Bacillus (shape)

Bacteria display a large diversity of cell morphologies and arrangements.

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. [1]

Bacilli usually divide in the same plane and are solitary, but can combine to form diplobacilli, streptobacilli, and palisades.[2]


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.[4]

Examples of Gram positive bacilli

Examples of Gram negative bacilli



  1. "The Size, Shape, And Arrangement Of Bacterial Cells". Midlands Technical College. Retrieved 8 August 2016.
  2. "Chapter 4: Functional Anatomy Of Prokaryotic And Eukaryotic Cells". Archived from the original on 23 September 2012.
  3. Kaiser GE. "Sizes, Shapes, and Arrangements of Bacteria". The Community College of Baltimore County. Retrieved 8 August 2016.
  4. "Gram Negative Bacilli". NYU School of Medicine. Archived from the original on 14 March 2009.
  5. "Gram negative bacilli". InfectionNet. Vancouver Island Health Authority. Retrieved 8 August 2016.

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