The Gram stain allows for the recognition of the shape andpattern 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.
The arrangements or patterns found in cocci are:
a. diplococci – pairs
b. streptococci – chains
c. staphylococci – grape-like clusters
d. tetrads – four in a square
e. sarcina – eight in a cube