多重耐药纹带棒杆菌BALB/c小鼠肺部感染模型的建立和评估

Establishment and evaluation of a BALB/c mouse model of pulmonary multidrug-resistant Corynebacterium striatum infection

目的建立多重耐药纹带棒杆菌小鼠肺部感染模型,对感染小鼠肺部病理改变及炎性指标变化进行评价,为更好认识纹带棒杆菌致病性提供实验依据。方法采用腹腔注射环磷酰胺的方法构建BALB/c小鼠免疫抑制状态,利用超声雾化方法将纹带棒杆菌混悬液(高浓度组:109 CFU/ml;低浓度组:108 CFU/ml)感染BALB/c小鼠。分别在感染后24、48、72和96 h观察小鼠状态,检测小鼠肺组织病理学改变、肺组织和支气管肺泡灌洗液(BALF)中细菌菌落计数及血清IL-6、TNF-α水平的变化。结果实验组小鼠于感染纹带棒杆菌后状态变差、体重下降。感染后24和48 h,小鼠肺组织外观呈明显充血、水肿状态;肺组织HE染色结果显示肺部炎性改变程度随感染时间延长不断加重,感染后96 h小鼠肺间质重度充血,大量炎细胞浸润。与低浓度组小鼠相比,各感染时间点高浓度组小鼠肺组织炎性改变程度更为严重。小鼠外周血白细胞及中性粒细胞计数在感染后24 h开始增高,96 h达到峰值。感染后24 h,肺组织及BALF中纹带棒杆菌大量增殖,并且高浓度组小鼠BALF中菌落计数明显高于低浓度组[(15.13±0.70)×105 CFU/ml vs(30.83±1.10)×105 CFU/ml,F=1253.498,P=0.000]。与对照组相比,实验组小鼠各感染时间点血清IL-6水平均高于对照组,但高低浓度组实验小鼠TNF-α水平变化趋势不完全一致。结论本研究成功构建了纹带棒杆菌BALB/c小鼠肺部感染模型。免疫抑制小鼠在纹带棒杆菌攻击下呈现典型肺部感染病理表现。临床样本特别是下呼吸道标本中分离到多重耐药纹带棒杆菌时应给予更多关注。

Objective To establish a mouse model of pulmonary multidrug-resistant Corynebacterium striatum infection and evaluate the pathological changes in mouse lung tissues as well as inflammatory indexes in order to provide reference for better understanding the pathogenicity of Corynebacterium striatum.Methods BALB/c mice were immunosuppressed by intraperitoneal injection of cyclophosphamide and then infected with Corynebacterium striatum suspension(high concentration group:109 CFU/ml,low concentration group:108 CFU/ml)by ultrasonic atomization.Several indexes,including mouse general condition,pathological changes in lung tissues,bacterial colony counts in lung tissues and bronchoalveolar lavage fluid(BALF)and the levels of IL-6 and TNF-αin serum,were observed and detected at 24,48,72 and 96 h after infection.Results The general condition of mice became worse and their body weight decreased after Corynebacterium striatum infection.Obvious hyperemia and edema were observed in mouse lung tissues at 24 and 48 h after infection.Hematoxylin and eosin(HE)staining results showed that pulmonary inflammatory changes in Corynebacterium striatum-infected mice worsened over time.Severe congestion and massive inflammatory cell infiltration were detected in mouse pulmonary interstitium at 96 h after infection.Compared with the low concentration group,severe inflammatory changes in lung tissues were found in the high concentration group at each time point.The counts of leukocytes and neutrophils in mouse peripheral blood began to increase at 24 h after infection and reached the peaks at 96 h.At 24 h after infection,Corynebacterium striatum proliferated greatly in lung tissues and BALF.The colony count in mouse BALF in the high concentration group was significantly higher than that in the low concentration group[(15.13±0.70)×105 CFU/ml vs(30.83±1.10)×105 CFU/ml,F=1253.498,P=0.000].Serum IL-6 levels in the low and high concentration groups were higher than that in the control group at each time point after infection,but the changing trends in TNF-αlevel were inconsistent between the high and low concentration groups.Conclusions The pulmonary infection model of Corynebacterium striatum in BALB/c mice was successfully established in this study.Classical pathological changes in lung tissues were detected in immunosuppressed mice after Corynebacterium striatum infection.More attention should be paid when multidrug-resistant Corynebacterium striatum strains were isolated from clinical samples,especially from lower respiratory tract samples.