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]

• Diplobacilli: Two bacilli arranged side by side with each other.
• Streptobacilli: Bacilli arranged in chains.
• Coccobacillus: Oval and similar to coccus (circular shaped bacterium).

^[3]

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

• Bacillus genus
• Clostridium genus
• Corynebacterium genus
• Listeria genus
• Propionibacterium genus

Examples of Gram negative bacilli

• Bacteroides genus
• Citrobacter genus
• Enterobacter genus
• Escherichia genus
• Pseudomonas genus
• Proteus genus
• Salmonella genus
• Serratia genus
• Shigella genus
• Yersinia genus

^[5]

References

1. "The Size, Shape, And Arrangement Of Bacterial Cells". midlandstech.edu.
2. "Chapter 4: Functional Anatomy Of Prokaryotic And Eukaryotic Cells". Archived from the original on 23 September 2012.
3. "Sizes, Shapes, and Arrangements of Bacteria". ccbcmd.edu.
4. "Gram Negative Bacilli".
5. "Gram negative bacilli". infectionnet.org.