Purified Recombinant Phage Lysin LySMP: An Extensive Spectrum of Lytic Activity for Swine Streptococci

Bacteriophage lysin has attracted considerable attentions as possible antimicrobial agents for solution of antibiotic resistance. SMP was a Streptococcus suis serotype 2 bacteriophage isolated from nasal swabs of healthy Bama minipigs. The putative SMP bacteriophage lysin, designated LySMP, was recombinantly expressed in Escherichia coli BL21, and chromatographically purified. Treated with 0.8% of β-mercaptoethanol, LySMP exhibited an extensive lysin spectrum than those of whole phage against bacteria investigated. S. suis serotype 2, S. suis serotype 7 and S. suis serotype 9 strains were recovered from diseased pigs between 1998 and 2005 in China. Fifteen of seventeen strains of S. suis serotype 2 could be lysed, as well as S. suis serotype 7 and 9, Streptococcus equi ssp. zooepidemicus and Staphylococcus aureus. But E. coli and Salmonella enterica were not affected. Purified LySMP showed high degrading efficiency against PMSF or lysozyme treated cells comparing to PBS washed cells. Optimum pH and temperature conditions for the lysin were investigated by turbidity reduction assay. The lysin exerted efficient lysis activity at 37°C, pH 5.2. The turbidity of bacterium investigated was observed to decrease by 1.2–68% in 30 min. Result indicated that putative LySMP could be a candidate antimicrobial agent in controlling S. suis infection.