少动鞘氨醇单胞菌混合感染对猪大肠杆菌的致病性研究

Study of mixed infection of Sphingomonas paucimobilis on the pathogenicity of porcine Escherichia coli

本研究首次从患有呼吸道疾病的病死猪肺脏样品中同时分离到1株大肠杆菌(E. coli)和1株少动鞘氨醇单胞菌(Sphingomonas paucimobilis),为探究大肠杆菌和少动鞘氨醇单胞菌混合感染的致病作用,本研究比较了大肠杆菌-少动鞘氨醇单胞菌混合感染组、大肠杆菌单独感染组和少动鞘氨醇单胞菌单独感染组小鼠的临床症状,结果显示混合感染组小鼠的临床症状评分显著高于其他两组。进一步利用平板菌落计数的方法测定了单独感染和混合感染各组小鼠肝、脾、肺脏组织菌载量以及体外对猪肺泡巨噬细胞(PAM)的粘附、侵袭能力,结果显示尽管少动鞘氨醇单胞菌在临床未显示致病作用,但混合感染组小鼠肺脏和肝脏中大肠杆菌的数量却显著多于大肠杆菌单独感染组;体外感染PAM试验发现少动鞘氨醇单胞菌促进了大肠杆菌对PAM的侵袭作用。同时利用荧光定量PCR检测了PAM中IL-1β、IL-6、IL-10和TNF-α的转录水平,结果显示大肠杆菌或少动鞘氨醇单胞菌单独感染PAM均可引起IL-1β和IL-10的转录水平升高;混合感染则会进一步上调促炎因子IL-1β的转录水平,降低抑炎因子IL-10的转录水平,而IL-6和TNF-α则无明显变化。以上结果表明少动鞘氨醇单胞菌增强了大肠杆菌对小鼠的致病性,且混合感染在体外能够诱导PAM强烈的炎症反应。本研究首次从患有呼吸道疾病的病死猪肺脏样品中同时分离到少动鞘氨醇单胞菌和大肠杆菌,并发现二者的混合感染促进了大肠杆菌对小鼠的致病性,同时初步探究了混合感染对PAM天然免疫功能的影响,这一发现提示应加强对少动鞘氨醇单胞菌混合感染的监测。

For the first time in this study, E. coli and Sphingomonas paucimobilis were simultaneously isolated from the lung of a dead pig suffering from respiratory diseases. In order to explore the pathogenic effects of mixed infection of E. coli and Sphingomonas paucimobilis, this study compared the clinical symptoms of mice in the E. coli-Sphingomonas paucimobilis mixed infection group, the E. coli-alone infection group, and the Sphingomonas paucimobilina-alone infection group. The results showed that the clinical symptom scores of mice in the mixed infection group were significantly higher than the other two groups.Furthermore, the plate colony counting method was used to determine the bacterial load of the livers, spleens, and lungs of eachgroup of mice infected with single strains or two strains, as well as the adhesion and invasion of E. coli to porcine alveolar macrophages(PAM) in vitro. The results showed that although Sphingomonas paucimobilis did not show pathogenic effects clinically, the amount of E. coli in the lungs and livers of mice in the mixed infection group was significantly higher than those in the E. coli alone infection group;in vitro infection of PAM showed that Sphingomonas paucimobilis promoted the invasion of E. coli to PAM. At the same time, RT-q PCR was used to detect the transcription levels of IL-1β, IL-6, IL-10 and TNF-α in PAM,and the results showed that E. coli or Sphingomonas sphingomonas alone infection of PAM increased IL-1β and IL-10 transcription levels;and the mixed infection further upregulated the transcription level of the pro-inflammatory factor IL-1β and reduced the transcription level of the anti-inflammatory factor IL-10, while IL-6 and TNF-α did not exhibit significant changes. This is the first study to isolate both Sphingomonas paucimobilis and E. coli in the lungs of dead pigs suffering from respiratory diseases, and we found that mixed infection promoted the pathogenicity of E. coli in mice, and preliminarily explored the effect of mixed infection on PAM’s innate immunity function. These findings suggest that monitoring of mixed infections with Sphingomonas paucimobilis should be strengthened.