What Is a Bacterial Biofilm and Why Does It Matter?

A bacterial biofilm is a community of bacteria that adheres to surfaces and becomes encased in a self-produced, protective matrix. This structure allows bacteria to persist and adapt in ways individual, free-floating bacteria cannot. Biofilms are widespread and have significant implications across various aspects of life and industry.

The Unique Structure of Biofilms

Biofilms are composed of two main elements: the bacterial cells themselves and a surrounding substance known as the extracellular polymeric substance (EPS). While bacterial cells constitute a smaller portion, typically 10-25% of the biofilm’s total mass, the EPS makes up the majority, ranging from 75-90%. This EPS acts as a structural scaffold, holding the microbial community together and anchoring it to a surface.

The EPS is a complex, slimy material primarily composed of polysaccharides (sugars), proteins, and extracellular DNA (eDNA). This mixture provides the biofilm with its structural integrity. The matrix also contains water, which can account for a large portion of the EPS and helps maintain a hydrated environment for the cells.

Within this matrix, the components of the EPS interact to create a cohesive and viscoelastic material. Polysaccharides, for example, act as a molecular glue, facilitating bacterial adhesion to each other and to surfaces. Proteins can contribute to matrix stabilization and cell-to-cell adhesion, while eDNA also plays a role in the initial steps of matrix formation and overall integrity. This protective environment within the EPS shields the bacterial inhabitants from external stressors and facilitates communication among them through biochemical signals.

How Biofilms Form and Mature

The formation of a bacterial biofilm is a dynamic and multi-step process, beginning with free-floating, or planktonic, bacteria encountering a suitable surface. Initially, these bacteria attach loosely and reversibly to the surface.

If conditions remain favorable, the bacteria establish a stronger, irreversible attachment to the surface. Following this firm adhesion, the attached microorganisms begin to multiply and aggregate, forming microcolonies. During this stage, the production of the extracellular polymeric substance (EPS) becomes significant, encapsulating the growing bacterial population.

The biofilm then enters a maturation phase, developing into a more complex, three-dimensional structure. This mature biofilm develops internal channels that allow for the circulation of water, nutrients, and waste products. As the biofilm matures, cells within it communicate through a process called quorum sensing, regulating gene expression and coordinating behaviors based on population density.

Finally, cells can actively detach or disperse from the mature biofilm to colonize new areas. This dispersion phase releases individual cells or small clusters back into the environment, allowing them to initiate new biofilm formation elsewhere. This cyclical process allows biofilms to spread and adapt to changing conditions.

Common Environments Where Biofilms Thrive

Biofilms are ubiquitous, found almost anywhere moisture and a surface exist. A familiar example encountered daily is dental plaque, the slimy bacterial buildup on teeth that can contribute to tooth decay and gum disease. Similarly, the slick, greenish-brown film on rocks in streams or rivers is a common natural biofilm.

Beyond these everyday occurrences, biofilms are prevalent in various constructed environments. They frequently form on medical devices such as catheters, prosthetic joints, stents, and pacemakers, posing significant concerns in healthcare settings. In industrial contexts, biofilms thrive in pipelines, heat exchangers, and cooling water systems, leading to issues like biofouling. They can also be found on household surfaces like shower curtains, sinks, and kitchen counters, or even in food processing equipment.

Biofilms can form on both living (biotic) and non-living (abiotic) surfaces. Their ability to adapt to diverse conditions contributes to their widespread presence across natural, industrial, and hospital environments.

Why Biofilms Matter

Biofilms are a significant concern because the bacteria encased within their protective matrix exhibit increased resistance to external threats compared to their free-floating counterparts. This resistance can be substantial, with biofilm-dwelling bacteria being up to 100 to 1000 times more resistant to common antibiotics and disinfectants. The EPS matrix acts as a physical barrier, limiting the penetration of antimicrobial agents, and the reduced metabolic rates of cells within the biofilm also contribute to their tolerance.

In healthcare, biofilms are a major contributor to persistent and chronic infections, accounting for more than 75% of microbial infections in humans. They are implicated in conditions such as cystic fibrosis lung infections, urinary tract infections, osteomyelitis (bone infections), and infections associated with medical implants. The presence of biofilms makes these infections particularly challenging to treat, often leading to prolonged illness, increased morbidity, and higher treatment costs, sometimes requiring device removal or additional surgeries.

Biofilms also pose considerable challenges in various industrial sectors. They cause biofouling, which involves the accumulation of microbial communities on surfaces, leading to reduced efficiency in systems like heat exchangers and pipelines. This can result in increased energy consumption and costly downtime for cleaning and maintenance. Furthermore, biofilms can contribute to microbiologically influenced corrosion (MIC), degrading metal surfaces and causing structural damage and equipment failure, particularly in oil, gas, and water distribution systems. In food and beverage manufacturing, biofilms can harbor pathogenic microorganisms, risking product contamination and public health.