Construction and characterization of plcR gene knockout mutant of Streptococcus suis serotype 2

Abstract:

[Objective] To construct the plcR gene knockout mutant of Streptococcus suis serotype 2 (SS2) highly virulent strain 05ZYH33 and analyze the role of plcR in the pathogenesis of SS2. [Methods] The plcR gene was replaced with a spectinomycin resistance cassette through homologous recombination, then multiple-PCR, RT-PCR, and sequence analysis were performed to identify the knockout strain ?plcR. The effects of plcR deletion on the basic biological characteristics and virulence of SS2 were then determined in this study. [Results] The results of RT-PCR confirmed that 05SSU0241 and 05SSU0242 should be transcribed as a single operon. The isogenic mutant ?plcR was successfully constructed verified by multiple-PCR and RT-PCR. No significant differences in biological characteristics, including growth rate, colony morphology and hemolytic activity, were detected between the two strains. Pathogenic trial in mouse showed that wild-type strain induced high fatality rate as much as 70%, whereas the ?plcR mutant caused a 40% fatality rate. Obviously that the virulence of the ?plcR mutant was attenuated remarkably compared with the wild type. [Conclusion] The plcR gene, a foreign gene exclusively existed in virulent SS2 strains, plays an important role in the pathogenesis of SS2 infection.