Abstract
Antibiotic-resistant infections are a growing problem; to combat multi-drug resistant bacterial infections, antibiotics with novel mechanisms of action are needed. Identification of potent bioactive natural products is an attractive avenue for developing novel therapeutic strategies against bacterial infections. As part of our ongoing research to explore bioactive natural products from diverse resources, we investigated the antimicrobial compounds from Woodfordia uniflora, a flowering shrub unique to the Dhofar region of Oman. The plant has been used as a remedy for skin infections in Oman. However, to date, no study has examined the antimicrobial compounds in W. uniflora. Phytochemical analysis of the methanolic extract of W. uniflora leaves in combination with LC/MS-based analysis allowed us to isolate and identify four flavonoid-type analogs (1–4), procyanidin B3-3-O-gallate (1), rhamnetin 3-O-(6″-galloyl)-β-D-glucopyranoside (2), rhamnetin 3-O-α-L-rhamnopyranoside (3), and quercetin 3-O-(6″-galloyl)-β-D-glucopyranoside (4). The isolates have a novel mechanism of action; the compounds inhibit biofilm formation in methicillin-resistant Staphylococcus aureus (MRSA) and synergize with methicillin. Our metabolite analysis revealed that this synergizing activity by compounds was achieved by remodeling metabolism including central carbon metabolism and glutamine biosynthesis that resulted in abnormal cell formation and reduction in biofilm formation of MRSA. Taken together, these findings provide experimental evidence that rhamnetin 3-O-(6″-galloyl)-β-D-glucopyranoside (2) and quercetin 3-O-(6″-galloyl)-β-D-glucopyranoside (4) can be considered as potential therapeutic agents for the treatment of methicillin-resistant S. aureus-associated diseases.
Highlights
Antibiotic-resistant bacterial infection remains a major threat to public health; the surge of hospitalized patients with COVID19 increases the probability of transmission of nosocomial bacterial infections between the patients
The intensive phytochemical investigation of the EtOAc-soluble fraction using successive column chromatography as well as preparative and semi-preparative HPLC purification monitored by liquid chromatography/mass spectrometry (LC/MS) analysis led to the isolation of four flavonoid-type analogs (1–4) (Figure 1)
Phytochemical analysis of bioactive natural products found in the methanolic extract of W. uniflora leaves led to the isolation and identification of four flavonoidtype analogs procyanidin B3-3-O-gallate (1), rhamnetin 3O-(6 -galloyl)-β-D-glucopyranoside (2), rhamnetin 3-O-α-Lrhamnopyranoside (3), and quercetin 3-O-(6 -galloyl)-β-Dglucopyranoside (4)
Summary
Antibiotic-resistant bacterial infection remains a major threat to public health; the surge of hospitalized patients with COVID19 increases the probability of transmission of nosocomial bacterial infections between the patients. R. et al, 2020; Yu et al, 2020a), we investigated the bioactive compounds from Woodfordia uniflora collected in Oman. W. uniflora is a tall slender shrub belonging to Lythraceae and a native plant species of Oman. This plant is abundant throughout the Dhofar region of Oman and in the highaltitude regions of East Africa and the Middle East. In our recent study on the phytochemicals of W. uniflora leaves—the first phytochemical examination of the species— we identified 19 polyphenols including three new polyphenols, using antifungal bioactivity-driven LC/MS-based analysis; strong antifungal compounds against Cryptococcus neoformans and Candida albicans human fungal pathogens (Yu et al, 2020b) were found. Its anti-inflammatory effects were found to be mediated via the inhibition of nuclear factor kappalight-chain-enhancer of activated B cells (NF-κB) activation and regulation of the expression of pro-inflammatory cytokines such as IL-6 and IL-1β (Kim et al, 2021)
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