Comparison of the antibacterial activity between essential oils of Citrus crenatifolia and Citrus sinensis against Staphylococcus aureus, Bacillus cereus and Escherichia coli

Abstract

The emergence of antimicrobial resistance and the frequent side effects of antibiotics has become a major global health concern. To combat this, natural plant-based products are considered to play a key role. This study aimed to determine the antibacterial activity of Citrus crenatifolia and Citrus sinensis essential oils and to investigate the synergism or antagonism of their combinations against Staphylococcus aureus, Bacillus cereus, and Escherichia coli bacterial species. The leaves of C. crenatifolia and C. sinensis, collected from Yakkaduwa Herbal Garden, were cut into small pieces and subjected to hydrodistillation using a Clevenger-type apparatus. The Kirby-Bauer Disk Diffusion method was used to test the antimicrobial susceptibility of pure essential oils of the two citrus plants and their combination (1:1 ratio). As positive controls, 0.1mg/mL for B. cereus and 0.01mg/mL of Amoxicillin for S. aureus and E. coli were used. According to the results, C. crenatifolia demonstrated statistically significant results against B. cereus (p = 0.0072974 vs S. aureus and p = 0.042552 vs E. coli). E. coli was the most susceptible bacterial strain for C. sinensis and the C. crenatifolia – C. sinensis combination. These could be due to the interaction of various bioactive compounds binding specifically to different cellular targets in the bacterial cell wall and possible synergistic or antagonistic effects. S. aureus was the least susceptible bacterial strain except for C. sinensis indicating antibacterial resistance. In conclusion, all three bacterial strains were susceptible to C. crenatifolia, and the combination was most effective against E. coli compared to Amoxicillin.