Star anise and oregano essential oil: A comparative evaluation of antibacterial effect

(1) Adlai E. Stevenson High School, (2) Science REACH Department, Adlai E. Stevenson High School
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Antibiotic resistance poses a growing threat, driving the need for new antimicrobial agents. This study aimed to assess the antibacterial effects of star anise and oregano essential oils against two pathogenic bacteria, Staphylococcus epidermidis (gram-positive) and Escherichia coli (gram-negative). We used a disc diffusion assay to demonstrate the antimicrobial properties of these essential oils and compare their efficacy between bacterial types. We hypothesized that oregano oil would have a larger zone of inhibition (ZOI) than star anise oil, due to the presence of a higher number of bioactive compounds such as carvacrol and thymol in oregano oil. However, we also hypothesized that both essential oils would be less effective than the positive control antibiotic tetracycline. To test this, paper discs were impregnated with essential oils, tetracycline, or a canola oil negative control and were placed on agar plates inoculated with E. coli or S. epidermis. The ZOI around each disc was measured. For both S. epidermis and E. coli, oregano oil had the largest mean ZOI, which was significantly greater than the ZOIs of star anise oil and tetracycline. However, for E. coli, star anise oil had the second highest ZOI followed by tetracycline. In conclusion, oregano oil displayed potent antibacterial activity against both gram-positive and gram-negative species. These findings highlight the potential role of natural essential oils as alternative antimicrobial agents to combat antibiotic resistance.

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