Mostafa Alamholo
Mohadeseh Shojaemehr
Jalal Soltani

Background: The resistance of pathogenic bacteria against synthetic drugs led scientists to conduct research on medicinal plants. The present study investigated the antioxidant and antibacterial activity of the aqueous, methanol, and ethanol alcoholic extracts of the plant Citrus maxima Merr. (Syn. Citrus grandis) against some human pathogenic bacteria. Then, the presence of secondary metabolites was evaluated in vitro, including alkaloid, saponin, and tannin. Methods: The samples (i.e., root, stem, and seed) of C. maxima were collected at Babolsar, Mazandaran province, Iran. The agar well diffusion assay was used to determine antibacterial activity. In addition, several bacteria were applied based on the aim of the study, including Streptococcus pyogenes (PTCC۱۴۴۷), Bacillus subtilis (PTCC-۱۱۵۶), Bacillus cereus (PTCC-۱۲۴۷), Enterococcus faecalis (PTCC-۱۱۸۵), Micrococcus luteus (ATCC-۱۰۹۸۷), and Staphylococcus aureus (PTCC-۱۱۸۹). Further, some Gram-negative bacteria were used, encompassing Escherichia coli (ATCC-۲۵۹۲۲), Shigella boydi(-), Salmonella typhi (PTCC-۱۶۰۹), Pseudomonas aeruginosa (PTCC-۱۱۸۱), Enterobacter aerogenes (PTCC-۱۲۲۱), and Klebsiella pneumoniae (PTCC-۱۱۳۹). Next, the minimum inhibitory and bactericidal concentrations were determined by the serial dilution method. Furthermore, free radical activity was identified by ۲,۲-diphenyl-۱-picrylhydrazyl. Moreover, the total phenolic and total flavonoid contents were conducted by Folin-Ciocalteu and aluminum chloride methods, respectively. Finally, the phytochemical compounds were investigated as well. Results: The highest sensitivity was observed on M. luteus against the root methanol extract. Additionally, the total phenolic content of root, seed, and leaf was determined as ۹۸.۲۲, ۸۹.۶۶, and ۷۷.۵۱ (mgGA/g), respectively. Similarly, the flavonoid content was determined as ۳.۵۲, ۳.۴۳, and ۳.۵۶ (mgQ/g), respectively. In addition, the IC۵۰ of the root, seed, leaf, and ascorbic acid were calculated as ۰.۱۲۹, ۰.۱۳۵, ۰.۱۱۳, and ۰.۱۰۹ mg mL-۱, respectively. Eventually, the methanol extract of the leaf and root showed the presence of alkaloid, saponin, and tannin. Conclusions: In general, C. maxima is suggested for producing natural drugs with antibiotic properties in the pharmaceutical industry due to the presence of secondary metabolites in its different parts.