Targeting Omp-A Protein of Acinetobacter Baumannii with the Bio-Active Compounds from Azadirachta Indica - an in-silico Approach

Background: Acinetobacter baumannii is a gram negative bacterium which is typically short, round, coccobacillus and was named after the bacteriologist Paul Baumann. It is an emerging dental pathogen since it acquires drug resistance and expression of several virulence genes. It is an opportunistic pathogen in humans, affecting people with compromised immune systems. Acinetobacter baumannii is an arising nosocomial microorganism causing serious complications because of the propensity of its multi-drug resistant property. Aim: The aim of the present study was to target omp-A protein of Acinetobacter baumannii with the bio active compounds from Azadirachta indica an in-silico approach. Materials and Methods: The crystal structure of ompA protein was obtained from the PDB protein data bank. The structures of the bio-active derivatives of A. indica were obtained from the chemsketch software. The generated 3D structures were then optimised. Auto Dock instrument was utilized for docking investigation to interpret the affinity between bio-compounds of A. indica against ompA protein of A. baumannii. Results: The 3D crystal structure of OmpA-like domain from A.baumannii was retrieved from PDB database and its PDB ID was 3TD3 – A chain. 3D Structure of OmpA visualization using Biovia-Discovery studio visualizer. The 2D structure of compounds from Azadirachta indica was drawn using ACD chemsketch and saved in MDL-mol format and converted to PDB format using open babel converter. The final docked structures for the drug ligand interactions were assessed for their binding energies and hydrogen bonds. Conclusion: The present study had achieved the anti-biofilm inhibitory effect of imidazole-2-carboxylic acid from A. indica exhibiting a great interaction between activity with ompA utilizing computational investigation.

Screening and Analysis of Anaplasma marginale Tunisian Isolates Reveal the Diversity of lipA Phylogeographic Marker and the Conservation of OmpA Protein Vaccine Candidate

Bovine anaplasmosis caused by Anaplasma marginale is a disease responsible for serious animal health problems and great economic losses all over the world. Thereby, the identification of A. marginale isolates from various bioclimatic areas in each country, the phylogeographic analysis of these isolates based on the most informative markers, and the evaluation of the most promising candidate antigens are crucial steps in developing effective vaccines against a wide range of A. marginale strains. In order to contribute to this challenge, a total of 791 bovine samples from various bioclimatic areas of Tunisia were tested for the occurrence of A. marginale DNA through msp4 gene fragment amplification. Phylogeographic analysis was performed by using lipA and sucB gene analyses, and the genetic relationship with previously characterized A. marginale isolates and strains was analyzed by applying similarity comparison and phylogenetic analysis. To evaluate the conservation of OmpA protein vaccine candidate, almost complete ompA nucleotide sequences were also obtained from Tunisian isolates, and various bioinformatics software were used in order to analyze the physicochemical properties and the secondary and tertiary structures of their deduced proteins and to predict their immunodominant epitopes of B and T cells. A. marginale DNA was detected in 19 bovine samples (2.4%). Risk factor analysis shows that cattle derived from subhumid bioclimatic area were more infected than those that originated from other areas. The analysis of lipA phylogeographic marker indicated a higher diversity of Tunisian A. marginale isolates compared with other available worldwide isolates and strains. Molecular, phylogenetic, and immuno-informatics analyses of the vaccine candidate OmpA protein demonstrated that this antigen and its predicted immunodominant epitopes of B and T cells appear to be highly conserved between Tunisian isolates and compared with isolates from other countries, suggesting that the minimal intraspecific modifications will not affect the potential cross-protective capacity of humoral and cell-mediated immune responses against multiple A. marginale worldwide strains.

Iron-Rich Conditions Induce OmpA and Virulence Changes of Acinetobacter baumannii

Background: Iron ions affect the expression of outer membrane protein A (OmpA), a major pathogenic protein in Acinetobacter baumannii.Objective: To analyze the effect of iron ions on the expression of the OmpA protein of A. baumannii and explore its association with the virulence of OmpA.Methods: Site-directed mutagenesis was used to construct ompA gene deletion strains and gene repair strains. The OmpA protein expression of A. baumannii under culture with different contents of iron ions was detected. The virulence of A. baumannii with different OmpA protein expression levels were evaluated in macrophages and mice.Results: OmpA protein levels of the three strains were enhanced under iron-rich conditions. They were reduced in the presence of the iron-chelating agent 2,2′-bipyridine. A. baumannii wild type and + ompA had a remarkable toxic effect on RAW246.7 macrophages (P < 0.05). In contrast, the ΔompA had a significantly reduced toxic effect on RAW246.7 macrophages (P < 0.05). The levels of the inflammatory factors IL-1β, IL-6, IL-8, and TNFα in the mice spleen were significantly increased in the + ompA strain treatment group compared with the ΔompA strain group (all P < 0.05). In addition, the levels were higher in the presence of iron ions than in the presence of the chelating agent.Conclusion: Iron-rich conditions increase the OmpA protein expression of A. baumannii. Strains with high OmpA protein expression were more invasive, which may be a key determinant of A. baumannii infection and pathogenicity. Iron control strategies might be used for the management of A. baumannii.

OmpA Protein-Deficient Acinetobacter baumannii Outer Membrane Vesicles Trigger Reduced Inflammatory Response

Multidrug resistant Acinetobacter baumannii shows a growing number of nosocomial infections worldwide during the last decade. The outer membrane vesicles (OMVs) produced by this bacterium draw increasing attention as a possible treatment target. OMVs have been implicated in the reduction of antibiotic level in the surrounding environment, transfer of virulence factors into the host cells, and induction of inflammatory response. Although the evidence on the involvement of OMVs in A. baumannii pathogenesis is currently growing, their role during inflammation is insufficiently explored. It is likely that bacteria, by secreting OMVs, can expand the area of their exposure and prepare surrounding matrix for infection. Here, we investigated the impact of A. baumannii OMVs on activation of macrophages in vitro. We show that OmpA protein present in A. baumannii OMVs substantially contributes to the proinflammatory response in J774 murine macrophages and to the cell death in both lung epithelium cells and macrophages. The loss of OmpA protein in OMVs, obtained from A. baumannii ∆ompA mutant, resulted in the altered expression of genes coding for IL-6, NLRP3 and IL-1β proinflammatory molecules in macrophages in vitro. These results imply that OmpA protein in bacterial OMVs could trigger a more intense proinflammatory response.

Production of monoclonal antibody against Ompa protein of Candidatus Liberibacter asiaticus causing citrus greening disease

Citrus Greening, also known as HuangLongbing (HLB), is considered one of the most dangerous citrus diseases, and limiting the production of citrus trees all over the world. Production of antibodies against Ompa protein of Candidatus Liberibacter asiaticus (CLas) for detection of citrus greening disease is considered as promising research direction. In this study, for the purpose of producting antibodies against Ompa of CLas, we firstly used the camel VHH antibody library for screening VHH antibodies against Ompa using phage-display technique. Next, phages which had strong interaction with Ompa as shown in ELISA were selected for phagemid isolation and the DNA fragments encoding VHH antibodies were sequenced. The DNA fragment encoding the best VHH antibody was then selected and inserted into the expression vector pET-21a (+), then cloned in Ecoli DH5α strain and expressed in BL21 (DE3) strain. The expression of VHH antibodies against Ompa was optimized at different temperatures with an inductive concentration of 0.1 M IPTG. Anti-Ompa VHH antibodies were purified under denatured conditions then re-folded. The biological activity of the VHH antibody with Ompa antigen was assessed by indirect-ELISA reaction. Results indicated that the VHH antibody had a very strong interaction with the Ompa antigen. This opens up the prospect of applying VHH antibody in the detection of citrus greening disease.

Immunoprotective evaluation of Escherichia coli outer membrane protein A against the main pathogens of animal mastitis

Purpose: To evaluate prokaryotic expression of the Escherichia coli (E. coli) outer membrane protein A (OmpA) and its immunoprotective function against the main pathogens of animal mastitis.Methods: A molecular cloning method was used to develop a prokaryotic strain expressing OmpA protein, which was purified by Ni-affinity chromatography. Polyclonal antiserum was generated in mice immunized with OmpA protein. Enzyme-linked immunosorbent assay (ELISA) and western blotting were used to determine the titer and verify anti-OmpA serum specificity, respectively. Interaction between OmpA antiserum and main pathogens of animal mastitis was verified by ELISA and a pull-down method. The immune protective function of OmpA protein was evaluated in mice challenged with pathogens of animal mastitis. Optimal fermentation conditions to produce OmpA protein were determined by the L9(34) orthogonal test.Results: A prokaryotic strain expressing OmpA protein was developed, and purified OmpA was used to develop a mouse polyclonal antibody. The anti-OmpA serum exhibited high specificity and a titer of 1:1600. Anti-OmpA serum directly interacted with E. coli and Staphylococcus aureus (S. aureus). OmpA demonstrated a significant immune protective function of 58.33 % against E. coli and 46.15 % against S. aureus. The optimal conditions for expressing fermentation OmpA were a strain absorbance of 0.5 at a wavelength of 600 nm, IPTG final concentration of 0.3 mmol/L, induction time of 12 h, and induction temperature of 28 °C.Conclusion: OmpA possesses selective immunogenicity and a significant immune protective effect against the main pathogens of animal mastitis. The results suggest that OmpA may potentially be used as a vaccine for animal mastitis. Keywords: E. coli, OmpA protein, Immunoprotection, Animal mastitis, Protein fermentation

The Mutation of Conservative Asp268 Residue in the Peptidoglycan-Associated Domain of the OmpA Protein Affects Multiple Acinetobacter baumannii Virulence Characteristics

Acinetobacter baumannii is a nosocomial human pathogen of increasing concern due to its multidrug resistance profile. The outer membrane protein A (OmpA) is an abundant bacterial cell surface component involved in A. baumannii pathogenesis. It has been shown that the C-terminal domain of OmpA is located in the periplasm and non-covalently associates with the peptidoglycan layer via two conserved amino acids, thereby anchoring OmpA to the cell wall. Here, we investigated the role of one of the respective residues, D268 in OmpA of A. baumannii clinical strain Ab169, on its virulence characteristics by complementing the ΔompA mutant with the plasmid-borne ompAD268A allele. We show that while restoring the impaired biofilm formation of the ΔompA strain, the Ab169ompAD268A mutant tended to form bacterial filaments, indicating the abnormalities in cell division. Moreover, the Ab169 OmpA D268-mediated association to peptidoglycan was required for the manifestation of twitching motility, desiccation resistance, serum-induced killing, adhesion to epithelial cells and virulence in a nematode infection model, although it was dispensable for the uptake of β-lactam antibiotics by outer membrane vesicles. Overall, the results of this study demonstrate that the OmpA C-terminal domain-mediated association to peptidoglycan is critical for a number of virulent properties displayed by A. baumannii outside and within the host.