Extracts of Sida cordifolia contain polysaccharides possessing immunomodulatory activity and rosmarinic acid compounds with antibacterial activity

Haroon Iqbal, Claire L Wright, Sue Jones, Goncalo Rosas da Silva, John McKillen, Brendan F Gilmore, Owen Kavanagh, Brian D Green

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BACKGROUND: The overuse of antibiotics has led to increased antimicrobial resistance, but plant-derived biological response modifiers represent a potential alternative to these drugs. This investigation examined the immunomodulatory and antibacterial activities of Sida cordifolia (used in ethnomedicinal systems to treat infectious disease).

METHODS: Successive extractions were performed from the roots of these plants in hexane, chloroform, methanol and water. Immunomodulatory activity was determined in a series of experiments measuring the responses of splenocytes, macrophages and an in vivo model of innate immunity (Galleria mellonella). Antibacterial activity was assessed by determining minimum inhibitory/bactericidal concentrations (MIC/MBCs) for various Gram-positive and Gram-negative bacterial strains.

RESULTS: Immunomodulatory activity was confined to the aqueous extract, and further fractionation and biochemical analysis yielded a highly potent polysaccharide-enriched fraction (SCAF5). SCAF5 is a complex mixture of different polysaccharides with multiple immunomodulatory effects including immune cell proliferation, antibody secretion, phagocytosis, nitric oxide production, and increased expression of pro-inflammatory cytokines. Furthermore, Galleria mellonella pre-treated with SCAF5 produced more haemocytes and were more resistant (P < 0.001) to infection with methicillin-resistant Staphylococcus aureus (MRSA) with a 98% reduction in bacterial load in pre-treated larvae compared to the negative control. The antibacterial activity of Sida cordifolia was confined to the methanolic fraction. Extensive fractionation identified two compounds, rosmarinic acid and its 4-O-β-d-glucoside derivative, which had potent activity against Gram-positive antibiotic-resistant bacteria, including MRSA.

CONCLUSIONS: Sida cordifolia counters bacterial infections through a dual mechanism, and immunomodulatory polysaccharides from this plant should be isolated and characterised to realise their potential as anti-infective agents. Such properties could be developed as an antibiotic alternative (1) in the clinic and (2) alternative growth promoter for the agri-food industry.

Original languageEnglish
Article number27
JournalBMC complementary medicine and therapies
Publication statusPublished - 27 Jan 2022

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© 2022. The Author(s).


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