Bacteria are classified on the basis of their shapes into the following categories:
- Rod-shaped bacteria (bacilli): These are aerobic rod-shaped, spore-producing bacteria. They are often occurring in chain-like formations, and they are found primarily in soil; e.g., Lactobacillus.
- Spherical-shaped bacteria (cocci): They are spherical or nearly spherical bacteria; e.g., Streptococcus.
- Curved-shaped bacteria (vibrio’s): They are curved-shaped bacteria; e.g., Vibrio.
Spiral-shaped bacteria (spirilla): They are flagellated, aerobic bacteria, having a spirally twisted rod-like form; e.g., Treponema.
