A biofilm is composed of microorganisms, such as bacteria, that exist as a colony, or community. Biofilms are a group of one or more types of microorganisms that can grow on different surfaces. For instance, dental plaque, a slimy buildup of bacteria that forms on the surfaces of teeth and pond scum. Biofilms have been found on metal’s surface, underwater, underground and above the ground surface. It can grow on plants and animal tissues.
Formation of Biofilms
The microorganisms form an attachment to the surface of the object by secreting a glue-like substance and in the presence of moisture, nutrients, and surface exist. A biofilm colony can be formed by a single kind of microorganism or mixtures of many species of bacteria, as well as fungi, algae, yeasts, protozoa, along with non-living debris and corrosion products. It can be formed on metals, plastics, natural materials, medical implants, kitchen counters, contact lenses, the walls of a hot tub or swimming pool, human and animal tissues. It is present in form of thick or thin layer on the surface of objects which may or may not be visible with naked eye.
Biofilm formation can be divided into following four stages:
- Initial reversible attachment
- Irreversible attachment,
- Maturation
- Dispersion
Initially, contact of the moving planktonic bacteria with the surface, which is still reversible at this stage. The microorganism will then start to form a monolayer and will produce an extracellular matrix or “slime” for protection. The matrix made up of extracellular polysaccharides, structural proteins, cell debris and nucleic acids; which also known as extracellular polymeric substances (EPS). The matrix formation is dominated by extracellular DNA, whereas polysaccharides and structural proteins take over later on. In these stages, the formation of micro colonies takes place, which exhibit significant growth and cell-cell communication such as quorum sensing. The biofilm grows in a three-dimensional manner and the attachment with object’s surface is now irreversible. In the final stage, some cells of the mature biofilm start to detach and disperse into the environment as planktonic cells again to potentially start a new cycle of biofilm formation.
Examples of biofilms
Dental plaque
The biofilms of dental plaque are hard and not elastic, due to the presence of inorganic salts, which give rigidity to the polymeric matrix. It is an interesting example of a complex community that lives in biofilms.
Biofilms in black water
Another example is waste water, where nitrifying bacteria’s that are oxidizing ammonium, nitrite and autotrophic nitrifying bacteria live in biofilms attached to pipes.
Sub-aerial Biofilms
Sub-aerial biofilms are characterized by patchy growth on solid surfaces such as rocks and old stone buildings. These biofilms are formed by fungi, algae, cyanobacteria, heterotrophic bacteria, protozoa, as well as microscopic animals.
Biofilms of causative agents of human diseases
Many of the bacteria known as causative agents of human disease live in biofilms. Among these are: Vibrio cholerae, Vibrio parahaemolyticus, Streptococcus mutants, Y Legionella pneumophyla, these are responsible for skin, UTI and respiratory tract infection.
Bubonic plague
The transmission of bubonic plague by flea bites is interesting, a relatively recent adaptation of the bacterial agent named Yersinia pestis. Plague is transmissible infection; it grows as an attached biofilm in the foregut of the vector.
