Bacillus (shape)

A bacillus (plural bacilli) is a rod-shaped cylindrical bacterium.^[1] Bacilli are found in many different taxonomic groups of bacteria.

• When the name Bacillus is capitalized and italicized, it refers to a specific genus of bacteria.^[2]

• If it is not capitalized or italicized the name refers to any rod-shaped bacterium.^[2]

A typical bacillus, Gram stained: click for enlarged view

There is no connection between the shape of a bacterium and its colors in the gram staining. In other words, some of them are gram negative and some are gram positive.