Deletion of the crp gene affects the virulence and the activation of the NF-κB and MAPK signaling pathways in PK-15 and iPAM cells derived from G. parasuis serovar 5.

Glaesserella parasuis can cause serious systemic disease (Glasser's disease) that is characterized by fibrinous polyserositis, polyarthritis and meningitis. cAMP receptor protein (CRP) is among the well studied global regulator proteins which could modulate the virulence of many pathogenic bacteria. Our previous study showed that the crp gene was involved in the regulation of growth rate, biofilm formation, stress tolerance, serum resistance, and iron utilization in G. parasuis. However, whether the crp gene could regulate the virulence of G. parasuis has not been analyzed previously. In this study, it was observed that the crp gene in G. parasuis serovar 5 (HPS5) was involved in regulating the adhesion and invasion abilities on iPAM cells, and the mRNA expression of various virulence-related factors. It also possessed the ability to induce the mRNA expression of pro-inflammatory cytokines (IL-1α, IL-1β, IL-6, IL-8 and TNF-α), promoted the activation of the nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways in porcine kidney epithelial (PK-15) and immortalized swine pulmonary alveolar macrophage (iPAM) cells, and contributed to the pathogenicity and organs colonization in mice. As compared with the wild type, both the expression of virulence-related factors in the crp mutant strain and its ability to induce the mRNA expression of pro-inflammatory cytokines, as well as the expression of phospho-p65 and phospho-p38 in PK-15 and iPAM cells was reduced significantly. Furthermore, it also found that the virulence of crp mutant was significantly reduced as compared with the wild type. However, the abilities of adherence and invasion on iPAM cell of Δcrp strain was noted to be significantly enhanced as compared with the wild type. These results suggested that the crp gene deletion could effectively attenuate the virulence of G. parasuis, and crp gene may act as an important potential target for the formulation of a novel vaccine against G. parasuis.