XcpQ from Pseudomonas aeruginosa: A potential vaccine candidate with immunogenic properties in zebrafish

XCP is one of two major subtypes of the type II secretion system in Pseudomonas aeruginosa strains. XcpQ, the outer-membrane component of Xcp, facilitates protein secretion. This study aimed to evaluate the potential of XcpQ as a vaccine antigen against P. aeruginosa. Bioinformatics and immunoinformatics analyses identified XcpQ as a promising vaccine candidate based on antigenicity and epitope prediction. The XcpQ gene was cloned into the pET28a⁺ vector using BamHI and SacI, and the construct was induced in E. coli BL21(DE3) with IPTG to a final concentration of 1 mM. The Xcp-AN (heterologous protein) was purified using a Ni-NTA column. The function of the Xcp-AN was investigated with respect to biofilm formation, adherence to the A549 human alveolar epithelial cell line (A549), and cytotoxicity was assessed via the MTT assay. Zebrafish (Danio rerio) served as the in vivo infection model. Exposure of P. aeruginosa to 6.5 μg/ml of Xcp-AN led to a 46.41% increase in biofilm biomass. At a multiplicity of infection (MOI) of 100:1 (bacteria to A549 cells), no detectable bacterial adherence was observed, suggesting that Xcp-AN does not significantly mediate epithelial cell attachment. Over 99% of A549 cells retained viability following treatment with varying concentrations of Xcp-AN in the MTT assay. Immunization with Xcp-AN resulted in a 63% reduction in gill bacteria in zebrafish compared to the control group. Overall, these results suggest that the Xcp-AN domain is a promising candidate for vaccine development against P. aeruginosa. However, additional research is necessary to verify its efficacy as a vaccine candidate.