What shapes can bacterial cells have?

Bacterial cells exhibit significant diversity in their morphology, though they generally fall into three basic shapes:1

• Spherical: Known as coccus, these bacteria can appear singly or in characteristic arrangements, such as pairs (diplococci), chains (streptococci), random clumps (staphylococci), square or cubical packets, or groups of four (tetrads).12
• Rodlike: Known as bacillus, these cells typically occur singly, though some form long chains or attach at random angles. They may have pointed or squared ends.1
• Curved: This category includes vibrio (comma-shaped), spirillum (bent and rebent), and spirochete (corkscrew-shaped) bacteria.1

The specific shape of a bacterium is determined by its rigid cell wall, which is primarily composed of peptidoglycan. While these represent the primary classifications, individual cells can exhibit variations, such as being stretched or compressed in one dimension.31