# Overcoming Multidrug Resistance by Bacterial Efflux Pump Inhibitors in Clinical Escherichia coli Strains

## TL;DR

This study explores how bacterial efflux pump inhibitors can help overcome antibiotic resistance in Escherichia coli by reducing resistance and biofilm formation.

## Contribution

The study evaluates specific efflux pump inhibitors for their ability to reverse multidrug resistance in clinical E. coli strains.

## Key findings

- PMZ, TZ, and CCCP effectively inhibited efflux pump function in ESBL-producing E. coli.
- PMZ and TZ showed moderate anti-biofilm activity across different strains.
- Synergistic effects between PMZ and antibiotics were weak and not statistically significant.

## Abstract

Background/Objectives: Antimicrobial resistance (AMR) is an escalating global threat driven by antibiotic misuse and bacterial adaptation. Efflux pumps are major contributors to multidrug resistance in Escherichia coli, as they expel antibiotics and reduce their intracellular activity. This study examined efflux-mediated resistance in extended-spectrum beta-lactamase (ESBL)-producing E. coli and evaluated the potential of several efflux pump inhibitors (EPIs)—promethazine (PMZ), thioridazine (TZ), carbonyl cyanide m-chlorophenyl hydrazine (CCCP), reserpine (RES), and phenyl-arginine-β-naphthylamide (PAβN)—as therapeutic adjuncts. Methods: Antibacterial and anti-biofilm activities of EPIs were tested using broth microdilution, real-time fluorimetry, and crystal violet assays, while ceftriaxone–PMZ interactions were assessed by checkerboard analysis. Results: TZ and CCCP showed strain-specific antibacterial activity, whereas PMZ, RES, and PAβN did not exert any effect. PMZ, TZ, and especially CCCP effectively inhibited efflux pump function, while RES and PAβN were less active. Biofilm inhibition varied between strains, with PMZ and TZ producing moderate reductions. We observed a quite weak synergism between ciprofloxacin, ceftriaxone, and PMZ; however, the result was not significant. Conclusions: Overall, the results highlight the central role of efflux pumps in ESBL-producing E. coli and indicate that EPIs can reverse resistance (e.g., PMZ) and exhibit potent anti-biofilm activity and show additive interactions with antibiotics. However, further studies are needed to optimize their safety, pharmacokinetics, and antibiotic pairing for potential clinical use.