Changes in Cell Wall Synthesis and Ultrastructure during Paradoxical Growth Effect of Caspofungin on Four Different Candida Species
Changes in Cell Wall Synthesis and Ultrastructure during Paradoxical Growth Effect of Caspofungin on Four Different Candida Species
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DOI：
10.1128/aac.00633-10
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发表时间：
2011-01-01
影响因子：
4.9
通讯作者：
Colombo, Arnaldo L.
中科院分区：
文献类型：
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作者：
Bizerra, Fernando C.;Melo, Analy S. A.;Colombo, Arnaldo L.
棘球菌素的反常生长(PG)已被描述，其特征是细胞在药物浓度高于最低抑菌浓度时生长。本研究采用最低抑菌浓度(MIC)、最低杀菌浓度(MFC)和时间-杀灭曲线分析方法，对对卡泊芬净敏感的两株白色念珠菌热带念珠菌、直立念珠菌和近平假丝酵母菌进行了PG水平的测定。对PG细胞的细胞壁成分和超微结构修饰进行了研究。结果表明，用MFC或时间-杀伤曲线评价细胞生长和存活时，高浓度卡泊芬净对PG细胞无杀菌活性。此外，在检测PG效应时，时间-杀灭曲线在检测PG效应方面比MFC更具区分性，对于近缘念珠菌和直立念珠藻。所研究的四种不同的念珠菌在与PG相关的细胞壁成分和超微结构上显示出相似的变化。在PG细胞中，β-1，3-葡聚糖含量从2.7倍下降到7.8倍，而甲壳素含量从4.0倍上升到6.6倍。对PG细胞的电子显微镜观察显示，PG细胞形态发生改变，细胞成团，细胞增大，无丝状突起，隔膜异常，细胞壁有甲壳素积聚。此外，PG细胞的细胞壁基本上呈现出单一的深色高密度层，表明β-1，3-葡聚糖层的丢失。我们的结果提供了在PG过程中发生在白色念珠菌、近缘念珠菌、直立念珠菌和热带念珠菌中的超微结构变化的新细节，并表明几丁质是PG细胞细胞壁的主要成分。促进甲壳素的合成可能代表了一种对抗卡泊芬净活性的拯救机制。
Paradoxical growth (PG) has been described for echinocandins and is characterized by cell growth at drug concentrations above the MIC. In this study, two isolates each of Candida albicans, C. tropicalis, C. orthopsilosis, and C. parapsilosis, all of which displaying PG in response to caspofungin, were subjected to MIC, minimal fungicidal concentration (MFC), and time-kill curve assays to evaluate the levels of PG. Cell wall components and ultrastructural modifications of the PG cells were also investigated. The results showed that when cell growth and survival were evaluated by MFC or time-kill curve assays, high concentrations of caspofungin did not show fungicidal activity against PG cells. Furthermore, for C. parapsilosis and C. orthopsilosis, time-kill curves were more discriminatory than MFCs in detecting the PG effect. The four different Candida species studied demonstrated similar alterations in cell wall components and ultrastructure associated with PG. In PG cells, beta-1,3-glucan content decreased from 2.7- to 7.8-fold, whereas chitin content increased from 4.0- to 6.6-fold. An electron microscopy study of the PG cells revealed morphological alterations, clumping of cells, enlarged cells, the absence of filamentation, abnormal septa, and accumulation of chitin in the cell wall. Also, PG cells basically exhibited a single dark high-density layer in the cell wall, indicating the loss of the beta-1,3-glucan layer. Our results present novel details about the ultrastructural alterations that occur in C. albicans, C. parapsilosis, C. orthopsilosis, and C. tropicalis during PG and show that chitin is the major component of the cell walls of PG cells. Stimulation of chitin synthesis may represent a rescue mechanism against caspofungin activity.