Reverting Multidrug-resistant Phenotypes of Escherichia coli Isolated from Cattle Using 1-(1-Naphthylmethyl)-Piperazine

Introduction:  The extensive use of antimicrobial agents, in both the health and food sectors, has led to the emergence of multidrug resistant (MDR) bacteria; a development of importance to public health. Efflux pumps extrude antimicrobial compounds from cells contributing to the development of resistance. Chemosensitisers, with the capacity to modulate efflux pump activity, are being studied as adjuvants, in efforts to reverse resistant phenotypes. However, little is known about their efficacy and mechanism of action.

Purpose:   The purpose of this study was to systematically analyse the MDR reversal activity of the chemosensitiser 1-(1-naphthylmethyl)-piperazine (NMP) when applied as an adjuvant with antibiotics onto both planktonic and sessile Escherichia coli isolates.

Methods:   Bovine E. coli isolates from the UCD Veterinary Hospital, were screened for their MDR phenotype. A panel of 12 isolates, resistant to different classes of antibiotics including fluoroquinolones, tetracyclines, and chloramphenicol, were studied. All isolates were characterised by whole genome sequencing. The ability to form biofilms and fimbriae was, also, determined. Minimum inhibitory concentration (MIC) for each antibiotic, alone or in combination with NMP at sub-MIC levels, was determined by broth microdilution using planktonic and sessile-grown cells. Transmission electron microscopy (TEM), using NMP was performed.

Results:   Isolates had diverse antimicrobial resistance (AMR) and virulence gene profiles. Based on these data the gsp operon appeared to be associated with strong biofilm formers. In planktonic cells, using NMP as adjuvant, the MIC of ciprofloxacin, chloramphenicol and tetracycline exhibited a 2-, 6- and 10-fold reduction in comparison to the antibiotic, alone. In the case of sessile cells, half showed reductions in biofilm biomass when tetracycline was combined with NMP. TEM imaging demonstrated cell wall damage with NMP.

Significance: These findings showed that NMP damaged the cell walls, thus, increasing drug permeabilisation. The use of NMP and NMP-like structures has the potential to reverse MDR in bacteria.