Flavonoids and chromones from Aloe barbadensis exhibit potent activity against Staphylococcus aureus: validation of in silico predictions

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) poses a serious public health threat, necessitating new antimicrobial agents. Our previous molecular docking study identified several phytochemicals from Aloe barbadensis as potential inhibitors of MRSA targets. This study experimentally validates the antibacterial activity of nine top‑ranking compounds against S. aureus. Nine compounds – aloesaponarin‑II, aloenin, methylaloesinol, luteolin, aloespanol‑II, ziganein‑5‑methyl‑ether, salicylic acid, kaempferol, and methyl salicylate were obtained from Sigma‑Aldrich. Antibacterial activity against S. aureus ATCC 25923, evaluated using the Kirby‑Bauer disk diffusion method. Gentamicin (10 µg/disk) served as positive control, and DMSO as negative control. Zones of inhibition (ZOI) were measured in triplicate after 24 h incubation at 37°C. Data were analyzed using one‑way ANOVA with Tukey’s post‑hoc test. Luteolin produced the largest inhibition zone (55.8 ± 3.6 mm), significantly exceeding gentamicin (35.7 ± 4.0 mm, p < 0.001). Kaempferol (43.0 ± 1.7 mm) and aloenin (38.7 ± 1.2 mm) also outperformed the antibiotic control (p < 0.05 and p < 0.01, respectively). Aloesaponarin‑II (35.4 ± 1.4 mm) and methylaloesinol (34.3 ± 0.6 mm) showed activity comparable to gentamicin. Salicylic acid (31.7 ± 2.9 mm) exhibited moderate activity, while methyl salicylate (22.3 ± 2.0 mm) and ziganein‑5‑methyl‑ether (13.0 ± 1.7 mm) were least effective. The negative control showed no inhibition. The ranking of activity strongly correlated with docking scores (Spearman’s ρ = 0.87, p = 0.002). Luteolin, kaempferol, and aloenin demonstrate potent in vitro activity against S. aureus, with efficacy surpassing that of gentamicin under disk diffusion conditions. These results validate our in silico predictions and identify lead compounds for further development as topical or systemic anti‑staphylococcal agents. The study determines that it is imperative to find the minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of luteolin, kaempferol, and aloenin using the standardized broth microdilution method (CLSI guidelines). This will provide a quantitative measure of intrinsic potency that is not confounded by differential diffusion rates through agar.