The study showed that bacterial signals across biofilms affected by surface structure

Similar to the way cells within human tissues communicate and work together as a whole, bacteria are also able to communicate with each other through chemical signals, a behavior known as quorum signaling (QS). These chemical signals are spread across a biomembrane in which colonies of bacteria form after they reach a certain density, and are used to help the colonies forage for food, as well as to defend against threats, such as antibiotics.

“QS helps them build infrastructure around them, like a city,” described Dharmesh Parmar, Postdoctoral Researcher in Jonathan Swedler Lab (CABBI/BSD/MMG), James R. Eiszner Family Endowed Chair in the Chemistry Department. “Biofilms have channels that allow nutrients and information to pass through in the form of chemical signals. They also allow for cross-talk between colonies if there is a threat or stress in the environment.”

Biofilm formation and subsequent antibiotic resistance can be especially dangerous for people who are immunocompromised or have diseases such as cystic fibrosis (CF), which stagnates a surface of mucus inside the lungs that bacteria can attach to more easily. To better understand the surface factors that influence or inhibit biofilm formation in the presence of antibiotics, researchers from Sweedler’s lab at the University of Illinois Urbana-Champaign, along with collaborators at the University of Notre Dame, measured the rate of biofilm formation via QS in bacteria normally acquired in infections. Hospitals, Pseudomonas aeruginosa.

P. aeruginosa rapidly forms biofilms on a variety of surfaces, hastening when colonies begin to communicate with QS, and making antibiotic treatment difficult. In addition, P. aeruginosa can vary in the thickness of the biofilm it produces. The “mucosal” strain produces a thicker biofilm than the non-mucosal strain, and is often associated with infection in patients with cystic fibrosis, an inherited condition that increases mucus stickiness and accumulation in the lungs.

In the study, both strains were grown on fabricated surfaces that varied in structure, one being uniform or “unformed,” the other “patterned” with blocky clumps. The researchers then measured how quickly the colonies were able to initiate communication with the QS while they were growing either in the presence of antibiotics or not. QS was detected using mass spectrometry and Raman imaging, which measures the presence of signaling molecules associated with behavior.

The first thing the researchers noticed was that the antibiotics slowed the growth of biofilms and the production of QS molecules across strains and types of structures. Next, the researchers found that surface type had a significant effect on the non-mucous strain, as the patterned structure was associated with a longer latency before expression of QS molecules peaked. This was not the case for the thick mucous strain.

“While the effect of antibiotics slowing biofilm growth did not surprise us, the significant and differential effect on surface structure was striking,” Swedler said.

“In the non-mucosal strain, the surface pattern had a significant effect on QS signal properties,” Parmar added. “In the case of the mucosa, the surface composition had very little effect on its metabolic signatures.”

The researchers also discovered how the distribution of QS signaling molecules varied across different parts of the biofilm when grown on a flat surface and exposed to antibiotics. Samples were taken from “static biofilms”, in which the biofilm adheres to the surface, “supernatants” or liquid culture medium, and “granular biofilms”, which form on top of the liquid medium and interact with air.

The researchers found that the supernatant and the biofilm contain signaling molecules associated with stress response, while the static biofilms do not. Researchers believe this is because the liquid component of the biofilm is what allows bacteria to float along and start new colonies elsewhere, but in the process bacteria are also exposed to threatening situations, such as the presence of antibiotics.

By comparing the behavior of QS during biofilm growth across these different treatments, researchers can better understand how and what type of molecules this type of bacteria uses, and gain new insights into bacterial growth.

“P. aeruginosa biofilm is very challenging to eradicate using currently available antibiotics, and so our aim for this study was to understand the factors governing the growth and stability of these biofilms, and how bacteria escape from these biofilm structures to colonize new sites,” Parmar explained.

“The chemically informative methods and analytical techniques we used allowed us to probe these complex molecular events related to biofilm formation across space and time,” Swedler explained.

The team says the next step is to use these improved analytical techniques to measure QS signals on lung slices from mice, rather than on fabricated structures like those used in the current study. Because Plasmodium aeruginosa is often associated with infections in the lungs of cystic fibrosis patients, understanding how it forms biofilms in the lungs can help scientists design ways to slow or prevent the growth of the bacteria in these patients.

Parmar described one potential future application could be engineering the surfaces of medical devices to deter bacterial adhesion and biofilm formation. These results can also be used to help prevent biofouling, which is when bacteria spoil or degrade biological products and surfaces.

The paper was published in ACS Infectious Diseases.