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

Bacterial efflux pump OMPs as vaccine candidates against multidrug-resistant Gram-negative bacteria

The emergence and propagation of bacteria resistant to antimicrobial drugs is a serious public health threat worldwide. The current antibacterial arsenal is becoming obsolete, and the pace of drug development is decreasing, highlighting the importance of investment in alternative approaches to treat or prevent infections caused by antimicrobial-resistant bacteria. A significant mechanism of antimicrobial resistance employed by Gram-negative bacteria is the overexpression of efflux pumps that can extrude several compounds from the bacteria, including antimicrobials. The overexpression of efflux pump proteins has been detected in several multidrug-resistant Gram-negative bacteria, drawing attention to these proteins as potential targets against these pathogens. This review will focus on the role of outer membrane proteins from efflux pumps as potential vaccine candidates against clinically relevant multidrug-resistant Gram-negative bacteria, discussing advantages and pitfalls. Additionally, we will explore the relevance of efflux pump outer membrane protein diversity and the possible impact of vaccination on microbiota.

DC-SIGN of Largemouth Bass (Micropterus salmoides) Mediates Immune Functions against Aeromonas hydrophila through Collaboration with the TLR Signaling Pathway

C-type lectins in organisms play an important role in the process of innate immunity. In this study, a C-type lectin belonging to the DC-SIGN class of Micropterus salmoides was identified. MsDC-SIGN is classified as a type II transmembrane protein. The extracellular segment of MsDC-SIGN possesses a coiled-coil region and a carbohydrate recognition domain (CRD). The key amino acid motifs of the extracellular CRD of MsDC-SIGN in Ca2+-binding site 2 were EPN (Glu-Pro-Asn) and WYD (Trp-Tyr-Asp). MsDC-SIGN-CRD can bind to four pathogen-associated molecular patterns (PAMPs), including lipopolysaccharide (LPS), glucan, peptidoglycan (PGN), and mannan. Moreover, it can also bind to Gram-positive, Gram-negative bacteria, and fungi. Its CRD can agglutinate microbes and displays D-mannose and D-galactose binding specificity. MsDC-SIGN was distributed in seven tissues of the largemouth bass, among which the highest expression was observed in the liver, followed by the spleen and intestine. Additionally, MsDC-SIGN was present on the membrane of M. salmoides leukocytes, thereby augmenting the phagocytic activity against bacteria. In a subsequent investigation, the expression patterns of the MsDC-SIGN gene and key genes associated with the TLR signaling pathway (TLR4, NF-κB, and IL10) exhibited an up-regulated expression response to the stimulation of Aeromonas hydrophila. Furthermore, through RNA interference of MsDC-SIGN, the expression level of the DC-SIGN signaling pathway-related gene (RAF1) and key genes associated with the TLR signaling pathway (TLR4, NF-κB, and IL10) was decreased. Therefore, MsDC-SIGN plays a pivotal role in the immune defense against A. hydrophila by modulating the TLR signaling pathway.

Identification of a potential antigen stimulating immune response against Vibrio parahaemolyticus infection in hybrid tilapia (Oreochromis aureus♂ × Oreochromis niloticus♀)

Vibrio parahaemolyticus (V. parahaemolyticus) is a major pathogen that causes substantial losses in the marine fishery. With the emergence of antibiotic resistance, vaccines have become the most effective approach against V. parahaemolyticus infection. Adhesion factors on the cell surface are pivotal in the colonization and pathogenesis of V. parahaemolyticus within the host, highlighting their potential as vaccine candidates. This study aims to assess the immunogenicity and potential of recombinant V. parahaemolyticus MAM7 (rMAM7) as a vaccine candidate. Initially, we cloned and purified the MAM7 protein of V. parahaemolyticus. Moreover, after 4 weeks of vaccination, the fish were challenged with V. parahaemolyticus. rMAM7 demonstrated a certain protective effect. Immunological analysis revealed that rMAM7 immunization-induced antibody production and significantly increased acid phosphatase (ACP) and alkaline phosphatase (AKP) activity in hybrid tilapia. Furthermore, serum bactericidal tests demonstrated a lower bacterial survival rate in the rMAM7 group compared to PBS and rTrxa. qRT-PCR results indicated that rMAM7 significantly upregulated CD4, CD8 and IgM gene expression, suggesting the induction of Th1 and Th2 responses in hybrid tilapia. Overall, these findings highlight the potential application of MAM7 from V. parahaemolyticus in the development of protein vaccines.

The Outer Membrane Proteins and Their Synergy Triggered the Protective Effects against Pathogenic Escherichia coli

Colibacillosis caused by pathogenic Escherichia coli (E. coli) is one of the most serious infectious diseases, causing an extensive burden on animal husbandry and the human healthcare system. Vaccination is one of the ideal ways to prevent E. coli infection. In this work, recombinant outer membrane protein A (rOmpA), outer membrane protein C (rOmpC) and BamA (rBamA) from E. coli O78 (CVCC CAU0768) were expressed in a prokaryotic expression system with the concentration of 1–2 mg/mL after purification. Considerable immune responses could be triggered in mice that were immunized with these recombinant proteins, high antibody titers, high total IgG level and various antibody isotypes were detected in antisera after booster immunizations. Moreover, mice immunized with several recombinant proteins in combination showed a higher survival rate with the challenge of homologous strain E. coli O78 and a more significant cross-protection effect against heterologous strain E. coli O157:H7 (CICC 21530) in vivo than those of immunized alone. The antisera from immunized mice showed high affinity to multiple strains of Escherichia, Shigella and Salmonella in vitro, indicating that recombinant outer membrane proteins from E. coli O78 had the potential to be developed into universal antigenic substances against not only E. coli but also a variety of Gram-negative bacteria. rOmpA was considered as the most immunogenic protein in this work and the combination of different proteins could further enhance the immune response of immunized mice, which provided the reference for the construction of novel antigens with higher efficiency.

Immunogenic characteristics of the outer membrane phosphoporin as a vaccine candidate against Klebsiella pneumoniae

In recent years, Klebsiella pneumoniae (KP) has caused disease outbreaks in different animals, resulting in serious economic losses and biosafety concerns. Considering the broad antibiotic resistance of KP, vaccines are the most effective tools against infection. However, there is still no KP vaccine available in the veterinary field. Our results indicate that the highly conserved outer membrane phosphoporin (PhoE) of KP is immunogenic in mice and elicits high titers of antibodies that were shown to be specific for PhoE by immunoblotting. Immunization with PhoE also induced robust cell-mediated immunity and elicited the secretion of high levels of IFN-γ and IL-4, suggesting the induction of mixed Th1 and Th2 responses. Sera from PhoE-immunized mice induced significantly higher complement-mediated lysis of KP cells than did sera from the PBS control mice. Finally, mice immunized with PhoE were significantly protected against KP challenge, with better survival and a reduced visceral bacterial load. Our data underscore the great potential of PhoE as a novel candidate antigen for a vaccine against KP infection.

OMPdb: A Global Hub of Beta-Barrel Outer Membrane Proteins

OMPdb (www.ompdb.org) was introduced as a database for β-barrel outer membrane proteins from Gram-negative bacteria in 2011 and then included 69,354 entries classified into 85 families. The database has been updated continuously using a collection of characteristic profile Hidden Markov Models able to discriminate between the different families of prokaryotic transmembrane β-barrels. The number of families has increased ultimately to a total of 129 families in the current, second major version of OMPdb. New additions have been made in parallel with efforts to update existing families and add novel families. Here, we present the upgrade of OMPdb, which from now on aims to become a global repository for all transmembrane β-barrel proteins, both eukaryotic and bacterial.