Candida Pathogenesis in Surgery and Trauma

念珠菌是医院内血流感染的第四大常见原因，在几乎所有的研究中，白色念珠菌占念珠菌种类的50%到75%。尽管进行了适当的抗真菌治疗，但死亡率仍为35%至75%。风险最高的患者包括免疫抑制患者、创伤患者和手术后患者，大部分病例发生在重症监护室。白念珠菌经历可逆的形态转换，产生萌芽酵母和丝状形态，包括芽管、假菌丝和真菌丝。许多研究人员认为，丝状细胞是上皮细胞侵袭的原因。然而，最近来自小鼠肠道外扩散模型的数据表明，在白色念珠菌穿透肠道上皮的过程中，酵母细胞可能比丝状细胞更重要。我们的工作假设是，酵母细胞在这种真菌与肠道上皮的相互作用(粘连和穿透)中发挥关键作用。一般的方法是使用野生型和特征良好的白色念珠菌突变株(具有形态转换缺陷)在体外(培养的肠细胞)和体内(小鼠模型)挑战这一假说。由于光滑念珠菌最近已成为第二常见的念珠菌病病因，而且光滑念珠菌是(已确认的80多种念珠菌中)唯一不形成细丝且仅以酵母形式存在的物种，因此实验也集中在光滑念珠菌上。体外实验旨在分别表征酵母菌和丝状菌与培养的肠细胞的相互作用(粘连、内化、细胞内存活)，分析系统包括ELISA和使用钙粉和活性染料FUN-1的双荧光分析。小鼠模型包括抗生素诱导的肠道念珠菌定植、结扎肠环和Stamper-Woodruff试验。还阐明了细菌细胞壁产物(脂多糖和肽聚糖)、地塞米松和低氧对念珠菌肠道外传播的影响。如果我们的假设得到证实(酵母细胞在肠道外传播中起主要作用)，那么设计更有效的体外敏感性分析以及更有效的预防和治疗方法的努力可能更可靠地针对酵母，而不是菌丝成分。这些知识应该会加速我们诊断、治疗和控制系统性念珠菌病的能力。

Candida species are the fourth most common cause of nosocomial blood stream infections, and C. albicans accounts for 50% to 75% of Candida species in essentially all studies. Despite appropriate antifungal therapy, mortality is 35% to 75%. Patients at highest risk include immunosuppressed patients, trauma patients, and postsurgical patients, and a large proportion of cases occur in intensive care units. C. albicans undergoes reversible morphologic switching, producing budding yeast and filamentous forms that include germ tubes, pseudohyphae and true hyphae. Many investigators have assumed that filamentous forms are responsible for epithelial invasion. However, recent data from mouse models of extraintestinal dissemination indicate that the yeast cell, rather than filamentous forms, might be more important in C. albicans penetration of intestinal epithelium. Our working hypothesis is that yeast cells play a key role in interactions (adherence and penetration) of this fungus with the intestinal epithelium. The general approach is to use wild type and well-characterized C. albicans mutant strains (with defects in morphologic switching) to challenge this hypothesis in vitro (cultured enterocytes) and in vivo (mouse models). Because C. glabrata has recently emerged as the second most frequent cause of candidiasis, and because C. glabrata is the only species (of the more than 80 recognized Candida species) that does not form filaments and exists only in the yeast form, experiments also focus on C. glabrata. In vitro experiments are designed to separately characterize the interactions (adherence, internalization, intracellular survival) of yeast and filamentous forms with cultured enterocytes, and assay systems include ELISA and a double fluorochrome assay using calcoflour and the vital dye FUN-1. Mouse models include antibiotic-induced intestinal Candida colonization, ligated intestinal loops, and the Stamper-Woodruff assay. The effect of bacterial cell wall products (lipopolysaccharide and peptidoglycan), dexamethasone, and hypoxia on extraintestinal dissemination of Candida is also clarified. If our hypothesis is validated (that the yeast cell is of primary importance in extraintestinal dissemination), then efforts to design more effective in vitro susceptibility assays, as well as more effective prophylactic and therapeutic modalities, might more reliably target yeast rather than hyphal elements. Such knowledge should accelerate our ability to diagnose, treat, and control systemic candidiasis.