Mucus flow changes the verdict on the antibiotic

The laboratory likes stillness. Bacteria in the body do not. Classic antibiotic susceptibility testing grows microbes in still culture media, like a motionless puddle. In a lung, a wound, or around a catheter there is almost always movement: mucus, blood, urine. That frictional drag on a surface — shear stress — changes how bacteria build a biofilm, the sticky shield that protects them from drugs and the immune system. The paradox is simple: a plate result can say “the drug works,” while in the patient the biofilm already blocks it.

A team at the Institute for Bioengineering of Catalonia (IBEC) in Barcelona built an answer to that mismatch. In Colloids and Surfaces B: Biointerfaces (DOI: 10.1016/j.colsurfb.2026.116013), Núria Blanco-Cabra, José Huguet, Josep Samitier, Romén Rodríguez-Trujillo and Eduard Torrents describe XpertBiofilm — a simple platform that grows biofilm under controlled, continuous liquid flow and then lets you read it out with an ordinary microplate reader, without specialized microscopy.

Still water lies about infection

A biofilm is not “dirt on a dish.” It is a community of bacteria stuck to a surface and wrapped in a viscous matrix they produce themselves. That structure protects the pathogen better than free-floating cells. That is why chronic infections in cystic fibrosis (CF), COPD, chronic wounds, and around catheters and implants are so hard to clear. Add rising antibiotic resistance, and clinics need tools that predict which drug will work for this patient — not only for a catalogue strain.

Most lab systems used to study biofilms sit still. The medium does not move. In the body, bacteria rarely get that luxury. Blood, mucus or other fluids constantly rub against surfaces — that is shear stress. IBEC’s analogy is apt: a stone in still water feels almost no friction; the same stone in a rushing river is dragged and scraped. At microscopic scale, the same thing happens on the surface where bacteria attach.

Devices that recreate controlled flow already exist. They are usually complex, expensive, and require specialized microscopy and highly trained staff. That is a barrier to routine use. XpertBiofilm aims at the gap: conditions closer to the body, equipment accessible to an ordinary lab.

What was built

The authors designed the growth-chamber geometry for homogeneous flow and controlled shear over a small, removable round coverslip. The biofilm grows on that surface. After culture, the coverslip can be removed and read directly in a microplate reader — a tool known in almost every microbiology or biochemistry lab. No separate imaging factory is required.

The flow range the platform recreates in the lab is about 0.02–0.9 mPa. That is a low-shear window typical of the thick mucus in lungs of people with cystic fibrosis and COPD. For comparison: in a healthy lung shear is on the order of ~80 mPa, and coughing can generate up to ~170,000 mPa. In other words, XpertBiofilm does not imitate a coughing storm. It models the quiet, viscous environment where Pseudomonas aeruginosa — an opportunistic pathogen common in CF, wounds, and device-related infections — can settle firmly.

Exactly in that low range the team showed the key result: the higher the flow (within the studied window), the more P. aeruginosa biofilm biomass. That is not the intuition “more motion = fewer bacteria.” In CF, low flow and sticky mucus mean the airways sweep pathogens away less effectively. Bacteria cling harder. The result helps explain why chronic infections in this setting are so stubborn — and why a test in a still puddle may miss that dynamics.

Eduard Torrents, head of the Bacterial Infections and Antimicrobial Therapies group at IBEC, associate professor at the University of Barcelona and ICREA Academia member, puts it plainly in the IBEC release: reproducing in the lab the flow conditions bacteria actually meet in disease is key to understanding biofilm formation and — above all — to better predicting whether an antibiotic will work. XpertBiofilm is meant to do that with simple, accessible equipment, without depending on specialized microscopy.

From reference strains to patient sputum

The platform does not stop at biomass measurement. The team checked whether it can assess antibiotic efficacy against an already formed biofilm. First they used P. aeruginosa strains with distinct, known resistance profiles. The device correctly detected the expected response to the drug used — it did not guess; it reflected the known profile.

Then they went further: they took sputum samples directly from cystic fibrosis patients, without first isolating a single strain in culture. In both cases the platform correctly indicated which antibiotic was more effective and which was not — consistent with each sample’s already-known resistance profile. That opens thinking about faster adjustment of microbial therapy, instead of waiting for a full isolation cycle and classic tests under conditions that do not resemble the lung.

Núria Blanco-Cabra, first author, stresses in the IBEC release that being able to form and analyze a biofilm directly from sputum, without prior cultures, opens the door to faster, more personalized susceptibility testing — especially relevant in chronic infections such as those in cystic fibrosis. That is the punchline of the paradox: not a new antibiotic, but a more honest measurement context.

A clinical paradox, not a marketing one

Why can classic AST mislead on biofilms? Because it often tests planktonic cells or biofilm grown in static conditions. The drug “kills” in the dish. In the patient the same population sits under a matrix, in a flow that shaped its structure. The lab result looks optimistic. The patient does not improve. The clinician raises the dose or changes the regimen — and the problem is not only a resistance gene, but the conditions in which the pathogen lives.

XpertBiofilm does not solve genetic resistance. It changes the question: how does this biofilm, under this flow, respond to the drug? For a hospital and a diagnostic lab that is a different category of value than another agar plate. It is closer to engineering disease conditions than to another stain.

At the same time the authors set their own limits. This is laboratory validation, with a limited number of strains and patient samples. Next step: more clinical samples and more bacterial species before claiming usefulness in routine practice. For now XpertBiofilm does not replace established hospital microbiology methods. It is proposed as a complementary tool that, in the future, could help choose a better-matched antibiotic faster. That modesty in the IBEC release matters: it is easy to sell an “AST revolution,” harder to keep the trust of a lab that answers for patient safety.

Here the paradox returns in practice. A hospital does not need another device that looks modern at a conference. It needs a test that lowers the risk of a wrong drug choice for biofilms — without stretching the diagnostic path by days and without requiring specialized microscopy. XpertBiofilm sits exactly at that junction: conditions closer to disease, readout closer to routine.

Maturity estimate: TRL 4. There is a platform prototype, controlled physical conditions, validation on strains with known profiles, and a first pass on CF sputum without isolation. There is no broad clinical validation, no proof the device will enter the IVDR/FDA path as a routine test, and no data on throughput in a large hospital lab. That is honest deep tech: already beyond a pure idea, still before standard of care.

What this means for the market and for Poland

The buyer perspective is clear: microbiology labs, hospitals with CF/COPD units, AST system makers, and IVD firms looking to differentiate from classic panels. The barriers are equally predictable:

• clinical validation against standard of care;
• diagnostic-device regulation (IVDR in the EU, FDA in the US);
• throughput and cost per sample in a real lab;
• intellectual-property protection versus existing flow cells and biofilm platforms;
• staff training — here the simplicity advantage (microplate reader instead of specialized microscopy) may be decisive.

For Poland, cystic fibrosis and chronic biofilm infections are not exotic. CF centers, pulmonology wards and hospital labs weigh antibiotic decisions daily amid rising resistance. The Barcelona platform will not rewrite guidelines tomorrow. It does show a direction for judging spin-offs and IVD projects: value does not always sit in a new drug molecule, but in measurement conditions that closer match the disease.

Polish labs have routine diagnostic experience and growing awareness of biofilms on implants and wounds. The gap is often equipment that joins flow physics with a simple readout. XpertBiofilm is a signal: deep tech in infection is also hydrodynamic engineering at coverslip scale, not only a new antibiotic from the catalogue.

Time is a separate issue. A chronic CF infection does not wait for a perfect protocol. Every day on the wrong antibiotic is another generation of biofilm and another chance to select resistance. That is why a result “without prior strain isolation” carries clinical weight even while the device remains a complement, not a replacement for the hospital standard.

A deep-tech investor should ask control questions: is the 0.02–0.9 mPa range enough for organs beyond the CF model? Will the sputum-without-isolation result hold on a larger cohort? Do cost and cycle time beat classic AST enough for a lab to change its workflow? For now the IBEC paper answers: within the described range — yes for the mechanism and for agreement with known profiles; in routine care — not yet known.

Still plate versus mucus current

The mode of this story is paradox, not layer-by-layer anatomy and not a company duel. Two conflicting pictures: the lab likes stillness; the body is almost never still. A classic test in still medium can be convenient and misleading at once. XpertBiofilm does not promise a magic drug. It promises a more honest context: the same biofilm, but under shear closer to a diseased lung, read out on equipment the lab already has.

If later stages — more species, more samples, comparison with standard of care — confirm the profile from the Colloids and Surfaces B paper, biofilm-infection diagnostics will get a tool closer to the patient’s reality than another motionless dish. For now we have concrete numbers worth remembering: the 0.02–0.9 mPa range, the contrast with a healthy lung (~80 mPa) and cough (up to ~170,000 mPa), and the finding that in this window higher flow means more biomass of P. aeruginosa. The rest is the road from TRL 4 to hospital routine — with a map of mucus physics instead of guessing at the plate.

Sources

1. Núria Blanco-Cabra, José Huguet, Josep Samitier, Romén Rodríguez-Trujillo, Eduard Torrents, A simple diagnostic platform reveals shear stress as critical in biofilm development, Colloids and Surfaces B: Biointerfaces 268 (2026) 116013. DOI: 10.1016/j.colsurfb.2026.116013
2. IBEC, An IBEC device simulates natural conditions to grow biofilms and test their antibiotic susceptibility more accurately (16 Sep 2026): ibecbarcelona.eu
3. Phys.org, Device simulates natural conditions to grow biofilms and test antibiotic susceptibility more accurately: phys.org/news/2026-09-device-simulates-natural-conditions-biofilms.html