A Time-Kill Assay Study on the Synergistic Bactericidal Activity of Pomegranate Rind Extract and Zn (II) against Methicillin-Resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa

Amal Alrashidi,Niamh Higgins,Ryan Moseley,Vildan Celiksoy,Carmine Varricchio,David M J Houston,Mohammed Jafar,Charles M Heard,Ciara Mulligan

doi:10.3390/biom11121889

Abstract

There is a need for new antimicrobial systems due to increased global resistance to current antimicrobials. Pomegranate rind extract (PRE) and Zn (II) ions both possess a level of antimicrobial activity and work has previously shown that PRE/Zn (II) in combination possesses synergistic activity against Herpes simplex virus and Micrococcus luteus. Here, we determined whether such synergistic activity extended to other, more pathogenic, bacteria. Reference strains of methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa were cultured and subjected to challenge by PRE, Zn (II), or PRE + Zn (II), in time-kill assays. Data were obtained independently by two researchers using different PRE preparations. Statistically significant synergistic activity for PRE + Zn (II) was shown for all four bacterial strains tested compared to untreated controls, although the extent of efficacy and timescales varied. Zn (II) exerted activity and at 1 h, it was not possible to distinguish with PRE + Zn (II) combination treatment in all cases. PRE alone showed low activity against all four bacteria. Reproducible synergistic bactericidal activity involving PRE and Zn (II) has been confirmed. Potential mechanisms are discussed. The development of a therapeutic system that possesses demonstrable antimicrobial activity is supported which lends itself particularly to topical delivery applications, for example MRSA infections.

Highlights

We examined the time-kill effects of pomegranate rind extract (PRE), Zn (II) and PRE/Zn (II) combination against the Gram-positive bacteria, methicillinresistant Staphylococcus aureus (MRSA), and Staphylococcus epidermidis and the Gram-negative bacteria, Escherichia coli, and Pseudomonas aeruginosa
Spiking with standard punicalagin gave rise to both α and β punicalagin peaks, and this was used to prepare a standard calibration curve from which it was determined that the mean punicalagin level in the 2 extracts was PRE was 21.7% (1 mg in each 4.61 mg of PRE)
Zn (II) alonetherapy—i.e., induced significant log ment of the potency of an antimicrobial agent by the simultaneous administration of a reductions in CFUs compared to PRE alone at all time-points

Summary

Introduction

Antimicrobial resistance is a natural phenomenon, occurring as a consequence of gradual changes in bacterial gene expression to facilitate the development of resistance against certain antibiotic modalities. The current global antibiotic resistance crisis has been attributed to the overuse and misuse of these therapeutics, in addition to other factors—such as inappropriate antibiotic prescribing, extensive agricultural use, and the lack of new antibiotic drug development—have all contributed to the dramatic emergence of modern drug-resistant pathogens [1,2]. With the recent dramatic increases in resistance to existing antimicrobial agents, certain infections have become extremely difficult to treat, with generally stricter regulations being applied to antibiotic administration.

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