FIG 4.

Isolation and purification of polymyxin-inactivating enzyme. (A) Analysis of secreted proteins by SDS-PAGE. Lane M, protein molecular weight marker; lanes 1 and 4, fermentation supernatant from stationary phase (incubation for 24 h); lane 2, whole-cell lysate from stationary phase (incubation for 24 h); lane 3, fermentation supernatant from logarithmic phase (incubation for 12 h); lane 5, 50% ammonium sulfate fraction; lane 6, 30% ammonium sulfate fraction. The arrow shows the predicted band. (B) Effects of different solutions on colistin inactivation. 1, phosphate-buffered saline (PBS); 2, LB broth; 3, fermentation supernatant of B. licheniformis DC-1 from stationary phase; 4, concentrated fraction. The residual antibacterial activity of colistin was determined by the cylinder-plate diffusion method.