**4. Materials and Methods**

#### *4.1. Bacterial Strains*

The *Escherichia coli* ATCC 35401, ATCC 35150, ATCC 25922, and SSI 82000, *Pseudomonas aeruginosa* ATCC 9027 and ATCC 27853, *Salmonella* ATCC13312 and ATCC9120, *Salmonella typhimurium* ATCC 14028, and *Staphylococcus aureus* ATCC 29213 strains were purchased from Guangdong Culture Collection Center. The *Escherichia coli* W25K strain was isolated from a piglet with diarrhea as described previously [35]. The strains were cultured in LB medium to logarithmic growth period (OD = 0.5) and then were transferred to Mueller-Hinton Broth (MHB) medium for the minimum inhibitory concentration (MIC) or minimum bactericidal concentration (MBC) test.

### *4.2. Peptide Synthesis*

The 7 AMPs were synthesized and purified by a Chinese peptide company (DgPeptides Co., Ltd., Hangzhou, China), and the sequences were confirmed via matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The purity of the AMPs was higher than 95%, which was measured by reversed-phase high-performance liquid chromatography.

#### *4.3. Cell Culture*

IPEC-J2 cells were cultured at 37 ◦C in 100% humidity and 5% CO2 conditions with DMEM/F12 (Thermo, Waltham, MA, USA) supplemented with 5% fetal bovine serum (Gibco, Waltham, MA, USA) and 1% penicillin/streptomycin. The medium was changed every other day.
