TolC2 is required for the resistance, colonization and virulence of Actinobacillus pleuropneumoniae

Purpose. To colonize and cause infection in the host, pathogens must be well equipped to respond to and survive in several hostile conditions. TolC, an outer membrane channel component used by multidrug efflux pumps and type I secretion systems, is considered to be largely involved in bacterial physiology and virulence. In this study, we attempted to investigate the possible roles of TolC2, a homologue of TolC, in the pathogenesis of Actinobacillus pleuropneumoniae . Methodology. The cell viability was investigated under stress conditions (oxidative, thermal, acid and osmotic). Virulence was assessed by lethal intraperitoneal injection of mice. The underlying mechanisms of the attenuation were further explored by serum bactericidal, in vivo phagocytosis and organ burden assays. Results/Key findings. The deletion of olC2 caused increased sensitivity to oxidative, thermal and acid challenges, indicating a critical role of TolC2 in A. pleuropneumoniae survival under stress conditions. The intraperitoneal injection of mice showed that the Δ olC2 mutant caused significantly decreased mortality, suggesting the involvement of TolC2 in the virulence of A. pleuropneumoniae . In the serum-killing assays, the Δ olC2 mutant showed significantly reduced survival ability when exposed to fresh serum. By the in vivo phagocytosis assays, we found that the loss of olC2 rendered the mutant susceptible to phagocytosis by macrophages. Finally, the organ burden assays revealed decreased colonization of Δ olC2 in lungs, indicating a higher bacterial clearance rate in mice in the absence of TolC2. Conclusion. Our findings demonstrate that TolC2 contributes to the virulence of A. pleuropneumoniae by helping survival and maximal colonization in the host.