Pathogenic Effects Of Biofilm In A Rat Model Of Chronic Pseudomonas Aeruginosa Pulmonary Infection

Objective To establish an animal model of pseudomonas aeruginosa biofilm associated with chronic pulmonary infection in vivo and to observe its bacteriological,pathological features and to investigate the pathogenic effects of biofilmMethods (1)Experiments in vivio,Mueller-Hinton broth by the tube macrodilution methed, measured the MICS,MBCS of LFX,CAZ in PAO579 in Alginate beads and planktonic PAO579. (2)Experiments in vivo,Sixty Wistar SPF rats were randomly divided into two groups:Alginate beads group and planktonic bacteria group.Both groups were respectively intratracheally challenged with 0.1ml of PAO579(109CFU/ml) in alginate beads and 0.1ml of planktonic PAO579(109CFU/ml), 3,7,14 days after challenging, bacteriological,pathological features and cytokine reaction of lung tissue were observed.Result (1)Antibiotic study in vivio: The MICS,MBCS of LFX,CAZ in PAO579 in Alginate beads were higher than those in planktonic PAO579. (2)Bacteriology: On 3,7,14days,CFU/lung in Alginate beads group was significantly higher than that in planktonic bacteria group(P=0.002 P=0.004 P=0.002 respectively).On 14 days,PA could be cultured from the lungs in Alginate beads group, but could not be cultured in planktonic bacteria group(P<0.001). (3)Microscopic lung pathology in Alginate beads group was significantly more severe compared to that in planktonic bacteria group,the score of 4 was predominary in Alginate beads group,the score of 1-2 was predominary in planktonic bacteria group.On 3,7days, the score of 4 and the incidence of lung abscesses in Alginate beads group were significantly higher than that in planktonic bacteria group(P<0.001 P<0.013 respectively). (4)Histopathology of the lungs: the inflammation in Alginate beads group was significantly more severe than that in planktonic bacreria group, 3 days after challenging, the acute inflammatory response was found in both groups,and predominant infiltration of PMN in the lung tissues was seen. On 14 days,the chronic inflammatory response was found in Alginate beads group,the hyperplasia of lymphocytes,macrophages,the presence of multinucleated giant cells, and(or) the presence of red blood cells,the hyperplasia of and fibrous tissue,but normal lung tissues were found in planktonic bacteria group. (5)3,7,14days after challenging, the level of TNF-a in Alginate Beads group is higher than that in planktonic bacteria group(P=0.002 P=0.002 P=0.022).Simple regression analysis showed a possive correlation between the level of TNF-a and microscopic lung pathology.Conclusion (1)Antibiotic study in vivio showed that P.aeruginosa in alginate beads was less susceptible to antibiotics than planktonic P.aeruginosa. P.aeruginosa biofilm(Alginate) presented a barrier which inhibited or delayed penetration of the antimirobial molecules through biofilm and protected bacterium from killing of antibiotics. (2)Experiments in vivo showed that the inflammation and the lung tissues damage in Alginate beads group were significantly more severe than that in planktonic bacreria group, P.aeruginosa biofilm(Alginate) might mediate the host immune damage in the lung tissues. (3)Because of P.aeruginosa biofilm,s (Alginate) protection ,PA could clonized,multiplied in the lungs,existed for a long time.The study suggested P.aeruginosa biofilm(Alginate) made bacterium evade the host immune defense and P.aeruginosa biofilm(Alginate) was the important pathogen in chronic P.aeruginosa pulmonary infection.