Isolation and characterization of a VHH targeting the Acinetobacter baumannii cell surface protein CsuA/B

Acinetobacter baumannii is a Gram-negative bacterial pathogen that exhibits high intrinsic resistance to antimicrobials, with treatment often requiring the use of last-resort antibiotics. Antibiotic-resistant strains have become increasingly prevalent, underscoring a need for new therapeutic interventions. The aim of this study was to use A. baumannii outer membrane vesicles as immunogens to generate single-domain antibodies (VHHs) against bacterial cell surface targets. Llama immunization with the outer membrane vesicle preparations from four A. baumannii strains (ATCC 19606, ATCC 17961, ATCC 17975, and LAC-4) elicited a strong heavy-chain IgG response, and VHHs were selected against cell surface and/or extracellular targets. For one VHH, OMV81, the target antigen was identified using a combination of gel electrophoresis, mass spectrometry, and binding studies. Using these techniques, OMV81 was shown to specifically recognize CsuA/B, a protein subunit of the Csu pilus, with an equilibrium dissociation constant of 17 nM. OMV81 specifically bound to intact A. baumannii cells, highlighting its potential use as a targeting agent. We anticipate the ability to generate antigen-specific antibodies against cell surface A. baumannii targets could provide tools for further study and treatment of this pathogen.

Automated summary

The aim of this study was to generate single-domain antibodies (VHHs) against cell surface targets of Acinetobacter baumannii using the bacterium's outer membrane vesicles as immunogens. Llama immunization with the vesicle preparations resulted in a strong immune response and the selection of VHHs against cell surface and/or extracellular targets. One VHH, OMV81, specifically recognized the protein subunit CsuA/B of the Csu pilus with high affinity. OMV81 also bound to intact A. baumannii cells, suggesting its potential as a targeting agent.