What are biofilms?
Biofilms are microorganism colonies attached together, embedded in an extracellular matrix and adhered to a solid base. They represent a perfect strategy for bacteria, as they provide stability and protection in a humid and nutrient-rich environment.
It is a defence mechanism used by organisms against their environment.
Moreover, the matrix acts as a protection that facilitates survival to external agents, such as disinfectants and other products.
Due to the cross-contamination risks, it is important to detect and remove them from work surfaces where food products are handled.
etapas de formación de los biofilms
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.
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Factores de formación de los biofilms
There are several factors involved in the biofilm development :
1. Properties of the contact surface
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.
2. Contact time
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.
3. Microbial features
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.
4. Nutrient availability
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.
5. Composition of the microbial community
Multispecies biofilms show a greater thickness, and they are more stable to environmental factors than those with just a single species.
6. Water availability
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.
Composition
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.
Risks
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.
Main problems
- Contamination of food or products, lowering the quality and shortening the shelf life.
- Infections by pathogenic microorganisms.
- Clogging lines and pipes, causing a reduction of the flow speed and increasing the energy costs.
- Clogging and deteriorating membranes, causing a permeability reduction.
- Reduction of energy transfer and energy efficiency.
- Corrosion of metallic surfaces when sulphate-reducing or acid-reducing bacteria grown in the biofilm.
Control
- Anticipate and identify where biofilms may be formed: places with water, organic matter, and contaminant microorganisms. Places with poor cleaning and disinfection.
- Implement strategies to prevent the new biofilm formation.
- Fine tune cleaning and disinfection programmes to remove them.
- Alternate the use of chemicals to prevent the microorganisms from adapting to them.
- Visual and microbiological inspection of the equipment after cleaning.
- Regularly verify the effectiveness of cleaning and disinfection methods.
