Abstract：
Streptococcus suis is an important zoonotic pathogen that is difficult to control with antibiotics due to the widespread development of multidrug-resistant strains. Phage lysin is considered a potential therapeutic agent to combat S. suis. In this study, the novel lysin Ply1228 derived from the prophage of S. suis type 12 was identified. Bioinformatics analysis showed that Ply1228 contains a CHAP catalytic domain, which is a binding domain composed of a CW-7 binding motif and an amidase-2 catalytic domain. The CHAP catalytic domain is essential for the bactericidal function of lysin Ply1228 and does not depend on the presence of Ca2+. C34 and H99 of the CHAP domain were identified as the key active sites. The CW-7 binding motif plays a key binding role in Ply1228. Ply1228 can specifically lyse S. suis, including types 2, 3, 7, 9, 10, 12, 14, and 27. Within 10 min, Ply1228 killed 4 log of the S. suis population, which had a starting concentration of approximately 107 CFU/mL. In addition, Ply1228 showed favourable thermal and pH stability. The therapeutic effect of Ply1228 was further investigated in a mouse model of S. suis bacteremia. The administration of the lysin Ply1228 (200 μg/mouse) 1 h after the intraperitoneal injection of 2 × MLD of SS2 strain SC225 was sufficient to protect the mice (P < 0.0001) and significantly reduced the bacterial loads in the blood and organs (livers, spleens, lungs and kidneys). The levels of inflammation and histopathological damage in infected mice were effectively relieved after the Ply1228 treatment. These results indicate that Ply1228 might represent a new enzybiotic candidate for S. suis infection.
摘要：
猪链球菌是一种重要的人畜共患病原体，由于多重耐药菌株的广泛发展，难以用抗生素控制。噬菌体溶素被认为是对抗猪链球菌的潜在治疗剂。在这项研究中,鉴定了源自猪链球菌12型原形的新型溶素Ply1228。生物信息学分析表明Ply1228含有一个CHAP催化结构域,其是由CW-7结合基序和酰胺酶-2催化结构域组成的结合结构域。CHAP催化结构域对于溶素Ply1228的杀菌功能至关重要，并且不依赖于Ca2的存在。CHAP结构域的C34和H99被鉴定为关键活性位点。CW-7结合基序在Ply1228中起关键结合作用。Ply1228可以专门裂解猪链球菌，包括类型2、3、7、9、10、12、14和27。10分钟内,Ply1228杀死了4个猪链球菌种群，其具有约107CFU/mL的起始浓度。此外,Ply1228显示出有利的热稳定性和pH稳定性。在猪链球菌菌血症的小鼠模型中进一步研究Ply1228的治疗效果。在腹膜内注射2×MLD的SS2菌株SC225后1小时施用溶素Ply1228（200μg/小鼠）足以保护小鼠（P<0.0001）并显着降低血液和器官中的细菌负荷（肝脏，脾脏,肺和肾脏)。Ply1228治疗后，感染小鼠的炎症水平和组织病理学损伤得到有效缓解。这些结果表明Ply1228可能代表猪链球菌感染的新候选酶。
