Bacterial strains and growth conditions
Lactobacillus casei Zhang (provided by Inner Mongolia Agricultural University Key Laboratory of Dairy Biotechnology and Engineering, Inner Mongolia, China) was grown in De Man, Rogosa, and Sharpe (MRS) broth (Solarbio Life Science, Beijing, China) at 37℃ under microaerophilic conditions. The isolate of E. coli ATCC 25922 (China General Microbiological Culture Collection Center, Beijing, China) was incubated in Tryptone Soya Broth (TSB, Solarbio Life Science, Beijing, China) at 37℃. For all treatments, E. coli and LCZ were plated on Tryptose Soya Agar (TSA, Solarbio Life Science, Beijing, China) and MRS agar (Solarbio Life Science, Beijing, China), respectively, after serial dilution and quantified by determination of colony-forming units (CFU).