Abstract:[Background] Caseinolytic protease L (ClpL), a member of the heat shock protein (HSP) 100 family, is involved in various cellular processes, such as the stress tolerance response, long-term survival, virulence, and antibiotic resistance, playing important roles in the infection of pathogenic bacteria. [Objective] The present study aimed to elucidate the contributions of HSP100/ClpL to the stress tolerance and virulence of Streptococcus suis type 2. [Methods] We used the thermo-sensitive suicide vector pSET4s and the Escherichia coli-Streptococcus suis shuttle vector pSET2 to construct an isogenic clpL mutant strain (ΔclpL) and a complemented strain (CΔclpL), respectively. We then compared the growth characteristics of the wild-type strain SS2-1, ΔclpL, and CΔclpL under various stress conditions (including high temperature, acidic environment, and oxidative stress) in vitro and in pig whole blood. Furthermore, we employed a mouse model of infection and challenged mice with SS2-1+ΔclpL or SS2-1+CΔclpL to compare the virulence of SS2-1, ΔclpL, and CΔclpL. [Results] The mutant strain ΔclpL showed reduced survival rates under stress conditions and in pig whole blood. In addition, it showed attenuated virulence in BalB/C mice. Furthermore, ΔclpL had significantly lower colonization ability than SS2-1 in mice. [Conclusion] The data indicate that the SsClpL is involved in the stress response and pathogenicity of SS2.
