CRISPRi-mediated silencing of efflux pump genes restores antibiotic susceptibility in multidrug-resistant Acinetobacter baumannii

Multidrug efflux pumps are a critical mechanism underlying both intrinsic and acquired resistance in Acinetobacter baumannii. One of the most perilous multidrug-resistant (MDR) bacterial infections. Resistance-nodulation-division transporters, including AdeABC, AdeIJK, and AdeFGH, are critical efflux systems that diminish intracellular antibiotic levels, enhance bacterial persistence, support biofilm-related tolerance, and lead to treatment failure. Recent advancements in CRISPR interference (CRISPRi), a programmable gene-silencing method using catalytically inactive Cas9 (dCas9), have enabled a versatile platform for reversible, sequence-specific transcriptional repression without inducing double-strand DNA breaks. CRISPRi has emerged as an essential instrument for functional genomics, antimicrobial target validation, and the investigation of complex resistance networks in multidrug-resistant bacteria because to its precision, adaptability, and multiplexing capacities. This work primarily focuses on the recent advancements in CRISPRi-mediated silencing of efflux pump genes and their regulatory circuits in A. baumannii. Targeted suppression of key RND transporters, including adeB, adeJ, and adeG, along with regulatory components such as adeRS, has demonstrated in experiments a substantial decrease in efflux activity, an increase in intracellular antibiotic accumulation, a reduction in minimum inhibitory concentrations, and a reinstatement of susceptibility to various antimicrobial classes, including carbapenems, fluoroquinolones, aminoglycosides, tetracyclines, tigecycline, and chloramphenicol. CRISPRi-based functional screening has identified weaknesses in lipooligosaccharide synthesis, outer membrane biogenesis, and global regulatory pathways, which together augment antibiotic effectiveness with direct efflux pump inhibition. Recent research suggests that the multifactorial resistance mechanisms of MDR A. baumannii may be addressed by multiplex CRISPRi methods and combination therapies that include gene silencing with conventional antibiotics or efflux pump inhibitors. The evaluation also critically examines current delivery techniques, which will eventually determine the feasibility of translating CRISPRi medicines. Examples of contemporary platforms include plasmid-based systems, chromosomally integrated expression cassettes, conjugation-mediated transfer, bacteriophage-mediated delivery, and innovative nanotechnology-assisted carriers designed to improve intracellular delivery and bacterial targeting. Despite substantial advancements in experimental CRISPRi methodologies, the efficient delivery to infected tissues and clinical isolates remains a considerable challenge. Challenges include restricted infiltration into established biofilms, variable gene repression among genetically diverse strains, potential off-target effects, emergence of escape mutations, preservation of genetic stability, immune-mediated elimination of delivery vehicles, large-scale production and regulatory hurdles, and the absence of dependable animal and clinical studies validating therapeutic efficacy and safety. Current knowledge indicates that CRISPRi-mediated efflux pump silencing is a very promising precision antimicrobial adjuvant method that might enhance the efficacy of existing antibiotics against MDR A. baumannii. Before this technique can be integrated into regular clinical practice, substantial technological advancements, improved delivery systems, comprehensive biosafety evaluations, and rigorous in vivo and clinical validations will be required.