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Technologies for Emerging Infectious Diseases

Technologies for Emerging Infectious Diseases - Poster Session B

Poster K17 - Impact of antibacterial properties of Manuka Honey on planktonic cultures of Staphylococcus aureus over 5-hour and 17-hour treatment

Thursday, October 24, 2024
2:45 PM - 3:45 PM EST
Location: Exhibit Hall E, F & G

Introduction:  Honey has been used as a treatment for wound injuries for thousands of years due to its antimicrobial properties. The acidic pH, high sugar content, and low moisture levels of the honey create an inhospitable environment for bacterial growth. To explore the fundamental means through which honey act as an antibacterial, Manuka 249 (M-249) from “Happy Valley” was used during this experiment. Manuka honey is commonly known for its medical properties and antimicrobial effectiveness in part due to its high levels of methylglyoxal (MGO) groups and it is the most studies type of honey worldwide for medicinal purposes. In the medical setting, ESKAPE pathogens are a common cause of hospital acquired infections (HAIs). These infections are challenging to treat once acquired; resulting in longer hospital stays, increased financial burden on patients, and higher mortality rates. Staphylococcus aureus is a Gram-positive ESKAPE pathogen that causes a wide array of infections. These infections are challenging to treat if the pathogen found its entry to the bloodstream or internal tissues. Biofilm formation is one of the main means through which bacteria develop infections that are hard to treat. Motivated by its medicinal properties, the abilities of Manuka honey 249 to get rid of S. aureus planktonic cultures and biofilms leading to infections is being investigated.

Materials and

Methods:  The efficiency of Manuka Honey 249 in inhibiting the growth of planktonic cultures of S. aureus grown till the late exponential phase of growth was explored over 5 and 17 hours. S. aureus (ATCC 25923) was cultured in Tryptic Soy Broth (TSB) at 37oC and 150 rpm. Bacterial cells were then harvested when they reached the late exponential phase of growth. 96 well plates were used to test the efficacy of various concentrations of Manuka Honey 249 in preventing the growth of S. aureus over 5 and 17-hour periods. Specifically, a mother solution of 0.5 g Honey in 1 ml water was prepared. A 50%, 40%, 30%, 20%, and 10% solutions of honey were then applied to bacterial culture. A positive control of bacteria without treatment was also tested. Negative controls of TSB as well as pure honey solutions at the concentrations above were also prepared. The absorbances of bacterial culture in the presence and absence of honey were read at 600 nm using a multiplate reader kept at 37 oC while continuously shaking. Absorbances were read every 20-30 minutes. All experiments were run in triplicates.

Results, Conclusions, and Discussions: Exposure of S. aureus planktonic cells to Manuka honey at concentrations higher than 30% was sufficient to induce killing of all cells, even within 5 hours (Figures 1A and 1B). Specifically applying 50%, 40%, and 30% Manuka honey at 17 hours resulted in 98%, 91%, 89% killing of cells, respectively (Figure 1B). However, when cells were exposed to 20% Manuka honey, the bacteria were still able to grow slightly over 5 hours (Figure 1 A) and gained a bit of resistance as evident from positive slope of growth kinetics during the 17 hours of growth (Figure 1B). When quantified, the application of 20% Manuka honey killed 45% of S. aureus over 5 hours and 78% over 17 hours. Finally, when the 10% Manuka honey was applied, our data suggest that it was not sufficient to kill the bacteria specifically over long periods of times. This indicates that the bacteria developed resistance to the Manuka honey at that concentration. When cultured for 5 hours under exposure to 10% Manuka honey, 30% of the cells were killed (Figure 1A). However, when cells were left exposed to the 10% Manuka Honey for 71 hours, almost no cells were killed as evident from overlapping kinetics with these of bacteria untreated (positive control, Figure 1B). Ongoing experiments are currently testing the effects of the concentration of Manuka honey on the biofilms of S. aureus. Biofilms are being allowed to grow for variable amounts of time from 5 hours to 24 hours and Manuka honey with similar concentrations tested hire are being utilized. Our results overall suggest that Manuka honey has the efficiency to be used as an antibiotic agent against S. aureus planktonic cultures and ongoing studies are testing their efficacy against biofilms. This study is instrumental to developing natural antibiotic compounds that can be used to treat multi-drug resistant bacterial infections in clinical settings.

Acknowledgements (Optional):  NIH ESTEEMED 2R25EB027605-06