Table 1. The bacterial strains used in this paper.

Strain	Number	Source
Escherichia coli BL21		stored in our laboratory
Salmonella	ATCC 11778	stored in our laboratory
L. monocytogenes	CMCC 55004	China Institute of Veterinary Drug Control
Lactobacillus casei		Professor Tian, Agriculture University of Hebei
Bacillus subtilis		stored in our laboratory
Bacillus thuringiensis		stored in our laboratory
Bacillus licheniformis	CGMCC 1.106	Institute of Microbiology, Chinese Academy of Sciences
Bacillus perfringens		stored in our laboratory