Adhesion. Under the right conditions, microorganisms stay over a surface and start to adhere to it.
Colonisation. Microbial cells generate colonies. It is no longer possible to reverse the adhesion process.
Formation. Microbial cells start developing the extracellular matrix, creating a mature biofilm.
Growth. Interstices and canals are formed inside the biofilm matrix to carry water and nutrients.
Dispersion. Biofilm fragments break off and attach to other surfaces, thus facilitating the biofilm expansion.
There are several factors involved in the biofilm development :
The substrate will have an impact on the bonding characteristics. So, bacteria tend to adhere to hydrophilic surfaces creating a single even layer, while they form clusters on hydrophobic surfaces.
A greater contact time between cells and substrate means a greater number of bonds are created. In addition, the adhesion becomes irreversible over time.
Other factors such as the environmental conditions, the type of microorganism, the substrate and the pressure on work surfaces or equipment, may also have a considerable impact on the potential for biofilm formation.
The features of the cellular surface such as flagella, pili, adhesion proteins and capsules, may also influence the process. Pili act as a Velcro to anchor bacteria on to some surfaces. They can also act as chemoreceptors, guiding the bacteria towards specific sites.
Nutrients have a greater influence on the biofilm structure and composition. Some research projects completed on Listeria biofilms revealed that low phosphate levels promote biofilm development, although the effect diminishes after a few days.
Multispecies biofilms show a greater thickness, and they are more stable to environmental factors than those with just a single species.
This is a crucial factor for the biofilm development because a relative humidity between 90-100% facilitates its growth.
Therefore, most biofilms are found in aqueous environments, such as line or pipe systems in dairy industries.
However, values around 70-80% have also been found to be enough for the biofilm development. This indicates that environments with a high relative humidity (such as sprays), may significantly increase the risk of formation.
Biofilms include microbial cells, such as bacteria, fungi, and an extracellular matrix. The matrix represents 80% of the biofilm composition and it is made of exopolysaccharides, with internal canals for the circulation of water, enzymes, nutrients, and waste.
They develop on surfaces that favour their adhesion (porous, grated, or rough) or that have been subjected to a poor cleaning and disinfection programme.
In addition, they provide a protective function to the microorganisms they harbour, reducing the effectiveness of disinfection treatments.
The presence of biofilms in the food industry is as common as worrying.
When found in the facilities, they represent an important risk to food safety and can also cause operational problems in systems and equipment.
The environmental conditions that can be found inside a factory in many cases favour the presence of a diverse microbial ecology. This promotes the development of multispecies biofilms, which can harbour pathogenic microorganisms, such as Listeria monocytogenes, Salmonella, or Pseudomonas aeruginosa.