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Background:Antibiotics are frequently used to treat critically ill patients,and its use is often accompanied by intestinal dysbiosis that might further lead to bacterial translocation (BT).Nevertheless,studies on the relationship between antibiotic therapy and BT are rare.In the present study,we investigated the effect of broad-spectrum antibiotics on BT in an experimental rat model of b or sepsis injury.Methods:The septic rat model was simulated by a second insult with lipopolysaccharides after b injury.Ninety-two male Sprague-Dawley rats were randomly divided into control,b,and sepsis groups (n =8 or 9,each group),and the latter two groups were then treated with imipenem or ceftriaxone for 3 or 9 days.The mesenteric lymph nodes,liver,lungs,and blood were collected at each time point under sterile conditions for quantitative bacterial culture and strain identification.The differences between the groups were compared by Fisher exact test or Mann-Whitney U test.Results:Only minimal Escherichia coli translocation to the mesenteric lymph nodes was observed in the normal control group,in which the BT rate was 12.5％.Bum injury did not affect the BT rate (B group vs.Control group,12.5％ vs.12.5％,P =1.000),whereas the BT rate showed an increased trend after the second insult with lipopolysaccharide (Sepsis group us.Control group,44.4％ vs.12.5％,P =0.294),and many strains ofEnterobacteria spp.were detected in distant organs (liver,lung,and blood) [Sepsis group vs.Control group,0 (0,3) vs.0 (0,0),U =20,P =0.045].After the antibiotic treatment,BT to the distant organs was increased in bed rats [B IT3 group vs.B group,0 (0,2) vs.0 (0,0);B IT9 group vs.B group,0 (0,1) vs.0 (0,0);B CT9 group vs.B group,0 (0,2) vs.0 (0,0);all U =20 and P =0.076] but decreased in septic rats [Sepsis CT3 group vs.Sepsis group,0 (0,0) vs.0 (0,3),U =20,P =0.045].The total amount of translocated bacteria,regardless of which antibiotic was used,was increased in bed rats [B IT9 group vs.B group,2.389 (0,2.845) vs.0 (0,2.301) Log10 colony-forming units (CFU)/g,U =14,P =0.034;B CT3 group vs.B group,2.602 (0,3.633) vs.0 (0,2.301) Log10 CFU/g,U =10.5,P =0.009],but there was a slightly decreased trend in septic rats [Sepsis IT9 group vs.Sepsis group,2.301 (2,3.146) vs.0 (0,4.185) Log10 CFU/g,U =36,P =0.721;Sepsis CT9 group vs.Sepsis group,2 (0,3.279) vs.0 (0,4.185) Log10 CFU/g,U =32.5,P =0.760].Remarkably,the quantity of Enterococci spp.dramatically increased after broad-spectrum antibiotic treatment in both the bed and septic groups [B IT3 group vs.B group,1 (0,5.164) vs.0 (0,0) Log10 CFU/g,U =16;B IT9 group vs.B group,1 (0,2.845) vs.0 (0,0) Log10 CFU/g,U =16;B CT3 group vs.B group,2.602 (0,3.633) vs.0 (0,0) Log10 CFU/g,U =8;B CT9 group vs.B group,1 (0,4.326) vs.0 (0,0)Log10 CFU/g,U =16;Sepsis IT3 group vs.Sepsis group,2.477 (0,2.903) vs.0 (0,0) Log10 CFU/g,U =4.5;Sepsis IT9 group vs.Sepsis group,2 (0,3.146) vs.0 (0,0) Log10 CFU/g,U =9;Sepsis CT3 group vs.Sepsis group,1.151 (0,2.477) vs.0 (0,0) Log10 CFU/g,U =18;Sepsis CT9 group vs.Sepsis group,2 (0,3) vs.0 (0,0) Log10 CFU/g,U =13.5;all P ＜ 0.05].Conclusions:Broad-spectrum antibiotics promote BT in bed rats but prevent BT in septic rats,especially preventing BT to distant organs,such as the liver and lung.Moreover,Enterococci spp.with high drug resistance and high pathogenicity translocated most after antibiotic treatment.