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Acinetobacter baumannii is one of the most notorious nosocomial pathogens with high mortality rates. Recently, egg yolk antibody (IgY), has been considered as a promising biomolecule against pneumonia caused by this bacterium. Loop 3 of outer membrane protein 34 (Omp34) was predicted as a highly exposed immunogenic peptide. However, its immunogenicity remains to be experimentally elucidated. In the current study, a construct composed of 5 copies of loop3 of Omp34 labeled as Omp34L3X5 was designed. This construct as well as the recombinant Omp34 were expressed, purified, and injected into laying hens to raise specific antibodies. The specific IgYs were extracted from hyperimmune egg yolks. The Omp34L3X5 and whole cells (WC) of A. baumannii served as antigens in indirect ELISA to assess the purified IgYs reactivity. These antibodies were administered to neutropenic mice 1 h before the challenge with 10 × LD

Type VI Secretion System (T6SS) contributes to both virulence and antimicrobial resistance in Acinetobacter baumannii. Valine-glycine repeat protein G (VgrG) is the core component of T6SS that exists in many bacterial pathogens that have emerged as a potent mediator of pathogenicity in A. baumannii. Two conserved sequences of vgrG 1263-2295 and vgrG1263-1608 were identified antigenic in various strains of Acinetobacter baumannii. The vgrg1263-1608 sequence was implanted in the Loopless C lobe (LCL) from N. meningitidis for surface display and exposure to functional epitopes. The VgrG and LCL-VgrG were expressed and purified. Groups of BALB/c mice were immunized with these proteins and challenged with A. baumannii. Specific IgG titers, whole-cell ELISA, animal survival rates in active and passive immunizations, the bacterial burden in mice tissues, and cytotoxicity of the proteins were determined. The specific IgG suppressed bacterial burdens in the organs, and increased survival rates were noted in the immunized mice. LCL-VgrG immunization provided better protection against A. baumannii infection than the VgrG immunization. The conserved region of VgrG is probably a safe immunogen to effective vaccine development or an antiserum to control A. baumannii infections.

Acinetobacter baumannii causes severe nosocomial infections and is a difficult-to-treat pathogen due to the development of multidrug-resistant (MDR) strains. Vaccines and antibody therapy represent alternative promising strategies for the control of infections caused by A. baumannii or its MDR strains. OmpA and BauA have been assigned as protective antigens. However, the efficacy of the combination of these antigens is yet to be investigated. In this study, we targeted two critical antigens of A. baumannii (BauA and OmpA) to enhance immunoprotecting against A. baumannii.The recombinant BauA and OmpA were expressed and purified. The purified proteins were administered to BALB/c mice alone and in combination. Immune sera were assessed against BauA, OmpA and two constructs harboring immunogenic loops of these antigen. The mice were then challenged with a clinical isolate of A. baumannii. Indirect ELISA confirmed significant antibody rise to the antigens. The immunogenic loops were detected in the hybrid construct. The specific sera detected OmpA, BauA and constructs harboring immunogenic loops of these antigen with different affinities. A significant decrease in the bacterial loads was noted in the spleen, liver, and lungs of the immunized mice groups. However, the group received combination of BauA and OmpA showed lower bacterial burden in the spleen and liver.Combination of BauA and OmpA enhances immunoprotection against A. baumannii infections.

Acinetobacter baumannii is a common causative agent of nosocomial infections, with a mortality rate of 43% in infected patients. Due to the emergence of multidrug-resistant (MDR) strains, vaccine development has become necessary. Since the 34 kDa outer membrane protein Omp34 has been identified as a potential vaccine target, we implemented a hybrid antigen approach to target its extracellular loops. Using bioinformatic and structural analyses, we selected Loop 3 from Omp34 and displayed it on the loopless C-lobe (LCL) of TbpB of Neisseria meningitidis. The hybrid antigen and the LCL were produced and used to immunize mice for passive and active immunization and challenge experiments in which the reactivity of the sera was assessed by ELISAs, the bacterial load in the tissues measured and the survival of immunized mice compared. LCL was ineffective in immunization against A. baumannii thus the resulting immunity was due to the presence of Omp34 loop 3. It resulted in increased survival and a reduced bacterial load in the tissues compared to the control groups. The findings indicate that the immunogenicity of Omp34 loops can induce protection against A. baumannii infection, and it could probably be used as a vaccine candidate to control the pathogenesis of A. baumannii.

Highlights • Designed ACE2 lacks enzymatic activity and bears higher thermostability and affinity towards RBD. • The Thr27Arg mutation was introduced to increase the binding affinity against RBD. • The Arg273Gln and Thr445Gly mutations were introduced to reduce the ACE2 enzymatic activity. • The Asp427Arg mutation was done to decrease the flexibility of the ACE2. • The Pro451Met and Gly448Trp mutations were introduced to increase thermostability., The interaction between the angiotensin-converting enzyme 2 (ACE2) and the receptor binding domain (RBD) of the spike protein from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) plays a pivotal role in virus entry into the host cells. Since recombinant ACE2 protein has been suggested as an anti-SARS-CoV-2 therapeutic agent, this study was conducted to design an ACE2 protein with more desirable properties. In this regard, the amino acids with central roles in enzymatic activity of the ACE2 were substituted. Moreover, saturation mutagenesis at the interaction interface between the ACE2 and RBD was performed to increase their interaction affinity. The best mutations to increase the structural and thermal stability of the ACE2 were also selected based on B factors and mutation effects. The obtained resulted revealed that the Arg273Gln and Thr445Gly mutation have drastically reduced the binding affinity of the angiotensin-II into the active site of ACE2. The Thr27Arg mutation was determined to be the most potent mutation to increase the binding affinity. The Asp427Arg mutation was done to decrease the flexibility of the region with high B factor. The Pro451Met mutation along with the Gly448Trp mutation was predicted to increase the thermodynamic stability and thermostability of the ACE2. The designed therapeutic ACE2 would have no enzymatic activity while it could bear stronger interaction with Spike glycoprotein of the SARS-CoV-2. Moreover, decreased in vivo enzymatic degradation would be anticipated due to increased thermostability. This engineered ACE2 could be exploited as a novel therapeutic agent against COVID-19 after necessary evaluations.

Epsilon toxin of the Clostridium perfringens garnered a lot of attention due to its potential for toxicity in humans, extreme potency for cytotoxicity in mice and lack of any approved therapeutics prescribed for human. However, the intricacies of the Epsilon toxin action mechanism are yet to be understood. In this regard, various in silico tools have been exploited to model and refine the 3D structure of the toxin and its two receptors. The receptor proteins were embedded into designed lipid membranes within an aqueous and ionized environment. Thereafter, the modeled structures subjected to series of consecutive molecular dynamics runs to achieve the most natural like coordination for each model. Ultimately, protein-protein interaction analyses were performed to understand the probable action mechanism. The obtained results successfully confirmed the accuracy of employed methods to achieve high quality models for the toxin and its receptors within their lipid bilayers. Molecular dynamics analyses lead the structures to a more native like coordination. Moreover, the results of previous empirical studies were confirmed, while new insights for action mechanisms including the detailed roles of Hepatitis A virus cellular receptor 1 (HAVCR1) and Myelin and lymphocyte protein (MAL) proteins were achieved. In light of previous and our observations, we suggested novel models which elucidated the existing interplay between potential players of Epsilon toxin action mechanism with detailed structural evidences. These models would pave the way to have more robust understanding of the Epsilon toxin biology, more precise vaccine construction and more successful drug (inhibitor) design.

Background Infections caused by drug-resistant strains of Acinetobacter baumannii and Pseudomonas aeruginosa are now a global problem that requires the immediate development of new antimicrobial drugs. Combination therapy and using antimicrobial peptides are two strategies with high potential to solve this issue. By these strategies, this study aimed to determine the antimicrobial effect of Nisin and P10 antimicrobial peptides on extensively drug-resistant Acinetobacter baumannii and colistin-resistant Pseudomonas aeruginosa isolates, and investigate the most effective combination of an antimicrobial peptide with an antibiotic. Material and methods This study was performed on five resistant clinical isolates and one standard strain for each kind of bacterium. First, the minimum inhibitory concentrations of two antimicrobial peptides (Nisin and P10) and five common antibiotics for the treatment of Gram-negative bacteria (ceftazidime, tobramycin, ciprofloxacin, doripenem, and colistin) was determined using Scanner-Assisted Colorimetric MIC Method. Then, the combination effect of P10+Nisin, P10+antibiotics, Nisin + antibiotics was investigated using checkerboard method. Results The MIC value of Nisin and P10 against studied pathogens were 64–256 and 8–32 μg/ml, respectively. P10+Nisin combination showed synergistic effect against standard strains and additive effect against drug-resistant clinical isolates. It was also found that the combination effect of P10+ceftazidim, P10+doripenem, and Nisin + colistin was synergistic in most cases. Nisin + tobramycin combination showed synergistic effect in exposure to standard strains, while the synergy is strain-dependent against drug-resistant clinical isolates. Conclusion In conclusion, the synergism of Nisin + colistin and P10+ceftazidime/doripenem could be of great therapeutic value as antimicrobial drugs against infections caused by colistin-resistant P.aeruginosa and XDR A. baumannii.

Background With the increasing rate of antibiotic resistance in Acinetobacter, the World Health Organization introduced the carbapenem-resistant isolates in the priority pathogens list for which innovative new treatments are urgently needed. Antimicrobial peptides (AMPs) are one of the antimicrobial agents with high potential to produce new anti-Acinetobacter drugs. This review aims to summarize recent advances and compare AMPs with anti-Acinetobacter baumannii activity. Methods Active AMPs against Acinetobacter were considered, and essential features, including structure, mechanism of action, anti-A. baumannii potent, and other prominent characteristics, were investigated and compared to each other. In this regard, the Google Scholar search engine and databases of PubMed, Scopus, and Web of Science were used. Results Forty-six anti-Acinetobacter peptides were identified and classified into ten groups: Cathelicidins, Defensins, Frog AMPs, Melittin, Cecropins, Mastoparan, Histatins, Dermcidins, Tachyplesins, and computationally designed AMPs. According to the Minimum Inhibitory Concentration (MIC) reports, six peptides of Melittin, Histatin-8, Omega76, AM-CATH36, Hymenochirin, and Mastoparan have the highest anti-A. baumannii power against sensitive and antibiotic-resistant isolates. All anti-Acinetobacter peptides except Dermcidin have a net positive charge. Most of these peptides have alpha-helical structure; however, β-sheet and other structures have been observed among them. The mechanism of action of these antimicrobial agents is divided into two categories of membrane-based and intracellular target-based attack. Conclusion Evidence from this review indicates that AMPs would be likely among the main anti-A. baumannii drugs in the post-antibiotic era. Also, the application of computer science to increase anti-A. baumannii activity and reduce toxicity could be helpful.

Objective Vaccination of at-risk people against Acinetobacter baumannii is a promising method to inhibit infections. Mucociliary clearance in the nasal cavity and hard transportation of protein agents over the epithelial barrier are justifying the development of encapsulated vaccines. Methods In this study, we used chitosan as an adjuvant and antigen delivery system. Mucosal immunity brought about by the conserved region of A. baumannii biofilm-associated Protein (Bap) loaded on chitosan was assessed following intranasal (i.n) inoculation of mice. Mucosal and systemic immune responses were evaluated. Passive immunization was studied both in vivo and in vitro. Results Antigen-specific IgG and IgA antibodies were raised in serum and fecal and lung extractions in mice administered intranasally with Bap-chitosan particles. Passive immunization with serum obtained from chitosan-Bap immunized mice conferred higher survival compared to immunization with subcutaneously immunized mice serum. Conclusions: Passive immunization with antibodies triggered with chitosan-Bap could be an additional immunization strategy for preventing A. baumannii pneumonia.

Predefined and pre-weighted objective criteria and essential role of Wilms׳ tumor wild type gene (WT1) for maintaining transformed features of cancer cells confirm the high potency of WT1 as a valuable cancer antigen. The antigen was at the top of the ranking among 75 representative cancer antigens. In the present study, an in silico approach was launched to characterized novel CTL epitopes and design a novel multi-epitope DNA vaccine to elicit a desirable immune response against cancers over expressing WT1. Forty-four novel epitopes were described. A multi-epitope construct was designed based on predicted epitopes which is 310 residues in length. The vaccine candidate designed here displays acceptable population coverage (>65%) in different ethnicities as well as high probability of eliciting WT1 antibodies which both are pertinent goals in the context of appropriate multi-epitope vaccines. Various in silico analyses indicate that final vaccine is a qualified immunotherapy candidate capable of eliciting both CD4+ and CD8+ T cell responses.

Objectives Typhoid fever is caused by Salmonella enterica serovar Typhi. OmpC, OmpF and OmpA, the three major outer membrane proteins (OMPs), could serve as vaccine candidates. Methods The porins antigenicity was predicted in silico . The OMP genes were amplified, cloned and expressed. Sero-reactivities of the recombinant proteins purified by denaturing method were assayed by ELISA. BALB/c mice were immunized with the recombinant porins followed by bacterial challenge. Results Bacterial challenge of the animal model brought about antibody triggering efficacy of the antigen in OmpF > OmpC > OmpA order. Experimental findings validated the in silico results. None of the antigens had synergic or antagonistic effects on each other from immune system induction points of view. Despite their high immunogenicity, none of the antigens was protective. However, administration of two or three antigens simultaneously resulted in retardation of lethal effect. Porins, in addition to their specific functions, share common functions. Hence, they can compensate for each other's functions. Conclusions The produced antibodies could not eliminate the pathogenicity by blockade of one or some of the antigens. Porin antigens are not suitable vaccine candidates alone or in denatured forms. Native forms of the antigens maybe studied for protective immunogenicity.

Listeria monocytogenes , a facultative intracellular fast-growing Gram-positive food-borne pathogen, can infect immunocompromised individuals leading to meningitis, meningoencephalitis and septicaemias. From the pool of virulence factors of the organism, ActA, a membrane protein, has a critical role in the life cycle of L. monocytogenes . High mortality rate of listeriosis necessitates a sensitive and rapid diagnostic test for precise identification of L. monocytogenes . We used bioinformatic tools to locate a specific conserved region of ActA for designing and developing an antibody–antigen based diagnostic test for the detection of L. monocytogenes . A number of databases were looked for ActA related sequences. Sequences were analyzed with several online software to find an appropriate region for our purpose. ActA protein was found specific to Listeria species with no homologs in other organisms. We finally introduced a highly conserved region within ActA sequence that possess several antibody binding sites specific to L. monocytogenes . This protein sequence can serve as an antigen for designing a relatively cheap, sensitive, and specific diagnostic test for detection of L. monocytogenes.

Acinetobacter baumannii is a problematic nosocomial pathogen. The resistance to a wide range of antimicrobial agents, attributable to its biofilm phenotype, makes the treatment very difficult. Biofilm is a common feature of most pathogens. Biofilm associated proteins (Bap) are cellular surface components directly involved in biofilm formation process. The dearth of a fast precise diagnostic test and versatility of Bap sequences in A. baumannii were intuitions to design this study. In silico analysis is a reliable alternative to laborious experimental work in this connection. Databases were searched for an antigenic conserved region of Bap specific to A. baumannii. The region was selected based on alignments and propensity scales. Tertiary structure for this region was built and predicted B-cell epitopes were mapped on the surface of the built model. Our protein subunit was found to be a potential antigen, possessing several antigenic determinants, eliciting antibody. Hence this subunit could be used as a suitable agent for antibody-antigen based diagnostic test. This specific antigen can minimize laboratory errors in identification of A. baumannii and thus help clinicians to quick and precise diagnosis of the bacteria and initiatives to the treatment of the infection. Antigenicity of the region could also be explored for elicitation of antibody to protect the individuals exposed to A. baumannii.

Listeria monocytogenes causes listeriosis with mortality rate >20%. Listeriolysin-O (LLO), a pore-forming hemolysin, belongs to the family of cholesterol-dependent toxins (CDTX) and plays roles in the pathogenicity. In this study bioinformatic analyses were carried out on LLO sequence as a major immunodominant listerial antigen toward designing a DNA vaccine stimulating cytotoxic T-lymphocytes (CTLs). Mouse and human constructs were designed based on predicted T cell epitopes and MHC class I binders, which were then tandemly fused together. LLO-derived construct codons and a variety of critical gene expression efficiency parameters were optimized. Post-translational modifications such as glycosylation, phosphorylation were analysed. The constructs corresponded to LLO sequences of L. monocytogenes in BLAST search. Neither human nor mouse construct was allergen. Secretory pathway was location of the human construct that enhances immune induction and contribute to the efficacy of the vaccine candidate. mRNAs from optimized DNA sequences of both human and mouse constructs are more stable than the native and are suitable for initiation of translation. The constructs contain several sites for phosphorylation that could improve its degradation and subsequent entry into the MHC class I pathway. Addition of GPI anchor, myristoylation and ubiquitin signals or proline (P), glutamic acid (E), serine (S), threonine (T) (PEST)-like motifs at the N-terminal of constructs increase efficacy of the DNA vaccine. Close physical contact between the favorable immunogen and the suitable CpG oligodeoxynucleotides (CpG ODN) promotes immune response. Vectors for checking the expression of constructs in mammalian cells and for harboring the foreign genes as DNA vaccine are suggested.