Antibacterial activity of selected varieties of Malaysian honey against Escherichia coli: A comparative study

Background: 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. 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 honey samples 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 honey samples, 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 samples. 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. Antibacterial activity of selected varieties of Malaysian honey against Escherichia coli: A comparative study Mohammad A. Al-kafaween1, Hamid A. Nagi Al-Jamal1, Abu Bakar Mohd Hilmi1 1 Faculty of Health Sciences, Universiti Sultan Zainal Abidin, Terengganu, Malaysia. Contact information: Hamid A. Nagi Al-Jamal, Mohammad A. Al-kafaween. mohammadalkafaween25@yahoo.com The InTernaTIonal arabIc Journal of anTImIcrobIal agenTs ISSN: 2174-9094 2021 Vol. 11 No. 1:3 doi: 10.3823/854 This article is available at: www.iajaa.org 2 Introduction 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]. This reputation has continued up to the present day, leading to the emergence of a relatively new branch of alternative medicine, called "apitherapy", which focuses on medical applications of honey and other bee products [2-3]. Nowadays, 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]. E. coli is particularly interesting because it has been recognized as one of the most frequently isolated bacteria in nosocomial and surgical-site infections [8]. Although some studies have examined the effects of honeybees on bacterial structures [9, 10], the majority of these studies were conducted on one type of honey, known as Manuka honey, and were mostly focused on Pseudomonas aeruginosa and Staphylococcus aureus. The antimicrobial activity of honey may be attributed to several factors, including high osmolality, acidity, in addition to the presence of hydrogen peroxide (H2O2) [11] and non-peroxide components, such as methylglyoxal [12]. In addition to exerting direct antimicrobial effects, some honey varieties have been implicated in the differential expression of a number of genes essential for bacterial survival and virulence, including those involved in virulence factor production [13], stress tolerance [14], as well as multicellular behaviours, such as biofilm formation [15], and quorum sensing [16]. Honey’s composition (and hence its antimicrobial activity) is dependent on the environmental and geographical locations from which the original nectar was collected [17]. This is attributed to natural variations in floral sources and climatic conditions at different locations [17]. 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 [18-20]. However, 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. To the best of our knowledge, only three published studies to date have focused on the honey-induced expression patterns in E. coli [15-17, 21-22]. Therefore, the objectives of the present study were threefold: (a) to evaluate the direct antimicrobial activity of three varieties of the Malaysia honey against E. coli in vitro; (b) to