Biofilm is the slimy extracellular matrix formed when groups of cells adhere to each other and to a proper surface. It is a conglomeration of extracellular polymeric substances including polysaccharides, proteins and DNA. Besides formation in human, biofilm also exists on object surfaces external to our body. When it is formed on medical facilities or water supplying tubes, it makes the process of disinfection ineffective. The firm excellular matrix prevents the microorganisms inside the biofilm from being washed away or being in contact with disinfectors. Thus, an effective and environmentally friendly way of biofilm degradation is indispensable for many industries.

Biological methods of degrading biofilm have the advantages of harmless, sustainable, and effective over traditional chemical methods. Through research, our team finds that lactic acid produced by Lactobacillus delbruckii ND02 is an acid with considerable effect of biofilm degradation. In order to support Lactobacillus delbruckii for acid secretion, lysozyme is used to hydrolyze polysaccharides in the biofilm to smaller fragments of mono and disaccharides. Sequence that codes for lysozyme is combined with sequence of Lactobacillus breris that codes for S-layer protein signal peptide, which promotes the secretion of lysozyme. The combined sequence is then transferred to the acid producing Lactobacillus delbruckii for expression.

When biofilm is treated by our modified Lactobacillus delbruckii, lysozyme hydrolyzes polysaccharides and disrupts the structure of biofilm. With nutrients provided by hydrolyzed polysaccharides, Lactobacillus delbruckii secretes lactic acid that further degrades the biofilm. As the pH of the system gradually decreases, the ability of Lactobacillus delbruckii adhering to biofilm increases, In addition, hydrogen peroxide is secreted for sterilization when the pH drops below 3. This produces a positive feedback loop for biofilm degradation and its effect is expected to be significant.