Characteristics Of Antimicrobial Substance Produced By Lactobacillus Paracasei

To obtain potential antibacterial activity strain, lactic acid bacteria were screened from traditional dairy products koumiss in Inner Mongolia region by double agar diffusion method. A strain was chosen and identified. And the biological characteristics of its antimicrobial substance were studied. The results were as follows:(1) 8 strains of lactic acid bacteria showed antibacterial activity to Bacillus subtilis and Salmonella typhimurium. A strain Q-1-4 was chosen and identified as lactobacillus paracasei by physiological-biochemical testing and molecular-biological testing.(2) After eliminating the organic acids and hydrogen peroxides, the inhibitory activity still exists. However, the antimicrobial substance was sensitive to proteases, such as trypsin, pepsin, protease K and papain, and it implies the antibacterial substance may contain protein.(3) Antibacterial substance of Lb. paracasei Q-1-4 show antibacterial activity after 6h incubation and reached the maximum at 22h’s incubation. And its action mode for Bacillus subtilis and Salmonella typhimurium was both antibacterial way.(4) Antibacterial activity of Lb. paracasei Q-1-4 for Bacillus subtilis was ranging from pH2.0-pH5.0, and for Salmonella typhimurium, the pH was between 2.0 to 5.5. The antimicrobial substance had good thermal stability in this pH range. UV light did not affect the activity of the substance. SDS and EDTA can enhance the antibacterial activity, but surfactants, organic solvents, metal ions did not affect the antibacterial activity. Also, the antibacterial activity remained stable at room temperature and low temperature (-20℃,4℃) for 60 days. In addition, the antimicrobial substance had a broad inhibitory spectrum.