Abstract: ObjectiveTo study the effect of antimicrobial residues in milk on the growth of Bifidobacterium and Lactobacillus.MethodsAn in vitro gut simulation model was used to mimic the situation of antimicrobial residues passing through human gastrointestinal tract,then the standard Bifidobacterium infantis(B.infantis)or Lactobacillus acidophilus(L.acidophilus) was added to the culture in anaerobic incubation.The number of bacteria was counted to explore the effect of antimicrobial residues on B.infantis and L.acidophilus.ResultsThe effective inhibitory concentration of ampicillin residues in milk on L.acidophilus was 2 μg/L(P<0.05)and that on B.Infantis was 100 μg/L(<0.05).There was an obvious dose-response relationship when the concentration of ampicillin residues in milk was 2-8 μg/L.The effective inhibitory concentration of streptomycin sulfate on B.infantis and L.acidophilus was 20 mg/L(P<0.05). The effective inhibitory concentration of sulfamonomethoxin on B.infantis and L.acidophilus.was 800 μg/L(P<0.05).ConclusionL.acidophilus was sensitive to ampicillin.The growth of L.acidophilus was inhibited when the concentration of ampicillin in the milk was 2μg/L,which was lower than the current Chinese maximum residue level(MRL)(10 μg/kg)in milk.