Immunogenicity and protective efficacy of Vibrio vulnificus flagellin protein FlaB in a wound infection model

Construction and analysis of the immune effect of subunit vaccines based on the flagellin FlaB and FlaC of Vibrioharveyi

Vibrio harveyi is a common sort of pathogenic bacterium in marine, which annually gives rise to huge financial losses in aquaculture industry. Flagellin is one of the important virulence factors for bacteria, but meanwhile it is also a preferable vaccine candidate. In this study, we have identified and analyzed two flagellin antigens of V. harveyi, FlaB and FlaC; and moreover, on this basis, two subunit vaccines (rFlaB and rFlaC) were constructed, and the potential as vaccines against V. harveyi infection were determined and compared. Sequence analysis indicated that the coding region of FlaB was 1131 bp, sharing the highest sequence identity (97.07 %) with the counterparts of V. campbellii, and that FlaC (1155 bp) shared the highest sequence identity (98.18 %) with the counterparts of V. campbellii. The vaccine potential of subunit vaccines, rFlaB and rFlaC, were analyzed in the Epinephelus coioides model. The results showed that fish vaccinated with rFlaB or rFlaC at 4-week post-vaccination (p.v.), exhibiting a relative percent survival (RPS) of 81.8 % and 59.1 %, respectively; when fish were vaccinated with rFlaB or rFlaC at 8-week p.v., the RPS of rFlaB and rFlaC were 76.2 % and 42.9 %, respectively. Compared to control group, immunological analysis showed that both rFlaB and rFlaC could elicited specific antibody expression and innate immune responses. Of note, rFlaB could induce higher levels of IgM, AKP, LZM, ACP and SOD activity in fish in comparison with rFlaC. Additionally, qPCR results manifested that the expressions of IL-1β, CD4, CD8α, IgM, IFNγ, MHCⅠα, MHCⅡα, TLR5M and TLR5S were significantly up-regulated in the fish immunized with rFlaB and rFlaC, indicating their ability to activate innate immunity and trigger the inflammatory and cell immune responses. Overall, FlaB is superior to FlaC as regards potential as vaccines. This research has developed two promising subunit vaccines against diseases caused by V. harveyi that are well-suited for application in aquaculture.

Light-triggered on-site rapid formation of antibacterial hydrogel dressings for accelerated healing of infected wounds

An optimal wound dressing can seal variously shaped wounds and provide a complete barrier to resist bacterial invasion; more importantly, the dressing can be stretched or compressed when the wounds are subjected to external forces and quickly return to its original state after the forces are withdrawn. Here, we designed dressings with light-triggered on-site rapid formation of antibacterial hydrogel for the accelerated healing of infected wounds. The pro-hydrogel, composed of acrylamide (AM) and dopamine-hyaluronic acid-ε-poly-l-lysine (DA-HA-EPL), was filled into the Vibrio vulnificus-infected wound. A 405-nm blue light was exerted on the wound to rapidly photopolymerize AM to its polymer, i.e., polyacrylamide (PAM). A hydrogel network of PAM/DA-HA-EPL immediately formed on site within several seconds to insulate the wound. PAM/DA-HA-EPL possessed adhesion performance to adapt to changes in wound morphologies due to external forces. Moreover, it presented high antibacterial ability due to the presence of EPL, in vitro biocompatibility and the ability to promote cell migration. Vibrio vulnificus-infected wounds were established on full-thickness mouse skin, and the hydrogel dressing exhibited high healing efficiency in terms of skin tissue regeneration, collagen deposition, and angiogenesis. PAM/DA-HA-EPL is a promising hydrogel dressing for the accelerated healing of infected wounds.

Evaluation of the efficacy of a novel Vibrio vulnificus vaccine based on antibacterial peptide inactivation in turbot, Scophthalmus maximus

Tongue sole tissue factor pathway inhibitor 2 (TFPI-2) C-terminus derived peptide, TC38, has previously been shown to kill Vibrio vulnificus cells without lysing the cell membrane; thus, the remaining bacterial shell has potential application as an inactivated vaccine. Therefore, this study aimed to evaluate the immune response induced by the novel V. vulnificus vaccine. The protective potential of TC38-killed V. vulnificus cells (TKC) was examined in a turbot model. Fish were intramuscularly vaccinated with TKC or FKC (formalin-killed V. vulnificus cells) and challenged with a lethal-dose of V. vulnificus. The results showed that compared with FKC, TKC was effective in protecting fish against V. vulnificus infection, with relative percent of survival (RPS) rates of 53.29% and 63.64%, respectively. The immunological analysis revealed that compared with the FKC and control groups, the TKC group exhibited: 1) significantly higher respiratory burst ability and bactericidal activity of macrophages at 7 d post-vaccination; 2) increased alkaline phosphatase, acid phosphatase, lysozyme, and total superoxide dismutase levels post-vaccination; 3) higher serum agglutinating antibody titer with corresponding higher serum bactericidal ability, and a more potent serum agglutination effect, as well as an increased IgM expression level; 4) higher expression of immune relevant genes, which were involved in both innate and adaptive immunity. Taken together, this is the first study to develop a novel V. vulnificus inactivated vaccine based on AMP inactivation, and TKC is an effective vaccine against V. vulnificus infection for aquaculture.

Identification of in vivo Essential Genes of Vibrio vulnificus for Establishment of Wound Infection by Signature-Tagged Mutagenesis

Vibrio vulnificus can cause severe necrotic lesions within a short time. Recently, it has been reported that the numbers of wound infection cases in healthy hosts are increasing, for which surgical procedures are essential in many instances to eliminate the pathogen owing to its rapid proliferation. However, the mechanisms by which V. vulnificus can achieve wound infection in healthy hosts have not been elucidated. Here, we advance a systematic understanding of V. vulnificus wound infection through genome-wide identification of the relevant genes. Signature-tagged mutagenesis (STM) has been developed to identify functions required for the establishment of infection including colonization, rapid proliferation, and pathogenicity. Previously, STM had been regarded to be unsuitable for negative selection to detect the virulence genes of V. vulnificus owing to the low colonization and proliferation ability of this pathogen in the intestinal tract and systemic circulation. Alternatively, we successfully identified the virulence genes by applying STM to a murine model of wound infection. We examined a total of 5418 independent transposon insertion mutants by signature-tagged transposon mutagenesis and detected 71 clones as attenuated mutants consequent to disruption of genes by the insertion of a transposon. This is the first report demonstrating that the pathogenicity of V. vulnificus during wound infection is highly dependent on its characteristics: flagellar-based motility, siderophore-mediated iron acquisition system, capsular polysaccharide, lipopolysaccharide, and rapid chromosome partitioning. In particular, these functions during the wound infection process and are indispensable for proliferation in healthy hosts. Our results may thus allow the potential development of new strategies and reagents to control the proliferation of V. vulnificus and prevent human infections.