Evaluation of the Trimeric Autotransporter Ata as a Vaccine Candidate against Acinetobacter baumannii Infections

Abstract

Acinetobacter baumannii is a multidrug-resistant (MDR) nosocomial pathogen for which immunotherapeutic alternatives are needed. We previously identified a surface autotransporter of A. baumannii, Ata, that bound to various extracellular matrix/basal membrane proteins and was required for full virulence, biofilm formation, and the adhesion of A. baumannii to collagen type IV. We show here that Ata binding to collagen type IV was inhibited by antibodies to Ata. In addition, in the presence of complement and polymorphonuclear cells (PMNs), antibodies to Ata were highly opsonic against A. baumannii ATCC 17978 and showed low to moderate killing activity against four heterologous A. baumannii strains, whereas in the absence of PMNs, antibody to Ata efficiently promoted complement-dependent bactericidal killing of all of the tested A. baumannii isolates. Using a pneumonia model of infection in both immunocompetent and immunocompromised mice, we found that, compared to normal rabbit sera, antisera to Ata significantly reduced the levels of A. baumannii ATCC 17978 and two MDR strains in the lungs of infected mice. The ability of Ata to engender anti-adhesive, bactericidal, opsonophagocytic, and protective antibodies validates its potential use as an antigenic target against MDR A. baumannii infections.

Physiology and Pathology of Multidrug-Resistant Bacteria: Antibodies- and Vaccines-Based Pathogen-Specific Targeting

“…Rabbit sera from Ata vaccination can opsonize A. baumannii isolates efectively in complement and polymorphonuclear cells dependent manners [181]. Moreover, the rabbit sera can signiicantly lower the burden of mice lung infection from MDR A. baumannii strains, showing that Ata is one more potential vaccine target [181].…”

Identification of novel vaccine candidates againstAcinetobacter baumanniiusing reverse vaccinology

“…11 Their respective genes were successfully expressed in E. coli as shown in Figure 3. After single-step purification using Ni-affinity chromatography, highly-purified OmpK, FKIB, and Ompp1 (>95% purity) were obtained and their purity was confirmed by SDS-PAGE (Fig.…”

“…11,30,31 Briefly, mice (n D 5/group) were immunized under isoflurane inhalation anesthesia with recombinant antigens (OmpK, FKIB and Ompp1 at 3 £ 3 ug or 3 £ 10 mg/mouse) at 2-week intervals on days 0, 14, and 28. The initial vaccination was performed subcutaneously (s.c.) with individual recombinant protein emulsified with complete Freund's adjuvant (CFA) (Sigma), whereas for the next 2 immunizations, immunogens were formulated with incomplete Freund's adjuvant (IFA) (Sigma).…”

“…They include outer membrane vesicles (OMVs), outer membrane protein A (OmpA), auto-transporter (Ata), biofilm-associated protein (Bap), K1 capsular polysaccharide and Poly-N-acetyl-b-(1-6)-glucosamine (PNAG). [7][8][9][10][11][12][13][14] The sequence variability of these antigens and their absence in the circulating Ab strains may result poor cross-protective efficacy against HAI caused by new emerging Ab strains that may possibly mutate under selective immunological pressure and down-regulate the target antigens. In our hand, recombinant OmpA and a truncated fragment of Bap have been tested and found no protection in mouse pneumonia challenge studies; only inactivated Ab and/or PNAG-protein conjugate showed good protection in the mouse pneumonia challenge model (Chong et al, unpunished results).…”

“…In order to identify novel antigens; we excluded proteins which had been tested and found to be not protective in our hands. Our current approach may have failed to identify potential vaccine immunogens, such as biofilm associated protein (Bap, ABAYE0792), 12 trimeric autotranspoter (Ata), 11 and other unknown putative proteins that could play critical role in A. baumannii pathogenesis. In addition, a limitation in our approach is the fact that immuno-proteomic data could be influenced by different culture conditions such as growing the pathogen in clinically relevant media reflecting the infection environment.…”