The Gram stain also allows for the recognition of the shape and pattern or arrangement of bacteria.  The shapes are cocci (round), bacilli (rod), or spirilla (spiral).

Based on how the bacteria divides during replication, different patterns or arrangements may be produced. The cellular morphology, or shapes, of the individual cells and their arrangement in pairs, chains, or clusters are useful in the identification of the bacteria.

Spiral bacteria usually occur singly. Some are very tightly coiled, whereas others are long and slightly curved or only curved at one end.