Phage-loaded hydrogel coating cuts drug-resistant biofilms on catheters and tubes in lab tests

A laboratory-made hydrogel coating loaded with a two-virus cocktail stripped mature biofilms of multidrug-resistant Acinetobacter baumannii from the surfaces of urinary catheters and endotracheal tubes, according to a new study published in Frontiers in Microbiology. In tests on real device segments, the coating reduced bacterial counts on latex Foley catheters by roughly 4 to 5 log units and on polyvinyl chloride endotracheal tubes by roughly 4 to 7 log units, depending on the incubation time, with the strongest effects seen after 48 hours. The work, led by researchers at KS Hegde Medical Academy and partner institutes at Nitte (Deemed to be University) in Mangalore, India, addresses a persistent problem in hospitals: indwelling devices give bacteria a surface to colonize, and once a biofilm forms, antibiotics struggle to penetrate it.

The study, published on 30 October 2026, was designed as an in vitro evaluation rather than a clinical trial. The authors developed a hydrogel composed of sodium alginate and polyvinyl alcohol, two polymers widely used in biomedical materials because of their biocompatibility and mechanical stability. Into this gel they embedded a cocktail of two bacteriophages, viruses that infect and kill specific bacteria, previously isolated from sewage water collected at Justice KS Hegde Charitable Hospital. The two phages, named vB_AbaM_561a and vB_AbaS_561b, were combined in equal proportions and mixed into the polymer solution at a concentration of 10^9 plaque-forming units per milliliter, a dose chosen to compensate for an anticipated loss of roughly one log of phage titre during gel formulation and storage.

Device segments were dip-coated in the phage-laden gel. Latex catheter pieces needed a single 15-minute immersion, while the more chemically resistant PVC endotracheal tubes required three sequential 15-minute dips to build an even film. The coated devices then underwent a crosslinking sequence: three to four freeze-thaw cycles alternating 12 hours at minus 20 degrees Celsius with 4 hours of thawing, which physically organizes the polyvinyl alcohol into a stronger network, followed by treatment with 2 percent calcium chloride, which ionically crosslinks the alginate into what polymer chemists call an egg-box structure. After an overnight incubation and a wash to remove residual calcium chloride, the result was a thin, solid film bonded to each device surface.

Physical characterization confirmed that the gel network survived phage loading. Scanning electron microscopy showed an interconnected porous architecture with a mean pore size of about 8 micrometers in the plain crosslinked gel and 8.5 micrometers in the phage-loaded version, with only minor surface irregularities and localized pore occupancy attributable to the embedded virus particles. Fourier transform infrared spectroscopy identified the expected hydrogen bonding between alginate and polyvinyl alcohol and confirmed calcium-mediated coordination of the alginate carboxylate groups, supporting formation of the crosslinked network without new chemical bonds that would indicate unwanted modification. Mechanical testing showed that crosslinking raised tensile strength from 1.22 megapascals in the uncrosslinked blend to 3.58 megapascals, with strain at break increasing from 14.4 to 22.1 percent. Adding phages caused a negligible drop in tensile strength to 3.51 megapascals but reduced elongation at break to 10.56 percent and lowered Young’s modulus from 17 to 13.6 megapascals, suggesting the virus particles slightly disrupt the polymer network’s uniformity while leaving it structurally adequate for coating applications.

Swelling and degradation behaviour shaped the choice of formulation. Pure sodium alginate swelled most at neutral pH, reaching a swelling index of 813.2 percent, while pure polyvinyl alcohol reached 513.9 percent. Among the blends tested at ratios of 1:2, 1:1 and 2:1 alginate to polyvinyl alcohol, the 1:1 mixture showed moderate swelling of 716.5 percent at neutral pH, which the researchers judged most suitable for coating device surfaces without obstructing lumens. Degradation proceeded gradually over 7 days in phosphate-buffered saline at both pH 6, chosen to mimic urinary tract conditions, and pH 7.5, representing near-neutral physiological conditions, with faster mass loss under acidic conditions, likely reflecting protonation of ionizable groups and accelerated hydrolytic cleavage of polymer chains.

Storage stability and release kinetics determined whether the encapsulated viruses remained viable long enough to be useful. Over 5 weeks of storage, phage titres in the hydrogel declined from 8.95 to 7.12 log10 PFU/mL at 4 degrees Celsius, a loss of less than one log unit, and from 8.78 to 6.98 log10 PFU/mL at 25 degrees Celsius, a loss of roughly two log units. Release assays in phosphate-buffered saline at 37 degrees Celsius showed pH-dependent behaviour: approximately 79 percent of the phages were released within 6 hours at neutral pH, compared with nearly 85 percent at acidic pH, with peak titres between 6 and 24 hours ranging from 7 to 9.7 times 10^8 PFU per square centimeter. The authors attribute the faster acidic release to partial disintegration of the gel network as ionizable functional groups become protonated, a property that could prove useful in the acidic environment of the urinary tract.

Antibacterial testing confirmed the coating’s activity against A. baumannii ATCC 19606, the host strain used in the study. In agar diffusion assays, hydrogel without phages produced no zone of inhibition, confirming the polymer matrix itself has no intrinsic antibacterial effect, while the phage-loaded hydrogel produced the largest clear zone after 24 hours of incubation, exceeding even the zone produced by directly applied phage lysate, consistent with sustained release of active viruses from the matrix. Growth inhibition assays in broth showed the same pattern: tubes with unloaded hydrogel turned turbid with bacterial growth, while tubes treated with either free phage lysate or phage-loaded hydrogel remained clear.

The antibiofilm results on actual device materials were the study’s central finding. Urinary catheter segments tested at pH 6 and endotracheal tube segments tested at pH 7.5 were incubated with A. baumannii for 24 and 48 hours across four conditions: untreated control, hydrogel coating without phages, direct phage lysate treatment, and phage-loaded hydrogel coating. At 24 hours, untreated catheter segments carried a bacterial load of 8.64 log10 CFU per milliliter, while phage-loaded hydrogel-coated segments showed a reduction of approximately 4 log units, comparable to the reduction achieved with direct lysate treatment, with p values below 0.0001. At 48 hours, the coated catheters showed roughly a 5 log reduction and the coated endotracheal tubes roughly a 7 log reduction relative to untreated controls, again with p values below 0.0001. Hydrogel-only coatings matched untreated controls in bacterial counts across all conditions. Scanning electron microscopy corroborated these counts, showing dense organized biofilm on hydrogel-only controls but marked disruption of biofilm structure at 24 hours and substantial depletion of bacterial cells with minimal residual biofilm at 48 hours on phage-loaded hydrogel-coated surfaces.

Cytocompatibility testing in a human gingival fibroblast cell line supported the material’s biological tolerance. MTT assays after 24 and 48 hours of exposure showed viability comparable to untreated controls, with a minor non-significant decrease at 48 hours. Colony formation assays over 14 days showed no significant reduction in colony-forming ability for cells exposed to the phage cocktail alone or to hydrogel alone, with colony formation percentages of 92.3 and 94.8 respectively, while cells exposed to the phage-loaded hydrogel showed a slight but statistically significant decrease to 87 percent relative to control. Acridine orange and ethidium bromide dual staining and Annexin V flow cytometry found apoptotic cell fractions of 0.46 percent for phage cocktail, 2.27 percent for hydrogel alone, and 1.6 percent for phage-loaded hydrogel after 48 hours, comparable to the 0.83 percent seen in untreated controls at the same time point, with no statistically significant differences detected.

The authors note that their two-phage cocktail may have limited host-range coverage against diverse A. baumannii isolates, and that the study was restricted to in vitro conditions that do not fully reproduce the physiological and microbial complexity of clinical settings. They identify further in vivo validation as essential before any clinical application. Within those limits, the work demonstrates that a sodium alginate and polyvinyl alcohol hydrogel can encapsulate lytic bacteriophages, preserve their activity through crosslinking and storage, release them in a pH-responsive and sustained manner, and deliver measurable antibiofilm reductions on the surfaces of two clinically common indwelling device materials, positioning the approach as a candidate strategy for preventing device-associated infections caused by multidrug-resistant bacteria.

Subject of Research: A phage cocktail-loaded sodium alginate and polyvinyl alcohol hydrogel coating tested in vitro against multidrug-resistant Acinetobacter baumannii biofilms on urinary catheters and endotracheal tubes

Article Title: Phage cocktail-loaded hydrogel coating prevents the biofilm formation of MDR Acinetobacter baumannii on indwelling medical devices

Article References: Rai, N. K., Suchithra, K. V., Mohan Raj, J. R., Patil, P., Mohana Kumar, B., & Shetty, V. A. (2026). Phage cocktail-loaded hydrogel coating prevents the biofilm formation of MDR Acinetobacter baumannii on indwelling medical devices. Frontiers in Microbiology, 17, Article 1990693. https://doi.org/10.3389/fmicb.2026.1990693

Image Credits: AI Generated

DOI: 10.3389/fmicb.2026.1990693

Keywords: Acinetobacter baumannii, bacteriophage, hydrogel, biofilm, medical devices, urinary catheter, endotracheal tube, antibiofilm, sodium alginate, polyvinyl alcohol, multidrug resistance, in vitro