Evaluation of Physiological Effects Induced by Manuka Honey Upon Staphylococcus aureus and Escherichia coli

Abstract

Several studies have explored the antimicrobial properties of manuka honey (MkH). However, the data available regarding antibacterial action mechanisms are scarcer. The aim of this study was to scrutinize and characterize primary effects of manuka honey (MkH) upon the physiological status of Staphylococcus aureus and Escherichia coli (as Gram-positive and Gram-negative bacteria models, respectively), using flow cytometry (FC) to reveal its antibacterial action mechanisms. Effects of MkH on membrane potential, membrane integrity and metabolic activity were assessed using different fluorochromes in a 180 min time course assay. Time-kill experiments were carried out under the same conditions. Additionally, MkH effect on efflux pumps was also studied in an E. coli strain with an over-expression of several efflux pumps. Exposure of bacteria to MkH resulted in physiological changes related to membrane potential and membrane integrity; these effects displayed slight differences among bacteria. MkH induced a remarkable metabolic disruption as primary physiological effect upon S. aureus and was able to block efflux pump activity in a dose-dependent fashion in the E. coli strain.

Antibacterial Action Mechanisms of Honey: Physiological Effects of Avocado, Chestnut, and Polyfloral Honey upon Staphylococcus aureus and Escherichia coli

“…Under some treatment conditions, bacteria were able to gradually repolarize and recover, partially or completely, their membrane potential. Similar behavior was previously observed in S. aureus and E. coli exposed to MkH [28].…”

“…The results obtained in this study reveal that treatment time and honey concentration are key factors regarding the induction of membrane injury in S. aureus and E. coli. Moreover, these results revealed that the distinct honey samples act differently between gram positive and gram negative bacteria, a fact which was already described in some previous studies with MkH [15,16,28,29]. While the effect of the different honey samples on S. aureus membrane integrity was limited, in the case of E. coli, the results obtained confirmed more meaningful effects.…”

“…The loss of the equilibrium of ion concentration inside and outside of bacteria may affect their viability [27]. Honey-induced physiological changes on bacterial membrane potential were described for the first time in a previous study with MkH [28]. Similarly, in this study AH, ChH, and PH induced alterations upon S. aureus and E. coli membrane potential.…”

“…However, membrane depolarization caused by these three honey types was greater and sooner than that caused by MkH at the same treatment conditions [28]. S. aureus cells exposed to 10% of MkH showed significant increase of fluorescence after 120 min of exposure [28], while at that concentration, AH and PH induced alterations after 30 min of exposure and after 60 min in the case of ChH. Similarly, E. coli cells exhibited a significant membrane depolarization after 120 min of treatment with 20% (w/v) of MkH and after 60 min at a higher concentration of MkH (30% (w/v)).…”

“…Similarly, in this study AH, ChH, and PH induced alterations upon S. aureus and E. coli membrane potential. However, membrane depolarization caused by these three honey types was greater and sooner than that caused by MkH at the same treatment conditions [28]. S. aureus cells exposed to 10% of MkH showed significant increase of fluorescence after 120 min of exposure [28], while at that concentration, AH and PH induced alterations after 30 min of exposure and after 60 min in the case of ChH.…”