Biofilms: What Are They, Formation, Removal

What Are They, Formation, Removal, and More

Author: Anna Hernández, MD

Editor: Alyssa Haag

Editor: Emily Miao, PharmD

Editor: Kelsey LaFayette, DNP

Illustrator: Jessica Reynolds, MS

Copyeditor: David G. Walker

Modified: Feb 26, 2024

What is a biofilm?

A biofilm is a community of living microorganisms embedded in a slimy matrix that provides protection against external aggressors, like desiccation, antibiotics, or disinfectants, as well as the host’s immune system.

In the environment, bacteria can alternate between two different states, a planktonic, or free-floating state; and a sessile, or immobile state, where bacteria live in biofilms. The planktonic is where bacterial cells behave individually like plankton in the sea. This state is the one typically portrayed in science books and the most common way bacteria are grown in laboratories to test antibiotic sensitivity. In nature, however, most bacteria live in communities called biofilms which allow thousands of bacteria to work together to survive.

How does a biofilm form?

Biofilm formation is a cyclic process. It begins when free-floating bacteria come in contact with and attach to a surface. Many types of bacteria attach to other cells and surfaces through hair-like structures on their surface called pili and fimbriae. This initial attachment is often fragile and is facilitated by adhesins, which are proteins that help bacteria stick more securely to a surface. Once attached, bacteria start to multiply, forming a microcolony. At the same time, they secrete a slimy matrix consisting of extracellular polymeric substances (EPS), which are complex sugars and proteins that shield bacteria from the environment. Comparing a biofilm to strawberry jam, the seeds of the jam would be the bacteria and the rest of the jam would be the EPS. As the biofilm grows, the outer layer becomes scarce in nutrients, and parts of it break off, allowing bacteria to spread to another area where they can begin the formation of a new biofilm.

The bacteria in a biofilm work together as a colony and communicate through signaling molecules called autoinducers that are produced in response to changes in cell-population density. This mechanism of cell-to-cell communication is called “quorum sensing”, and is responsible for promoting the expression of specific genes needed for the development of the biofilm. Surprisingly, these genetic changes only occur when a significant amount of bacteria are present, meaning they are not expressed when bacteria are in a planktonic state.

What are examples of biofilms?

Biofilms are found everywhere around us; in nature, at home, in the human body, and even in food. Bacteria prefer wet or humid environments, so biofilms are commonly found near water sources. Examples of biofilms include the slippery coating on rocks near rivers and hot springs, the gunk that clogs water pipes, and the slime that forms on shower tiles or the walls of a swimming pool. In hospital settings, biofilms are commonly found on high-touch surfaces, such as sanitizing bottles, water taps, door handles, beds, and monitoring systems. At home, they are usually found in humid areas like the kitchen or bathroom, as well as in domestic water systems like air conditioning.

Biofilms also colonize mucosal surfaces like the respiratory or gastrointestinal tract, where they are capable of facilitating a disease process or protecting from infections. Dental plaque, for example, is a type of biofilm formed by a sticky collection of bacteria, salivary proteins, and dead cells from the oral mucosa that increases the risk of dental caries. On the other hand, biofilm-forming bacteria on the gastrointestinal tract protect the gut by preventing pathogens like Clostridium difficile from proliferating.

Not all biofilms are harmful. For example, the soil is home to many types of bacteria and other microbes that live attached to plant roots. These bacteria help protect plants from plagues and act as natural fertilizers to improve crop productivity. Surprisingly, biofilms are also used in the food industry to achieve fermentation processes that give certain foods their unique taste. Examples include kombucha, which is a fermented tea drink, cocoa, and coffee beans.

How can a biofilm affect the human body?

Biofilms are responsible for around 60 to 80% of the infections that affect the human body, particularly those associated with the use of medical devices. Indwelling catheters and implants (e.g., pacemakers, prosthetic heart valves, joint prostheses) offer the perfect surface for specific bacteria to attach to and create biofilms. Examples of biofilm-producing bacteria include Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, and Pseudomonas aeruginosa, among others.

A common example of biofilm infections is catheter-associated urinary tract infections (CAUTI) which occur in individuals with indwelling urinary catheters. People with prosthetic heart valves are at risk of developing infectious endocarditis, an infection of the inner layer of the heart. Similarly, bacteria can contaminate endotracheal tubes in mechanically ventilated individuals, putting them at risk for ventilator-associated pneumonia.

In addition to implant-related infections, biofilms are responsible for a wide number of difficult-to-treat infections, including recurrent respiratory infections in individuals with cystic fibrosis, chronic sinusitis, otitis media, skin and wound infections, and osteomyelitis.

How are harmful biofilms removed?

Strategies to remove biofilms include antibiotics, mechanical removal methods, and more recently, novel agents that aim to inhibit biofilm formation.

When the infection is associated with medical devices, a common practice is to replace the device with a new one. Medical equipment surfaces can also be treated with bactericidal or bacteriostatic substances to prevent bacteria from attaching to them. For example, a coating of vancomycin can be applied on metal implants, like hip or knee prostheses, to prevent prosthetic joint infections. This antibiotic can provide coverage for gram-positive bacteria that are often implicated in biofilm production. Of note, biofilms can be difficult to remove due to the sticky protective nature of the biofilm matrix. Additionally, bacteria in a biofilm are around 100 to 1000 times more resistant to antibiotics compared to when they are free-floating. This means that commonly used antibiotics may not be as effective to treat biofilm infections.

Dental professionals recommend brushing the teeth with a soft-bristle toothbrush 2 to 3 times a day for at least two minutes to prevent dental plaques. Brushing alone doesn’t remove all of the plaque, since it can build up in hard-to-reach areas like between the teeth and on the gumline. Therefore, flossing daily and getting a professional cleaning every 6 to 12 months can help get rid of stubborn plaque ensuring adequate oral health.

To tackle the problem of antibiotic resistance, researchers are investigating novel strategies to inhibit biofilm formation. One of the proposed mechanisms is to block the quorum-sensing (QS) signaling mechanism, thereby preventing bacteria from communicating with one another. Another strategy is to use enzymes that degrade the biofilm matrix, making bacteria more sensitive to antibiotics and the host’s immune system.

What are the most important facts to know about biofilms?

A biofilm is a community of microorganisms embedded in a slimy, glue-like matrix that provides protection against the environment. Biofilm formation is a cyclic process that involves the attachment of free-floating bacteria to a surface, the growth of a microcolony, secretion of the biofilm matrix, and dispersion, which enables bacteria to spread and colonize new surfaces. It is thought that biofilms cause around 60 to 80% of all microbial infections, particularly those associated with medical devices (e.g., catheters, prosthetic heart valves, medical implants). Removing biofilms can be difficult due to the sticky protective nature of the biofilm matrix. Antibiotics, disinfectants, and mechanical removal methods are commonly used to remove biofilms and fight off associated infections.

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Biofilms

What Are They, Formation, Removal, and More

What is a biofilm?

How does a biofilm form?

What are examples of biofilms?

How can a biofilm affect the human body?

How are harmful biofilms removed?

What are the most important facts to know about biofilms?

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