Aptamer-nanobody based ELASA for specific detection of Acinetobacter baumannii isolates

• Specific aptamers binding to A. baumannii were developed by whole-cell SELEX.
• The high-affinity aptamers could detect 95.47% of clinical isolates of A. baumannii.
• The outcomes verify that along with suitable efficiency, the method presents an easy and feasible technique in comparison with other laborious and time-consuming techniques.
• A detection limit of 10 CFU/mL was achieved by ELASA using the hybrid aptamer/nanobody system.

Acinetobacter baumannii has turned into an important threat in nosocomial outbreak infections and multidrug resistance leading to high mortality rates in the 21 st century. In recent years its mortality has increased by 15% which in part could be due to lack of a rapid and sensitive diagnostic test. In this work we introduced a new detection test for A. baumannii with two highly specific aptamer and nanobody molecules. High binding affinity DNA oligonucleotide aptamers toward A. baumannii were selected through 12 rounds of whole cell System Evolution of Ligands by EXponential enrichment process (SELEX). The SELEX procedures was monitored by flow cytometry. The dissociation constant and binding efficiency of the selected aptamer Aci49 was 7.547 ± 1:353 pM and 47.50%, respectively. A sandwich enzyme linked aptamer sorbent assay (ELASA) was designed with the biotinylated Aci49 aptamer and our previously developed nanobody against biofilm associated protein (Bap). The assay system was optimized with A. baumannii (ATCC 19606) and 47 clinical isolates of A. baumannii were tested. The threshold of detection in sandwich ELASA process was103 CFU/ml. The sensitivity of test toward the clinical isolates was 95.47%. Our results reveal that the sandwich ELASA is sensitive and specific enough for the rapid detection of A. baumannii from clinical isolates.