Effect Of Bacteroides Fragilis In Necrotizing Enterocolitis Mouse Model And Role Of Streptococcus Mitis In Pseudomonas Aeruginosa Infection

PART ? EFFECT OF BACTEROIDES FRAGILIS IN NECROTIZING ENTEROCOLITIS MOUSE MODELObjective: Necrotizing enterocolitis(NEC)is a severe disease in neonates,especially in preterm babies.Some patients often require surgery.Survivors may have sequelae such as short bowel syndrome,cholestasis,and nervous system developmental disorders.Domestic and foreign researches finded that the proportion of Bacteroides fragilis in the NEC neonates was significantly lower than that of normal neonates.This study explored the role of Bacteroides fragilis in the development of NEC through the gavage of Bacteroides fragilis and the establishment of NEC model.Methods: Sixty C57BL/6 neonatal mice were randomly divided into two groups(n = 30): PBS group and Bacteroides fragilis group.On the third day after birth,PBS and Bacteroides fragilis were given by gavage once a day for 7 days,NEC model was established by hypoxia,cold stimulation and artificial feeding.The newborn mice were sacrificed overnight after modeling.HE staining was used to observe the pathological changes of intestinal tissue.The expression of IL-?1,IL-6,IL-10 and TGF-?1were measured by quantitative real-time PCR.The levels of IL-10,TGF-?1 in intestine tissues were tested by ELISA.Flow cytometry was used to analyze the ratio of regulatory T cells(Treg)on CD4 + T cells.Results: Compared with PBS group,the weight of B.fragilis group decreased less and the intestinal injury were milder.q PCR results in the intestinal tissue showed that B.fragilis group had lower expression of IL-1? and IL-6 than PBS group(P<0.05),and the expression of IL-10 was higher in B.fragilis group than that in PBS group(P<0.05);ELISA showed that the expression of IL-10 were higher in B.fragilis group(P<0.05).Regulatory T cells(Treg)of CD4+T cells in the intestinal lamina propria of B.fragilis group were higher than those in PBS group(P<0.05).Conclusion: Bacteroides fragilis plays a protective role in the intestinal injury of necrotizing enterocolitis mouse model.The mechanism maybe that Bacteroides fragilis can promote the differentiation of T cells into Treg cells,and up-regulate the expression of cytokines IL-10.PART ? ROLE OF STREPTOCOCCUS MITIS IN PSEUDOMONAS AERUGINOSA INFECTIONObjective: Pseudomonas aeruginosa and Streptococcus mitis are common microorganisms on the endotracheal tube of children with mechanical ventilation.We had found that TLR4 plays an important role in the infection of Streptococcus mitis and Pseudomonas aeruginosa.TLR2 is an important receptor in lung tissues that recognizes pathogens and activates the body to produce an immune response.The purpose of this study was to investigate the role of TLR2 in the infection of Pseudomonas aeruginosa and Streptococcus mitis.Methods: Wild-type C57BL/6 and TLR2-/-mice were randomly assigned into 4 groups.They were treated with an intratracheal instillation of Pseudomonas aeruginosa(PAO1 group),Streptococcus mitis(S.mitis group),Pseudomonas aeruginosa and Streptococcus mitis(PAO1+ S.mitis group),and phosphate-buffered saline(PBS group),respectively.the pathological changes in lung tissues were examined with hematoxylin-eosin(H&E),the levels of IL-6 and TNF-? in bronchoalveolar lavage fluid(BALF)were evaluated by ELISA,the total cell counts and neutrophil counts in the BALF were quantified.Results: In wild-type C57 / BL6 mice,P.aeruginosa caused the most severe inflammation with alveolar septum thickening in lung tissues,IL-6,TNF-? expression,and total cell counts and neutrophils in BALF also increased(P<0.05).PAO1 + S.mitis group has slightly thicker alveolar septum,and the total number of alveolar lavage fluid cells,neutrophil counts,and the expression of IL-6 and TNF-? were alleviated.In TLR2-/-mice,alveolar septum thickening was observed in all the mice of PAO1 group and PAO1 + S.mitis group.The total number of alveolar lavage fluid cells,neutrophil count and IL-6,TNF-? also significantly increased,there was no statistical difference between the two groups.Conclusion: Streptococcus mitis can alleviate the inflammatory response of Pseudomonas aeruginosa and is related to TLR2.