Mining and evaluating the high-effectiveness and broad-spectrum endolysin encoded by prophage harbored in Streptococcus suis serotype 7

Abstract:

[Objective] In recent years, there has been an increasing worldwide prevalence of bacterial resistance to a wide range of antibiotics, resulting in a focus of research interest in bacteriophage. Unfortunately, streptococcus suis (SS) bacteriophage is not easy to isolate, and the endolysin encoded by phage has been examined as a potential agent for SS control. [Methods] In this study, based on the analysis of genomic information of several streptococcus suis deposited in GenBank, we mined and analyzed one endolysin named Ly7917 encoded by a prophage harbored in Streptococcus suis serotype 7 (SS7) genome. The ly7917 gene was amplified by PCR using bacterial genome purified from a SS7 strain 7917 as template and then inserted into the pET28a(+) plasmid. The recombinant plasmid pET28a(+)-ly7917 was transformed into Escherichia coli DH5α, the sequencing of positive colony showed 100% homology with the target gene. The recombinant plasmid was then transformed into E. coli BL21 and induced with IPTG for expression. [Results] The result of plate analysis showed that Ly7917 has highly activity and can lysis Streptococcus suis serotype 2 strain HA9801. In addition, bacterial turbidity test showed that Streptococcus suis serotype 7, serotype 9, most of serotype 2 strains, Streptococcus equi subsp. zooepidemicus strain, Staphylococcus aureus (including Methicillin-resistant Staphylococcus aureus) were highly sensitive to Ly7917. [Conclusion] Effective and broad-spectrum characteristics of Ly7917 mined from prophage brings hope for mixed infection in clinical as an effective therapeutic.