Rod-shaped

A bacillus (plural bacilli) is a rod-shaped bacterium. Bacilli are found in many different taxonomic groups of bacteria. However, the name Bacillus, capitalized and italicized, refers to a specific genus of bacteria. The name Bacilli, capitalized but not italicized, can also refer to a less specific taxonomic group of bacteria that includes two orders, one of which contains the genus Bacillus. When the word is formatted with a lowercase and not italicized, 'bacillus', it will most likely be referring to shape and not to the genus at all. The shape bacillus can also be called rods.

Bacilli usually divide in the same plane and are solitary, but can combine to form diplobacilli, streptobacilli, and palisades.

There is no connection between the shape of a bacterium and its color in the Gram staining. MacConkey agar can be used to distinguish among Gram negative bacilli such as E. coli and salmonella.

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