First two domains at the lp-1643 protein N terminus inhibit pathogen adhesion to porcine mucus in vitro

Abstract

Gastrointestinal probiotics are important members of intestinal microflora in both healthy animals and human beings, and these bacteria may reduce the risk of infection caused by certain opportunistic pathogens through exclusive inhibition, competition, and displacement. The lp-1643 protein on the cell surface of Lactobacillus plantarum WCFSI was assumed to possess a mucus-binding capability. This study aimed to determine if purified His-N2 protein exclusively inhibits pathogen adhesion to porcine mucus. The interaction of the His-N2 protein with porcine mucus was determined by indirect enzyme-linked immunosorbent assay (ELISA), and the adhesion was assessed by a traditional plating method to count the bacteria adhered to the porcine mucus. Indirect ELISA showed that His-N2 protein adhered to porcine mucus, and its interacting molecules existed. The His-N2 protein effectively inhibited the adhesion of Escherichia coli DH5α, Listeria monocytogenes CMCC54004, Salmonella Typhimurium ATCC 14028, and Shigella flexneri CMCC(B)51572 to porcine mucus. Results showed that inhibition of pathogen adhesion to porcine mucus depended on dose and strain. The adhesion of L. monocytogenes CMCC54004, Salmonella Typhimurium ATCC 14028, and S. flexneri CMCC(B)51572 was reduced by 95.7, 97.0, and 95.7%, respectively, by pre-adding 100 ml of 3.92 mg/ml of His-N2 protein, whereas that of E. coli DH5α was only 50.4%. The inhibition of adhesion of some pathogens by His-N2 was different at pH 6.6 and 7.5. The inhibition of E. coli DH5α, L. monocytogenes CMCC54004, and Salmonella Typhimurium ATCC 14028 at pH 6.6 was significantly higher than that at pH 7.5, whereas no statistically significant difference was observed in S. flexneri CMCC(B)51572. These results suggest that various types of inhibition mechanisms of His-N2 were involved in different pathogens.