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:

1. Initial reversible attachment
2. Irreversible attachment,
3. Maturation
4. Dispersion

Initial contact between migrating planktonic bacteria and surfaces. This is still reversible at this point. Microorganisms then begin to form a monolayer and produce an extracellular matrix or “slime” for protection. A matrix of extracellular polysaccharides, structural proteins, cell debris, and nucleic acids. Also called extracellular polymeric substance (EPS). Matrix formation is dominated by extracellular DNA, followed by polysaccharides and structural proteins. These stages lead to microcolony formation and exhibit important growth and cell-to-cell communication such as quorum sensing. Biofilms grow three-dimensionally and their binding to surfaces is now irreversible. In the final stage, some cells of the mature biofilm may begin to slough off and redistribute into the environment as planktonic cells, initiating a new cycle of biofilm formation.

Examples of biofilms

Plaque
Plaque biofilms are hard and inelastic due to the presence of inorganic salts that give rigidity to the polymer matrix. This is an interesting example of the complex communities that live in biofilms.
Blackwater biofilm
Another example is sewage. Here, ammonium, nitrite-oxidizing nitrifiers and autotrophic nitrifiers live in biofilms on pipes.

                                     Dental plaque                                                                         

                                Biofilm formation in pipes

Sub-aerial Biofilms

Subterranean biofilms are characterized by patchy growths on solid surfaces such as rocks and ancient stone buildings. These biofilms are formed by fungi, algae, cyanobacteria, heterotrophic bacteria, protozoa, and microzoa.

Biofilms of causative agents of human diseases

Many of the bacteria known to cause human disease live in biofilms. Among them are Vibrio cholerae, Vibrio parahaemolyticus, Streptococcus mutans, and Legionella pneumophila. They can cause skin, UTI, and respiratory tract infections.

                         Respiratory Tract Infection                                                        Transmission of Bubonic Plague

Bubonic plague

Of interest is transmission of bubonic plague through flea bites, a relatively recent adaptation of a bacterial pathogen called Yersinia pestis. Plague is a contagious infectious disease. It grows as an adherent biofilm in the foregut of the vector.