Universidad del País Vasco, Bilbao, Spain.
Instituto de Investigación Sanitaria La Fe, Valencia, Spain.
Mycoses. 2020 May;63(5):461-470. doi: 10.1111/myc.13061. Epub 2020 Mar 22.
Candida parapsilosis is the second or third most frequently isolated Candida species related to nosocomial infections, even overtaking Candida albicans in some hospitals. C. parapsilosis constitutes a complex of closely related species: Candida parapsilosis sensu stricto, Candida orthopsilosis and Candida metapsilosis. Accurate detection of these species is of importance, as the incidence of C. orthopsilosis has been reported to surpass that of Candida krusei.
To evaluate the diagnostic utility of two PCR-RFLP methods targeting the SADH and FKS1 genes and to determine the prevalence of cryptic species in 96 bloodstream isolates of C. parapsilosis from 93 patients.
Restriction patterns of the SADH and FKS1 genes were analysed, and sequencing of the D1/D2 regions of the ribosomal RNA was used to evaluate the reliability of both PCR-RFLP methods.
In our study, 77 C. parapsilosis sensu stricto, 13 C. orthopsilosis and five C. metapsilosis were identified by sequencing. Both PCR-RFLP methods demonstrated strong agreement with D1/D2 sequencing in the identification of C. parapsilosis and C. orthopsilosis, while both methods were unable to identify the C. metapsilosis isolates. Moreover, unexpected restriction patterns were observed for two isolates on SADH PCR-RFLP and for four isolates on FKS1 PCR-RFLP. Mixed bloodstream infections of C. parapsilosis sensu stricto and C. orthopsilosis were detected for three patients, for which differential growth characteristics were observed.
The molecular method chosen for identification could have an impact on determination of the real prevalence of C. metapsilosis in candidaemia, and mixed fungaemias can remain undetected.
近平滑假丝酵母是与院内感染相关的第二或第三大常分离假丝酵母种，甚至在某些医院超过了白色假丝酵母。近平滑假丝酵母构成了一个密切相关的种复合体：近平滑假丝酵母严格意义上的种、中间假丝酵母和构巢假丝酵母。准确检测这些种非常重要，因为已经报道中间假丝酵母的发病率超过了克柔假丝酵母。
评估针对 SADH 和 FKS1 基因的两种 PCR-RFLP 方法的诊断效用，并确定 93 例患者的 96 株血流分离近平滑假丝酵母中隐种的流行率。
分析 SADH 和 FKS1 基因的限制图谱，并对核糖体 RNA 的 D1/D2 区进行测序，以评估两种 PCR-RFLP 方法的可靠性。
在本研究中，通过测序鉴定出 77 株近平滑假丝酵母严格意义上的种、13 株中间假丝酵母和 5 株构巢假丝酵母。两种 PCR-RFLP 方法在鉴定近平滑假丝酵母和中间假丝酵母方面与 D1/D2 测序具有很强的一致性，而两种方法均无法鉴定出构巢假丝酵母的分离株。此外，在 SADH PCR-RFLP 中有两个分离株和在 FKS1 PCR-RFLP 中有四个分离株观察到了意想不到的限制图谱。对三名患者检测到了近平滑假丝酵母严格意义上的种和中间假丝酵母的混合血流感染，观察到了不同的生长特征。
选择用于鉴定的分子方法可能会影响对血流感染中真正的构巢假丝酵母流行率的确定，并且可能会漏检混合真菌血症。
