Breine, A.; Jooris, E.; Valcek, A.; Van Meerbeek, S.; Pardon, E.; Van Haver, D.; Timmerman, E.; Impens, F.; Steyaert, J.; Remaut, H.; Van Molle, I.; Gheorghiu, M.; Tudor, D.; David, S.; Gheorghiu, E.; Van der Henst, C.

Acinetobacter baumannii is a top-priority, ESKAPE pathogen that poses a major challenge to human health. The pathogen is difficult to combat due to its extensive arsenal of antibiotic resistance and its protective polysaccharide capsule. In addition, A. baumannii isolates are highly heterogeneous, which complicates the development of rapid detection methods or novel targeted therapeutic approaches. Here, we discovered and characterized a new biotechnological tool, the nanobody H7 (NbH7), along with its conserved target, the surface-exposed Omp25 protein of A. baumannii, and elucidated their interaction at the molecular level. Moreover, we demonstrate that NbH7-functionalized magnetic beads enable selective and efficient capture of A. baumannii from bacterial mixtures, including non-pathogenic intestinal bacteria. This provides proof of concept for a new targeting system that remains effective across diverse A. baumannii clinical isolates and capsule types and holds potential for use in diagnostic cell enrichment and targeted therapies.