Aras Part Medical International Press International Journal of Medical Parasitology and Epidemiology Sciences 2766-6492 7 2 2026 06 29 Impact of AcrAB-TolC Pump of Efflux on Biofilm-Associated Antibiotic Resistance in Escherichia coli 44 53 10.34172/ijmpes.6245 EN Rand Diaa Mohammed https://orcid.org/0009-0004-3435-1711 Aida Hussain Ibrahim https://orcid.org/0000-0001-6808-6822 Journal Article 10.34172/ijmpes.6245 2026 04 03 2026 05 21 Introduction: Multidrug-resistant (MDR) Escherichia coli strains causing urinary tract infections pose therapeutic challenges due to biofilms and efflux-mediated tolerance. The AcrAB-TolC system expels antibiotics and promotes biofilm formation. To investigate the contribution of the AcrAB-TolC pump to biofilm-associated resistance in E. coli and evaluate chlorpromazine (CPZ) as an efflux inhibitor to restore antimicrobial efficacy. Methods: Sixty clinical E. coli isolates from UTI patients were identified by phenotypic and molecular testing. Antibiotic susceptibility was assessed using the Kirby–Bauer method, and biofilm formation was quantified using a microtiter plate assay. Efflux activity was phenotypically evaluated using the ethidium bromide (EtBr) cartwheel method. The presence of acrA, acrB, tolC, and gapA was confirmed by PCR, and their relative expression levels were quantified by RT-qPCR using the 2-ΔΔCt method. Results: Of the 60 isolates, 70% were MDR, and 66.6% produced strong or moderate biofilms. Active efflux was observed in 68.3% of the isolates and was strongly correlated with multidrug resistance. PCR confirmed the presence of acrA, acrB, and tolC in all MDR isolates. Combining a sub-inhibitory CPZ concentration with ciprofloxacin reduced the CPZ MIC by two- to fourfold, thereby restoring susceptibility. RT-qPCR revealed significant downregulation of acrA, acrB, and tolC expression following CPZ. Conclusion: The AcrAB-TolC efflux pump is central to the pathogenesis and persistence of MDR E. coli infections. Integrating targeted efflux inhibitors, such as CPZ, with antibiotics holds significant promise for dismantling biofilm resilience and restoring their efficacy.