Division of Infectious Diseases, Universidade Federal de São Paulo, São Paulo, SP, Brazil.
Antimicrob Agents Chemother. 2011 Jan;55(1):302-10. doi: 10.1128/AAC.00633-10. Epub 2010 Nov 8.
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, β-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 β-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.
棘白菌素类药物已被描述为存在反常生长（PG）现象，其特征是在药物浓度高于 MIC 时细胞仍能生长。在本研究中，对 2 株白色念珠菌、1 株热带念珠菌、1 株近平滑念珠菌和 1 株葡萄牙念珠菌的分离株进行 MIC、最小杀菌浓度（MFC）和时间杀伤曲线检测，以评估 PG 水平。还研究了 PG 细胞的细胞壁成分和超微结构变化。结果表明，当通过 MFC 或时间杀伤曲线检测细胞生长和存活时，高浓度的卡泊芬净对 PG 细胞没有杀菌活性。此外，对于近平滑念珠菌和葡萄牙念珠菌，时间杀伤曲线比 MFC 更能检测到 PG 作用。研究的四种不同的念珠菌物种表现出与 PG 相关的细胞壁成分和超微结构的相似改变。在 PG 细胞中，β-1,3-葡聚糖含量从 2.7 倍降至 7.8 倍，而几丁质含量从 4.0 倍增加至 6.6 倍。PG 细胞的电子显微镜研究显示出形态改变、细胞聚集、细胞增大、无丝状形成、异常隔膜以及细胞壁中几丁质的积累。此外，PG 细胞的细胞壁基本呈现单一暗高密度层，表明β-1,3-葡聚糖层缺失。我们的结果提供了关于棘白菌素类药物治疗期间白色念珠菌、近平滑念珠菌、葡萄牙念珠菌和热带念珠菌 PG 时发生的超微结构改变的新细节，并表明几丁质是 PG 细胞细胞壁的主要成分。几丁质合成的刺激可能代表一种针对卡泊芬净活性的挽救机制。
