jiangsu 210042, China.

出版信息

Chin Med J (Engl). 2010 Sep;123(17):2446-50.

PMID:21034563

Abstract

BACKGROUND

Candida albicans (C. albicans) strains can spontaneously switch at a very low frequency from white to opaque phase. The ability to switch reversibly between white and opaque phenotype and contributes to the pathogenicity of C. albicans. White and opaque switching can be induced by various environmental signals. Previous study showed that opaque cells switch en masse to white when transferred in vitro to 37°C, the temperature of their animal host. The objective of the present study was to determine the effect of different concentration of carbon dioxide and temperature on white-opaque switching, and to determine the different anti-candida killing activity of white and opaque form by human monocyte-macrophage cell line THP-1.

METHODS

White-opaque switching and opaque-white switching were assayed. Modified Lee's medium supplemented with phloxine B was used to detect white and opaque forms of C. albicans under 0.03% CO2 at 25°C, 0.03% CO2 at 37°C and 5% CO2 at 37°C. Growth curve of C. albicans was monitored using OD value at 630 nm simultaneously. White and opaque forms of C. albicans and THP-1 cells were cocultured at ratio of 1:10. Colony serial dilutions were used to assay for intracellular candidacidal activity. MTT assay was used to measure the extracellular candidacidal activity.

RESULTS

Phenotype switching was successfully induced in vitro in all three strains of C. albicans. When evaluating white to opaque switching, opaque colony proportion of all colonies was 0.572 ± 0.087, 0.920 ± 0.030 and 0.985 ± 0.026 exposure of white cells to 0.03% CO2 at 25°C, 0.03% CO2 at 37°C and 5% CO2 at 37°C. When evaluating opaque to white switching, opaque colony proportion of all colonies was 0.600 ± 0.114, 0.983 ± 0.003 and 0.998 ± 0.003 exposure of white cells to 0.03% CO2 at 25°C, 0.03% CO2 at 37°C and 5% CO2 at 37°C. No significant difference of white or opaque form growth rate was found among three conditions (P > 0.05). THP-1 mediated extracellular anti-candida activity in white form was (79.80 ± 3.71)% and (56.28 ± 19.12)% at different dilution ratio, which were significantly lower than that in opaque form (100%, P < 0.01). THP-1 mediated intracellular anti-candida activity in white form ((62.98 ± 5.02)%) was significantly lower than that in opaque form ((87.07 ± 1.80)%, P < 0.01).

CONCLUSIONS

Our results showed that opaque form is more vulnerable and less virulent than that in white form. It suggested that higher concentration of CO2 and 37°C in host niches stabilize the less virulent opaque cell of C. albicans, which might have implications for pathogenesis, commensalism and mating.

摘要

背景

白色念珠菌（C. albicans）菌株可以在非常低的频率下自发地从白色相转换为不透明相。白色和不透明表型之间的可逆转换能力有助于 C. albicans 的致病性。白色和不透明的转换可以被各种环境信号诱导。先前的研究表明，当在体外转移到 37°C（其动物宿主的温度）时，不透明细胞会大量转换为白色。本研究的目的是确定不同浓度的二氧化碳和温度对白色-不透明转换的影响，并确定人单核巨噬细胞系 THP-1 对白和不透明形式的不同抗真菌杀伤活性。

方法

测定白色-不透明转换和不透明-白色转换。在 0.03% CO2 下于 25°C、0.03% CO2 下于 37°C 和 5% CO2 下于 37°C 下，用改良的 Lee 培养基补充 phloxine B 来检测白色和不透明形式的 C. albicans。同时，通过 630nm 处的 OD 值监测 C. albicans 的生长曲线。将白色和不透明形式的 C. albicans 与 THP-1 细胞以 1:10 的比例共培养。用菌落连续稀释法检测细胞内杀真菌活性。MTT 法检测细胞外杀真菌活性。

结果

在三种白色念珠菌菌株中均成功地在体外诱导了表型转换。在评估白色到不透明的转换时，所有菌落中不透明菌落的比例分别为 0.572±0.087、0.920±0.030 和 0.985±0.026 白色细胞暴露于 0.03% CO2 于 25°C、0.03% CO2 于 37°C 和 5% CO2 于 37°C。在评估不透明到白色的转换时，所有菌落中不透明菌落的比例分别为 0.600±0.114、0.983±0.003 和 0.998±0.003 白色细胞暴露于 0.03% CO2 于 25°C、0.03% CO2 于 37°C 和 5% CO2 于 37°C。在三种条件下，白色或不透明形式的生长速度均无显著差异（P＞0.05）。白色形式的 THP-1 介导的细胞外抗真菌活性在不同稀释比时分别为（79.80±3.71）%和（56.28±19.12）%，明显低于不透明形式（100%，P＜0.01）。白色形式的 THP-1 介导的细胞内抗真菌活性（（62.98±5.02）%）明显低于不透明形式（（87.07±1.80）%，P＜0.01）。