Abstract
Background: The purpose of this study was to investigate antibacterial activity of three varieties of Malaysian honey; Tualang honey (TH), Gelam honey (GH), and Acacia honey (AH) against Escherichia coli.
 Methods: The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the honey samples against E. coli were determined by the broth microdilution assay in the presence and absence of catalase enzyme. The mode of inhibition of honey samples against E. coli was investigated by the effect of time on viability. Impacts of the honeys on the expression profiles of the selected genes of E. coli were examined using RT-qPCR analysis.
 Results: The results showed that TH and GH honey possessed lowest MIC and MBC values against E. coli with 20% and 25% (w/v) respectively. Highest MIC and MBC values were observed by AH honey against E. coli with 25% (w/v) and 50% (w/v) values respectively. Among the tested honeys, TH and GH exhibited the highest total antibacterial activity and the highest levels of peroxide-dependent activity. Time–kill curve demonstrated a bactericidal rather than a bacteriostatic effect; with a 2-log reduction estimated within 540 min. Viable cells were not recovered after 9 hours exposure to MIC of all honey-treated. The RT-qPCR analysis showed that all honey-treated cells share a similar overall pattern of gene expression, with a trend toward reduced expression of the virulence genes of interest.
 Conclusion: This study demonstrates that Malaysian honey have the potential to be effective inhibitor and virulence modulator of E. coli via multiple molecular targets.
Highlights
Honeybees is one of the oldest traditional medicines that has been highly reputed and widely used for the treatment of several human diseases for thousands of years [1]
To examine the influence of H2O2 on the antibacterial activity of the tested honeys, samples were pre-treated with catalase prior to the incubation with E. coli, which was followed by evaluation of their minimum inhibitory concentration (MIC) values
The highest reduction in antibacterial activity was observed in the case of Acacia honey (AH) honey, in which the removal of H2O2 caused an approximate three-fold increase in the MIC against E. coli (Table 3)
Summary
Honeybees is one of the oldest traditional medicines that has been highly reputed and widely used for the treatment of several human diseases for thousands of years [1]. Different types of honey have been used in many countries as an alternative to pharmaceutical products for treating contaminated, infected, and burn wounds [4,5] This is attributed to the effectiveness of these honeybees in inhibiting or killing a broad spectrum of bacteria [6,7]. Several studies have addressed different aspects of Malaysian honey varieties, including their physicochemical properties, their chemical composition, their antibacterial and antibiofilm activities and their therapeutic usefulness [18,19,20] It is not yet known whether these anti-biofilm activities, as well as any possible anti-quorum sensing and anti-virulence activities possessed by these honeys could be attributed to alteration of bacterial gene expression. The purpose of this study was to investigate the antibacterial activity of three varieties of Malaysian honeybees; Tualang honey (TH), Gelam honey (GH), and Acacia honey (AH) against Escherichia coli
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