Ancient Chinese Herb Yields a Polysaccharide That Kills Staph and Calms Runaway Inflammation

A polysaccharide extracted from the rhizome of Polygonatum kingianum, a perennial herb long prized in Traditional Chinese Medicine, has shown the ability to kill Staphylococcus aureus, dismantle established bacterial biofilms, and simultaneously rebalance the immune response in infected laboratory animals. The study, published in Food Science & Nutrition, arrives at a moment when the global toll of antimicrobial resistance has never been clearer. A recent systematic analysis attributed roughly 4.95 million deaths to bacterial resistance in 2019 alone, and projections suggest that burden will keep climbing through 2050 if new therapeutic options are not found. Against that backdrop, a natural compound that attacks pathogens and calms the host’s own inflammatory storm at the same time is exactly the kind of multi-target strategy researchers have been calling for.

The molecule, designated PKP, was isolated from dried rhizomes by hot-water extraction and ethanol precipitation, yielding nearly 36 grams of material from 200 grams of root with a carbohydrate purity of 99.4 percent. Structural characterization using high-performance gel permeation chromatography, monosaccharide analysis, and two-dimensional nuclear magnetic resonance revealed a mixed-type fructan with an average molecular weight of about 3.0 kilodaltons. Its backbone is composed overwhelmingly of fructose, 91.3 percent, linked through a combination of β-2,1 and β-2,6 fructofuranose bonds in a ratio of roughly 2.5 to 1, with smaller amounts of glucose and mannose and terminal α-glucopyranose units capping the chain. That architecture, the team reasoned, might allow the polysaccharide to interact with bacterial membranes while also serving as a recognizable signal to the mammalian immune system.

In laboratory assays, PKP proved markedly more potent against Gram-positive S. aureus than against Gram-negative Escherichia coli. The minimum inhibitory concentration against S. aureus was 400 milligrams per milliliter, and the minimum bactericidal concentration was 700 milligrams per milliliter, a ratio of 1.75 that formally classifies the compound as bactericidal rather than merely bacteriostatic. At that MIC, PKP killed 89.8 percent of S. aureus cells, with killing rates of 73.2 and 82.6 percent at 200 and 300 milligrams per milliliter respectively. E. coli proved far more stubborn, requiring concentrations up to 600 milligrams per milliliter to reach a killing rate of 72.1 percent. The researchers attribute this differential susceptibility to the outer membrane, selective porin channels, and powerful tripartite efflux pumps that shield Gram-negative bacteria from large, negatively charged molecules, whereas the teichoic-acid-rich envelope of Gram-positive organisms may offer PKP more accessible binding targets.

Time-kill kinetics added an important nuance. At the MIC, PKP held S. aureus growth flat for the first twelve hours, but optical density readings crept upward after the sixteen-hour mark, indicating a transient bacteriostatic effect that gradually waned. Doubling the concentration to 800 milligrams per milliliter abolished growth entirely across the full 24-hour observation window, a pattern typical of membrane-active agents whose killing accelerates sharply with concentration. The authors are candid about a limitation here: at such high polysaccharide concentrations, viscosity and osmotic pressure could contribute to apparent growth suppression, and they recommend future experiments with an inert high-molecular-weight control such as dextran to fully separate specific antimicrobial action from nonspecific physical effects.

Perhaps the most striking laboratory result concerned biofilms, the slimy, matrix-encased bacterial communities that make chronic S. aureus infections so notoriously resistant to antibiotics. Biofilm-embedded bacteria can tolerate antimicrobials at concentrations ten to a thousand times higher than their free-swimming counterparts, which is a principal reason chronic rhinosinusitis so often defeats conventional therapy. Yet when mature 36-hour S. aureus biofilms were challenged with PKP for 48 hours, crystal violet staining showed a steep, concentration-dependent collapse in biomass. Half the MIC left 74 percent of the biofilm intact, the MIC cut it to 52.6 percent, and twice the MIC reduced it to just 13.1 percent of control levels, an effect the authors describe as near-complete eradication. The steepness of that dose-response hints at a threshold mechanism, possibly saturation of the extracellular polymeric matrix or membrane disruption triggered only once a critical polysaccharide concentration is reached within the biofilm microenvironment.

To test whether any of this mattered in a living body, the team induced chronic rhinosinusitis in rats by placing S. aureus-soaked sponges in the nasal cavity and administering repeat bacterial instillations twice weekly for three weeks. All 60 animals modeled successfully, and the 24 most severely symptomatic rats were randomized to receive daily intranasal treatment with PKP at 200, 400, or 600 milligrams per milliliter for 14 days, alongside untreated infected and healthy control groups. The dose selection was deliberately grounded in translational math: converting the mid-dose of 177.8 milligrams per kilogram to a human equivalent dose using body-surface-area factors yields roughly 28.8 milligrams per kilogram, or about 1.73 grams of PKP per day for a 60-kilogram adult. Given the 17.96 percent extraction yield, that would require approximately 9.6 grams of dried herb, comfortably within the range of traditional daily intakes.

The histopathology told a clear story. Untreated infected rats showed dense neutrophilic infiltration in the sinus mucosa, averaging 139 neutrophils per high-power field, along with fibrous tissue hyperplasia, focal necrosis, and abscess formation. The lowest PKP dose barely moved the needle, but the 400 and 600 milligram-per-milliliter groups dropped infiltration to 55 and 34 neutrophils per high-power field respectively, with abscesses disappearing entirely at both higher doses. Cytokine profiling reinforced the picture: serum interleukin-6, a key driver of neutrophilic inflammation and tissue remodeling in chronic rhinosinusitis, fell significantly at the highest dose, while interleukin-22, a cytokine that maintains epithelial barrier integrity and stimulates antimicrobial peptide production, rose dose-dependently from depressed infection levels back toward healthy baseline values at 600 milligrams per milliliter.

Hematological analysis extended the findings to the whole animal. Infected rats treated with PKP showed leukocyte counts falling from 11.47 to roughly 6.5 × 10⁹ per liter, lymphocyte counts dropping from 9.23 to between 4.28 and 4.63 × 10⁹ per liter, and neutrophil counts declining as well, all pointing to a dampening of systemic inflammatory activation. Spleen and thymus indices rose relative to the untreated infected group, suggesting restored immune organ function, and total cholesterol declined modestly, hinting at metabolic effects the authors say warrant further study. Crucially, a parallel safety experiment in healthy, uninfected rats receiving identical intranasal regimens found no mucosal irritation, no significant changes in cytokine levels, and no disruption of red cells, platelets, hemoglobin, or most white cell parameters, with all values remaining within normal physiological ranges.

That last result may be the study’s most conceptually important contribution. Because PKP left the immune systems of healthy animals untouched while powerfully rebalancing the dysregulated immunity of infected ones, the compound appears to act through context-dependent immunomodulation rather than blunt stimulation or suppression. The authors are appropriately careful about the limits of their evidence: they did not directly quantify residual bacterial loads in the infected sinuses, so they frame the therapeutic benefit as a combined direct antibacterial and host-mediated effect rather than claiming definitive bacterial eradication. Testing against clinical isolates, including MRSA strains, and against a broader panel of Gram-positive and Gram-negative pathogens remains to be done, as does direct visualization of how PKP penetrates biofilm architecture.

Even with those caveats, the work bridges a gap that stalls many natural-product candidates: the leap from promising petri-dish data to demonstrable efficacy in a physiologically relevant disease model. A plant-derived fructan that kills planktonic S. aureus, erodes established biofilms, suppresses pathological interleukin-6 signaling, restores barrier-protective interleukin-22, and does so at doses achievable from ordinary quantities of a traditional herb, delivered by a route suitable for topical nasal therapy, offers a genuinely dual-pronged template for anti-infective development. If future studies confirm bacterial clearance in tissue and extend the findings to drug-resistant clinical strains, this humble Solomon’s seal relative could move from the apothecary shelf toward the front line of the resistance crisis.

Subject of Research: Antibacterial and immunomodulatory effects of a Polygonatum kingianum polysaccharide against Staphylococcus aureus infection

Article Title: Antibacterial and Immunomodulatory Activities of a Natural Polysaccharide Against Staphylococcus aureus Infection

Article References: Xia, X.-C., Peng, Y.-Q., Liu, L.-X., Cao, B., Zhong, X.-K., Wu, X.-D., & Liu, T. (2026). Antibacterial and Immunomodulatory Activities of a Natural Polysaccharide Against Staphylococcus aureus Infection. Food Science & Nutrition, 14(10), Article e72411. https://doi.org/10.1002/fsn3.72411

Image Credits: AI Generated

DOI: 10.1002/fsn3.72411

Keywords: Polygonatum kingianum, polysaccharide, fructan, Staphylococcus aureus, antimicrobial resistance, biofilm, chronic rhinosinusitis, immunomodulation, interleukin-6, interleukin-22, natural products, MRSA