Biofilm

A biofilm is a collection of microbial cells that secrete a substance that enables them to stick together to create a film, or thin layer, on a liquid or surface. The film can be limited to one species of microbe, but most commonly is made up of multiple types of cells, including bacteria, algae, protozoa, and yeast. One type of film can include hundreds of different microbial cells.

Liquid is required for the formation of a biofilm, which can form on a natural surface, including parts of the human body, as well as plants, rocks, metals, plastics, and other materials. Some familiar examples of biofilms include the sludge that forms in drains, dental plaque, and the slippery slime-type substance that sometimes forms on rocks along a body of water.

Formation

Biofilms can form anywhere a microbe encounters a surface in a liquid environment. Within minutes of settling on the surface—for example, an underwater rock—the previously free-floating cells start making extracellular polymeric substances (EPS). These slippery, slimy substances serve as a glue to help individual microbes form a complex community or colony. Within hours of the first microbe landing on a surface, the colony is formed and is ready to propagate by releasing either individual cells or sections of the developed colony.

The cells that become a biofilm have specific patterns of behavior when it comes to the ways they attach, develop into a colony, and detach from that colony that differ from other microbial forms.

Significance

As a natural occurrence, biofilms have existed for as long as microbes and liquids have been present. Researchers were aware that films such as dental plaque were teeming with tiny microorganisms since Dutch scientist Antony van Leeuwenhoek (1632-1723) first used his microscope to observe small organisms moving in a sample collected from between someone's teeth in 1684. Leeuwenhoek is credited with discovering biofilm, but he and other scientists lacked the tools to adequately study the full formation of biofilm for several centuries. In the 1940s, scientists began to realize the difference between planktonic, or floating, microbes and sessile cells, or those that had attached to surfaces and could form a biofilm. In the latter part of the 20^th century, researchers finally were able to study biofilms in enough detail to understand the magnitude of their effect and growth.

Biofilms can be helpful. They are part of the food chain, providing nutrient sources for some insects and other species. They can also help break down soil contaminants from accidental spills and are helpful to the nutrient absorption process of some plants. The powers of biofilms can also be harnessed to help with such processes as water and wastewater treatment and to extract some metal ores through a process known as microbial leaching. While some biofilms that form on humans, including dental plaque, can cause infections or decay, others—such as those in the digestive tract—can have beneficial properties and present few if any problems.

There are also many harmful effects from biofilms. They can foul water supplies by depleting oxygen and cause the formation of harmful algal blooms on the surfaces of bodies of water. They can help spread toxic chemicals like mercury and arsenic, as well as diseases such as cholera, plague, and West Nile virus. Biofilms can also produce gases that affect the atmosphere.

Biofilm colonies demonstrate behaviors, properties, and abilities that the individual cells do not possess alone. For example, an antibiotic dose that would kill an individual cell might need to be hundreds of times stronger to kill the biofilm colony. Understanding how biofilms form and how they interact with the human body is important to medical professionals. Biofilms can contain microbes such as bacteria that cause illness and infection. For example, biofilms can be responsible for chronic otitis media, or ear infections, and for wounds that will not heal. Pneumonia in cystic fibrosis patients is sometimes the result of a biofilm infection as well. The solid surfaces of catheters and implants, which are often close to bodily fluids such as urine and blood, provide a surface for microbes to begin the process of forming a biofilm and causing a related infection. The presence of these biofilms is often identified when the infection cannot be fought off by the body's normal defenses and is also resistant to treatment with antibiotics.

The infectious biofilms can also form on equipment used in medical procedures, and their tenacious nature makes them difficult to remove by the usual disinfection processes. This can lead to the spread of the infection within a medical facility and force the replacement of thousands of dollars of medical equipment. These infections can take hold on implanted medical devices such as artificial joints, pacemakers, and stents, subjecting patients who already have a health issue to new problems, increased need for surgery and antibiotics, and the risk of further infections.

Medical Research

Researchers are very interested in learning how these biofilm colonies develop to be so much stronger than the sum of the individual parts to eliminate these costly and dangerous problems. In 2015, researchers at University of Maryland and University of Michigan, working under the auspices of the US National Institutes of Health and National Science Foundation, conducted studies into how one common hospital bacteria, Pseudomonas aeruginosa, forms a biofilm.

Scientists had previously determined that when microbes detect a change in their environment that makes it favorable to the formation of a biofilm, they use signaling molecules to trigger the start of this process. They also determined that a molecule called Cyclic-di-GMP, also known as c-di-GMP, is used by many forms of bacteria to initiate the biofilm-making process. The c-di-GMP is then converted into another molecule, known as pGpG, which continues the signaling process.

What was not known previously was what signaled biofilms to stop the formation process. The researchers from the Universities of Maryland and Michigan were the first to identify an enzyme known as oligoribonuclease as the off-switch for the biofilm process. It works by disrupting and pulling apart the pGpG, putting an end to the signal and stopping the biofilm formation process. While the study focused on the biofilms formed by P. auruginosa, oligoribonuclease is also known to be a signaling trigger for ending several other types of bacterial biofilms. Researchers believe this discovery can be applied to developing disinfectants, antibiotics, and other treatments and preventions for the formation of a number of different types of biofilm. They are also searching for similar shut-off triggers in other infective microbes.

Bibliography

"Biofilm Basics." Montana State University Center for Biofilm Engineering. Web. 4 February 2016. http://www.biofilm.montana.edu/biofilm-basics.html

Bjarnshot, T. "The Role of Bacterial Biofilms in Chronic Infections." Acta Pathologica, Microbiologica et Immunologica Scandinavica. 2013 May. Web. 4 February 2016. http://www.ncbi.nlm.nih.gov/pubmed/23635385

Donlan, Rodney M. "Biofilms: Microbial Life on Surface." Emerging Infectious Diseases. US Centers for Disease Control. Vol. 8 No. 9, Sept 2002. Web. 4 February 2016. http://wwwnc.cdc.gov/eid/article/8/9/02-0063‗article

Hernandez, Anna, et al. "Biofilms." Osmosis, 26 Feb. 2024, www.osmosis.org/answers/biofilm. Accessed 24 Nov. 2024.

"Off Switch for Biofilm Formation Discovered." Science Daily. Published 24 August 2015. Web.4 February 2016. http://www.sciencedaily.com/releases/2015/08/150824163001.htm

Sanders, Robert. "Discovery Opens Door to Attacking Biofilms that Cause Chronic Infections." Berkeley News. University of Berkeley. Published 12 July 2012. Web. 4 February 2016. http://news.berkeley.edu/2012/07/12/discovery-opens-door-to-attacking-biofilms-that-cause-chronic-infections/