Effects Of Neonatal Streptococcus Pneumoniae Pneumonia On Lung Structure And Function Of Mice

Background:Bacterial pneumonia has a high mortality and morbidity rate in the world.Although effective antibiotics and vaccines have been developed,a large number of susceptible people still face the risk of bacterial pneumonia infection.Streptococcus pneumoniae is the most common pathogen of community-acquired pneumonia,Neonatal Streptococcus pneumonia Pneumonia(S.pp)is the main cause of morbidity and mortality among children under the of 5 in developing countries.which is characterized by a sharp increase in the number of lung bacteria,diffuse lung active epithelial injury,and a large number of leukocytes influx of pneumococcal.Although the toxicity of pneumococcal bacteria and the host factors that cause bacterial pneumonia are becoming clear,so far,the damage to alveolar cells caused by neonatal Streptococcus pneumoniae pneumonia and the later structural changes in the lungs are still unclear.Objective:To study the effect of Streptococcus pneumoniae pneumonia(S.pp)on lung structure and function.Methods:Neonatal Balb/c mice(1-week-old)were infected intranasally with 2×10~7CFU of S.pneumoniae(D39)in 5μl,the same dose PBS were used in control group.Five weeks after the infection,the airway hyperresponsiveness(AHR)was evaluated by EMKA pulmonary system.Three weeks and Five weeks after the infection,The lungs were collected.lung inflammatory cells infiltration and alveolar septum thickness were evaluated by H&E staining,collagen deposition was identified by Masson staining.Results:H&E staining showed that alveolar inflammatory cell infiltration in the S.pp mice both in infants and early-adult were significantly increased compared with the control group(p<0.05);the radial alveolar count(RAC)in the S.pp group decreased significantly(p<0.05),mean alveolar diameter(MAD),mean linear intercept(MLI),alveolar septum thickness were significantly increased when compared to the control group(p<0.05)during infants.In adulthood,the RAC was significantly reduced(p<0.05),MLI and alveolar septum were significantly increased(p<0.05),while there was no statistical difference in MAD between two groups(p>0.05).Collagen deposition around alveoli in the S.pp group was significantly increased in adulthood(p<0.001),while there was no statistical difference during infants(p>0.05).Lung resistance in S.pp group mice increased significantly in adulthood when the concentration of aerosolized methacholine inhaled by mice ranged from 12.5 to 50 mg/ml(P<0.001).Conclusion:Neonatal Streptococcus pneumoniae pneumonia can cause in abnormal lung tissue structure and function.