Biofilm describes the collection of microorganisms on a surface where the cells adhere to each other. Generally, an extracellular polymeric substance (EPS) exists over the biofilm and also contains it itself. The EPS is mainly composed of proteins, polysaccharides and DNA. Biofilms have the potential to exist on living organisms and surfaces as well as on non-living surfaces.
Different types of microorganisms such as bacteria, protozoa, fungi, archaea, algae and others can form biofilms. Some microorganisms of the same type form a biofilm exclusive for that type of microorganism.
Microorganisms can grow individually or in the form of a collection. These microorganisms experience a phenotypic behaviour change when they shift from individual growth to biofilm growth.
Biofilms form when microorganisms start attaching and clustering on a specific surface. Initially, the microorganisms are not attached permanently and are still removable. The initial microorganisms use the Van der Waals force to stay attached. If the surface is not cleaned, the formation of the biofilm occurs. Eventually, these microorganisms become more strongly and permanently attached. This happens when the microorganisms use the cell adhesion structures within to bond with the surface.
When the first colonists of the microorganisms on the surface become attached permanently, other microorganisms can easily attach as well. In this way, the clustering of the microbes continues. Some microorganisms do not have the ability to attach themselves to surfaces. However, they could easily attach themselves to the already existing microorganisms.
Unless formation and development stop, it will continue to grow and increase in size. This clustering of microbes can become exceedingly antibiotic resistant.
There are five stages of the formation and development of biofilms;
- Initial attachment
- Irreversible attachment
- Maturation I
- Maturation II
The dispersion stage is when the biofilm spreads and starts colonizing other new surfaces as well.
Typically, biofilms exist on solid substrate surfaces which are also exposed to an aqueous solution. Nonetheless, it can also exist on liquid surfaces such as floating mats or even on leaves. Anywhere with high humidity. When first formed, the biofilm is invisible to the naked eye. But if the formation and development are not stopped, it can grow to a size which is easily visible.
The extracellular polymeric substance (EPS) effectively protect the microorganisms in the biofilm and also facilitates the communication between the microbes. The communication between the microorganisms occurs via biochemical signals. The EPS is strong enough to protect the microbes and sometimes the biofilms become fossilized.
Microorganisms in the air and microorganisms in a biofilm possess different properties, even though they may be the same species. Biofilm offers a dense and protected environment, hence provides different properties. Microorganisms of the biofilm become more resistant to antibiotics and detergents. The extracellular polymeric substance and the outer layer of the cells prove to be very protective for these microbes. The resistance of a biofilm against antibiotics is a hundred times higher than the resistance of a free-floating microorganism.
Biofilms in humans
Biofilms in the human body can lead to various types of infections. The diseases and conditions in humans, such as catheter infection, gingivitis, periodontal disease, the formation of dental plaque, urinary tract infections, middle-ear infections and coating contact lenses are all caused by biofilms.
Dental plaque is the formation of biofilm on the teeth. This biofilm comprises of bacteria in the oral cavity. That can cause numerous dental problems and conditions. Unremoved dental plaque can turn into tartar – a harder form of plaque. Tartar becomes more difficult to remove and is more precarious than the dental plaque.