金黄色葡萄球菌经静脉和腹腔诱导小鼠血流感染的炎症反应和病理变化

Mechanism of inflammatory responses and histopathological changes in Staphylococcus aureus induced bloodstream infections in mice

目的：建立简单可靠的金黄色葡萄球菌血流感染小鼠模型,探讨血流感染小鼠的炎症反应和病理变化。方法：C57BL/6小鼠分别通过静脉或腹腔注射金黄色葡萄球菌标准菌株以诱导血流感染;观察各组小鼠生存率、体重变化及脓毒症评分（MSS）;进行血样本及组织匀浆培养以确定细菌负荷;ELISA法检测血清或组织匀浆中的CRP、PCT及细胞因子（IL-1β、IL-6和TNF-α）水平;同时观察各组小鼠肝、肺、肾脏的病理改变及病理炎症评分。结果：4.5×10^8CFU/ml金黄色葡萄球菌血流感染小鼠的生存率约为70%。感染后24 h,小鼠体重明显减轻,MSS明显升高,且静脉组高于腹腔组。WBC于感染后3 h显著升高;感染后48 h血清CRP、PCT水平达到峰值,分别为静脉组：60.80±5.63、6.796±1.16,腹腔组：40.58±7.54、2.740±0.36;血清及组织匀浆（肝、肺、肾）中IL-1β、IL-6和TNF-α水平均有不同程度的升高,且静脉组高于腹腔组。感染12h后开始出现肝、肺、肾组织不同程度的病理炎症改变,且病理炎症评分随之显著升高。结论：成功建立金黄色葡萄球菌小鼠血流感染模型,比较静脉及腹腔两种途径的炎症反应强度及病理改变,有助于进一步探讨血流感染的早期诊断及临床治疗预后。

Objective： To establish mice models of Staphylococcus aureus bloodstream infections so as to investigate the inflammatory responses and histopathological changes in bloodstream infections（ BSIs） mice. Methods： C57 BL /6 mice were inoculated with S. aureus intravenously or intraperitoneally to induce BSIs. Survival rate,weight loss and murine sepsis scores（ MSS） were observed. Blood samples and tissue homogenates were plated on agar to determine bacterial burden. Inflammatory proteins（ CRP,PCT） and cytokines（ IL-1β,IL-6 and TNF-α） were determined by ELISA kits. Histopathologic changes were also assessed by pathological inflammation scores（ PIS）,macroscopic and microscopic examination. Results： About 70% survival rate was observed in 4. 5 × 10^8 CFU / ml S. aureus induced BSIs mice. Body weight decreased and sepsis scores increased significantly since 24 h post-infection in BSIs mice,and more prominent in IV group. The counts of WBC began to significantly increase at 3 h post-infection,while CRP and PCT levels peaked at 48 hours in IV and IP groups（ 60. 80 ± 5. 63 vs 40. 58 ± 7. 54 for CRP; 6. 796 ± 1. 16 vs 2. 740 ± 0. 36 for PCT）. Moreover,the levels of IL-1β,IL-6 and TNF-α in serum and tissue homogenates（ liver,lungs,and kidneys） were significantly elevated in BSIs mice. Pathological changes in tissues（ liver,lungs and kidneys） and higher pathological inflammation scores（ PIS） were also observed in BSIs mice. Conclusion： Our study represents an effective approach for S. aureus BSIs model to mimic human sepsis. Our results demonstrated that inflammation protein（ PCT,CRP） and cytokines（ IL-6,IL-1β and TNF-α） play an important role in the inflammatory response and histopathological changes during BSIs caused by S. aureus.