Bacteria cells were obtained as described above and resuspended in PDB dilutions (1:50) containing 20%v/v bacterial cell-free culture filtrate to yield different working concentrations (0.33, 1, 1.67, 2.33, 3.0 and 3.67 × 107CFUmL−1). These solutions were used to bioassay for trap formation. The negative controls were 20% NB (v/v) prepared by PDB dilutions (PDB 1:50). The experiments were prepared in triplicate and repeated three times.