Brazilian Cerrado Plant Extract Restores Antibiotic Power Against Resistant Superbugs

Deep in the Brazilian Cerrado, a vast tropical savanna recognized as one of the planet’s most important biodiversity hotspots, grows an unassuming tree whose leaves may hold a partial answer to one of medicine’s most urgent problems. Researchers at the Federal University of Mato Grosso do Sul have reported that an ethanolic extract of Mouriri elliptica leaves, a species long used in traditional medicine to treat gastric ulcers and gastritis, can weaken multidrug-resistant bacteria and, crucially, restore the killing power of antibiotics that these pathogens had learned to defeat. The study, published in the open-access journal MicrobiologyOpen, combined detailed chemical profiling, microbiological testing, high-resolution microscopy, and animal safety studies into one of the most complete evaluations yet of this underexplored species.

The threat the researchers set out to address is well documented. The World Health Organization’s 2024 Bacterial Priority Pathogens List places carbapenem-resistant Gram-negative bacteria, including Acinetobacter baumannii and members of the Enterobacteriaceae family, among the most critical targets for new treatment strategies. In Brazilian hospitals, surveillance by the national health regulatory agency ANVISA has catalogued a grim roster of resistant organisms, from carbapenem-resistant Pseudomonas aeruginosa to cephalosporin-resistant Klebsiella pneumoniae. Because resistance genes circulate freely among humans, animals, and the environment, the field increasingly favors a One Health approach, and the new study embraced that perspective by testing bacteria isolated from both human hospital patients and veterinary clinical cases.

Chemically, the extract proved remarkably rich. Using high-performance liquid chromatography coupled with high-resolution tandem mass spectrometry, the team tentatively annotated 41 distinct metabolites. Eleven peaks belonged to the flavonoid family, largely in glycosylated forms, including derivatives of quercetin, kaempferol, and myricetin, along with catechin, epicatechin, epigallocatechin gallate, procyanidin B2, tiliroside, and prodelphinidin B3. Several of these flavonoid dimers and glycosides had never before been reported in the genus Mouriri. The analysis also revealed ellagic acid derivatives and, for the first time in this genus, pentacyclic triterpenes, with fragmentation patterns consistent with asiatic acid and terminolic or myrianthic acid. These compound classes are well known in the natural products literature for antimicrobial and antibiofilm properties, providing a plausible chemical basis for the biological effects that followed.

On its own, the extract showed meaningful but moderate antibacterial activity. Against a reference strain of Staphylococcus aureus, the minimum inhibitory concentration fell below 78.1 micrograms per milliliter, a level the authors classify as strong. Clinical isolates of S. aureus and S. pseudintermedius required 156.25 micrograms per milliliter, while the notoriously hardy Gram-negative pathogens Acinetobacter baumannii and Klebsiella pneumoniae yielded MIC values of 312.5 and 625 micrograms per milliliter, respectively. The reduced susceptibility of these Gram-negative organisms is unsurprising: their outer membranes, studded with lipopolysaccharides and restrictive porin proteins, form a formidable barrier that excludes many antimicrobial compounds, including most unmodified plant extracts.

The real headline came from the combination experiments. When the extract was paired with conventional antibiotics using the checkerboard microdilution method, synergistic interactions emerged against several of the most resistant strains. Combining the extract with ampicillin produced a fractional inhibitory concentration index of 0.09 against a beta-lactamase-producing Escherichia coli strain, 0.5 against clinical S. aureus, and 0.19 against K. pneumoniae when paired with ciprofloxacin. In practical terms, the presence of the extract cut the required antibiotic dose fourfold against S. aureus and K. pneumoniae and an impressive sixteenfold against E. coli. Additive effects extended this modulatory reach to S. pseudintermedius, a Shiga toxin-producing E. coli of veterinary origin, a multidrug-resistant Staphylococcus species, and A. baumannii. Notably, the K. pneumoniae isolate in the study was resistant to seventeen different antibiotics, including last-resort drugs such as colistin, meropenem, and ertapenem, yet the extract combination partially restored ciprofloxacin susceptibility.

Beyond killing planktonic bacteria, the extract attacked one of the most stubborn forms of resistance: the biofilm. Biofilms are sessile microbial communities encased in a self-produced extracellular matrix that shields cells from antibiotics and immune attack, and they are implicated in more than 65 percent of human infections, from endocarditis to catheter-associated disease. At 500 micrograms per milliliter, the extract inhibited biofilm formation by 73.3 percent in S. aureus and 68 percent in E. coli, and inhibition against the Gram-positive strain remained near 70 percent even at half that concentration. Atomic force microscopy provided striking visual confirmation: untreated S. aureus formed dense, well-organized biofilms of spherical cells roughly 780 nanometers in diameter, whereas extract-treated surfaces showed fragmented, disrupted architecture with markedly reduced matrix deposition.

One curious observation deserves attention. At the highest concentration tested, 1000 micrograms per milliliter, the extract actually stimulated biofilm formation in both strains, a paradoxical reversal reminiscent of the so-called Eagle effect described previously in bacterial and fungal biofilms, where higher antimicrobial concentrations sometimes exert weaker effects than lower ones. The authors caution that the mechanism behind this response remains unknown and will require further study, but the finding underscores a practical lesson for natural product development: dose optimization matters, and more is not always better.

Safety data provided an essential green light. In an acute oral toxicity assay following OECD guideline principles, mice received a single 2000 milligram per kilogram dose of the extract and were monitored for fourteen days. Body weight gain, relative organ weights, gross necropsy findings, and histopathology of the spleen, heart, liver, kidneys, lungs, and stomach all remained within normal limits in both sexes. Hematological parameters were largely unchanged, with the exception of a modest but significant rise in white blood cell counts in males, which the authors interpret as possible immunomodulatory activity rather than pathology. Serum biochemistry showed no signs of liver injury, though bilirubin levels dropped significantly in both sexes, a change the researchers link to the antioxidant properties previously described for Mouriri extracts.

The study’s One Health dimension amplifies its significance. Several of the most resistant organisms tested, including veterinary isolates of S. pseudintermedius resistant to eight antibiotics and E. coli strains resistant to up to eight drugs, came from animal clinical sources, reminding readers that resistant bacteria travel readily between animals and people through direct contact, food chains, and the environment. The authors also point to broader ecological and socioeconomic stakes: M. elliptica is native to the fire- and drought-adapted Cerrado, propagates readily under cultivation, and produces edible, antioxidant-rich fruits, meaning that a single species could simultaneously supply antimicrobial leads, nutrition, and income for local communities, strengthening the case for conserving a biome under severe threat.

Caveats remain, and the researchers are candid about them. The checkerboard assay, while a widely used screening tool with documented agreement with time-kill kinetics in prior literature, is not the gold standard for confirming synergy, and the precise molecular mechanisms by which the extract sensitizes bacteria, whether through efflux pump inhibition, membrane permeabilization, or interference with beta-lactamase enzymes, have not yet been demonstrated directly. Sub-chronic and chronic toxicity studies are also needed before any therapeutic development. Still, the convergence of chemical novelty, synergistic potency against WHO priority pathogens, demonstrable antibiofilm action, and a clean acute safety profile marks Mouriri elliptica as a promising candidate in the global search for antibiotic adjuvants, and a vivid reminder that solutions to the resistance crisis may be growing quietly in the world’s threatened savannas.

Subject of Research: Antibiotic-adjuvant and antibiofilm activity of Mouriri elliptica leaf extract against multidrug-resistant Gram-negative clinical bacteria

Article Title: Adjuvant Antibacterial Effects of Mouriri Elliptica Against Clinical Multidrug Resistant Gram‐Negative Bacterial Strains

Article References: Freire, T. V., Marques, A. C. D. F., Gonçalves, V. D. S., Moslaves, I. S. B., Toffoli‐Kadri, M. C., Silva, A. F. C. D., Giz, M. J., Figueiredo, P. D. O., Micheletti, A. C., & Yoshida, N. C. (2026). Adjuvant Antibacterial Effects of Mouriri Elliptica Against Clinical Multidrug Resistant Gram‐Negative Bacterial Strains. MicrobiologyOpen, 15(5), Article e70392. https://doi.org/10.1002/mbo3.70392

Image Credits: AI Generated

DOI: 10.1002/mbo3.70392

Keywords: antimicrobial resistance, Mouriri elliptica, Brazilian Cerrado, antibiotic adjuvants, multidrug-resistant bacteria, biofilm, flavonoids, triterpenes, Klebsiella pneumoniae, Acinetobacter baumannii, One Health, natural products