Role of G-quadruplexes in adeABC efflux pump antibiotic resistance activity

Antimicrobial resistance (AMR) has become an increasingly concerning threat to human life claiming an estimate of 700,000 lives in 2014 and 1.27 million lives in 2019. Acinetobacter baumannii strains expressing multi-drug resistance (MDR) characteristics are identified as critical priority pathogens in need of urgent research and therapy development by the W.H.O. Investigations within this study identified and characterised secondary DNA structures, G-quadruplexes (GQs), to establish their potential application as targets in the development of novel antimicrobial therapies. To predict the assembly formalism of putative quadruplex sequences (PQSs), a review of published intramolecular GQs identified most to have the ‘ppp’ loop type arrangement. Further analysis revealed the first and third loops to mostly be of shorter lengths and of the same loop type in comparison with the second loop that allowed for flexibility in loop length and type composition. The application of QGRS Mapper identified 17 PQSs in adeABC and characterisation of these sequences showed five to demonstrate characteristics of GQ assembly using UV-Vis TDS and CD biophysical techniques, and DNase assays. One of the five PQSs, Ade09, in combination with an antibiotic, ertapenem, was used as treatment against A. baumannii and showed changes in the pathogen’s MIC to ertapenem. Although seven variations with single base mutations were observed, Ade09 was conserved within 40 clinical A. baumannii strains, and the G-tetrads predicted to contribute to GQ assembly were preserved. These findings indicate that identifying and targeting the role of GQs in combination with antimicrobial drugs can inhibit resistance mechanisms of the efflux pump genes. The non-random clustering of GQs in key regulatory genes proffers its potential application as a novel therapy against AMR. The combinational approach from this study can be applied with an aim to restore the efficacy of available therapeutics in addressing AMR and other life-threatening diseases.