PNAG和Bap在鲍曼不动杆菌临床分离株致病中的作用及其诊断价值分析

Acinetobacter baumannii (Ab) is a common opportunistic pathogen for nosocomial infection, and recent studies reveal that Ab infection can dramatically increase the attributable mortality of patients. However its pathogenicity and mechanisms remain poorly understood. Biofilm often plays an important role in bacteria pathogenesis. PNAG and Bap are key molecules in Ab biofilm formation, and our hypothesis is that they play an important role in Ab pathogenesis. On the basis of our previous collection of Ab clinical isolates for several years, we propose to choose the isolate (positive in biofilm phenotype, PANG and Bap) from epidemic clone (ST92) for further study. The specific aims are: 1) Construct the mutant isolates deleted of PNAG and (or) Bap, and confirm the loss of biofilm phenotype; 2) Compare the differences of pathogenicity among maternal isolate, its deletion mutant counterparts and other biofilm phenotype negative isolates in Galleria mellonella (the model organism to study Ab pathogenecity) and mammalian cells respectively, then investigate the possible mechanisms (promoting adherence to cells, defending phagocytes and preventing from complement killing); 3) Conduct the case-control study to compare the severity and prognosis of infection caused by PNAG and (or) Bap positive isolates and negative isolates; 4) Analyze the value of PNAG and Bap in predicting the pathogenicity of Ab clinical isolates and the prognosis of infected patients. This project will hopefully provide some references for early diagnosis and control of such infection.

鲍曼不动杆菌(Ab)是引起医院内感染的常见条件致病菌，近年来研究表明Ab感染可显著增加患者的归因死亡率，但对其致病性及机制的认识仍很有限。生物被膜常在细菌致病中发挥重要作用，PNAG和Bap是参与Ab生物被膜形成的关键分子，我们推测其在Ab致病中发挥重要作用。本项目拟在我们前期多年收集的Ab临床分离株基础上，选定流行株(ST92型)中生物被膜、PNAG和Bap均阳性的菌株。首先构建PNAG和(或)Bap缺失株，验证其是否失去生物被膜。然后分别在大蜡螟(研究Ab致病性的模式生物)和细胞水平比较母体株、缺失株及其它生物被膜阴性株的致病性强弱，并探讨可能的机制(促进细胞粘附，抗吞噬和抗补体杀伤)。之后通过病例对照研究比较PNAG和(或)Bap阳性株与阴性株引起感染的严重程度与预后。最后分析PNAG和Bap对预测Ab临床分离株致病性强弱和患者预后的价值，以期为临床早期诊断和控制此类感染提供依据。

鲍曼不动杆菌(Ab)是引起医院内感染的常见条件致病菌，近年来研究表明Ab感染可显著增加患者的归因死亡率，但对其致病性及机制的认识仍很有限。生物被膜常在细菌致病中发挥重要作用，PNAG和Bap是参与Ab生物被膜形成的关键分子。我们在前期多年收集的Ab临床分离株基础上，选定PNAG和Bap均阳性的菌株(MLST分型为ST92型)，构建了PNAG和(或)Bap缺失株并验证了其正确性。然后在大蜡螟(研究Ab致病性的模式生物)和细胞水平比较母体株、缺失株、和生物被膜阴性菌株的致病性强弱，发现缺失株比母体株的致病性明显降低(P<0.05)。并发现PNAG可能通过促进细胞粘附、抗吞噬作用而不是抗补体杀伤来增强鲍曼不动杆菌的致病性，而在Bap则未观察到这种现象。还发现PNAG阳性组的患者感染更严重，预后差。PgaB基因是编码PNAG的关键基因，它的mRNA表达水平与菌株致病性强弱密切相关，可用此指标早期预测鲍曼不动杆菌临床分离株的致病性强弱。以上结果为临床早期诊断和控制此类感染提供了依据。