近平滑念珠菌临床分离菌株毒力因子差异表达研究

Differential expression of virulence factors in clinical isolates of Candida parapsilosis

摘要:

目的 比较近平滑念珠菌临床分离株毒力相关因子天冬氨酸蛋白酶和生物膜形成及其基因表达的差异。 方法 采用基因测序及微卫星分型方法, 对临床真菌感染患者分离的近平滑念珠菌进行鉴定, 检测各菌株产生分泌型天冬氨酸蛋白酶及生物膜形成的能力, 比较各菌株生物膜形成相关基因BCR1、EFG1、HWP1及天冬氨酸蛋白酶毒力基因SAPP1、SAPP2、SAPP3表达的差异。 结果 共收集8株临床分离的近平滑念珠菌, 经基因鉴定均为基因Ⅰ型。微卫星分型结果显示, 8株临床菌株分为4个微卫星型别, G1、G2、G3菌株为不同型别, 分别分离自甲患者的尿、经外周静脉置入中心静脉导管(PICC)和血; J1、J2、J3、J4、J5菌株为同一型别, 分离自乙患者不同时期血标本。8株临床菌株均能形成生物膜, 生物膜形成能力均高于近平滑念珠菌标准菌株ATCC 22019, 其中G1、G3和J5菌株生物膜形成能力强, J1、J2、J3、J4菌株生物膜形成能力中等, G2菌株生物膜形成能力弱。8株临床分离菌株均分泌天冬氨酸蛋白酶, 酶体外表达水平均高于近平滑念珠菌标准菌株ATCC 22019, G3、G1、G2菌株分别为低表达、中表达、高表达, 酶体外表达水平比较, 差异均有统计学意义(均P＜0.05);J1、J5菌株为中表达, J2、J3、J4菌株为高表达, 中表达菌株与高表达菌株比较, 差异有统计学意义(P＜0.05)。甲、乙患者分离的各菌株生物膜形成基因BCR1、EFG1、HWP1表达水平均增加, 其中甲患者G1菌株EFG1基因表达水平高于G2菌株(P＜0.05), 乙患者分离的菌株BCR1、EFG1、HWP1基因表达水平差异无统计学意义。甲、乙患者分离的各菌株天冬氨酸蛋白基因SAPP1、SAPP2、SAPP3表达水平均增加, 其中G1菌株的SAPP1和SAPP2表达水平高于G2、G3(均P＜0.05), 乙患者SAPP1、SAPP2、SAPP3基因表达水平差异无统计学意义。 结论 近平滑念珠菌临床分离株生物膜形成和天冬氨酸蛋白酶产生能力均高于标准菌株, 分离自不同标本的菌株毒力因子表达具有差异性, 不同时期分离的菌株毒力因子表达差异不明显。患者可能存在同一时期多部位感染不同MT型别近平滑念珠菌的情况。

Abstract:

Objective To compare the differences in virulence-related factor aspartate protease, biofilm formation, and gene expression among clinical isolates of Candida parapsilosis (C. parapsilosis). Methods Gene sequencing and microsatellite typing (MT) method were adopted to identify C. parapsilosis isolated from patients with clinical fungal infection. The production of secreted aspartate protease and biofilm formation ability of each strain were detected, and the expression of biofilm formation related-genes BCR1, EFG1, and HWP1, as well as aspartate protease virulence genes SAPP1, SAPP2, SAPP3 were compared among the strains. Results A total of 8 clinically isolated C. parapsilosis strains were collected, all of which were identified as genotype Ⅰ. Based on microsatellite typing results, 8 clinical strains were divided into 4 microsatellite types. G1, G2, and G3 strains isolated from the urine, peripherally inserted central catheters (PICC), and blood of patient A were of different subtypes. J1, J2, J3, J4, and J5 strains were of the same type, and isolated from blood specimens of patient B at different periods. All 8 clinical strains could form biofilm, and their biofilm formation ability was higher than that of the standard strain of C. parapsilosis (ATCC 22019). G1, G3 and J5 strains had strong biofilm formation ability, J1, J2, J3, and J4 strains had moderate biofilm formation ability, and G2 strain had weak biofilm formation ability. All of the eight clinical isolates secreted aspartate protease, and their in vitro expression levels of the enzyme were higher than that of the standard strain (ATCC 22019). G3, G1, and G2 strains showed low, moderate, and high in vitro enzyme expression respectively, with statistical differences (all P<0.05). Enzyme expressed moderately in J1 and J5 strains, and highly in J2, J3, and J4 strains. Difference between moderate and high expressions was statistically significant (P<0.05). The expression levels of biofilm formation genes BCR1, EFG1, and HWP1 in various strains isolated from patients A and B increased. In strains isolated from patient A, the expression level of EFG1 gene in G1 strain was higher than that in G2 strain (P<0.05). There was no statistically significant difference in BCR1, EFG1, and HWP1 gene expression levels among strains isolated from patient B. The expression levels of aspartate protein genes (SAPP1, SAPP2, and SAPP3) in various strains isolated from patients A and B increased. The expression levels of SAPP1 and SAPP2 in strain G1 were higher than those in G2 and G3 (both P<0.05). There was no statistically significant difference in the expression levels of SAPP1, SAPP2, and SAPP3 genes in strains from patient B. Conclusion Clinical isolates of C. parapsilosis have higher biofilm formation and aspartate protease production abilities than standard strain. The expression of virulence factors varies among strains isolated from different specimens, while there is no significant difference in the expression of virulence factors among strains isolated at different periods. Patients may have been infected with different MT types of C. parapsilosis in multiple sites during the same period.