Deformation factor: an extracellular protein synthesized by Bartonella bacilliformis that deforms erythrocyte membranes.

Bartonella bacilliformis, a hemotropic bacterium and the causative agent of the human disease bartonellosis, when incubated in a tryptone-based medium produces an extracellular factor, termed deformation factor (DF), which induces extensive indentations and trenches in trypsinized erythrocyte membranes. The factor is stable during storage at 4 degrees C. It can be inactivated by proteases or brief heating to 70 to 80 degrees C, can be precipitated by ammonium sulfate, is nondialyzable, and is retained by membranes with a 30,000-molecular-weight cutoff. These properties suggest that DF is probably a protein. Incubation of erythrocytes with phospholipase D renders them resistant to deformation by DF.