Mucus Thickness Dictates Bacterial Behavior, Affecting Infection Potential

The telltale signs of cold and flu season—sniffles, snorts, and the sound of noses being blown—serve as indicators of increased mucus production.

A recent study conducted by researchers at Penn State suggests that this surge in mucus is precisely what bacteria exploit to launch a coordinated assault on the immune system.

The research team observed that as the consistency of the mucus thickened, bacteria exhibited a more efficient ability to swarm. This discovery carries potential implications for treatments aimed at diminishing the bacteria's capacity to spread.

Published in the journal PNAS Nexus, the study illustrates how bacteria leverage mucus to amplify their self-organization, potentially leading to heightened infection.

Using synthetic pig stomach mucus, natural cow cervical mucus, and a water-soluble polymer compound called polyvidone in their experiments, the researchers found that bacteria demonstrated improved coordination in thicker mucus compared to more watery substances.

These findings shed light on the mechanisms through which bacteria colonize mucus and mucosal surfaces. Furthermore, the study underscores how mucus contributes to the collective motion of bacteria, known as swarming, which could contribute to an increased resistance to antibiotics within bacterial colonies.

To the best of our knowledge, our study is the first demonstration of bacteria collectively swimming in mucus. We have shown that mucus, unlike liquids of similar consistency, enhances the collective behavior.”

Igor Aronson, Study Corresponding Author and Huck Chair Professor of Biomedical Engineering, Chemistry and Mathematics, The Pennsylvania State University

Aronson elucidates that mucus plays a crucial role in various biological functions. It forms a protective lining on the surfaces of cells and tissues, safeguarding against pathogens like bacteria, fungi, and viruses.

However, mucus also serves as the breeding ground for bacterial infections, encompassing sexually transmitted and gastric diseases. Aronson suggests that gaining a deeper comprehension of how bacteria engage in swarming within mucus could open avenues for innovative strategies to combat infections and address the escalating challenge of antibiotic resistance.

Our findings demonstrate how mucus consistency affects random motion of individual bacteria and influences their transition to coordinated, collective motion of large bacterial groups.”

Igor Aronson, Study Corresponding Author and Huck Chair Professor of Biomedical Engineering, Chemistry and Mathematics, The Pennsylvania State University

Aronson added, “There are studies demonstrating that collective motion or swarming of bacteria enhances the ability of bacterial colonies to fend off the effect of antibiotics. The onset of collective behavior studied in our work is directly related to swarming.”

Understanding mucus poses a formidable challenge due to its dual nature, combining liquid-like and solid-like characteristics, as elucidated by Aronson. While liquids are typically defined by viscosity, indicating thickness or thinness, and solids by elasticity, denoting their resistance to breaking, mucus, as a viscoelastic fluid, demonstrates attributes of both liquid and solid states.

In their quest to unravel the intricacies of mucus infection, the research team employed microscopic imaging techniques to observe the collective motion of concentrated Bacillus subtilis bacteria in synthetic pig stomach mucus and natural cow cervical mucus.

They contrasted these observations with Bacillus subtilis movements in a water-soluble polymer, polyvidone, across a broad spectrum of concentrations. The researchers also aligned their experimental findings with a computational model for bacterial collective motion in viscoelastic fluids like mucus.

The team’s discoveries highlighted the profound impact of mucus consistency on bacterial collective behavior. The results indicated that the denser the mucus, the higher the likelihood of bacteria displaying coordinated collective movement, forming a cohesive swarm.

We were able to show how the viscoelasticity in mucus enhances bacterial organization, which in turn leads to coherently moving bacterial groups that cause infection.”

Igor Aronson, Study Corresponding Author and Huck Chair Professor of Biomedical Engineering, Chemistry and Mathematics, The Pennsylvania State University

Aronson added, “Our results reveal that the levels of elasticity and viscosity in mucus are a main driver in how bacterial communities organize themselves, which can provide insight into how we can control and prevent bacterial invasion in mucus.”

Aronson clarified that the team anticipates human mucus to display analogous physical properties, underscoring the relevance of their findings to human health as well.

“The onset of the collective motion of bacteria and their interaction with mucus should be the same as in cow, pig, or human mucus since these substances have similar mechanical properties,” stated Aronson.

Aronson added, “Our results have implications for human and animal health. We’re showing that mucus viscoelasticity can enhance large-scale collective motion of bacteria, which may accelerate how quickly bacteria penetrate mucus protective barrier and infect internal tissues.”