NEWS
A Cow Rumen Enzyme Dissolves Superbug Biofilms on Gauze
IISc bound a cow rumen enzyme to gauze that strips Acinetobacter biofilms without killing the bacteria, a bet on old antibiotics rather than a new drug.
An IISc enzyme from cow-rumen microbes cut Acinetobacter baumannii on gauze by 5.3 log10, a study published 31 July 2026 found. The protein, named CRhAB, leaves the bacteria alive and dissolves the sugar matrix that hides them from drugs and immune cells. Researchers chemically bound it to clinical gauze and tested the dressing on infected mouse wounds.
The work sits in the peer-reviewed CRhAB gauze study in npj Biofilms and Microbiomes, from a team led by Debasis Das of inorganic and physical chemistry and Dipshikha Chakravortty of microbiology and cell biology at the Indian Institute of Science in Bengaluru. First author Reshma Ramakrishnan, a former Ph.D. student in Das’s lab, is also named on an IISc patent filed in July 2025.
A Cow’s Stomach Was the Search Site
The group did not purify a protein from cow tissue. It searched genomic catalogues of rumen microbes that already cut the tough plant sugars in cattle feed, then made the standout enzyme in the lab. Das, a co-corresponding author, said sugar chains are one of the main parts of bacterial biofilms, “constituting 45% to 95%,” and that those chains cross-link into a scaffold that holds the community together.
CRhAB, short for cow rumen hydrolase against A. baumannii, belongs to glycoside hydrolase family 10, a class of proteins better known for chewing plant cell walls than for hospital work. The rumen was a rational place to look, because cellulose and related sugars dominate a cow’s diet, and similar sugar-cutting enzymes sit in the guts of other grazers. The animal in the headline is the sampling site, not a unique factory.
Biofilms are not a smear of loose cells. They are packed communities wrapped in sugars, proteins, fats, and extracellular DNA, a physical barrier that slows drugs and immune cells. A. baumannii builds that wrap on wounds and on plastic surfaces in wards, which is why the same bug keeps turning up on catheters, ventilators, and dressings after a course of antibiotics has already failed.
CRhAB Erodes the Matrix and Stops There
Most new antibacterial programs still try to kill the cell. This enzyme is built to do the opposite. It strips the wrap so macrophages can reach the bacteria and so older drugs can move through the wreckage. Heat-killed CRhAB did not give the same immune lift, which is the control that shows the live protein, not a leftover contaminant, is doing the cutting.
Matrix inhibition or disruption makes A. baumannii more vulnerable. Instead of directly killing the bacteria, it weakens their defenses, potentially restoring the effectiveness of existing antibiotics while reducing the selective pressure that drives antibiotic resistance.
Reshma Ramakrishnan, first author, Indian Institute of Science
After the matrix came off, RAW 264.7 macrophages took up about 20% more of the freed cells than they did with untreated or heat-inactivated controls, the preprint figures show. The combined treatment group cut viable cells by 4.1 log10. The enzyme also damped the bacteria’s own biofilm genes, so the community was worse at rebuilding the wrap while it was being torn down.
What the enzyme does in the dish:
- New films: CRhAB blocked biofilm from forming on test surfaces when it was present from the start.
- Mature films: It tore down established A. baumannii communities under conditions the authors call compatible with living tissue.
- A second pathogen: The same protein hit biofilms of Klebsiella pneumoniae, another ESKAPE hospital bug.
- Immune access: With the wrap gone, more macrophages stuck to and swallowed the exposed cells.
Chakravortty, the other co-corresponding author, said both species “are among the most notorious pathogens in the ESKAPE group, and thankfully, this enzyme acts against both.” ESKAPE is the shorthand clinicians use for Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species, the cluster that dominates hard-to-treat hospital infections. One enzyme that cuts two of those films is a practical lure for wound-care makers who cannot stock a different protein for every species on a swab.
The Bengaluru lab has been on this path before. In 2024 the same group reported a different rumen enzyme, GH-B2, that made hospital K. pneumoniae strains more open to meropenem, Nature India said at the time, including a 15-fold rise in sensitivity in lab tests and a 250-fold rise when the enzyme was present as the film first formed. CRhAB is the later protein, aimed at A. baumannii, with Klebsiella still in range, and this time the team sewed the chemistry onto cloth.
How Many New Drugs Target WHO Critical Bacteria?
WHO’s 2024 Bacterial Priority Pathogens List keeps carbapenem-resistant A. baumannii as critical, alongside carbapenem-resistant Enterobacterales (the family that includes Klebsiella) and rifampicin-resistant tuberculosis. Critical is the top bin, above high and medium. Carbapenem drugs are among the last pills that still work on many Gram-negative rods, so a bug that shrugs them off has few remaining options on a standard chart.
A 2024 Lancet analysis by the Global Research on Antimicrobial Resistance project estimated 4.71 million deaths associated with AMR in 2021, including 1.14 million deaths attributable to resistance. Among Gram-negative bacteria, carbapenem resistance was tied to 1.03 million associated deaths that year. Forecasts in the same paper put attributable deaths at 1.91 million a year by 2050 if current trends hold.
The drug pipeline that is supposed to meet that list is thin. WHO’s October 2025 review counted 90 antibacterials in clinical development, down from 97 in 2023. Fifty are classic small-molecule antibiotics and 40 are non-traditional bets such as phages, antibodies, and microbiome agents. Only 15 of the 90 met WHO’s bar for innovation, and the agency said only five drugs against critical bacteria in that set had clear activity. Since July 2017, 17 new agents against priority pathogens have won marketing rights, and only two belong to a new chemical class.
| Pipeline fact (WHO, cut-off 15 February 2025) | Number |
|---|---|
| Antibacterials in clinical development | 90 (down from 97 in 2023) |
| Traditional small-molecule agents | 50 |
| Non-traditional agents (phages, antibodies, others) | 40 |
| Agents WHO judged innovative | 15 |
| Agents with activity against at least one critical pathogen | 5 |
| New chemical classes approved since July 2017 | 2 of 17 authorizations |
| Preclinical programs, mostly at firms with under 50 staff | 232 |
Dr Yukiko Nakatani, WHO’s assistant director-general for health systems, said the pipeline of new treatments and diagnostics is “insufficient to tackle the spread of drug-resistant bacterial infections.” That is the hole a matrix enzyme is trying to occupy. If the wrap is the thing that makes old drugs fail, a protein that cuts the wrap does not need to win a new-class designation to change a wound.
The Enzyme Gauze Cut Colonization 5.3 Logs
Free enzyme in a well is a paper. A dressing a nurse can tape down is a product sketch. The team chemically bound CRhAB to clinical-grade gauze and ran three loadings, then picked the heaviest coat for the animal work.
Three Enzyme Doses on Clinical Gauze
| Dressing | Enzyme on the cloth | What the plate assay showed |
|---|---|---|
| CRhAB-0.5-G | 0.5 mg/cm² | Biofilm on the gauze fell as the dose rose |
| CRhAB-1.2-G | 1.2 mg/cm² | Further drop in colony counts over three days at 37 C |
| CRhAB-2.6-G | 2.6 mg/cm² | 5.3 log10 fewer A. baumannii than plain gauze |
Unmodified gauze and oxidized gauze without enzyme were the controls. Colony counts fell in step with how much protein was stuck to the fibers, and CRhAB-2.6-G was the only loading the authors carried into mice. Binding the protein to the cloth is the practical move: a rinse or a trickle of wound fluid is less likely to wash a tethered enzyme off the wound in the first hour.
Colistin Plus Gauze in Infected Mice
The mouse design ran four days. Infected groups had five animals each. Uninfected wounds, used as a healing baseline, had three. Treatment arms were plain gauze, plain gauze plus subcutaneous colistin at 20 mg/kg every 48 hours, CRhAB gauze at 2.6 mg/cm² alone, and CRhAB gauze plus the same colistin course. Colistin is a last-resort Gram-negative drug with a narrow safety margin, which is why pairing it with a non-killing enzyme is a deliberate test: if the wrap is gone, a hard drug might work at the doses already in use.
Tissue from day 4 was stained for macrophages (F4/80) and neutrophils (Ly6G). The abstract’s claim is blunt for a methods paper: the enzyme dressing suppressed colonization and sped closure in the infected-wound model. The authors did not report a human trial. They did report that the dressing had to stay put, which turned out to be the messy part.
The Mouse Model Almost Failed on Tape
Ramakrishnan said building a reliable mouse wound infection model was a central obstacle, and that “maintaining the enzyme-immobilized gauze over the wound throughout the study was particularly difficult because the mice naturally tried to remove the dressing.” The group had to change the setup so the cloth stayed on without extra stress on the animals. Anyone who has watched a postoperative patient pick at tape will recognize the problem. A bioactive dressing that works in a restrained mouse still has to survive a human who rolls over in bed.
That is also why the next object in the lab is not another well plate. The team is building a patch-style dressing for hard wounds, including diabetic foot infections, where biofilms and poor blood flow already stall closure. Ramakrishnan has also described an inhalable or nebulizable CRhAB mix aimed at the lung, where A. baumannii and K. pneumoniae cause stubborn respiratory infections. Delivery is the whole remaining argument. An enzyme that dies in the bloodstream, or that never reaches a film on a ventilator tube, is a bench result.
Dispersin B’s Two-Decade Detour
Matrix-cutting enzymes are not a new idea, which is the caution hanging over CRhAB. Dispersin B, a glycoside hydrolase family 20 protein from the oral bacterium Aggregatibacter actinomycetemcomitans, cuts poly-N-acetylglucosamine, a different sugar polymer that many staphylococci and some Gram-negatives use to glue a film together. A 2024 review in Pathogens walked through nearly 100 studies of dispersin B published since the enzyme was found about 20 years ago, including work that made biofilms easier for antibiotics, silver dressings, phages, and macrophages to finish off.
Kane Biotech licensed that enzyme and built a hydrogel. Company filings in 2026 still describe product work on a DispersinB hydrogel for surgical and acute wounds, with a safety trial penciled for 2027. An acne cleanser using the same protein has a ClinicalTrials.gov record (NCT06729450). The commercial wound gel Kane is selling in the United States, revyve, is a separate 510(k)-cleared antimicrobial product, not the rumen enzyme and not a completed dispersin B drug. Two decades after the first papers, the best-studied antibiofilm hydrolase is still circling the clinic.
Enzyme antibiofilm, in order:
- Early 2000s: Dispersin B is identified as a PNAG-cutting hydrolase from A. actinomycetemcomitans.
- 2014: Dispersin B gels and sprays are tested with silver dressings and antimicrobial peptides against wound bacteria, including A. baumannii.
- May 2024: WHO’s updated priority list keeps carbapenem-resistant A. baumannii in the critical bin.
- November 2024: The IISc group publishes GH-B2, a rumen enzyme, against K. pneumoniae biofilms.
- 15 July 2025: IISc files Indian patent 202541067611 on the CRhAB findings, naming Das, Chakravortty, Ramakrishnan, and Kirti Parmar as inventors.
- 31 July 2026: The CRhAB gauze paper is published, with mouse wounds and a 2.6 mg/cm² dressing.
CRhAB and dispersin B cut different sugars and come from different microbes. The shared lesson is regulatory and practical: an enzyme that does not kill can be classed as a device, a biologic, or a combination product, and that paperwork has eaten years. IISc’s move to lock the protein onto gauze is an attempt to enter that process with a familiar object, a piece of cloth, rather than a free protein drip.
IISc Filed a Patent and Began a Patch
The competing-interest note on the Nature page is unusually specific for a methods paper. A patent application went to India’s Patent Office on 15 July 2025, serial 202541067611, filed by IISc, covering the data in the article. Status at publication was filed, not granted. Funding listed for Das includes the Department of Biotechnology, BFI-BIOME, the Anusandhan National Research Foundation, and the Science and Engineering Research Board; Ramakrishnan held a Prime Minister’s Research Fellowship.
Velpandi Ramachandran, a co-author in Das’s department, produced the gauze images that ran with the paper. The dressing in those frames is still a lab object. No hospital has it. No regulator has judged it. The mouse groups were small, the follow-up was four days, and the animals had to be stopped from peeling the test article off their own backs. Those are ordinary limits for this stage, and they are also why a 5.3 log10 plate result is not a wound-care launch.
The bet the paper is making is narrower than the cow-gut headlines. If the sugar wrap is why last-resort drugs fail on a wound, then a hydrolase that only cuts the wrap can sit next to colistin, meropenem, or a macrophage and change the outcome without adding another killing pressure. That is the product the patent is trying to own: an enzyme on a dressing, resistance-agnostic because it never had to win a fight with the cell wall.
Frequently Asked Questions
What is the CRhAB enzyme made of, chemically?
CRhAB is a glycoside hydrolase family 10 protein catalogued as UniProt E9NSH9, found by searching carbohydrate-active enzymes in cow-rumen microbial genomes and then produced in the laboratory as a recombinant protein. Family 10 hydrolases are better known as xylanases and related plant-sugar cutters; the IISc screen asked whether that chemistry would also cut the sugar polymers inside an A. baumannii film. It is not a cow gene product in the sense of a bovine enzyme purified from tissue.
Why can a biofilm force doctors to raise an antibiotic dose so far?
The wrap slows diffusion, so the concentration that reaches buried cells can fall far below the dose in the blood or on the dressing, and the same wrap blocks immune cells. In coverage of the group’s 2024 Klebsiella paper, IISc said the matrix can raise the antibiotic dose needed by 1,000 times in some cases. Biofilms also contain proteins, fats, and extracellular DNA; CRhAB is aimed at the sugar fraction, which Das said can be 45% to 95% of the matrix, not at every component at once.
Did IISc already patent the enzyme dressing?
IISc filed Indian patent application 202541067611 on 15 July 2025, with inventors Debasis Das, Dipshikha Chakravortty, Reshma Ramakrishnan, and Kirti Parmar, and the Nature paper states that the filing covers the data reported there. Filing is not a grant, and it is not a license to sell a dressing. It is a claim on the matrix-cutting enzyme and the bound-gauze format while the group works on a patch and, later, a lung formulation.
How is CRhAB different from dispersin B?
Dispersin B is a family 20 hydrolase from Aggregatibacter actinomycetemcomitans that cuts poly-N-acetylglucosamine, a polymer many staphylococci use to hold a film together, and it has been in the literature for about 20 years. CRhAB is a family 10 rumen-microbe enzyme aimed at A. baumannii polysaccharides, with extra activity against K. pneumoniae, and it was only characterized in this 2026 paper. They share a strategy, strip the wrap rather than kill the cell, and they do not share a sugar target or a clinical history.
Disclaimer: This article is news reporting on a published laboratory and mouse study; it is for information only. It is not medical advice, a treatment recommendation, or a claim that CRhAB gauze, CRhAB patches, or any enzyme dressing is safe or effective in people. Readers who have a wound infection, a diabetic foot ulcer, or a drug-resistant illness should see a qualified physician or infectious-disease specialist before changing any dressing, antibiotic, or care plan. Figures, patent status, and product plans reflect the cited papers, WHO reports, and company records as of 25 August 2026 and may change as trials and filings move.
