Biofilms are complex microbial communities that adhere to a surface and encase themselves in a viscous matrix they produce themselves. This structure protects bacteria from antibiotics and the immune system far more effectively than if they lived in a free-floating state, making biofilms one of the most common causes of hard-to-treat chronic infections — such as respiratory infections in people with cystic fibrosis and chronic obstructive pulmonary disease (COPD), chronic wounds, or infections associated with catheters and prosthetic devices. Added to this is the global rise in antibiotic resistance, which makes it increasingly urgent to have tools capable of predicting which treatment will work in each case.
A team at the Institute for Bioengineering of Catalonia (IBEC) has developed XpertBiofilm, a simple and accessible device that allows biofilms to be grown under continuous, controlled liquid flow, similar to what bacteria encounter in the human body — for example, in lung mucus, blood or urine. The study, published in the journal Colloids and Surfaces B: Biointerfaces, was led by Eduard Torrents, principal investigator of the Bacterial Infections and Antimicrobial Therapies group and associate professor at the University of Barcelona, together with Núria Blanco-Cabra, a researcher in the same group and first author of the study.
Most laboratory systems used to study how biofilms form rely on static plates, where the culture medium does not move. In the body, however, bacteria almost never grow in a still environment: the flow of blood, mucus or other fluids constantly generates friction on surfaces, known as shear stress. To use an analogy, shear stress is similar to what a stone experiences in a riverbed: in stagnant water it barely experiences any friction, but if the water flows strongly, that same stone is subject to constant drag and friction. This is what the researchers analyze in this work, at a microscopic scale: the shear stress that a moving liquid exerts on any surface it comes into contact with, including the surfaces where bacteria adhere.
Devices capable of reproducing this flow in a controlled way already exist, but they tend to be complex, expensive, and require specialized microscopy and staff with advanced technical training to analyze the results, which limit their use.
Flow, a key factor in biofilm formation
To overcome this limitation, the team designed and optimized the geometry of XpertBiofilm's growth chamber to achieve homogeneous flow and controlled shear stress over a small, removable piece (a round coverslip) on which the biofilm forms. Once the biofilm has grown, this piece can be analyzed directly with a microplate reader, without the need for specialized microscopes, allowing for more accessible and streamlined observation.
This finding is especially relevant in the context of cystic fibrosis and COPD, chronic lung diseases in which mucus is thicker and more viscous than usual, and which are frequently complicated by Pseudomonas aeruginosa biofilm infections. In the lungs of these patients, shear stress is far below the levels found in a healthy lung (around 80 mPa) or those generated by coughing (up to 170,000 mPa). The flow range that XpertBiofilm is able to reproduce in the laboratory — from 0.02 to 0.9 mPa — matches this low-shear-stress environment, which the authors themselves highlight as supporting the device's clinical relevance for modeling lung infections in cystic fibrosis.
Precisely within that low flow range, the team showed that the higher the flow, the more biofilm biomass P. aeruginosa forms — an opportunistic pathogen also very common in chronic wounds and infections associated with medical devices. According to the authors, this result helps explain why bacteria manage to adhere strongly to the airways in cystic fibrosis, and why, given the very low shear stress present, the airways' ability to sweep away and clear bacteria is greatly reduced in these patients, leading to chronic infections.
"Reproducing in the laboratory the flow conditions that bacteria actually encounter in the body in the context of a disease is key to understanding how biofilms form and, above all, to better predicting whether an antibiotic will work. XpertBiofilm allows us to do this with simple, accessible equipment, without relying on specialized microscopy," explains Eduard Torrents, who is also an ICREA Academia member.
A step toward faster, more personalized antibiotic testing
In addition to studying how the biofilm forms, the team confirmed that XpertBiofilm can be used to assess whether a given antibiotic is effective against an already-formed biofilm, using P. aeruginosa strains with distinct, known resistance profiles — demonstrating that the device correctly detected the expected response to the antibiotic used.
The team then went a step further: they used sputum samples directly from cystic fibrosis patients, without needing to first isolate a single bacterial strain in the laboratory. In both cases, the platform correctly predicted which antibiotic was more effective and which was not, consistent with each sample's already-known resistance profile, and allowing the most appropriate microbial therapy to be adjusted.
"Being able to form and analyze a biofilm directly from a sputum sample, without prior cultures, opens the door to faster antibiotic susceptibility testing tailored to each patient — something especially relevant in chronic infections such as those seen in cystic fibrosis," notes Núria Blanco-Cabra, first author of the study.
Next steps
Although the results are very promising, the study's authors themselves note that this is a laboratory-based validation, carried out with a limited number of bacterial strains and patient samples. The next step will therefore be to expand testing to a larger number of clinical samples and bacterial species before confirming its usefulness in routine clinical practice.
For now, XpertBiofilm does not replace the microbiological diagnostic methods already established in hospitals; rather, it is proposed as a complementary tool that, in the future, could help clinical staff more quickly choose the most appropriate, personalized antibiotic treatment for each patient.
