A hypothetical adhesin protein induces anti-biofilm antibodies against multi-drug resistant Acinetobacter baumannii

Hypothetical adhesin CAM87009.1 formulated in alum or biogenic silver nanoparticles protects mice from lethal infection by multidrug-resistant Acinetobacter baumannii

Due to its antimicrobial resistance characteristics, the World Health Organization (WHO) classifies A. baumannii as one of the critical priority pathogens for the development of new therapeutic strategies. Vaccination has been approached as an interesting strategy to overcome the lack of effective antimicrobials and the long time required to develop and approve new drugs. In this study, we aimed to evaluate as a vaccine the hypothetical adhesin protein CAM87009.1 in its recombinant format (rCAM87009.1) associated with aluminum hydroxide (Alhydrogel®) or biogenic silver nanoparticles (bio-AgNP) as adjuvant components against lethal infection by A. baumannii MDR strain. Both vaccine formulations were administered in three doses intramuscularly in BALB/c murine models and the vaccinated animals were tested in a challenge assay with A. baumannii MDR strain (DL100). rCAM87009.1 protein associated with both adjuvants was able to protect 100 % of animals challenged with the lethal strain during the challenge period. After the euthanasia of the animals, no A. baumannii colonies were detected in the lungs of animals vaccinated with the rCAM87009.1 protein in both formulations. Since the first immunization, high IgG antibody titers were observed (1:819,200), with results being statistically similar in both vaccine formulations evaluated. rCAM87009.1 associated with both adjuvants was capable of inducing at least one class of isotypes associated with the processes of neutralization (IgG2b and IgA for bio-AgNP and Alhydrogel®, respectively), opsonization (IgG1 in both vaccines) and complement activation (IgM and IgG3 for bio-AgNP and Alhydrogel®, respectively). Furthermore, reduced tissue damage was observed in animals vaccinated with rCAM87009.1 + bio-AgNP when compared to animals vaccinated with Alhydrogel®. Our results indicate that the rCAM87009.1 protein associated with both bio-AgNP and Alhydrogel® are combinations capable of promoting immunity against infections caused by A. baumannii MDR. Additionally, we demonstrate the potential of silver nanoparticles as alternative adjuvant molecules to the use of aluminum salts.

Non-antibiotic prevention and treatment against Acinetobacter baumannii infection: Are vaccines and adjuvants effective strategies?

Acinetobacter baumannii (A. baumannii) is a Gram-negative opportunistic pathogen widely attached to the surface of medical instruments, making it one of the most common pathogens of nosocomial infection, and often leading to cross-infection and co-infection. Due to the extensive antibiotic and pan-resistance, A. baumannii infection is facing fewer treatment options in the clinic. Therefore, the prevention and treatment of A. baumannii infection have become a tricky global problem. The requirement for research and development of the new strategy is urgent. Now, non-antibiotic treatment strategies are urgently needed. This review describes the research on A. baumannii vaccines and antibacterial adjuvants, discusses the advantages and disadvantages of different candidate vaccines tested in vitro and in vivo, especially subunit protein vaccines, and shows the antibacterial efficacy of adjuvant drugs in monotherapy.

Safety and Prophylactic Efficacy of Liposome-Based Vaccine against the Drug-Resistant Acinetobacter baumannii in Mice

In recent years, the emergence of multidrug-resistant Acientobacter baumannii has greatly threatened public health and depleted our currently available antibacterial armory. Due to limited therapeutic options, the development of an effective vaccine formulation becomes critical in order to fight this drug-resistant pathogen. The objective of the present study was to develop a safe vaccine formulation that can be effective against A. baumannii infection and its associated complications. Here, we prepared liposomes-encapsulated whole cell antigens (Lip-WCAgs) as a vaccine formulation and investigated its prophylactic efficacy against the systemic infection of A. baumannii. The immunization with Lip-WCAgs induced the higher production of antigen-specific antibody titers, greater lymphocyte proliferation, and increased secretion of Th1 cytokines, particularly IFN-γ and IL-12. Antisera from Lip-WCAgs-immunized mice showed the utmost bactericidal activity and potently inhibited the biofilm formation by A. baumannii. Interestingly, Lip-WCAgs-induced immune response was translated in in vivo protection studies as the immunized mice exhibited the highest resistance to A. baumannii infection. Mice in the group immunized with Lip-WCAgs had an 80% survival rate and a bacterial burden of 5464 ± 1193 CFUs per gram of the lung tissue, whereas the mice immunized with IFA-WCAgs had a 50% survival rate and 51,521 ± 8066 CFUs. In addition, Lip-WCAgs vaccinated mice had lower levels of the inflammatory markers, including CRP, IL-6, IL-1β, and TNF-α. The findings of this study suggest that Lip-WCAgs may be considered a potential vaccine formulation to protect individuals against A. baumannii infection.