Artificial biofilm model - a useful tool for biofilm research

For biofilm studies, artificial models can be very helpful in studying proc esses in hydrogels of defined composition and structure. Two different type s of artificial biofilm models were developed. Homogeneous agarose beads (5 0-500 mu m diameter) and porous beads (260 mu m mean diameter) containing p ores with diameters from 10 to 80 mu m (28 mu m on average) allowed the emb edding of cells, particles and typical biofilm matrix components such as pr oteins and polysaccharides. The characterisation of the matrix structures a nd of the distribution of microorganisms was performed by confocal laser sc anning microscopy. The physiological condition of the embedded bacteria was examined by redox activity (CTC-assay) and membrane integrity (Molecular P robes LIVE/DEAD-Kit). Approximately 35% of the immobilised cells (Pseudomon as aeruginosa SG81) were damaged due to the elevated temperature required f or the embedding process. It was shown that the surviving cells were able t o multiply when provided with nutrients. In the case of homogeneous agarose beads, cell growth only occurred near the bead surface, while substrate li mitation prevented growth of more deeply embedded cells. In the porous hydr ogel, cell division was observed across the entire matrix due to better mas s transport. It could be shown that embedding in the artificial gel matrix provided protection of immobilized cells against toxic substances such as s odium hypochlorite (0.5 mg/l, 30 min) in comparison to suspended cells, as observed in other immobilized systems. Thus, the model is suited to simulat e important biofilm matrix properties.