Phytochemical, antioxidant, and antimicrobial evaluation of Eucalyptus camaldulensis Dehnh. leaf extract

Abstract

Rising antimicrobial resistance and infection-associated oxidative stress have renewed interest in plant-derived agents that combine antimicrobial and antioxidant properties. Eucalyptus camaldulensis still has limited integrated data linking its phytochemical profile to antioxidant and antimicrobial activities. This study characterised the phytochemical composition of E. camaldulensis leaf and evaluated its antioxidant and antimicrobial activities using complementary quantitative assays. Phytochemical screening and quantification were done by standard spot tests and gravimetric assays. Total phenolic, flavonoid and tannin contents were determined spectrophotometrically.
Antioxidant activity was assessed by DPPH, FRAP, and Phosphomolybdenum assays. Antimicrobial activity was evaluated against six bacterial species and two fungal isolates by agar-well diffusion and broth dilution, using ciprofloxacin and ketoconazole as standards. Phytochemical screening confirmed the abundance of flavonoids, terpenoids, saponins and alkaloids. Mean TPC, TFC and total tannins were 165.93 ± 0.12 mg GAE/g, 131.13 ±1.34 mg QE/g and 152.9 ± 1.04 mg TAE/g, respectively. The extract showed moderate DPPH activity (IC₅₀ =275.2 µg/mL), concentration-dependent FRAP increment (~6.7 to 37.2 mg AAE/g), with TAC also rising progressively with dose. Antimicrobial testing produced broad-spectrum, dose-dependent inhibition with zones of inhibition ranging from 0–16 mm for bacteria and 0–18 mm for fungi; the strongest activity was against Proteus mirabilis and Fusarium sp. Bacterial MICs ranged from 6.25–25 mg/mL, with corresponding bactericidal effects at higher concentrations; fungal MIC/MFC values indicated greater tolerance in Candida sp. and Fusarium sp. The extract demonstrated measurable antioxidant and broad-spectrum antimicrobial activities, although its potency was
lower than that of the reference drugs under the assay conditions. Ultimately, the phenolic- and flavonoid-rich profile of E. camaldulensis supports its traditional use and justifies further fractionation and compound isolation to identify more potent bioactive constituents for possible drug development.