*3.5. Bacteria (E. coli K12) Culture and Preparation*

*E. coli* K12 were inoculated into the Luria-Bertani broth and shaken (300 rpm) constantly in an incubator shaker at 37 ◦C. After overnight incubation, the *E. coli* K12 suspensions (8 mL) were centrifuged (8000 rpm) for 2 min and the sediments were retained. The obtained precipitates were resuspended by adding 6 mL of sterile normal saline. By measuring the optical density (OD) value at 600 nm, the bacterium liquid concentration was adjusted to a proper level for after use. Different colonies were distributed on LB plates and incubated at 37 ◦C overnight. The relevant colony-forming units (CFU) were calculated to obtain the number of bacteria per milliliter.
