EFFLUX PUMP INHIBITORY POTENTIAL OF CURCUMIN IN MDR ESHCHERICHA COLI CLINICAL ISOLATES COLLECTED FROM BANGLADESH

Abstract

Effluxing of antibiotic molecules out of the bacterial cell is the potential mechanism of developing resistance against diverse classes of antibiotics.  Therefore, inhibition of these efflux pumps by using different efflux pump inhibitors (EPIs) may restore the efficacy of large number of antibiotics.  Curcumin, a natural yellow pigment commonly found in turmeric, has been evaluated for its role as EPI in clinical isolates.  Disc diffusion and broth dilution method were applied to evaluate the antimicrobial susceptibility whereas ethidium bromide-agar cartwheel method was used to evaluate the efflux pump activity of the 16 MDR clinical isolates of E. coli.  Molecular docking studies of both the ‘enol’ and ‘keto’ structure of curcumin (due to tautomerism) and reference standards were carried out by using Autodock vina algorithm against different efflux pump proteins.  Antimicrobial susceptibility tests showed high resistance to cefixime, linezolid, and chloramphenicol, among other antibiotics.  Around 37.5% of the clinical isolates showed enhanced efflux pump activity compared to S. aureus ATCC 25922.  Investigation into curcumin showed that it reduced the MIC of linezolid, and ciprofloxacin in efflux pump active isolates by 2-8 folds with a fractional inhibitory capacity ranging from 0.156-1.062.  The results suggested that concomitant use of curcumin with ciprofloxacin and linezolid showed synergistic and additive effects.  Reserpine was used as a reference standard efflux pump inhibitor, reducing the MIC of linezolid and ciprofloxacin among those same strains by 2-8 folds.  The docking studies showed that the binding affinities of ‘enol’ form of curcumin were found -7.3, -7.7, -7.5 and -7.1 Kcal/mol for AcrB, EmrD, MacA and MdfA efflux pump proteins, respectively.  The result showed that curcumin may show synergistic or additive effects when used with current antibiotics by inhibiting ABC, MFS and RND efflux pump family.  Further studies are recommended to understand the molecular mechanism of this activity by curcumin.