2.3. Preparation of inocula
E. Coli O78 obtained from Institute of Microbiology, Chinese Academy of Sciences, was used in this study. The bacterium was cultured in 200 mL nutritional broth at 37 °C for 24 h with agitation (160 r/min). Following incubation, 100 mL of each culture was harvested by centrifugation for 10 min at 6000 r/min in a centrifuge (Model GL-20B, Shanghai Anting Equipment Company, China)