Identification of a novel vaccine candidate by immunogenic screening of Vibrio parahaemolyticus outer membrane proteins

Influence of Vibrio anguillarum culture conditions on the efficacy of bacterin-based vaccines in lumpfish (Cyclopterus lumpus)

Lumpfish (Cyclopterus lumpus) is used as cleaner fish to control sea lice infestations in Atlantic salmon (Salmo salar) farms across the North Atlantic. Vibrio anguillarum, the causative agent of vibriosis, is a recurrent bacterial pathogen affecting lumpfish. Bacterin-based vaccines are frequently used to control vibriosis in finfish, but their efficacy is not always consistent. Culture conditions significantly influence synthesis of bacterial outer membrane and secreted proteins, which are critical antigens, and thus impact the immunogenicity of bacterin-based vaccines. In this study, we assessed the effect of V. anguillarum culture conditions on vaccine efficacy in lumpfish. V. anguillarum was cultured under iron-limited at 15 °C, and iron-rich or iron-limited conditions at 28 °C with 2 % NaCl, and these cultures were used to prepare bacterins. A commercial vaccine was used as positive control, while PBS and PBS adjuvant were negative controls. Lumpfish were intraperitoneally immunized and challenged 12 weeks post-immunization with 10-100 times the LD50 dose of V. anguillarum. Bacterins prepared from V. anguillarum grown under iron-limited conditions at 28 °C with 2 % NaCl and mixed with adjuvant conferred the highest protection compared to other preparations and commercial vaccines. In contrast, bacterins derived from V. anguillarum cultured under iron-limited conditions at 15 °C conferred the lowest protection. Reverse vaccinology and transcriptomic analyses of V. anguillarum grown under optimal immunogenic conditions revealed 323 upregulated genes, of which 211 were high-antigenicity proteins suitable for subunit vaccines. This study provides critical knowledge for effective vaccine formulation against V. anguillarum and identifies potential antigens for subunit vaccine development.

MAM7 from Vibrio parahaemolyticus: Expression, purification and effects on RAW264.7 cells

V. parahaemolyticus is a Gram-negative bacterium that causes gastroenteritis. Within the realm of bacterial interactions with the gut, the outer membrane protein MAM7 plays a key role. However, the precise function of MAM7 in intestinal inflammation, particularly its interactions with macrophages, remains unclear. In this study, we successfully expressed and purified recombinant MAM7. After optimization of the MAM7 expression condition, it was found that the optimal concentration and temperature were 0.75 mM and 15 °C, respectively, resulting in a 27-fold increase in its yield. Furthermore, RAW264.7 cytotoxicity assay was conducted. The CCK-8 results revealed that MAM7 substantially stimulated the proliferation of RAW264.7 cells, with its optimal concentration determined to be 7.5 μg/mL. Following this, the NO concentration of MAM7 was tested, revealing a significant increase (p < 0.05) in NO levels. Additionally, the relative mRNA levels of IL-1β, IL-6, and TNF-α in RAW264.7 cells were measured by qRT-PCR, showing a remarkable elevation (p < 0.05). Moreover, ELISA results demonstrated that MAM7 effectively stimulated the secretion of IL-6 and TNF-α by RAW264.7 cells. In summary, these findings strongly suggest that MAM7 serves as a proinflammatory adhesion factor with the capacity to modulate immune responses.

OmpU and OmpC are the key OMPs for Litopenaeus vannamei hemocyanin recognizes Vibrio parahaemolyticus

Hemocyanin is a multifunctional protein present in arthropods and mollusks, responsible for oxygen transport and participating in multiple roles of immune defense including antibacterial activity. However, the molecular basis of how hemocyanin recognizes pathogens and exerts antibacterial activity remains poorly understood. In the present study, the pull-down assay was used to isolate Vibrio parahaemolyticus outer membrane proteins (OMPs) that bind to Litopenaeus vannamei hemocyanin. Two interacting OMPs bands were determined as OmpC and OmpU, and the heterogeneous interaction between hemocyanin and the two OMPs was further confirmed by far-Western blot. After construction of ompC and ompU deletion mutants, we found that the agglutinating activity and antibacterial activity of hemocyanin significantly decreased compared to the wild-type strain. After hemocyanin treatment, we identified four intracellular proteins of V. parahaemolyticus, including fructose-bisphosphate aldolase and ribosomal proteins could interact with rOmpC and rOmpU, respectively. Furthermore, we found that the mRNA levels of ompC, ompU, fbaA, rpsB and rpsC significantly decreased after hemocyanin treatment. These findings indicated that OmpC and OmpU are the key targets for L. vannamei hemocyanin recognize pathogens and exert its antibacterial activity.

A review of bacterial disease outbreaks in rainbow trout (Oncorhynchus mykiss) reported from 2010 to 2022

Outbreaks of bacterial infections in aquaculture have emerged as significant threats to the sustainable production of rainbow trout (Oncorhynchus mykiss) worldwide. Understanding the dynamics of these outbreaks and the bacteria involved is crucial for implementing effective management strategies. This comprehensive review presents an update on outbreaks of bacteria isolated from rainbow trout reported between 2010 and 2022. A systematic literature survey was conducted to identify relevant studies reporting bacterial outbreaks in rainbow trout during the specified time frame. More than 150 published studies in PubMed, Web of Science, Scopus, Google Scholar and relevant databases met the inclusion criteria, encompassing diverse geographical regions and aquaculture systems. The main bacterial pathogens implicated in the outbreaks belong to both gram-negative, namely Chryseobacterium, Citrobacter, Deefgea Flavobacterium, Janthinobacterium, Plesiomonas, Pseudomonas, Shewanella, and gram-positive genera, including Lactococcus and Weissella, and comprise 36 new emerging species that are presented by means of pathogenicity and disturbance worldwide. We highlight the main characteristics of species to shed light on potential challenges in treatment strategies. Moreover, we investigate the role of various risk factors in the outbreaks, such as environmental conditions, fish density, water quality, and stressors that potentially cause outbreaks of these species. Insights into the temporal and spatial patterns of bacterial outbreaks in rainbow trout aquaculture are provided. Furthermore, the implications of these findings for developing sustainable and targeted disease prevention and control measures are discussed. The presented study serves as a comprehensive update on the state of bacterial outbreaks in rainbow trout aquaculture, emphasizing the importance of continued surveillance and research to sustain the health and productivity of this economically valuable species.

Field Efficacy of a Feed-Based Inactivated Vaccine against Vibriosis in Cage-Cultured Asian Seabass, Lates calcarifer, in Malaysia

Vibrio spp. are important aquaculture pathogens that cause vibriosis, affecting large numbers of marine fish species. This study determines the field efficacy of a feed-based inactivated vaccine against vibriosis in cage-cultured Asian seabass. A total of 4800 Asian seabass, kept in a field environment, were separated equally into two groups (vaccinated and non-vaccinated) in duplicate. Fish of Group 1 were orally administered the feed-based vaccine on weeks 0 (prime vaccination), 2 (booster), and 6 (second booster) at 4% body weight, while the non-vaccinated fish of Group 2 were fed with a commercial formulated pellet without the vaccine. Fish gut, mucus, and serum were collected, the length and weight of the fish were noted, while the mortality was recorded at 2-week intervals for a period of 16 weeks. The non-specific lysozyme activities were significantly (p < 0.05) higher in the fish of Group 1 than the non-vaccinated fish of Group 2. Similarly, the specific IgM antibody levels in serum and mucus were significantly (p < 0.05) higher in Group 1 than in Group 2, as seen in the second week, with the highest level 8 weeks after primary immunization. At week 16, the growth performance was significantly (p < 0.05) better in Group 1 and showed lower bacterial isolation in the gut than Group 2. Despite the statistical insignificance (p > 0.05), the survival rate was slightly higher in Group 1 (71.3%) than Group 2 (67.7%). This study revealed that feed-based vaccination improves growth performance, stimulates innate and adaptive immune responses, and increases protection of cultured Asian seabass, L. calcarifer, against vibriosis.

Recombinant expression and immunogenicity evaluation of a TonB-dependent receptor of Vibrio parahaemolyticus

This study constructed the recombinant plasmid of a TonB-dependent receptor from V. parahaemolyticus and evaluated the immunogenicity of the recombinant protein in mice. The TonB-dependent receptor gene (GI: 28901321) was obtained by PCR amplification and cloned into plasmid pET-32a (+). The recombinant plasmids were transformed into Escherichia coli BL21, and the protein expression was induced by isopropyl-β-d-thiogalactopyranoside (IPTG). The 6 × His-tagged TonB-dependent receptor inclusion bodies were purified by Ni-NTA Agarose column and renatured by gradient urea dialysis. The soluble and inclusion bodies of the TonB-dependent receptor were emulsified with Freund's adjuvant and subcutaneously injected into BALB/c mice. The serum titers with seven V. parahaemolyticus strains, eight Vibrio species, and nine other bacteria were studied by enzyme-linked immunosorbent assay and immunoblotting. The results showed that the serum homogenously bound the target protein in the V. parahaemolyticus cell lysates. The titers against the immunized protein were above 89K, while the titer against whole cells of seven V. parahaemolyticus strains ranged from 4.12K to 12.5K. However, the titers were higher for the soluble TonB-dependent receptor. The serums reacted with E. coli strains but did not cross-react with eight Vibrio species and Photobacterium damselae. These results showed that the TonB-dependent receptor proteins in this study were immunogenic, and the serums showed adequate specificity for V. parahaemolyticus. However, the availability of the TonB-dependent receptor on V. parahaemolyticus cells is probably limited.

Comparative Reverse Vaccinology of Piscirickettsia salmonis, Aeromonas salmonicida, Yersinia ruckeri, Vibrio anguillarum and Moritella viscosa, Frequent Pathogens of Atlantic Salmon and Lumpfish Aquaculture

Marine finfish aquaculture is affected by diverse infectious diseases, and they commonly occur as co-infection. Some of the most frequent and prevalent Gram-negative bacterial pathogens of the finfish aquaculture include Piscirickettsia salmonis, Aeromonas salmonicida, Yersinia ruckeri, Vibrio anguillarum and Moritella viscosa. To prevent co-infections in aquaculture, polyvalent or universal vaccines would be ideal. Commercial polyvalent vaccines against some of these pathogens are based on whole inactivated microbes and their efficacy is controversial. Identification of common antigens can contribute to the development of effective universal or polyvalent vaccines. In this study, we identified common and unique antigens of P. salmonis, A. salmonicida, Y. ruckeri, V. anguillarum and M. viscosa based on a reverse vaccinology pipeline. We screened the proteome of several strains using complete available genomes and identified a total of 154 potential antigens, 74 of these identified antigens corresponded to secreted proteins, and 80 corresponded to exposed outer membrane proteins (OMPs). Further analysis revealed the outer membrane antigens TonB-dependent siderophore receptor, OMP assembly factor BamA, the LPS assembly protein LptD and secreted antigens flagellar hook assembly protein FlgD and flagellar basal body rod protein FlgG are present in all pathogens used in this study. Sequence and structural alignment of these antigens showed relatively low percentage sequence identity but good structural homology. Common domains harboring several B-cells and T-cell epitopes binding to major histocompatibility (MHC) class I and II were identified. Selected peptides were evaluated for docking with Atlantic salmon (Salmo salar) and Lumpfish MHC class II. Interaction of common peptide-MHC class II showed good in-silico binding affinities and dissociation constants between −10.3 to −6.5 kcal mol−1 and 5.10 × 10−9 to 9.4 × 10−6 M. This study provided the first list of antigens that can be used for the development of polyvalent or universal vaccines against these Gram-negative bacterial pathogens affecting finfish aquaculture.

Laboratory and Field Assessments of Oral Vibrio Vaccine Indicate the Potential for Protection against Vibriosis in Cultured Marine Fishes

Vibriosis is one of the most common threats to farmed grouper; thus, substantial efforts are underway to control the disease. This study presents an oral vaccination against multiple Vibrio spp. in a marine fish with double booster immunisation. The Vibrio harveyi strain VH1 vaccine candidate was selected from infected groupers Epinephelus sp. in a local farm and was formalin inactivated and combined with commercial feed at a 10% ratio (v/w). A laboratory vaccination trial was conducted for seventy days. The induction of IgM antibody responses in the serum of Asian seabass Lates calcarifer immunised with the oral Vibrio harveyi strain VH1 was significantly (p < 0.05) increased as early as week one post-primary vaccination. Subsequent administration of the first and second booster for 5 consecutive days, starting on days 14 and 42, respectively, improved the specific antibody level and reached a highly significant (p < 0.05) value at days 35 and 49 before slightly decreasing from day 56 onwards. Antibody titres of the control unvaccinated group remained relatively stable and low throughout the experimental period. At the end of the 70-day vaccination trial, 23 days post final boost, an intraperitoneal challenge with a field strain of Vibrio harveyi, V. alginolyticus, and V. parahaemolyticus was carried out. Our challenge study showed that oral Vibrio harveyi strain VH1 vaccine candidate could induce significant protection, with an RPS of 70–80% against different Vibrio species. Thereafter, a field trial was conducted in a mariculture farm to study the effect of field vaccination using the oral Vibrio harveyi strain VH1 vaccine candidate. A total of 3000 hybrid grouper juveniles were divided into two groups in triplicate. Fish of Group 1 were not vaccinated, while Group 2 were vaccinated with the feed-based vaccine. Vaccinations were carried out on days 0, 14, and 42 via feeding the fish with the vaccine at 4% body weight for 5 consecutive days. At the end of the study period, the fish survival rate was 80% for the vaccinated group, significantly (p < 0.05) higher than the 65% seen in the control unvaccinated group. Furthermore, the vaccinated fish showed significantly (p < 0.05) better growth performances. Therefore, the oral Vibrio vaccine from the inactivated Vibrio harveyi strain VH1 is a potential versatile vaccine candidate that could stimulate good immune responses and confer high protection in both Asian seabass, Lates calcarifer, and farm hybrid grouper Epinephelus fuscoguttatus × Epinephelus lanceolatus.

Two bicistronic DNA vaccines against Vibrio anguillarum and the immune effects on flounder Paralichthys olivaceus

Chemokines are cytokines that can promote the activation and migration of immune cells, and increase the recognition of antigen by antigen-presenting cells (APC). Previous studies showed that a DNA vaccine can induce humoral and cellular immune responses of flounder after immunization. To explore the improvement of chemokines on the efficiency of OmpK vaccine, two bicistronic DNA candidate vaccines were constructed and the immune responses they induced in the flounder were investigated by reverse transcription polymerase chain reaction (RT-PCR), indirect immunofluorescent assay (IFA), H&E staining, flow cytometry (FCM), and quantificational real-time polymerase chain reaction (qRT-PCR). pBudCE4.1 plasmid as an expression vector, bicistronic DNA vaccines encoding OmpK gene and CC-motif ligand 4 gene (p-OmpK-CCL4), or Ompk gene and CC-motif ligand 19 gene (p-OmpK-CCL19) were successfully constructed. The results showed that two bicistronic DNA vaccines expressed Ompk protein of Vibrio anguillarum and CCL4/CCL19 proteins of flounder both in vitro and in vivo. After immunization, a large number of leucocytes in muscle were recruited at the injection site in treatment groups. The constructed vaccines induced significant increases in CD4-1⁺ and CD4-2⁺ T lymphocytes, and sIgM⁺ B lymphocytes in peripheral blood, spleen, and head kidney. The percentage of T lymphocytes peaked on the 14^th post-vaccination day whereas that of B lymphocytes peaked in the 6^th post-vaccination week. Moreover, the expression profiles of 10 immune-related genes increased in muscles around the injection site, spleen, and head kidney. After the challenge, p-OmpK-CCL4 and p-OmpK-CCL19 conferred a relative percentage survival (RPS) of 74.1% and 63.3%, respectively, higher than p-OmpK alone (40.8%). In conclusion, both CCL4 and CCL19 can improve the protection of p-OmpK via evoking local immune response and then humoral and cellular immunity. CCL4 and CCL19 will be potential molecular adjuvants for use in DNA vaccines.

Immune correlates of NF-κB and TNFα promoter DNA methylation in Japanese flounder (Paralichthys olivaceus) muscle and immune parameters change response to vibrio anguillarum infection

Vibrio anguillarum infection can activate NF-κB/TNFα pathway in the immune organs of fish. Fish muscle is also an important immune organ, but the research on its immune function is few. Our aim was to study regulating mechanism of NF-κB and TNFα gene expressions in the muscle of Japanese flounder (Paralichthys olivaceus) which was under Vibrio anguillarum infection (0, 24, 48, 72 and 96 h). The results showed that the expressions of NF-κB and TNFα increased significantly at 48 h, and there was a significant positive correlation between them. In situ hybridization confirmed the co-existence of NF-κB and TNFα genes in Japanese flounder muscle. Interestingly, the expression of the TNFα gene was regulated by the DNA methylation and its methylation level was negatively correlated with the expression. The lowest methylation level of TNFα occurred at 48 h under Vibrio anguillarum infection (P < 0.05). And more, when the fragment (-2122 ∼ -730) was deleted on TNFα gene promoter, double luciferase activity was the highest, indicating that fragment (-730-0) was the transcription factor binding region. The site (-78 ~ -69) on the fragment (-730-0) binding NF-κB was mutated, and double luciferase activity decreased significantly. The results confirmed that the site (-78 ~ -69) was indeed an important binding site for NF-κB. In addition, the activity of TNFα in the serum of Japanese flounder changed with the prolongation of vibrio anguillarum infection, and the concentration of other immune factors such as ALP, ALT, AST and LDH also changed in the muscle under vibrio anguillarum infection. They all showed a trend of first increasing and then decreasing. Above studies implied that Japanese flounder responded to Vibrio anguillarum infection at the immune level with the change of its methylation status and the activation of transcription factor. By studying the mechanism of immune pathways, understanding the response to immune stress is great significant to the research of fish breeding for disease resistance.

Comparative immunogenicity of outer membrane protein K and whole-cell antigens of Vibrio parahaemolyticus for diagnosis

The immunogenicity of soluble outer membrane protein K (OmpK)- small ubiquitin-like modifier, OmpK inclusion bodies, formalin, and heat-killed Vibrio parahaemolyticus cells were prepared and studied in a mouse model. The results of whole-cell ELISA and Western blot (WB) revealed that the serum against soluble OmpK and OmpK inclusion bodies reacted only with homologous V. parahaemolyticus. Furthermore, recombinant OmpK proteins were not recognized by the serum against whole-cell V. parahaemolyticus antigens. Unexpectedly, the serum against formalin and heat-killed V. parahaemolyticus reacted broadly with homologous (an immunization strain) and heterologous (non-immunization strains) V. parahaemolyticus and Vibrio species. The WB results revealed that the serum against the two V. parahaemolyticus whole-cell antigens primarily reacted with proteins that were approximately 100, 70, 36, 28, and 22 kDa in the cell lysates from different Vibrio strains, rather than the recombinant OmpK. The 70 and 28 kDa proteins exhibited specificity to Vibrio species, while the 22 kDa protein was more specific to V. parahaemolyticus. This study showed the limitation of recombinant OmpK to prepare diagnostic antibodies and revealed several specific Omps of Vibrio sp. and V. parahaemolyticus that were promising in diagnosis and vaccine development.

Reverse vaccinology approach for the identifications of potential vaccine candidates against Salmonella

Salmonella is a leading cause of foodborne pathogen which causes intestinal and systemic diseases across the world. Vaccination is the most effective protection against Salmonella, but the identification and design of an effective broad-spectrum vaccine is still a great challenge, because of the multi-serotypes of Salmonella. Reverse vaccinology is a new tool to discovery and design vaccine antigens combining human immunology, structural biology and computational biology with microbial genomics. In this study, reverse vaccinology, an in-silico approach was established to screen appropriate immunogen targets by calculating the immunogenicity score of 583 non-redundant outer membrane and secreted proteins of Salmonella. Herein among 100 proteins identified with top-ranked scores, 15 representative antigens were selected randomly. Applying the sequence conservation test, four proteins (FliK, BcsZ, FhuA and FepA) remained as potential vaccine candidates for in vivo evaluation of immunogenicity and immunoprotection. All four candidates were capable to trigger the immune response and stimulate the production of antiserum in mice. Furthermore, top-ranked proteins including FliK and BcsZ provided wide antigenic coverage among the multi-serotype of Salmonella. The S. Typhimurium LT2 challenge model used in mice immunized with FliK and BcsZ showed a high relative percentage survival (RPS) of 52.74 % and 64.71 % respectively. In conclusion, this study constructed an in-silico pipeline able to successfully pre-screen the vaccine targets characterized by high immunogenicity and protective immunity. We show that reverse vaccinology allowed screening of appropriate broad-spectrum vaccines for Salmonella.

Recombinant FimH, a fimbrial tip adhesin of Vibrio parahaemolyticus, elicits mixed T helper cell response and confers protection against Vibrio parahaemolyticus challenge in murine model

Vibrio parahaemolyticus causes vibriosis in wide range of marine organisms, and is responsible for food borne illnesses in humans through consumption of contaminated uncooked/partially cooked seafood. Continued and widespread antibiotics usage to increase the productivity has led to antibiotics resistance development. This has necessitated the need to develop alternative methods to control its infection. Use of safe and effective vaccines against the virulence factors not only protects from infection, it also minimizes antibiotic usage. The colonization of V. parahaemolyticus in the host and disease development requires several adhesins present on the cell surface, and thereby make them attractive vaccine candidates. V. parahaemolyticus produces extracellular type 1 fimbriae that have been shown to play a role in adhesion, biofilm formation and virulence. FimH is one of the minor components of the type 1 fimbriae occurring on its very tip. Being present on the cell surface, it is highly immunogenic, and can be targeted as a potential vaccine candidate. The present study describes the immunogenic and vaccine potential of recombinant V. parahaemolyticus FimH (rVpFimH) expressed in E. coli. Immunization of BALB/c mice with the rVpFimH elicited a strong mixed immune response, T-cell memory (evidenced by antibody isotyping, cytokine profiling and T-cell proliferation assay), and agglutination positive antibodies. FACS analysis and immunogold labeling showed that the polyclonal anti-rVpFimH antibodies were able to recognize the FimH on V. parahaemolyticus cells. In vivo challenge of the rVpFimH-immunized mice with 2×LD₅₀ dose of live bacteria showed one hundred percent survival. Thus, our findings clearly demonstrate the potential of FimH as an effective vaccine candidate against V. parahaemolyticus.

Identification of Vibrio parahaemolyticus and Vibrio spp. Specific Outer Membrane Proteins by Reverse Vaccinology and Surface Proteome

The discovery of outer membrane proteins (OMPs) with desirable specificity and surface availability is a fundamental challenge to develop accurate immunodiagnostic assay and multivalent vaccine of pathogenic Vibrio species in food and aquaculture. Herein 101 OMPs were systemically screened from 4,831 non-redundant proteins of Vibrio parahaemolyticus by bioinformatical predication of signaling peptides, transmembrane (TM) α-helix, and subcellular location. The sequence homology analysis with 32 species of Vibrio spp. and all the non-Vibrio strains revealed that 15 OMPs were conserved in at least 23 Vibrio species, including BamA (VP2310), GspD (VP0133), Tolc (VP0425), OmpK (VP2362), OmpW (VPA0096), LptD (VP0339), Pal (VP1061), flagellar L-ring protein (VP0782), flagellar protein MotY (VP2111), hypothetical protein (VP1713), fimbrial assembly protein (VP2746), VacJ lipoprotein (VP2214), agglutination protein (VP1634), and lipoprotein (VP1267), Chitobiase (VP0755); high adhesion probability of flgH, LptD, OmpK, and OmpW indicated they were potential multivalent Vibrio vaccine candidates. V. parahaemolyticus OMPs were found to share high homology with at least one or two Vibrio species, 19 OMPs including OmpA like protein (VPA073), CsuD (VPA1504), and MtrC (VP1220) were found relatively specific to V. parahaemolyticus. The surface proteomic study by enzymatical shaving the cells showed the capsular polysaccharides most likely limited the protease action, while the glycosidases improved the availability of OMPs to trypsin. The OmpA (VPA1186, VPA0248, VP0764), Omp (VPA0166), OmpU (VP2467), BamA (VP2310), TolC (VP0425), GspD (VP0133), OmpK (VP2362), lpp (VPA1469), Pal (VP1061), agglutination protein (VP1634), and putative iron (III) compound receptor (VPA1435) have better availability on the cell surface.

Immunogenic characterization and protective efficacy of recombinant CsgA, major subunit of curli fibers, against Vibrio parahaemolyticus

Vibrio parahaemolyticus is one of the major pathogens responsible for vibriosis and zoonotic infections in teleosts, marine invertebrates, and also humans through consumption of contaminated or unprocessed seafood. Emergence of resistance against current accessible antibiotics and spread to the food chain and environment necessitate the development of safe and effective subunit vaccine against this bacterium. Many bacteria including V. parahaemolyticus produce extracellular curli fibrils, heteropolymeric filaments of major and minor subunit, which have been implicated in adhesion, biofilm formation, and virulence. Adhesins are the primary contact points with the host which help in establishing infection and colonization. CsgA, an adhesin, is the major structural component of the curli fiber that forms homopolymers of several hundred units. Due to their exposure on the cell surface, the curli fibers are recognized by the host's immune system, would generate high immune response, and therefore can serve as effective vaccine candidate. In the present study, we describe characterization of the csgA gene, and preparation of recombinant soluble CsgA of V. parahaemolyticus (rVpCsgA), and evaluation of its vaccine potential. Immunization of BALB/c mice with the rVpCsgA mounted a strong immune response. Cellular immune assays such as antibody isotyping, in vitro splenocyte proliferation analysis, and cytokine profiling revealed mixed T-helper cell immune response. The anti-rVpCsgA antiserum was agglutination positive and specifically cross-reacted with the curli CsgA present on the outer membrane of V. parahaemolyticus cells, thus demonstrating its neutralization potential. One hundred percent survival of the immunized mice upon challenge with the lethal dosage of the bacterium established that the rVpCsgA could serve as an effective vaccine against the bacterium. KEY POINTS: • Recombinant histidine-tagged CsgA of V. parahaemolyticus, rVpCsgA, was purified. • The rVpCsgA immunization produced mixed immune response and agglutinating antibodies. • Immunization with the rVpCsgA protected mice against V. parahaemolyticus challenge.

Evaluation of the β-barrel outer membrane protein VP1243 as a candidate antigen for a cross-protective vaccine against Vibrio infections

Vibrio parahaemolyticus is a Gram-negative halophilic bacterium that causes acute gastroenteritis after the consumption of contaminated food, wound infection, and seizures. Antibiotic therapy is the main method for controlling Vibrio infections, which inevitably leads to drug resistance. Therefore, a vaccine is urgently needed to avoid this problem. Outer membrane proteins (OMPs) play a pivotal role in the interaction between the host immune system and bacteria. VP1243 is an OMP of V. parahaemolyticus, and it possessed immunogenicity in our previous study. The present study found that VP1243 was widely distributed, highly conserved and possessed similar surface epitopes among the major Vibrio species. The protein stimulated a strong antibody response and induced cross-reactive immune responses in V. parahaemolyticus, V. alginolyticus and V. vulnificus. Notably, it provided 100% immune protection against lethal challenges by the three Vibrio species in mice immunized with VP1243. Efficient clearance of cells of the three Vibrio bacterial species was observed in immunized mice. These findings provide solid evidence for VP1243 as a promising candidate for the development of a versatile vaccine to protect against Vibrio infections.

Selection and characterization of a Vibrio parahaemolyticus OmpU antibody by phage display

Vibrio parahaemolyticus (V. parahaemolyticus) is a well-known food-borne human pathogen that can cause a variety of clinical manifestations after the consumption of raw or undercooked seafoods. The crucial roles of Vibrio OmpU in bacterial pathogenesis have been found in recent studies. In the present study, we screened for single domain antibody fragment (sdAb) candidates that bind to V. parahaemolyticus OmpU by using a sdAb phage display library and isolated several positive phage clones. The UAb28, which was one of the positive clones, was shown high enrichment and affinity. The CDRs of UAb28 are speculated to perform the OmpU binding function by molecular docking. The capable of recognizing OmpU was verified by binding and inhibition assays. The UAb28 might be useful in future studies to develop the potential sdAb-based immunotherapeutics against V. parahaemolyticus infection.

Functional characterization of a broad and potent neutralizing monoclonal antibody directed against outer membrane protein (OMP) of Salmonella typhimurium

In the present study, we have generated a murine monoclonal antibody (mAb) named Sal-06 by using the crude outer membrane protein preparation of Salmonella enteric subsp. enterica serovar Typhimurium ATCC 14028 strain as antigen. Sal-06mAb belonging to IgG1 isotype demonstrated broad cross-reactivity to standard and isolated strains of genus Salmonella and others such as Escherichia coli, Klebsiella pneumonia, and Proteus mirabilis. Cross-reactivity across several bacterial genera indicated that the epitopes reactive to Sal-06mAb are conserved among these members. Neutralizing effects of Sal-06mAb on Salmonella growth and survival was evaluated in vitro using bacteriostatic and bactericidal activity with and without complement and bacterial invasion inhibition assay. Sal-06mAb demonstrated a bacteriostatic effect on the growth of S. typhimurium ATCC 14028 strain which is both time and concentration (of mAb) dependent. It was also found that the bacterial growth inhibition was complement independent. When the bacterial cells were preincubated with Sal-06mAb, it reduced the adherence and invasion of bacterial cells into A549 epithelial cell line. This was confirmed by CFU count analysis, phase contrast, and fluorescence microscopy. Scanning electron microscope (SEM) imaging confirmed the antimicrobial effects of Sal-06mAb on S. typhimurium ATCC 14028. The development of broadly reactive and cross protective Sal-06mAb opens new possibilities for immunotherapy of sepsis caused by Gram-negative Enterobacteriaceae members.

A multi-epitope plant-made chimeric protein (LTBentero) targeting common enteric pathogens is immunogenic in mice

KEY MESSAGE

A plant-based multiepitopic protein (LTBentero) containing epitopes from ETEC, S. typhimurium, and V. parahaemolyticus was produced in plants cells and triggered systemic and intestinal humoral responses in immunized mice. Around 200 million people suffer gastroenteritis daily and more than 2 million people die annually in developing countries due to such pathologies. Vaccination is an alternative to control this global health issue, however new low-cost vaccines are needed to ensure proper vaccine coverage. In this context, plants are attractive hosts for the synthesis and delivery of subunit vaccines. Therefore, in this study a plant-made multiepitopic protein named LTBentero containing epitopes from antigens of enterotoxigenic E. coli, S. typhimurium, and V. parahaemolyticus was produced and found immunogenic in mice. The LTBentero protein was expressed in tobacco plants at up to 5.29 µg g-1 fresh leaf tissue and was deemed immunogenic when administered to BALB/c mice either orally or subcutaneously. The plant-made LTBentero antigen induced specific IgG (systemic) and IgA (mucosal) responses against LTB, ST, and LptD epitopes. In conclusion, multiepitopic LTBentero was functionally produced in plant cells, being capable to trigger systemic and intestinal humoral responses and thus it constitutes a promising oral immunogen candidate in the fight against enteric diseases.

OmpW is positively regulated by iron via Fur, and negatively regulated by SoxS contribution to oxidative stress resistance in Escherichia coli

Iron plays a central role at the interface of pathogen and host. The ability to sequester iron from a host not only reduces host immune defenses but also promotes pathogen virulence, leading to the occurrence of infectious disease. Recently, outer membrane protein OmpW was shown to protect bacteria against harsh environmental conditions and to play a role in infectious disease. The expression of this versatile protein is controlled by iron, but the underlying mechanism of iron regulation has not been elucidated. In this study, the relation between OmpW expression and iron was investigated. Our results demonstrated that expression of OmpW is responsive to iron. Iron uptake analysis showed that an ompW mutant strain has a strong requirement for iron as compared to wild type and the ompW complemented strain. Moreover, ferric uptake regulation protein Fur, an iron binding transcriptional factor, was downregulated under iron limitation conditions and had a similar expression profile to OmpW in the presence or absence of iron. Based on these results, we suggest that iron regulates OmpW by binding to Fur. Furthermore, SoxS, a transcriptional factor involved in oxidative stress, was found to negatively regulate OmpW. We found that downregulating or knocking out OmpW results in bacterial resistance to oxidative stress. These findings provide new insight into the regulation of OmpW expression by iron, and may represent a new mechanism contributing to iron-mediated infectious disease.

Attenuated Listeria monocytogenes protecting zebrafish (Danio rerio) against Vibrio species challenge

Live attenuated bacteria is a promising candidate vector for the delivery of vaccines in clinic trials. In the field of aquaculture industry, live vector vaccine also could provide long-term and effective protection against fish bacterial diseases. In our previous work, we demonstrated attenuated Listeria monocytogenes (Lm) had the potential to be an aquaculture vaccine vector in cellular level and zebrafish model. To further investigate the potential application of attenuated Lm in aquaculture vaccines, the outer membrane protein K (OmpK) from Vibrio parahaemolyticus (V. parahaemolyticus), as a conservative protective antigen, was fused to a new antigen-delivery system, and introduced into double-gene attenuated Lm strain (EGDe-ΔactA/inlB, Lmdd) to get live-vector vaccine strain Lmdd-OmpK. The strain Lmdd-OmpK showed the stable secrete efficacy of OmpK and was tested the cross-protective immunity against Vibrio species. After intraperitoneal administration in zebrafish, Lmdd and Lmdd-OmpK strain both improved the survival rates of zebrafish infected by V. parahaemolyticus, Vibrio alginolyticus (V. alginolyticus) and Vibrio anguillarum (V. anguillarum), respectively. In summary, attenuated Lm is able to protect zebrafish against Vibrio species challenge, illustrating its potential value for further aquaculture vaccines development.

Response of hemocytes profile in the black tiger shrimp (Penaeus monodon) against Vibrio harveyi induced by Xylocarpus granatum leaves extract

Aim:

The present study investigated hemocytes profile of black tiger shrimp (Penaeus monodon) induced with Xylocarpus granatum leaves extract to protect against Vibrio harveyi infection.

Materials and Methods:

X. granatum leaves were chopped into small size, air-dried, and extracted with one of the following solvents: Ethanol, distilled water, and seawater, whereas each solvent was given in three different concentrations (750 ppm, 1.000 ppm, and 1.250 ppm, respectively). Extracts were induced to 60 post-larvae shrimp in each treatment (three replicates, 20 shrimp for each) by immersing method and subsequently challenged with V. harveyi.

Results:

This study demonstrated different effectiveness among solvents used to extract X. granatum leaves, in which distilled water showed the most effective solvent as can be seen from the lowest percentage on anorexia, lethargic, and weakened reflex of shrimp compared with another solvent, positive and negative controls. Pathological symptoms for shrimp induced by X. granatum leaves extract were minimum with the highest survival rate compared with those of positive and negative control. Total hemocyte cells and its cell constituents such as semi-granular, granular, and hyaline cells on treatment group at 1.250 ppm were higher than controls.

Conclusion:

Leaves extract of X. granatum extract effectively inhibited V. harveyi infection, increased survival rate, and hemocytes cell of the experimental shrimp. Distilled water extract of X. granatum at 1.250 ppm demonstrated the highest protective effect toward V. harveyi infection on P. monodon.

The preparation and antibacterial effect of egg yolk immunoglobulin (IgY) against the outer membrane proteins of Vibrio parahaemolyticus

BACKGROUND

Vibrio parahaemolyticus causes not only various diseases in aquaculture animals but also seafood-borne illness in humans. Outer membrane proteins (OMPs) are species-specific proteins found in bilayer membranes of gram-negative bacteria. Egg yolk immunoglobulin (IgY) has been reported to serve as oral administration of antibodies against bacteria and virus.

RESULTS

The present research extracted and identified OMPs from V. parahaemolyticus, and then the extracted OMPs were used to immunize hens to obtain specific IgY. The efficacy of IgY against V. parahaemolyticus were investigated in vitro and in vivo. The specific IgY effectively inhibited the growth of V. parahaemolyticus in liquid medium rather than Escherichia coli and Staphylococcus aureus. Specific IgY antibodies were incorporated into extruded food pellets and fed to bacteria-challenged white pacific shrimp to observe the anti-bacterial effect in vivo. The bacterial loads in muscles of V. parahaemolyticus infected shrimp fed with specific IgY-included diets were significantly fewer than those fed with non-specific IgY-included diets. The superoxide dismutase activities in muscles of infected shrimp fed with specific IgY-included diets were significantly higher than the control group.

CONCLUSION

The results suggested that the specific IgY effectively inhibited the growth of V. parahaemolyticus and introduced passive immunity to shrimp. © 2018 Society of Chemical Industry.

Molecular mechanisms of Vibrio parahaemolyticus pathogenesis

Vibrio parahaemolyticus is a Gram-negative halophilic bacterium that is mainly distributed in the seafood such as fish, shrimps and shellfish throughout the world. V. parahaemolyticus can cause diseases in marine aquaculture, leading to huge economic losses to the aquaculture industry. More importantly, it is also the leading cause of seafood-borne diarrheal disease in humans worldwide. With the development of animal model, next-generation sequencing as well as biochemical and cell biological technologies, deeper understanding of the virulence factors and pathogenic mechanisms of V. parahaemolyticus has been gained. As a globally transmitted pathogen, the pathogenicity of V. parahaemolyticus is closely related to a variety of virulence factors. This article comprehensively reviewed the molecular mechanisms of eight types of virulence factors: hemolysin, type III secretion system, type VI secretion system, adhesion factor, iron uptake system, lipopolysaccharide, protease and outer membrane proteins. This review comprehensively summarized our current understanding of the virulence factors in V. parahaemolyticus, which are potentially new targets for the development of therapeutic and preventive strategies.

Intramuscular administration of a DNA vaccine encoding OmpK antigen induces humoral and cellular immune responses in flounder (Paralichthys olivaceus) and improves protection against Vibrio anguillarum

Outer membrane protein K (OmpK) is an immunogenic protein that could act as subunit vaccine candidate for Vibrio anguillarum. In this study, a DNA vaccine encoding the OmpK gene of V. anguillarum was constructed and confirmed to express OmpK in vitro and in vivo. To evaluate the potential of pcDNA3.1-OmpK (pOmpK) as vaccine candidate, the humoral and cellular immune responses, and protective effects were analyzed in flounder model. The results showed that the transcription and translation of OmpK gene occurred in both transfected hirame natural embryo (HINAE) cells and injected fish muscles, indicating the functionality of pOmpK to express OmpK. Fish immunized with pOmpK showed significant increase of surface IgM positive (sIgM⁺), CD4-1⁺, CD4-2⁺ lymphocytes and production of specific anti-V. anguillarum or anti-rOmpK antibodies, which indicate the activation of humoral and cellular immune responses after vaccination. Moreover, a relative percent survival (RPS) rate of 50.00% against V. anguillarum infection was obtained for flounder immunized with pOmpK. In conclusion, this study indicates that pOmpK is able to induce humoral and cellular immune responses and can be used as a DNA vaccine candidate.

Vibriosis in Fish: A Review on Disease Development and Prevention

Current growth in aquaculture production is parallel with the increasing number of disease outbreaks, which negatively affect the production, profitability, and sustainability of the global aquaculture industry. Vibriosis is among the most common diseases leading to massive mortality of cultured shrimp, fish, and shellfish in Asia. High incidence of vibriosis can occur in hatchery and grow-out facilities, but juveniles are more susceptible to the disease. Various factors, particularly the source of fish, environmental factors (including water quality and farm management), and the virulence factors of Vibrio, influence the occurrence of the disease. Affected fish show weariness, with necrosis of skin and appendages, leading to body malformation, slow growth, internal organ liquefaction, blindness, muscle opacity, and mortality. A combination of control measures, particularly a disease-free source of fish, biosecurity of the farm, improved water quality, and other preventive measures (e.g., vaccination) might be able to control the infection. Although some control measures are expensive and less practical, vaccination is effective, relatively cheap, and easily implemented. In this review, the latest knowledge on the pathogenesis and control of vibriosis, including vaccination, is discussed.

Differential Antibody Responses to Outer Membrane Proteins Contribute to Differential Immune Protections between Live and Inactivated Vibrio parahemolyticus

It is widely accepted that live vaccines elicit higher immune protection than inactivated vaccines. However, the mechanisms are largely unknown. Here, an array with 64 recombinant outer membrane proteins of Vibrio parahemolyticus was developed to explore antibody responses of live and inactivated V. parahemolyticus post immunization of the 8th, 12th, 16th and 20th day. Among the 64 outer membrane proteins, 28 elicited antibody generation. They were all detected in live vaccine-induced immunity but only 15 antibodies were found in inactivated vaccine-induced immunity. Passive immunization showed that higher percent survival was detected in live than inactivated vaccine-induced immunities. Active immunization indicated that out of 19 randomly selected outer membrane proteins, 5 stimulated immune protection against V. parahemolyticus infection. Among them, antibodies to VP2309 and VPA0526 were shared in mice immunized by live or inactivated vaccines, whereas antibodies to VPA0548, VPA1745, and VP1667 were only found in mice immunized by live vaccine. In addition, live V. parahemolyticus stimulated earlier antibody response than inactivated bacteria. These results indicate that not all of the outer membrane proteins elicited antibody responses when they work together in the form of live or inactivated bacteria; live vaccine elicits more protective antibodies, which contribute to higher immune protection in live vaccine than inactivated vaccine. Notably, the recombinant proteins might be different from those separated from live bacteria, and they might be different in their immunogenic potencies.

In silico analysis of putative drug and vaccine targets of the metabolic pathways of Actinobacillus pleuropneumoniae using a subtractive/comparative genomics approach

Actinobacillus pleuropneumoniae is a Gram-negative bacterium that resides in the respiratory tract of pigs and causes porcine respiratory disease complex, which leads to significant losses in the pig industry worldwide. The incidence of drug resistance in this bacterium is increasing; thus, identifying new protein/gene targets for drug and vaccine development is critical. In this study, we used an in silico approach, utilizing several databases including the Kyoto Encyclopedia of Genes and Genomes (KEGG), the Database of Essential Genes (DEG), DrugBank, and Swiss-Prot to identify non-homologous essential genes and prioritize these proteins for their druggability. The results showed 20 metabolic pathways that were unique and contained 273 non-homologous proteins, of which 122 were essential. Of the 122 essential proteins, there were 95 cytoplasmic proteins and 11 transmembrane proteins, which are potentially suitable for drug and vaccine targets, respectively. Among these, 25 had at least one hit in DrugBank, and three had similarity to metabolic proteins from Mycoplasma hyopneumoniae, another pathogen causing porcine respiratory disease complex; thus, they could serve as common therapeutic targets. In conclusion, we identified glyoxylate and dicarboxylate pathways as potential targets for antimicrobial therapy and tetra-acyldisaccharide 4'-kinase and 3-deoxy-D-manno-octulosonic-acid transferase as vaccine candidates against A. pleuropneumoniae.

Immunogenicity study of an expressed outer membrane protein U of Vibrio vulnificus in Japanese eel (Anguilla japonica)

AIMS

Vibrio vulnificus is a common bacterial pathogen causing haemorrhagic septicaemia in eel farming. This study investigates the immunogenicity of an outer membrane protein U (OmpU) of V. vulnificus and the feasibility of the protein as a new subunit vaccine against V. vulnificus.

METHODS AND RESULTS

Partial gene sequence of the OmpU of V. vulnificus was cloned, and then the OmpU was expressed and purified. Three groups of Japanese eels (Anguilla japonica) were intraperitoneally (i.p) injected with bovine serum albumin (BSA group), formalin-killed whole cell of V. vulnificus (FKC group) or the expressed OmpU of V. vulnificus (OMP group). On 14, 21, 28 and 42 days postimmunization (dpi), the whole blood cells were collected to evaluate the stimulation index (SI) and bactericidal activity. The serum was obtained to assess the titres of specific antibody, lysozyme activity, complement activity and bactericidal activity. The lysozyme activities in the suspension of kidney, skin mucus and liver in eels were also ascertained. The results showed that the SI and the titres of anti-V. vulnificus antibody in the OMP group was significantly increased on 28 dpi; lysozyme activity in the kidney and skin mucus of OMP group on 42 and 14 dpi were both significantly higher than BSA group; eels in OMP group showed strong bactericidal capacity on 21 and 28 days; and the relative percent survival of OMP vs BSA group after challenged by V. vulnificus on 28 dpi was 80%.

CONCLUSIONS

These results showed that the expressed OmpU of V. vulnificus could significantly improve the immune function of Japanese eel and the resistance of eels to the infection of V. vulnificus.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study offered an alternative preliminary strategy of making aquaculture vaccines against V. vulnificus for eel farming.

Identification of immunogenic proteins and evaluation of recombinant PDHA1 and GAPDH as potential vaccine candidates against Streptococcus iniae infection in flounder (Paralichthys olivaceus)

Streptococcus iniae is a major Gram-positive pathogen that causes invasive disease in fish worldwide. In this study, in order to identify immunogenic proteins for developing highly effective vaccine against S. iniae, whole-cell lysate proteins of S. iniae were analyzed by western blotting using flounder anti-S. iniae antibodies, and two positive protein bands of molecular weight 37 kDa and 40 kDa were screened, which were identified as pyruvate dehydrogenase E1 subunit alpha (PDHA1), BMP family ABC transporter substrate-binding protein (BMP) and L-lactate dehydrogenase (LDH), as well as ornithine carbamoyltransferase (OCT), lactate oxidas (LOx) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) by mass spectrometry. Subsequently, the six recombinant proteins were produced and used to immunize healthy flounder, and the relative percent survival (RPS) value was 72.73%, 27.27%, 36.36%, 9.09%, 36.36% and 63.64% respectively after intraperitoneal challenge with live S. iniae, revealing that rPDHA1 and rGAPDH produced higher relative percent survival than formalin-killed S. iniae (36.36%). To further investigate the protective efficacy of rPDHA1 and rGAPDH, the proliferation of surface membrane immunoglobulin-positive (sIg+) lymphocytes in peripheral blood leucocytes, the total serum IgM, specific IgM against S. iniae and RPS were detected. The results showed that rPDHA1, rGAPDH and formalin-killed S. iniae significantly induced the proliferation of sIg+ lymphocytes, the production of total serum IgM and specific IgM as compared with the control group, and rGAPDH and rPDHA1 provide higher RPS (62.5% and 75%, respectively) again. These results demonstrated that rPDHA1 and rGAPDH are promising vaccine candidates against S. iniae infection in flounder.

LptD is a promising vaccine antigen and potential immunotherapeutic target for protection against Vibrio species infection

Outer membrane proteins (OMPs) are unique to Gram-negative bacteria. Several features, including surface exposure, conservation among strains and ability to induce immune responses, make OMPs attractive targets for using as vaccine antigens and immunotherapeutics. LptD is an essential OMP that mediates the final transport of lipopolysaccharide (LPS) to outer leaflet. The protein in Vibrio parahaemolyticus was identified to have immunogenicity in our previous report. In this study, broad distribution, high conservation and similar surface-epitopes of LptD were found among the major Vibrio species. LptD was further revealed to be associated with immune responses, and it has a strong ability to stimulate antibody response. More importantly, it conferred 100% immune protection against lethal challenge by V. parahaemolyticus in mice when the mice were vaccinated with LptD, and this finding was consistent with the observation of efficient clearance of bacteria in vaccination mice. Strikingly, targeting of bacteria by the LptD antibody caused significant decreases in both the growth and LPS level and an increase in susceptibility to hydrophobic antibiotics. These findings were consistent with those previously obtained in lptD-deletion bacteria. These data demonstrated LptD is a promising vaccine antigens and a potential target for antibody-based therapy to protect against Vibrio infections.

Identification of polyvalent protective immunogens from outer membrane proteins in Vibrio parahaemolyticus to protect fish against bacterial infection

Vaccination is one of the most effective and economic way to prevent infectious diseases in aquaculture. The development of effective vaccines, however, is still limited, especially for polyvalent vaccines, which are against multiple species. With this regard, identification of polyvalent protective immunogens, serving as polyvalent vaccines, became a key step in vaccine development. In the current study, 17 outer membrane proteins from Vibrio parahaemolyticus were identified as immunogens. Further, four of the 17 proteins including VP2309, VP0887, VPA0548 and VP1019 were characterized as efficiently protective immunogens against V. parahaemolyticus' infection through passive and active immunizations in zebrafish. Importantly, these four proteins showed cross-protective capability against infections by Aeromonas hydrophila or/and Pseudomonas fluorescens, which shared similar epitopes with V. parahaemolyticus in homology of these proteins. Further investigation showed that the expression level of the four protective immunogens elevated in response to fish plasma in a dose-dependent manner. These results indicate that the four protective immunogens are polyvalent vaccine candidates in aquaculture.

Immunoproteomic Approach for Screening Vaccine Candidates from Bacterial Outer Membrane Proteins

Outer membrane proteins (OMPs) are unique to Gram-negative bacteria and have been revealed as potential vaccine candidates for conferring protection against infections in recent years. Immunoproteomics is a powerful technique that is ideally suited to screen and identify potential vaccine candidates. This chapter presents a brief outline of the screening of immunogenic OMPs from Vibrio parahaemolyticus by an immunoproteomic strategy that was based on two-dimensional electrophoresis (2-DE) and immunoblotting. The protective efficacy provided by the immunogenic OMP Vp0802 determined by active protection experiment assays is also presented in brief.

Recombinant outer membrane protein A induces a protective immune response against Escherichia coli infection in mice

Pathogenic Escherichia coli (E. coli) is an important infectious Gram-negative bacterium causing millions of death every year. Outer membrane protein A (OmpA) has been suggested as a potential vaccine candidate for conferring protection against bacterial infection. In this study, a universal vaccine candidate for E. coli infection was developed and evaluated. Bioinformatics analysis revealed the OmpA protein from E. coli shares 96~100%, 90~94%, and 45% identity with Shigella, Salmonella, and Pseudomonas strains, respectively. The ompA gene was cloned from the genomic DNA of E. coli, and then the OmpA protein was expressed in BL21 (DE3) using the auto-induction method. The recombinant OmpA (rOmpA) protein had an average molecular weight of 36 kDa with the purity of 93.5%. Immunological analysis indicated that the titers of anti-rOmpA sera against rOmpA and whole cells were 1:642,000 and 1:140,000, respectively. Moreover, rOmpA not only conferred a high level of immunogenicity to protect mice against the challenge of E. coli, but also generated cross-protection against Shigella and Salmonella. The anti-rOmpA sera could enhance the phagocytic activity of neutrophils against E. coli. The survive ratios of mice immunized with rOmpA and PBS were 50% and 20% after 48 h post-challenge, indicating mice were protected from E. coli infection after immunization with rOmpA. All these results clearly indicate that rOmpA may be a promising candidate for the development of a subunit vaccine to prevent E. coli infection.