Peppermint Essential Oil Shows Antibacterial Activity Against Staphylococcus Aureas

by | Jun 9, 2020 | 2019, Botanicals, Essential Oils

Written by Angeline A. De Leon, Staff Writer. Peppermint essential oil (PEO) demonstrated potent antibacterial and anti-biofilm activities against Staphlococcus aureus.

mint oilStaphylococcus aureus (S. aureus) is a major bacterial pathogen associated with foodborne illness in both humans and animals 1. The process of contamination associated with S. aureus involves the bacteria’s attachment to the surface of food and food processing equipment through the formation of a biofilm, an extracellular matrix of polymeric substances that supports bacterial growth and resistance to antibiotics 2-4.  Studies suggest the need to explore natural alternatives to synthetic antibacterial drugs, which have been known to increase antimicrobial resistance of bacteria with longer-term use 5. Some types of essential oil demonstrate the ability to extend the shelf-life of food by protecting against foodborne pathogens 6. One such essential oil, peppermint essential oil (PEO), possesses notable anti-viral effects and has been linked to the prevention of Salmonella enteriditis and S. aureus 7. The mechanisms associated with PEO’s antibacterial effect and its potential anti-biofilm activity, however, are not well understood. To this end, a recent study 8 in China (2019) sought to investigate the effects of PEO on cell membrane permeability, cell viability, and biofilm formation of S. aureus.

Minimal inhibitory concentration (MIC, lowest concentration of PEO at which visible bacterial growth is inhibited) and minimal bactericidal concentration (MBC, lowest concentration of PEO capable of killing all bacterial colonies on surface of agar plates) values were determined. To examine cell membrane permeability, S. aureus cells were treated with PEO at concentration levels of 0 (control) and at MIC and MBC levels, and relative electrical conductivity was calculated. Cell viability was determined in an S. aureus suspension (about 107 CFU/mL) treated with PEO at 0, MIC, and MBC levels using flow cytometry, and a crystal violet quantitative assay was employed to examine the effects of PEO on biofilm formation of S. aureus (measured in terms of optical density). Finally, the effect of PEO against S. aureus biofilm formed on polystyrene microplates was estimated by counting the population of viable cells after 24 hours of incubation.

Experiments indicated an MIC value of 0.5 mg/mL and MBC value of 2 mg/mL for PEO against planktonic S. aureus. After treatment with PEO at MIC and MBC levels, relative electrical conductivity values of S. aureus cells were found to be significantly higher than that of controls (p < 0.01 for both) and appeared to increase with higher PEO concentrations, suggesting significant changes in cell membrane permeability. Flow cytometry showed that whereas about 98.71% of S. aureus cells in the control group had intact cell membranes, the percentage of injured and dead cells after treatment with PEO at the MIC level was 14.30-72.61%, and the percentage of dead cells after treatment with PEO at the MBC level was 52.91%. Regarding PEO’s impact on biofilm formation, analyses indicated  that PEO at a concentration  of  0.125 mg/mL was  able  to significantly inhibit S. aureus biofilm formation, as compared to control (p < 0.01), with  biofilm formation continuing to decrease with increasing PEO concentrations. Finally, relative to control, a PEO concentration of 0.25 mg/mL was demonstrated to significantly lower the number of viable cells in S. aureus biofilm formed on polystyrene microplates (p < 0.01). At PEO concentrations of 4 mg/mL and higher, no viable cells were detectable.

Research findings confirm the antibacterial and anti-biofilm capacities of PEO against planktonic S. aureus. Based on increases observed in relative electrical conductivity of cells, PEO appeared to significantly alter cell membrane permeability of S. aureus. PEO was also found to reduce cell viability (as evidenced by the number of damaged and dead cells after treatment at the MIC and MBC levels) and inhibit biofilm formation at doses of 0.125 mg/mL and higher. Moreover, mature formation of S. aureus biofilm on microplates was inactivated by PEO, suggesting that the essential oil can effectively inhibit formation of S. aureus on polystyrene surfaces and potentially other common kitchen surface areas as well. Overall, results indicate that PEO may be a promising alternative to conventional synthetic antiseptics used in food processing environments.

Source: Kang J, Jin Wenyuan, Wang Jingfan, et al. Antibacterial and anti-biofilm activities of peppermint essential oil against Staphylococcus aureas. LWT-Food Science and Technology. 2019; 101: 639-645. DOI: 10.1016/j.lwt.2018.11

© 2018 Published by Elsevier Ltd.

Posted June 9, 2020.

Angeline A. De Leon, MA, graduated from the University of Illinois at Urbana-Champaign in 2010, completing a bachelor’s degree in psychology, with a concentration in neuroscience. She received her master’s degree from The Ohio State University in 2013, where she studied clinical neuroscience within an integrative health program. Her specialized area of research involves the complementary use of neuroimaging and neuropsychology-based methodologies to examine how lifestyle factors, such as physical activity and meditation, can influence brain plasticity and enhance overall connectivity.

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