Lackner M, Tscherner M, Schaller M, Kuchler K, Mair C, Sartori B, Istel F, Arendrup M C, Lass-Flörl C
Division of Hygiene and Medical Microbiology, Innsbruck Medical University, Innsbruck, Austria
Medical University of Vienna, Department for Medical Biochemistry, Max F. Perutz Laboratories, Vienna, Austria.
Antimicrob Agents Chemother. 2014 Jul;58(7):3626-35. doi: 10.1128/AAC.00123-14. Epub 2014 Apr 14.
Candidemia is the fourth most common kind of microbial bloodstream infection, with Candida albicans being the most common causative species. Echinocandins are employed as the first-line treatment for invasive candidiasis until the fungal species is determined and confirmed by clinical diagnosis. Echinocandins block the FKS glucan synthases responsible for embedding β-(1,3)-d-glucan in the cell wall. The increasing use of these drugs has led to the emergence of antifungal resistance, and elevated MICs have been associated with single-residue substitutions in specific hot spot regions of FKS1 and FKS2. Here, we show for the first time the caspofungin-mediated in vivo selection of a double mutation within one allele of the FKS1 hot spot 1 in a clinical isolate. We created a set of isogenic mutants and used a hematogenous murine model to evaluate the in vivo outcomes of echinocandin treatment. Heterozygous and homozygous double mutations significantly enhance the in vivo resistance of C. albicans compared with the resistance seen with heterozygous single mutations. The various FKS1 hot spot mutations differ in the degree of their MIC increase, substance-dependent in vivo response, and impact on virulence. Our results demonstrate that echinocandin EUCAST breakpoint definitions correlate with the in vivo response when a standard dosing regimen is used but cannot predict the in vivo response after a dose escalation. Moreover, patients colonized by a C. albicans strain with multiple mutations in FKS1 have a higher risk for therapeutic failure.
念珠菌血症是第四常见的微生物血流感染类型，白色念珠菌是最常见的致病菌种。棘白菌素被用作侵袭性念珠菌病的一线治疗药物，直到通过临床诊断确定并确认真菌种类。棘白菌素可阻断负责将β-(1,3)-d-葡聚糖嵌入细胞壁的FKS葡聚糖合酶。这些药物的使用增加导致了抗真菌耐药性的出现，而最低抑菌浓度（MIC）升高与FKS1和FKS2特定热点区域的单残基取代有关。在这里，我们首次展示了卡泊芬净在体内对临床分离株中FKS1热点1的一个等位基因内的双突变进行选择。我们创建了一组同基因突变体，并使用血源性小鼠模型评估棘白菌素治疗的体内结果。与杂合单突变相比，杂合和纯合双突变显著增强了白色念珠菌的体内抗性。各种FKS1热点突变在MIC增加程度、物质依赖性体内反应以及对毒力的影响方面存在差异。我们的结果表明，当使用标准给药方案时，棘白菌素欧洲抗菌药物敏感性试验委员会（EUCAST）断点定义与体内反应相关，但不能预测剂量增加后的体内反应。此外，被FKS1中具有多个突变的白色念珠菌菌株定植的患者治疗失败风险更高。
