Achieving a Sustainable Bio-Economy: Exploring the Antibacterial Efficacy and Phytochemical Properties of Two Indigenous Plants in Sri Lanka, Citrus crenatifolia and Citrus reticulata

Bio-economy offers a beneficial solution for sustainable development by rationalising the use of financial and human resources to improve productivity and environmental stewardship. The citrus family encompasses various plant species known for their antimicrobial properties, and different parts of these plants have been used in traditional Sri Lankan medicine for an extended period. However, information on the antibacterial efficacy of two indigenous citrus plants in Sri Lanka, Citrus crenatifolia and Citrus reticulata, is limited in the literature. Additionally, antibiotic resistance in bacterial pathogens is a global challenge that poses a significant threat to public health, highlighting the need for effective alternative strategies. The present study was conducted to investigate the antimicrobial properties and phytochemical composition of C. crenatifolia and C. reticulata. Active phytochemicals present in the fruit peels were extracted using an aqueous reflux method. The antimicrobial properties of the peel extracts were assessed using the agar well diffusion method against six common pathogens: Staphylococcus aureus, Pseudomonas aeruginosa, Proteus mirabilis, Klebsiella pneumoniae, Escherichia coli, and Enterococcus faecalis. A 0.5 McFarland standard was used to standardise the bacterial inoculum, and double-distilled water served as the negative control. Diameters of inhibition zones were measured after incubation, and statistical analysis was performed using SPSS version 25. The independent sample t-test revealed a significant difference between the mean values of the control and both peel sample extractions against the selected pathogens (p < 0.05). However, no statistically significant difference in antimicrobial activity among the six microbes was observed for C. crenatifolia peel extract according to the one-way ANOVA test (p > 0.05), whereas a statistically significant difference was found for C. reticulata peel extract (p < 0.05). Tukey’s post hoc analysis for C. reticulata indicated that the mean diameters of inhibition zones for Staphylococcus aureus differed significantly from those of Pseudomonas aeruginosa (p = 0.044) and Klebsiella pneumoniae (p = 0.049). The antibacterial activity of both C. crenatifolia and C. reticulata is supported by the presence of phytochemicals such as alkaloids, steroids, flavonoids, phenols, and tannins, which may act synergistically. These findings highlight the potential of these citrus peel extracts as valuable sources of antimicrobial agents, warranting further investigation to elucidate their specific mechanisms of action and potential applications in microbial control.