院内感染性肺炎逆行感染途径的基因多态性研究

Study of retrograde transmission route of nosocomial pneumonia with random amplified polymorphism DNA

目的 为确证胃→咽→下呼吸道逆行感染途径存在与否 ,研究胃液pH值变化与院内感染性肺炎 (Nosocomialpneumonia ,NP)发生的关系。方法 以气管切开 (或插管 )病人为对象 ,用防污染标本刷 (PSB)采集标本 ,由细菌表型分型 ,直至质粒DNA、酶切、随机扩增多态性DNA(RAPD)等基因分型 ,前瞻性观察NP的发生情况。结果 11名患者有逆行感染存在 (发生率为 2 2 % ) ,即在胃部分离出病原菌 1、2d后 ,PSB在咽部及下呼吸道也检出相同的细菌 ,应用质粒图谱、酶切图谱和RAPD等分子生物学技术进行同源性分析 ,证明其具有很高的同源性。将美蓝经胃管注入病人胃内 ,1、2d后在咽部及下呼吸道可检出蓝色分泌物。随着胃液pH值升高 ,胃内细菌定植增加 ,NP的发生率升高。结论 存在胃→咽→下呼吸道的逆行感染途径。NP的发生与胃液pH值显著相关。

Objective To study the relationship between the incidence of nosocomial pneumonia (NP) and the pH value of gastric juice in order to verify whether there is the existence of a retrograde transmission route from the stomach through the pharynx to the lower respiratory tract. Methods One hundred and eight patients with mechanical ventilation (tracheotomy or intubation) were selected from our 3 teaching hospitals in this study. The secretion of lower respiratory tract was collected with protected specimen brush (PPB) and quantitatively cultured. Gastric aspirate was cultured and gastric pH was determined with a digital acid based analyzer. All the patients were observed every other day for the occurrence of NP. Gene typing of the bacteria from the secretion of the lower respiratory tract and gastric juice was done with plasmid profile analysis, restriction endonuclease fingerprint analysis and random amplified polymorphism DNA (RAPD) in the bacteria with same phenotype. Results fifty out of 108 patients developed NP and identical bacteria from 11 subjects of those with NP were first isolated from gastric juice and then from tracheal secretion 1 to 2 d later. The bacteria isolated from 2 places were quite homologous exhibiting same fingerprints in plasmid profile, endonuclease fingerprints and RAPD. Methylene blue was injected into the stomach through a gastric tube. One or 2 d later, blue secretion was found from the oropharynx and trachea. The bacterial count was increased along with the increase of gastric pH and the incidence of NP was increased simultaneously. Conclusion It is confirmed with our findings that the retrograde transmission route of NP definitely exists in our series of cases and the incidence of NP is positively correlated to gastric pH.