Expression Of Lysin Encoded By Streptococcus Suis Phage In Lactococcus Lactis As Effective Antibacterials

Streptococcus suis is an important zoonotic pathogen that causes meningitis, sepsis, arthritis, endocarditis and pneumonia in piglet or meningitis in human. It is a big threat to public hygiene and human life. Worse more, the severe antibiotics resistance of bacteria make it difficult to the prevention and the treatment of this disease. In this research, recombinant streptococcus suis phage lysin, designed LySMP, was expressed and characterized in Lactococcus lactis.LySMP was obtained by recombinant expression in Lactococcus lactis NZ9000. A pair of primers were designed according to the LySMP gene. After amplification by PCR, the products were then inserted into a prokaryotic expression plasmid, pNZ8148 to obtain the recombinant plasmid pNZ8148-LySMP. The recombinant plasmid pNZ8148-LySMP was introduced into Lactococcus lactis NZ9000 competent cells and sequenced to ensure a correct expression. After NZ9000 colones of pNZ8148-LySMP were induced by Nisin in an optimal centigrade, recombinant LySMP protein was analyzed by SDS-PAGE and zymogram. The expression product was about 53 kD and could form translucent band in the opaque background.In the western-blotting experiment, LySMP (53 kD) from pNZ8148-LySMP-NZ9000 and LySMP (55 kD) from pET-28a-LySMP-BL21 reacted with LySMP antiserum, and the results showed that the two have different expression levels.LySMP lysate exhibited an extensive lysis spectrum than those of the whole phage against bacteria investigated. S.suis serotype 2, S.suis serotype 7 and S.suis serotype 9 strains recovered from diseased pigs between 1998 and 2005 in China. Seven out of seventeen strains of S.suis serotype 2 could be lysed, as well as S.suis serotype 7 and 9. But Streptococcus equi ssp. Zooepidemicus, Staphylococcus aureus, E. coli and Salmonella enterica were not affected. Optimum pH and temperature conditions for the LySMP were investigated by turbidity reduction assay. LySMP exerted efficient lysis activity at 37℃, pH 7.2. The turbidity of bacterium investigated was observed to decrease by 30–77% in 30 min.