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Team:Lyon-INSA/StateArt
From 2012.igem.org
Biofilm removal: State of the art
Biofilm removal can be made using different ways, let us introduce you to theses techniques.
Mecanical and Chemical actions
Many strategies and chemical regimens have been defined for controlling biofilms. For open surface in food processing for example, biofilm removal is a multiple step process including pre-cleaning by scraping and rinsing surfaces, washing (detergent), rinsing (to remove dirt and detergent solutions) and sanitizing (to kill attached surviving bacteria and viruses). Closed surfaces such as pipes, tanks or filters require specific equipment such as flooded clean-in-place systems. Flooded systems involve filling all the pipes with successively water, chlorine, biocide, caustic or other chemicals. Other applications use continuous biocide injection procedures to prevent biofilm growth.
Mechanical action is often employed to remove biofilms : If only detergents or sanitizers are used to clean a food line or a pipe in which a biofilm is formed, chemicals contained in the detergent or in the cleaning product can be used to attack and destroy the matrix. But, when the chemical reaches the bacterial colony underlying the matrix, the product may have lost its effectiveness in fighting the cells themselves. Scraping or brushing will unstick the matrix and will expose the underlying bacteria to the action of detergents and sanitizers. Utility pigs allow operators to carry out pipe cleaning.
Clean In Place (CIP) systems are automatic cleaning system integrated into the machine during its design. A major advantage is that it does not require any system disassembling to operate. The tanks and pipes are cleaned using a parallel fluid circuit. In automated machines, cycles and programs are integrated from the construction. With this system it is possible to inject the cleaning solution to drain a pipe, but also to include an air- or water-pushed shuttle that scrapes the inner wall of the pipe. In this case, the shuttle is introduced by a parallel circuit or by an aperture in the main pipe. Implementation of an automated CIP system in an existing industrial plant leads to additional cost but is possible (see Packo Inox NV ).
For small industries, more suitable methods have to be considered, such as the injection of water or solutions at high flow, which will cause the detachment of the biofilm due to the shear forces. However, some fragments could contaminate the raw material that passes through the pipes like in the dairy farming. It is also possible to increase the temperature. A temperature increase will softens the biofilm but on the other hand, excessively hot temperatures can also lead to other problems such as milk proteins cooking on the milk line surface, thus facilitating the bacteria adhesion. The products used are terminal types chlorination (chlorine, sodium hypochlorite, monochloramine, chlorine dioxide) for generating a residual biocide. The hydrogen peroxide is also used. Products can be both alkaline and acid coupled with disinfectants.
Recent improvement : enzymatic solution
As chemical and mechanical actions to clean biofilm are not effective enough, recently (July 2012), the Belgian company Realco, working in collaboration with INRA de Lille, specifically with the Laboratoiry Processus aux Interfaces et Hygiène des Matériaux (Processes at Interfaces and Material Hygiene, INRA UR638 PIHM) began to sale their product Biorem in France and USA. This alternative method to chemicals for destroying biofilms is based on enzymatic detergents which allows the elimination of biofilms. The Biorem solution contains, among other things, sequestering agents, dispersants, surfactants, stabilizers and enzymes (BIOREM A1 + 10). Recommended for membrane filtration (ultra, micro and nano filtration) or the internal surfaces of CIP systems, this product is expected to eliminate biofilm and ensure optimum output stream, while guaranteeing perfect hygiene of surfaces. The cost of this solution is
arround 500€/m3 of solution in the case of a CIP use (telephone meeting with the R&D department head of Realco), including the analysis to check the cleaning effectiveness. Realco presents its product as a biofilm destroyer but also as a preventive treatment. This solution is expected to have a lower impact on the environment, with limited release of detergent and total biodegradability, but need to be employed at 50°C to be effective (INRA website recommendation).
Another solutions to avoid or limit chemicals use, is to prevent the colonization of pathogenic biofilms by spraying a positive bacterial biofilm on surfaces. For example, the Cobiotex® 112 product , based on a bacterial strain of Bacillus subtilis, is used to limit the development of flora contamination in poultry breeding, and allows animals to evolve in a bio securised area. An other example is the use of Bacillus strains on tomatoe seeds which promote a better growth of the crops.
