Figure 25.3 Bacterial Cell Shapes This composite, colorized micrograph shows the three most common bacterial shapes. Spherical cells are called cocci; those pictured are a species of Enterococcus from the mammalian gut. Rod-shaped cells are called bacilli; these Escherichia coli also reside in the gut. The helix-shaped spirilla are Leptospira interrogans, a human pathogen.