Crotalaria madurensis flavonol glycosides' antibacterial activity against Staphylococcus aureus

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) infections are prevalent in hospitals and often lead to significant health complications. This study aimed to explore the chemical composition of the aerial part of Crotalaria madurensis and evaluate its antioxidant and antibacterial properties. The impact of gamma irradiation on the antibacterial properties of the plant extract and metabolite 1 against MRSA was also examined. Fourier-transform infrared (FTIR) analysis was conducted on the filtrates of untreated MRSA and MRSA treated with the plant extract and metabolite 1. Four flavonol glycosides were identified as gossypetin 8-methoxy, 3-O-β-D-xylopyranoside (metabolite 1), gossypetin 8-O-β-D-glucopyranoside (metabolite 2), kaempferol 3-O-β-D-glucpyranoside (Astragalin, metabolite 3), and herbacetin 7-methoxy-3-O-β-D-glucopyranoside (metabolite 4). All metabolites exhibited significant antioxidant properties using different assays. The antibacterial efficacy of the extract and metabolite 1, which showed substantial antioxidant properties compared to the other isolated metabolites, was evaluated. Both the plant extract and metabolite 1 significantly reduced the viability and cell count of MRSA at concentrations of 1.0 and 0.5 mg/ml. The antibacterial activity of the plant extract and metabolite 1 was assessed after gamma irradiation at 50 and 100 Gy, which did not significantly affect the antibacterial efficiency. FTIR analysis indicated that the plant extract and metabolite 1 significantly altered the band frequency values, bandwidth, and peak intensity % of the treated MRSA filtrate. Molecular docking studies suggested that metabolite 1 exhibited the highest antioxidant and anti-MRSA activity, with strong binding scores like the ligand, indicating an effective interaction and high affinity between metabolite 1 and the target molecule.

Keywords: Crotalaria madurensis; Antibacterial; Antioxidant; Docking study; Flavonol; MRSA.

Fig. 1

The chemical structure of isolated metabolites from C. madurensis

Fig. 2

ABTS radical scavenging activity of C. madurensis metabolites1-4 compared to gallic acid as a reference drug. Data were analyzed using one-way analysis of variance (ANOVA) and were expressed as Mean ± SD (n = 3)

Fig. 3

Ferric reducing power ability of C. madurensis metabolites (1–4). Data were analyzed using one-way analysis of variance (ANOVA) and expressed as Mean ± SD (n = 3). Means bearing different letters differ significantly at p ≤ 0.05 by Duncan’s multiple range test

Fig. 4

Total antioxidant capacity assay of C. madurensis metabolites (1–4). Data were analyzed using one-way analysis of variance (ANOVA) and expressed as Mean ± SD (n = 3). Means bearing different letters differ significantly at p ≤ 0.05 by Duncan’s multiple range test

Fig. 5

The response of MRSA to antibiotics like levofloxacin, cefuroxime, rifaximin, streptomycin, and ampicillin/sulbactam SAM-20

Fig. 6

The antibacterial effect of the plant extract and metabolite 1 on MRSA at concentrations of 1.0, 0.5, and 0.25 mg/ml, with the error bar indicating the standard error (n = 3). Means bearing different letters differ significantly at p ≤ 0.05 by Duncan’s multiple range test

Fig. 7

The MRSA viability is depicted as follows: a The number of colonies after treatment with plant extract. b The number of colonies after treatment with metabolite 1. c The count of Colony Forming Units (CFU) per milliliter, and d The base-10 logarithm. e The count of colonies from the 10^–5 dilution at a concentration of 1.0 mg/ml on Nutrient Broth (NB) medium. Means bearing different letters differ significantly at p ≤ 0.05 by Duncan’s multiple range test

Fig. 8

Impact of gamma irradiation at doses of 50 and 100 Gy on the antibacterial efficacy of plant extract (PE) and metabolite 1 (M1) against MRSA

Fig. 9

FTIR of the filtrates from MRSA, MRSA treated with plant extract, and MRSA treated with metabolite 1