Anti-OmpA antibodies as potential inhibitors of Acinetobacter baumannii biofilm formation, adherence to, and proliferation in A549 human alveolar epithelial cells.

Outer membrane protein A (OmpA) is a critical virulence factor in Acinetobacter baumannii, influencing adhesion, biofilm formation, host immune response, and host cell apoptosis. We investigated the invasion of A549 alveolar epithelial cells by A. baumannii and examined how anti-OmpA antibodies impact these interactions. OmpA was expressed and purified, inducing anti-OmpA antibodies in BALB/c mice. The potential toxicity of OmpA was evaluated in mice by analyzing histology from six organs. A549 cells were exposed to A. baumannii strains 19606 and a clinical isolate. Using cell culture and light microscopy, we scrutinized the effects of anti-OmpA sera on serum resistance, adherence, internalization, and proliferation of A. baumannii in A549 cells. The viability of A549 cells was assessed upon exposure to live A. baumannii and anti-OmpA sera. OmpA-induced antibody demonstrated potent bactericidal effects on both strains of A. baumannii. Both strains formed biofilms, which were reduced by anti-OmpA serum, along with decreased bacterial adherence, internalization, and proliferation in A549 cells. Anti-OmpA serum improved the survival of A549 cells post-infection. Pre-treatment with cytochalasin D hindered bacterial internalization, highlighting the role of actin polymerization in invasion. Microscopic examination revealed varied interactions encompassing adherence, apoptosis, membrane alterations, vacuolization, and damage. A549 cells treated with anti-OmpA serum exhibited improved structures and reduced damage. The findings indicate that A. baumannii can adhere to and proliferate within epithelial cells with OmpA playing a pivotal role in these interactions, and the complex nature of these interactions shapes the intricate course of A. baumannii infection in host cells.

Passive immunization with anti-FimA egg yolk antibodies (IgYs) mitigate Acinetobacter baumannii pneumonia in mice.

Acinetobacter baumannii is a formidable pathogen, characterized by high mortality rates and pan-drug-resistant strains. Current commercial antibiotics lack efficacy against drug-resistant variants, necessitating the search for alternative treatments. This study investigates the potential of egg yolk immunoglobulin (IgY) as a cost-effective biomolecule for passive protection against A. baumannii pneumonia. FimA (ABAYE2132), a key virulence factor involved in biofilm development and lung cell adherence, emerges as a promising antigen for triggering protective IgY production. Recombinant FimA was expressed, purified, and used for intramuscular immunization of laying White Leghorn hens. IgY antibodies were subsequently extracted from egg yolks, with their reactivity assessed through indirect ELISA. Neutropenic mice received intranasal administration of IgYs one hour prior to the challenge with a clinical A. baumannii isolate (10 ×LD50). The specific anti-FimA IgYs detected recombinant FimA and provided 100% protection against bacterial infection, while non-specific IgYs prolonged survival for up to 72 h. In contrast, control mice succumbed to infection within 24 h. Analysis of bacterial loads in lungs and spleens after 16 h reveals the following order: control > non-specific IgY > anti-FimA IgY. These findings highlight FimA as a suitable antigen for the development of protective IgYs against A. baumannii.

Enhanced immunoprotection against Acinetobacter baumannii infection: Synergistic effects of Bap and BauA in a murine model.

BACKGROUND: The rise of multi-drug resistant Acinetobacter baumannii poses a grave threat to hospital settings, resulting in increased mortality rates and garnering global attention. The formation of biofilms facilitated by biofilm-associated protein (Bap) and the iron absorption capabilities mediated by Baumannii acinetobactin utilization A (BauA) contribute to the persistence and survival of multidrug-resistant strains. In this study, we aimed to investigate the potential of disrupting the function of BauA and Bap simultaneously as a strategy for controlling A. baumannii. METHODS: Recombinant Bap and BauA were expressed, purified, and subcutaneously administered individually and in combination to BALB/c mice. Subsequently, mice were intraperitoneally challenged with A. baumannii, and the bacterial load and tissue damage in the spleen, lung, and liver were assessed. Serum samples were evaluated to determine antibody titers in surviving mice. RESULTS: Specific IgG antibodies were significantly increased. A combination of the antigens resulted in enhanced titer of specific IgGs in comparison to either BauA or Bap alone. The antibodies remained stable over a seven-month period. The combination of Bap and BauA exhibited superior immunoprotection against A. baumannii infection compared to individual administration, resulting in a further reduction in bacterial load in the liver, spleen, and lungs. The histopathological analysis demonstrated successful protection of the tissues against A. baumannii-induced damage upon administration of the two immunogens. CONCLUSIONS: The combination of Bap and BauA has the potential to target a broader range of A. baumannii strains, including those expressing either Bap or BauA, thereby increasing its efficacy against a diverse array of strains.

Clinical efficacy of probiotics in prevention of infectious diseases among hospitalized patients in ICU and non-ICU wards in clinical randomized trials: A systematic review.

Background and Aims: The present study aimed to review probiotics' clinical efficacy in preventing infectious diseases among hospitalized patients in ICU and non-ICU wards. Methods: A search of Medline, EMBASE, The Cochrane Library, Science Direct, Open Grey, and Google Scholar was conducted for eligible publications from 2002 to 2020 following the requirements outlined in the PRISMA guideline. The search strategy was based on the combination of the following terms: "probiotics," "prebiotics," "synbiotics," and "cross-infection." The logical operators "AND" (or the equivalent operator for the databases) and "OR" (e.g., probiotics OR prebiotics OR synbiotics) were used. Results: The results indicated that the probiotic consumption caused a significant reduction in antibiotic-associated diarrhea (AAD) and Clostridioides difficile infection (CDI) in 2/8 randomized clinical trials (RCTs) investigating AAD/CDI. Also, 5/12 clinical trials highlighted the considerable effects of probiotics on the reduction or prevention of ventilator associated pneumoniae (VAP), so the mean prevalence of VAP was lower in the probiotic group than in the placebo group. The total rate of nosocomial infections among preterm infants was nonsignificantly higher in the probiotic group compared to the control group. Conclusion: This systematic review shows that the administration of probiotics has moderate preventive or mitigating effects on the occurrence of VAP in ICU patients, CDI, AAD, and nosocomial infections among children. Consequently, applying antibiotics along with the proper probiotic species can be advantageous.

A two-protein cocktail elicits a protective immune response against Acinetobacter baumannii in a murine infection model.

PURPOSE: Due to its high drug resistance, Acinetobacter baumannii is a priority for new therapeutic measures like vaccines. In this study, the protectivity of a combination cocktail of Omp34 and BauA as a vaccine against A. baumannii was studied in a murine sepsis model. METHODS: The antibody titers were raised to Omp34 and BauA in BALB/c mice and assessed by indirect ELISA. The immunized mice were challenged with A. baumannii ATCC 19606. The bacterial loads in the liver, spleen, and lungs were also determined. RESULTS: A significant increase in survival of the immunized mice was noted. In active immunity, the survival rates in mice receiving Omp34 and BauA alone or in combination were 100%. A significant decrease in the bacterial load was observed in the spleens, livers, and lungs of vaccinated mice. Anti-BauA and anti-Omp34 sera crossly detected Omp34 and BauA respectively. The decrease in bacterial load in body organs of mice vaccinated with a combination of the two proteins was significantly higher than those of the single proteins in both actively and passively immunized mice. In passive immunity, the survival rate of mice receiving specific sera raised to the combination of these proteins was 85.7%. CONCLUSION: Higher protection by a combination of Omp34 and BauA than Omp34 or BauA could be attributed to targeting simultaneously both surface antigens indicating the synergistic effect of Omp34 and BauA as suitable vaccine candidates in the prevention or treatment of A. baumannii infections.

Synergistic immunoprotection by Oma87 and Bap against Acinetobacter baumannii sepsis model.

Acinetobacter baumannii is the leading cause of nosocomial infection. A surface protein commonly known as biofilm associate protein (Bap) has been identified in a bloodstream isolate of A. baumannii. Bap of A. baumannii is involved in intercellular adhesion within the mature biofilm. Outer membrane protein Acinetobacter 87 kDa (Oma87) or ß-barrel assembly machinery A (BamA) has been introduced as an immunogenic outer membrane protein via in silico reverse vaccinology. Current research examines the synergistic effect of immunization of mice with both recombinant proteins viz., Oma87 and Bap. Antibodies were raised to the proteins. The mice were challenged with A. baumannii ATCC 19606 and the bacterial burden was enumerated in the mice's livers, spleens, and lungs followed by histological examination. IgG levels significantly increased, and a significant (p < 0.0001) difference was observed between bacterial burdens in the internal organs of the actively and passively immunized groups. Female BALB/c mice weighing 20-25 g, were divided into 4 groups of 14 mice each viz., control, Oma87, Bap, Oma87-Bap groups. The proteins were individually immunogenic, but the combination of both proteins had a synergistic protection property. This is further supported by the histological examination. Based on the results, the combination of Oma87 and Bap may be considered a promising vaccine candidate against A. baumannii .

Pseudomonas aeruginosa PAO1 outer membrane vesicles-diphtheria toxoid conjugate as a vaccine candidate in a murine burn model.

Pseudomonas aeruginosa is an opportunistic pathogen considered a common cause of nosocomial infection with high morbidity and mortality in burn patients. Immunoprophylaxis techniques may lower the mortality rate of patients with burn wounds infected by P. aeruginosa; consequently, this may be an efficient strategy to manage infections caused by this bacterium. Several pathogenic Gram-negative bacteria like P. aeruginosa release outer membrane vesicles (OMVs), and structurally OMV consists of several antigenic components capable of generating a wide range of immune responses. Here, we evaluated the immunogenicity and efficacy of P. aeruginosa PA-OMVs (PA-OMVs) conjugated with the diphtheria toxoid (DT) formulated with alum adjuvant (PA-OMVs-DT + adj) in a mice model of burn wound infection. ELISA results showed that in the group of mice immunized with PA-OMVs-DT + adj conjugated, there was a significant increase in specific antibodies titer compared to non-conjugated PA-OMVs or control groups. In addition, the vaccination of mice with PA-OMVs-DT + adj conjugated generated greater protective effectiveness, as seen by lower bacterial loads, and eightfold decreased inflammatory cell infiltration with less tissue damage in the mice burn model compared to the control group. The opsonophagocytic killing results confirmed that humoral immune response might be critical for PA-OMVs mediated protection. These findings suggest that PA-OMV-DT conjugated might be used as a new vaccine against P. aeruginosa in burn wound infection.

Vaccination with a combination of planktonic and biofilm virulence factors confers protection against carbapenem-resistant Acinetobacter baumannii strains.

Acinetobacter baumannii is a multi-drug resistant pathogen with the ability to switch between planktonic and biofilm phenotypes. Although there is no vaccine against A. baumannii infections, many attempts have been made to develop vaccines using planktonic or biofilm antigens. To cover the different phenotypes of A. baumannii during growth and attachment, we combined planktonic upregulated antigens of iron receptors with biofilm upregulated antigens of pilus rods and evaluated immune responses and protective efficacies of the combined vaccine using lethal and sub-lethal murine sepsis models. The results showed that the combined vaccine elicited high IgG antibody titers and conferred protection against lethal doses of two Carbapenem-resistant high adherent A. baumannii strains. Complete bacterial clearance from all the affected tissues of the mice challenged with A. baumannii was an excellent achievement with our quadrivalent immunogen. These results demonstrate both planktonic and biofilm antigens are important during antigen selection for vaccine design.

Combination of BauA and OmpA elicit immunoprotection against Acinetobacter baumannii in a murine sepsis model.

AIMS: 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. METHODS AND RESULTS: 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. CONCLUSIONS: Combination of BauA and OmpA enhances immunoprotection against A. baumannii infections.

Hybrid antigens expressing surface loops of BauA from Acinetobacter baumannii are capable of inducing protection against infection.

Acinetobacter baumannii is a human bacterial pathogen of increasing concern in clinical settings due to the emergence of antibiotic resistant strains and the lack of effective therapeutics. Researchers have been exploring new treatment options such as novel drug candidates and vaccines to prevent severe infections and mortality. Bacterial surface antigens that are essential to A. baumannii for acquiring micronutrients (e.g. iron, zinc) from nutrient restricted environments are being considered as targets for vaccines or immunotherapy due to their crucial role for growth and pathogenesis in the human host. BauA, the outer membrane receptor for the siderophore acinetobactin was targeted for vaccine development in this study. Due to challenges in the commercial production of membrane proteins for vaccines, a novel hybrid antigen method developed by our group was used. Exposed loops of BauA were selected and displayed on a foreign scaffold to generate novel hybrid antigens designed to elicit an immune response against the native BauA protein. The potential epitopes were incorporated into a scaffold derived from the C-lobe of Neisseria meningitidis transferrin binding protein B (TbpB), named the loopless C-lobe (LCL). Hybrid proteins displaying three selected loops (5, 7 and 8) individually or in combination were designed and produced and evaluated in an A. baumannii murine sepsis model as vaccine antigens. Immunization with the recombinant BauA protein protected 100% of the mice while immunization with hybrid antigens displaying individual loops achieved between 50 and 100% protection. The LCL scaffold did not induce a protective immune response, enabling us to attribute the observed protection elicited by the hybrid antigens to the displayed loops. Notably, the mice immunized with the hybrid antigen displaying loop 7 were completely protected from infection. Taken together, these results suggest that our hybrid antigen approach is a viable method for generating novel vaccine antigens that target membrane surface proteins necessary for bacterial growth and pathogenesis and the loop 7 hybrid antigen can be a foundation for approaches to combat A. baumannii infections.

Immunoprotective characterization of egg yolk immunoglobulin raised to loop 3 of outer membrane protein 34 (Omp34) in a murine model against Acinetobacter baumannii.

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 × LD50 of a clinical isolate of A. baumannii. The specific IgYs recognized recombinant Omp34 (P < 0.0001) as well as WC of A. baumannii (P < 0.05). The survival rate of mice that received anti- Omp34L3X5 or anti-Omp34 IgYs was 83.33 % and 100 % respectively. All control mice died within 24 h while mice that received non-specific IgYs died within 72 h. After 24 h, bacterial load in the lung of mice received non-specific IgYs, anti-Omp34L3X5 or anti-Omp34 IgYs were 2.03 × 108, 2.2 × 108, and 1.93 × 108 CFU/organ respectively. Bacterial load in the spleen of mice received non-specific IgYs, anti-Omp34L3X5 or anti-Omp34 IgYs were 1.03 × 108, 7.8 × 107, and 6.3 × 107 CFU/organ respectively. Bacterial load in lung and spleen of control mice were 3.03 × 109 and 1.45 × 108 CFU/organ respectively.

Immunogenicity of loop 3 of Omp34 from A. Baumannii in loopless C-lobe of TbpB of N. meningitidis.

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.

Specific egg yolk antibody raised to biofilm associated protein (Bap) is protective against murine pneumonia caused by Acinetobacter baumannii.

Acinetobacter baumannii easily turns into pan drug-resistant (PDR) with a high mortality rate. No effective commercial antibiotic or approved vaccine is available against drug-resistant strains of this pathogen. Egg yolk immunoglobulin (IgY) could be used as a simple and low-cost biotherapeutic against its infections. This study evaluates the prophylactic potential of IgY against A. baumannii in a murine pneumonia model. White Leghorn hens were immunized with intramuscular injection of the recombinant biofilm-associated protein (Bap) from A. baumannii on days 0, 21, 42, and 63. The reactivity and antibiofilm activity of specific IgYs raised against the Bap was evaluated by indirect ELISA and a microtiter plate assay for biofilm formation. The IgYs against Bap were able to decrease the biofilm formation ability of A. baumannii and protect the mice against the challenge of A. baumannii. IgYs antibody raised here shows a good antigen-specificity and protectivity which can be used in passive immunotherapy against A. baumannii. In conclusion, the IgY against biofilm-associated protein proves prophylactic in a murine pneumonia model.

BauA and Omp34 surface loops trigger protective antibodies against Acinetobacter baumannii in a murine sepsis model.

The complexity of treating Acinetobacter baumannii infections with the newly developed resistant strains has led researchers to confront this pathogen by developing vaccines. In this study, we used two important virulence factors of A. baumannii to elicit immunity against the A. baumannii. The immunogenic loops were from Baumannii acinetobactin utilization A (BauA) and 34kD outer membrane protein (Omp34). C-lobe derivative of the TbpB surface lipoprotein was used to display the superficial epitopes of the TbpA receptor protein of Neisseria meningitidis. The resulting loopless C-lobe (LCL) with implanted nucleotide sequences of the immunogenic loops from BauA and Omp34 was used as a hybrid antigen. The hybrid antigens were expressed in the E. coli and were used to immunize mice. The mice were challenged with a clinical isolate of A. baumannii (ABI022). Immunization with the hybrid antigens of the BauA loop 7 (BauAL7P3), Omp34 loop 3 Omp34L3P1, and the combination of both loops (BauAL7P3Omp34L3P1) brought about 42.86%, 42.86%, and 71.43% protection against A. baumannii infection. Histopathological findings in the immunized mice showed bronchioles clear from inflammatory cells and normal texture of the spleen and liver. The findings support the use of a multivalent vaccine to induce broadly reactive antibody responses against heterologous A. baumannii strains.

Immunity induced by valine-glycine repeat protein G imparts histoprotection of vital body organs against Acinetobacter baumannii.

BACKGROUND: Efforts toward the development of an effective vaccine against Acinetobacter baumannii, one of the most notorious nosocomial pathogens, are still ongoing. In this regard, virulence factors are interesting targets. Type VI secretion system (T6SS) participates in the pathogenicity of A. baumannii. VgrG is a crucial component of T6SS prevalent among A. baumannii strains. This study was conducted to evaluate the immunoprotectivity of recombinant VgrG (rVgrG) cloned and over-expressed in Escherichia coli BL21 (DE3). BALB/c mice were immunized with the purified rVgrG. Specific anti-VgrG IgG titers were assessed by ELISA. Actively and passively immunized mice were challenged with lethal doses of A. baumannii ATCC 19606. The survival rate, the bacterial burden, and histopathology of tissues in infected mice were examined. RESULTS: Anti-VgrG IgG (p < 0.0001) was significantly increased in immunized mice. No death was seen in actively immunized mice infected with the lethal dose (LD) of 1.9 × 108 CFU of A. baumannii ATCC 19606 within 72 h. Challenge with 2.4 × 108 CFU of the pathogen showed a 75% survival rate. All immunized mice infected with 3.2 × 108 CFU of the pathogen died within 12 h. In passive immunization, no death was observed in mice that received LD of the bacteria incubated with the 1:250 dilution of the immune sera. An increased number of neutrophils around the peribronchial and perivascular areas were seen in unimmunized mouse lungs while passively immunized mice revealed moderate inflammation with infiltration of mixed mononuclear cells and neutrophils. The livers of the unimmunized mice showed inflammation and necrosis in contrast to the livers from immunized mice. Hyperplasia of the white pulp and higher neutrophils were evident in the spleen of unimmunized mice as against the normal histology of the immunized group. CONCLUSIONS: VgrG is a protective antigen that could be topologically accessible to the host antibodies. Although VgrG is not sufficient to be assigned as a stand-alone antigen for conferring full protection, it could participate in multivalent vaccine developments for elevated efficacy.

Anti-Omp34 antibodies protect against Acinetobacter baumannii in a murine sepsis model.

Acinetobacter baumannii, an opportunistic extracellular pathogen is one of the major causes of nosocomial infections. Omp34, also known as Omp33-36, is a bacterial porin protein involved in the virulence and fitness of this pathogen by adhesion to the host cell. This antigen nominated as an appropriate candidate for immunization against A. baumannii. In this study, the expression of the recombinant Omp34 (rOmp34) was carried out in E. coli BL21 (DE3). The immunogenicity of the rOmp34 in A. baumannii was studied in a murine sepsis model. Antibody response in mice injected with the recombinant protein was assessed using indirect ELISA. Bactericidal activity of rOmp34-immunized mice sera (1:10 dilution) against A. baumannii ATCC 19606 after 0, 1, 2, 4, and 8 h of incubation at 37 °C was assessed. In addition to survival rate, load of bacteria in liver and spleen of the infected mice were evaluated. A high titer of specific antibody equivalent to optical density of 1.54 ± 0.06 against rOmp34 was elicited in the immunized mice sera. Viability of the A. baumannii incubated 8 h with immunized mice sera was 64%. Homogenized liver and spleen samples of the control mice challenged with A. baumannii were loaded with 8 × 103 and 9 × 103 CFU per gram tissue respectively 48 h post-challenge as against complete clearance of A. baumannii in the immunized group. The protective immunity was achieved by challenging the mice groups with 5 × LD50 of live A. baumannii. Omp34 can be nominated as an immunogen that can bring about protection against Acinetobacter baumannii.

Immunoprotectivity of Valine-glycine repeat protein G, a potent mediator of pathogenicity, against Acinetobacter baumannii.

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.

A conserved region of Acinetobacter trimeric autotransporter adhesion, Ata, provokes suppression of Acinetobacter baumannii virulence.

The Acinetobacter trimeric autotransporter adhesin (Ata) is an important virulence factor. The conserved region from the genomic sequence of a 6777bp/2258 amino acid of Acinetobacter baumannii ATCC®19606™ ata was explored. A 263aa of the C-terminal of Ata (rcAta263) was expressed. The effect of rcAta263 on A. baumannii virulence was studied in a murine model. IgG and IgA were elicited and the mice groups challenged with A. baumannii showed significant survival rates from 66 to 100%. The bacterial loads were determined in the spleens, livers, and lungs of both control and test groups. The adhesion rate of A. baumannii to A549 cells in the presence of serum, cytotoxicity, mutagenicity, and biofilm disruption potential of rcAta263 were determined. Intraperitoneally challenged groups showed a significantly reduced bacterial load in the organs of the immunized mice. Intranasal challenge reduced 4 logs of bacterial CFU/g in the test group. The immunized mice sera reduced adherence of A. baumannii to A549 cells to 80%. No cytotoxic or mutagenic effect was detected. Biofilm disruption was significantly increased in the presence of immunized mice sera. Immunization with the conserved region of Ata significantly combats the virulence of A. baumannii which could be considered as a therapeutic strategy to control A. baumannii infections.

Evaluation of Antibiotic Resistance Pattern, Alginate and Biofilm Production in Clinical Isolates of Pseudomonas aeruginosa.

BACKGROUND: Pseudomonas aeruginosa is one of the most common opportunistic bacteria causing nosocomial infections, which has significant resistance to antimicrobial agents. This bacterium is a biofilm and alginate producer. Biofilm increases the bacterial resistance to antibiotics and the immune system. Therefore, the present study was conducted to investigate the biofilm formation, alginate production and antimicrobial resistance patterns in the clinical isolates of P. aeruginosa. METHODS: One hundred isolates of P. aeruginosa were collected during the study period (from Dec 2017 to Jul 2018) from different clinical samples of the patients admitted to Milad and Pars Hospitals at Tehran, Iran. Isolates were identified and confirmed by phenotypic and genotypic methods. Antimicrobial susceptibility was specified by the disk diffusion method. Biofilm formation and alginate production were measured by microtiter plate and carbazole assay, respectively. RESULTS: Sixteen isolates were resistant to all the 12 studied antibiotics. Moreover, 31 isolates were Multidrug-Resistant (MDR). The highest resistance rate was related to ofloxacin (36 isolates) and the least resistance was related to piperacillin-tazobactam (21 isolates). All the isolates could produce the biofilm and alginate. The number of isolates producing strong, medium and weak biofilms was equal to 34, 52, and 14, respectively. Alginate production was more than 400 µg/ml in 39 isolates, 250-400 µg/ml in 51 isolates and less than 250 µg/ml in 10 isolates. CONCLUSION: High prevalence of MDR, biofilm formation, and alginate production were observed among the clinical isolates of P. aeruginosa. The results also showed a significant relationship between the amount of alginate production and the level of biofilm formation.

Protective response against Acinetobacter baumannii with ferric iron receptors HemTR-BauA in a murine sepsis model.

Aim: Iron uptake and metabolism pathways are promising targets in vaccine development as an alternative strategy for antibiotics. Methods & methods: HemTR, a putative heme receptor of Acinetobacter baumannii, was expressed and its protectivity against A. baumannii was determined singly or in combination with the siderophore receptor, BauA, in mice. Results: High level of IgG was elicited. There was a delay in mice mortality with reduced bacterial loads in internal organs in the sublethal challenge. Protection was better in the HemTR-BauA group in both lethal and sublethal challenges. Passive transfer of anti-HemTR and anti-BauA partially protected mice against A. baumannii infection. Conclusion: HemTR in combination with other iron receptors could contribute to the development of protective vaccines against A. baumannii.