Expression And Bactericidal Activity Of Streptococcus Suis Lysin Ply691

Streptococcus suis is an important zoonotic pathogen.In the cultivation and production,antibiotics are mainly used for the prevention and control of this pathogen.Due to the long-term large quantity and uncontrolled use of antibiotics,drug-resistant strains and multi-drug-resistant strains continue to appear,and the traditional antibiotic therapy is facing great challenges in the treatment of bacterial infection.Compared with traditional antibiotics,phage lysin has high efficiency and rapid bactericidal effect,and bacteria are not easy to develop resistance to it,which makes lysin become a very potential antibacterial agent.In this study,we successfully identified a prophage encoded lysin from the whole genome of Streptococcus suis and named it Ply691.By comparing the amino acid sequence of Ply691 with the database,it was found that it had low homology with the reported lysin of Streptococcus suis,indicating that this Ply691 was a new lysin.Prokaryotic strain BL21(DE3)-p ET28a(+)-Ply691 was successfully constructed by gene recombination technique.After induction and purification,the target protein with molecular weight of about 49.5 k Da was obtained.The in vitro activity of Ply691 was further determined.The results showed that Ply691 had a wide spectrum of Streptococcus suis and could lyse 11 serotypes of Streptococcus suis,including 2,3,5,9,10,12,17,18,19,29 and 30.Ply691 can not only make effect in a wide PH environment from7-10,but survive in virto between a wide temperature 4℃-37℃.Ply691 has bactericidal activity,and can reduce the number of Streptococcus suis colonies by about 1 Log in 20 min.It will not induce Streptococcus suis resistance to Ply691 in vitro continuous passage.These characteristics provide conditions for practical application of Ply691.The antiinfective effect of lysin Ply691 was evaluated by establishing bacteremia model in mice.Mice were treated by intrapitoneal injection of Streptococcus suis SC267 at a concentration of 2.0×108 CFU/ mouse with the lysin Ply691,which was found to protect 100% of the mice from death.After 48 h treatment with Ply691,the number of colonies in peripheral blood of mice decreased by 3 Log,and the bacterial load in heart,liver,lung,kidney,spleen and brain tissue decreased by 2,2.5,2,3,2.4 and 2.9 Log,respectively.We found that the bacteria in vivo did not develop resistance to Ply691.Compared with the control group,the pathological changes of the heart,liver,lung,kidney,spleen and brain tissues of mice in the treatment group were similar to those in the normal group,which indicated that Ply691 could significantly reduce the pathological changes of tissues and organs.Ply691 showed excellent protective effect.In summary,in this study,soluble Ply691 was efficiently expressed by gene recombination technology.Antibacterial activity analyzed in vitro and in vivo and therapeutic effect preliminarily evaluated,we provide a theoretical basis for the prevention and treatment of Streptococcus suis disease by using phage lysin of Streptococcus suis.